Long-term changes in macroalgal vegetation on the Swedish coast: An evaluation of eutrophication effects with special emphasis on increased organic sedimentation

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(22) Dissertation for the Degree of Doctor of Philosophy in Plant Ecology presented at Uppsala University in 2002 ABSTRACT Eriksson, B.K. 2002. Long-term changes in macroalgal vegetation on the Swedish coast. An evaluation of eutrophication effects with special emphasis on increased organic sedimentation. Acta Universitatis Upsaliensis. Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 746. 34 pp. Uppsala. ISBN 91-554-5394-5. In this thesis I examine and evaluate the effects of a documented large-scale eutrophication on macroalgal vegetation on the Swedish coast. During the past century the load of nutrients has increased manifold in the Baltic Sea area, increasing primary production and organic sedimentation significantly. By re-investigating a unique reference material of macroalgal vegetation from the 1940-60s and by conducting new diving studies at the same sites, I showed that long-term trends in macroalgal community composition and species’ distributions are consistent with changes expected from an increased nutrient availability. In the Öregrund archipelago (northern Baltic Sea), I documented a declined depth distribution of the dominant canopy forming alga, Fucus vesiculosus, and an increased abundance of opportunistic ephemeral algae compared to 52-53 years ago. In the Gullmar Fjord area (Skagerrak), trends included increased abundances of functional groups with opportunistic algae, decreased abundances of large perennial algae and a general decline in the depth distribution of the vegetation compared to 36-57 years ago. Sediment removal experiments in the northern Baltic Sea confirmed the hypothesis that sedimentation influences macroalgal community composition. Species depending on short periods of reproduction were clearly favoured by sediment removal, especially F. vesiculosus that seemed limited in depth by the local sediment load. Species with long continuous periods of dispersal by spores and/or fragments (for example the ephemerals Cladophora glomerata, Ceramium tenuicorne and Enteromorpha spp.) were more tolerant to the natural sediment load. In general, sediment removal favoured macroalgal establishment and development, indicating that variation in the natural sediment load is an important constraint for sublittoral rocky-shore macroalgal community development. I conclude by suggesting that the documented long-term changes in macroalgal vegetation on the Swedish coast partly are explained by an increased organic sedimentation in these areas. Key words: Baltic Sea, Eutrophication, Fragmentation, Fucus vesiculosus, Functional group, Gullmar Fjord, Macroalgae, Long-term changes, Reproduction, Sedimentation Britas Klemens Eriksson, Department of Plant Ecology, Evolutionary Biology Centre, Uppsala University, Villavägen 14, SE-752 36 Uppsala, Sweden (klemens.eriksson@ebc.uu.se) © Britas Klemens Eriksson 2002 ISSN 1104-232X ISBN 91-554-5394-5 Printed in Sweden by Uppsala University, Tryck & Medier, Uppsala 2002. 2.

(23) Det finns en teori som säger att om någon någonsin upptäcker vad Universum är till för och varför det existerar kommer det omedelbart att försvinna och ersättas av någonting ännu mer bisarrt och obegripligt. Enligt en annan teori har detta redan inträffat. -Liftarens Guide till Galaxen. 3.

(24) LIST OF PAPERS This thesis is based on the following five papers, which will be referred to in the text by their Roman numerals.. I. Eriksson, B.K., Johansson, G., Snoeijs, P. (1998) Long-term changes in the sublittoral zonation of brown algae in the southern Bothnian Sea. European Journal of Phycology 33:241-249.. II. Johansson, G., Eriksson, B.K., Pedersén, M., Snoeijs, P. (1998) Long-term changes of macroalgal vegetation in the Skagerrak area. Hydrobiologia 385:121-138.. III. Eriksson, B.K., Johansson, G., Snoeijs, P. (2002) Long-term changes in the macroalgal vegetation of the inner Gullmar Fjord, Swedish Skagerrak coast. Journal of Phycology 38:284-296.. IV. Eriksson, B.K. & Johansson, G. Sedimentation reduces recruitment success of Fucus vesiculosus in the Baltic Sea. Submitted manuscript.. V. Eriksson, B.K. & Johansson, G. Effects of sedimentation on macroalgae: species-specific responses are related to reproductive traits. Submitted manuscript.. Papers I-III are reproduced with kind permission from the publishers. In papers I and III, I had the main responsibility for planning, compiling reference material and data analysis, while Gustav Johansson and I shared field work effort. In paper II, I took part in compiling reference material, fieldwork and assisted writing. In paper IV and V, I had the main responsibility for data analyses, while scientific planning and fieldwork was done in collaboration with Gustav Johansson. I wrote papers I, III, IV and V, assisted by comments from the co-authors.. 4.

(25) TABLE OF CONTENTS. LIST OF PAPERS .......................................................................................................... 4 TABLE OF CONTENTS................................................................................................ 5 PREFACE ....................................................................................................................... 7 INTRODUCTION .......................................................................................................... 8 Eutrophication: causes and consequences .............................................................. 8 The Swedish coastal zone ....................................................................................... 8 AIMS AND HYPOTHESES ........................................................................................ 10 Specific hypotheses investigated in this thesis ......................................................... 11 MATERIAL AND METHODS.................................................................................... 12 Long-term studies of vegetation change................................................................... 12 Study sites and reference material ........................................................................ 12 Methodological considerations and the use of functional groups ........................ 14 Field experiments on effects of sedimentation ......................................................... 14 Study site and species ........................................................................................... 14 General methods ................................................................................................... 15 Experimental set-up .............................................................................................. 15 RESULTS AND DISCUSSION................................................................................... 16 Long-term changes.................................................................................................... 16 Macroalgal changes in the Öregrund archipelago – northern Baltic Sea ............. 16 Macroalgal changes in the Gullmar Fjord – Skagerrak ........................................ 18 Effects of sedimentation ........................................................................................... 20 Fucus vesiculosus.................................................................................................. 22 Species-specific responses to sediment removal and strategies of propagation ................................................................................ 23 SYNTHESIS AND CONCLUSIONS .......................................................................... 25 ACKNOWLEDGEMENTS.......................................................................................... 26 CITED LITERATURE ................................................................................................. 28 POPULÄRVETENSKAPLIG SAMMANFATTNING (SWEDISH SUMMARY).... 33. 5.

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(27) PREFACE Coastal and estuarine ecosystems belong to the most productive marine environments. Benthic photosynthetic organisms cover the majority of shallow bottoms world-wide and add a structural complexity to the coastal environment that is absent in the open ocean. On soft bottoms a wide variety of angiosperms dominate, from Salicornia meadows in temperate salt-marshes and mangrove forests in tropical salt-swamps, to seagrass meadows in marine waters and reed vegetation in brackish to freshwaters. In tropical reef communities calcareous algae and corals form the basis of spectacularly complex ecosystems, while various forms of macroalgal vegetation dominate temperate rocky bottoms. Degeneration of these benthic communities is a frequently reported problem in a wide variety of aquatic ecosystems (for example coral reefs in the Caribbean, Rogers & Beets 2001; mangrove forests in Africa, Abuodha & Kairo 2001; reed vegetation in central Europe, van der Putten 1997; seagrass meadows in the Atlantic and Mediterranean, Duarte 2000). Causes of degeneration vary widely depending on the specific communities and understanding the processes regulating and changing our aquatic ecosystems is a major challenge for biology in the 21st century. THIS THESIS – describes long-term changes in macroalgal vegetation on the Swedish coast and analyses possible causes focusing on a major global concern – eutrophication.. 7.

(28) INTRODUCTION Eutrophication: causes and consequences During the last decades, marine eutrophication has become a major problem for coastal ecosystems on a global scale (Nixon 1990, Smith et al. 1999). Eutrophication is a process, a change in resources that Nixon (1995) defines as ‘an increase in the rate of supply of organic matter to an ecosystem’ which predominantly is caused by nutrient enrichment. Increases of coastal nutrient loads are mainly caused by human discharges. Globally, anthropogenic activities have increased terrestrial nitrogen fixation by more than 50 % and fluxes of phosphorus to the oceans almost three-fold compared to historic levels (Smith et al. 1999, Vitousek et al. 1997). The impact of human discharges accelerated in the 1960s and since then it has become evident that raised nutrient levels affect marine ecosystems by changing species diversity and community structure (Cloern 2001). A number of general processes are associated with eutrophication caused by increased nutrient loads in marine environments (Fig. 1). The primary effect of nutrient enrichment on macroalgal communities is a change in selective conditions, promoting a shift from dominance of slow-growing perennial algae to dominance of fast-growing ephemeral algae (Duarte 1995, Borum 1996, Cloern 2001). This process has been documented world-wide, for example in the Pacific (Littler & Murray 1975, Brown et al. 1990), the western Atlantic (Eleanor & Charles 1998), the North Sea (Rueness 1973, Schories et al. 1997), the Baltic Sea (Kangas et al. 1982, Kukk & Martin 1992), the Black Sea (Vasiliu 1996) and the Mediterranean Sea (Munda 1993, Rodriguez-Prieto & Polo 1996). There are also important secondary effects of nutrient enrichment by increased pelagic production, since increased turbidity and deposition of sediment on the bottom limit the amount of available light for the benthic vegetation (Fig. 1). Decreased light availability results in a shallower euphotic zone and limits the habitat for sublittoral macroalgae by decreasing their downward depth distribution (Kangas et al. 1982, Cloern 2001). Macroalgae have important functional qualities for associated fauna and reported effects by losses of algal community complexity include reduced diversity of marine invertebrates and reduced abundance of invertebrate prey for fish and shorebirds (reviewed by Cloern 2001). Large-scale changes of macroalgal communities have therefore major implications for ecosystem dynamics and performance in coastal areas. The Swedish coastal zone Most of the Swedish coastline belongs to the Baltic Sea area (Kattegat, Öresund, Danish Belt Seas and the Baltic Sea). The Baltic Sea is a semi-enclosed water body consisting of several connected sub-basins. The Swedish coastal zone has unique environmental conditions compared to other marine areas and provides special challenges for its macroalgal flora. The area is characterised by low salinity, low temperature and minute tidal amplitude. Salinity shows a clear gradient from the west coast of Sweden (Skagerrak 20-30 psu, Kattegat 15-25 psu) to the Baltic Sea proper. 8.

(29) Increased nutrient loads (N and P). Changes in selective conditions for benthic and pelagic communities. Changes in species compositions. Changes in interactions between trophic levels*. Increased pelagic production. Increased turbidity. Decreased water transparency and light availability for benthic communities. Increased organic sedimentation. Increased oxygen consumption resulting in oxygen depletion. FIG. 1. Outline of some general processes (large box) and subsequent effects (small boxes) associated with increased nutrient loads in coastal ecosystems. For a detailed model see Bonsdorff et al. (1997). * recent examples of nutrient enrichment changing interactions between trophic levels are presented in Worm et al. (2000) and Hemmi & Jormalainen (2002).. (6-7 psu) and northwards (Bothnian Sea ca 5 psu, Bothnian Bay < 2 psu). There is also a profound gradient in climate resulting in larger impact of ice cover and lower water temperatures in the north. The tidal amplitude decreases from 0.15-0.30 m in the Skagerrak to practically zero in the Baltic Sea. The Baltic Sea area is geologically young and the present environmental conditions stabilised only ca 3000 years ago (Ignatius et al. 1981). Therefore, few specialised brackish or endemic species have developed in the Baltic Sea and the Baltic macroflora is dominated by species of marine origin (Russell 1985). Accordingly, most of the Baltic macroalgae live close to their limit of tolerance to low salinity, resulting in an impoverished species pool with low number of species compared to Atlantic coasts (Wallentinus 1991). The distributions of almost 70 % of the macroalgae (> 1 mm) present in the Kattegat do not extend into the Baltic Sea proper (Snoeijs 1999). Fucus vesiculosus is the dominant canopy-forming macroalga in the Baltic Sea area and the only large perennial alga that tolerates the low-salinity environment in the northern Baltic Sea (Wallentinus 1991, Kautsky et al. 1992). Canopy algae are important habitat forming species that modify the physical and biological habitat for other organisms and thereby have a fundamental impact on their abundance and distribution (‘ecosystem engineers’, Jones et al. 1994). Thus, as the only abundant ecosystem engineer, F. vesiculosus forms the structural base for the most species-rich community in the Baltic ecosystem (Wallentinus 1991, Kautsky et al. 1992) and is exceptionally important for biodiversity in the Baltic Sea. The Baltic Sea area has been subjected to extensive eutrophication during the second half of the 20th century, as anthropogenic activities from a large and densely. 9.

(30) populated drainage area have increased the load of nutrients manifold compared to a century ago (Larsson et al. 1985, Rosenberg et al. 1990). Simultaneously, primary production has increased by approximately 100% in Kattegat (Richardson & Heilmann 1995) and spring and summer primary production is estimated to have doubled in the Baltic Sea (Elmgren 1989), resulting in an increased turbidity and sedimentation of organic material. In the northern Baltic proper, the water transparency (summer Secchi depth) has decreased by about 3 m during the last century (Sandén & Håkansson 1996) and the sedimentation of carbon originating from primary production has increased 510 fold (Jonsson & Carman 1994). Other well-documented large-scale effects on the Baltic Sea environment associated with the extensive eutrophication are for example decreased deep-bottom oxygen concentrations, increased frequencies of toxic blooms and altered community composition of macrofauna (reviewed by Bonsdorff et al. 1997 and Jansson & Dahlberg 1999). Changes in the macroalgal vegetation by locally increased nutrient loads have been documented from areas all around the Baltic Sea (for example Kangas et al. 1982, Rönnberg et al. 1985, Breuer & Schramm 1988, Kautsky et al. 1992, Kukk & Martin 1992, Middelboe & Sand-Jensen 2000). The macroalgal vegetation in these areas showed similar responses and the changes are consistent with those expected from eutrophication by nutrient enrichment: (1) a decline or complete disappearance of Fucus vesiculosus and other slow-growing perennial species, (2) an increase of fast-growing ephemeral and epiphytic algae and (3) a general decrease in depth penetration of the vegetation. Furthermore, Kautsky et al. (1986) reported that F. vesiculosus depth distribution had decreased by ca 3 m since the 1940s in an area free from local pollution on the Swedish east coast. This indicates that changes in the benthic vegetation are not confined to locally polluted areas and that the general eutrophication of the Baltic Sea area has a large-scale effect on the Baltic macroalgal community as well.. AIMS AND HYPOTHESES The general aim of this thesis was to examine and evaluate effects of the documented large-scale eutrophication in the Baltic Sea area on macroalgal vegetation in Swedish coastal waters. The first three papers contain three different long-term studies on vegetation change, where we reinvestigate earlier studies on macroalgal distribution and community composition. In paper I, we investigate long-term changes (between 1943-44, 1984 and 1996) in the macroalgal vegetation in the Öregrund archipelago on the east coast of Sweden, visiting some of the localities where Kautsky et al. (1986) described a decreased depth distribution of Fucus vesiculosus since the 1940s. In paper II and III, we investigate long-term changes (between 1960-61 and 1997 and between 1941 and 1998) in the macroalgal vegetation in the Gullmar Fjord area on the west coast of Sweden to compare possible trends and evaluate if similar processes are apparent on the Swedish east and west coast. The two last papers contain two field experiments where we specifically address one component of nutrient enrichment,. 10.

(31) increased organic sedimentation. In paper IV, we examine the effect of sedimentation on Fucus vesiculosus recruitment in a short-term experiment in the Baltic Sea. In Paper V, we examine effects of sedimentation on macroalgal colonisation and development in a long-term experiment in the Baltic Sea, focusing on species-specific responses in relation to different species’ reproductive strategies. SPECIFIC HYPOTHESES INVESTIGATED IN THIS THESIS. • Long-term trends in macroalgal vegetation in the Öregrund archipelago and the Gullmar Fjord are consistent with changes expected from eutrophication by nutrient enrichment: (1) increases of fast-growing opportunistic ephemeral algae, (2) decreases of slow-growing perennial algae, and (3) declined depth distributions of species (Paper I, II & III).. • Previously documented reductions in Fucus vesiculosus’ depth distribution in the Öregrund archipelago are persistent (Paper I).. • The present sediment load is an important constraint for the recruitment success of Fucus vesiculosus and for the colonisation and development of macroalgal vegetation in the Baltic Sea in general (Papers IV & V).. • Sedimentation has an effect on macroalgal community composition and speciesspecific effects of sedimentation correlate with species’ reproductive strategies (Paper V).. • The effects of sedimentation on the macroalgal vegetation documented in the experimental studies are consistent with the field-observations made in the longterm studies (Papers IV & V).. 11.

(32) MATERIAL AND METHODS LONG-TERM STUDIES OF VEGETATION CHANGE A major problem with long-term comparisons of vegetation is to obtain proper reference data. To evaluate if the macroalgal vegetation is affected by a general largescale eutrophication, it is necessary to identify sites that are described before the onset of the recent major environmental changes and that are situated outside locally polluted areas. The large-scale eutrophication of the Baltic Sea area started in the 1940s and accelerated in the 1960s (Jonsson et al. 1990, Jonsson & Carman 1994, Jansson & Dahlberg 1999). Most previous studies of long-term effects have mainly been floristically inclined (Rueness 1973, Hardy et al. 1993, Hill 1996, Schories et al. 1997, Munda 2000) and therefore provide limited information on the composition and structure of the vegetation. Existing quantitative time series of macroalgal vegetation are usually limited to the last 30 years (Lundälv et al. 1986, Raffaelli et al. 1989, Brown et al. 1990, Lavery et al. 1991, Kelly 1995). In our studies, we have taken advantage of access to early ecological studies that are sufficiently detailed to allow reinvestigation of the exact localities. This material consists of published and unpublished quantitative vegetation records from 1941-44 and 1960-61, collected by Mats Wærn and his students (Wærn 1952, Wærn unpublished material, Pedersén 1971). Study sites and reference material The long-term studies were conducted in two areas (Fig. 2), the Öregrund archipelago in the southern Bothnian Sea (northern Baltic Sea) and the Gullmar Fjord on the Swedish west coast (Skagerrak). The Öregrund archipelago (salinity 5 psu) consists of more than 1700 rocky islands (Wærn 1952). The area is not affected by pollution from any larger local sources and the water circulation is mainly regulated by a strong water current flowing southwards along the Swedish coast from the Bothnian Sea to the Baltic Sea proper (Ambjörn et al. 1981, Mälkki 1981). In the 1940s, Mats Wærn made extensive ecological studies of the macroalgal vegetation in the Öregrund archipelago (Wærn 1952). Using helmet diving, he described the vegetation along a number of depth profiles including species diversity and quantitative distribution (Wærn 1952; unpublished field notes of Mats Wærn 1938-1944, kept at the Department of Plant Ecology, Uppsala University). In 1984, Mats Wærn made a last investigation in the area describing changes in the Fucus vesiculosus belt (Kautsky et al. 1986). In 1996, we revisited five of the best-described diving profiles from 1943-44 and 1984 (Paper I). The Gullmar Fjord is the only true threshold fjord in Sweden. The hydrography of the fjord is ruled by Baltic currents with brackish water and annual inflows of saline deep water from the Skagerrak (Svansson 1984). These properties make the Gullmar Fjord comparable to the Baltic Sea, both being enclosed water bodies with a similar. 12.

(33) Öregrund archipelago. Bothnian Sea. Björkö Island Skagerrak. Gullmar Fjord. Kattegat. Sweden Baltic Sea proper. FIG. 2. Map showing the localities of the two long-term studies, the Öregrund archipelago and the Gullmar Fjord, and the experimental area at Björkö Island.. stratification and exchange of water with different salinity and origin. Since the late 1960s no major local sources of eutrophication affect the fjord (Nordberg et al. 2000). However, long-term declines in deep-bottom oxygen conditions in the fjord indicate that primary production and subsequent organic sedimentation have increased during the second half of the 20th century (Rosenberg 1990). This suggests that also long-term nutrient dynamics are comparable in the Gullmar Fjord and the Baltic Sea, making a comparison of long-term trends in the macroalgal vegetation highly interesting. In 1941, Mats Wærn made a detailed description of the macroalgal vegetation around the island Stora Bornö inside the Gullmar Fjord (unpublished field notes of Mats Wærn 1941, kept at the Department of Plant Ecology, Uppsala University). In 1960-61, Mats Wærns student, Torbjörn Pedersén, described the vegetation along three depth profiles, two on the threshold of the fjord and one in a small bay inside the fjord (Bergsviken). In 1997 we revisited Torbjörn Pederséns three diving profiles (Paper II), and in 1998 the two best-described diving profiles of Mats Wærn from Stora Bornö (Paper III).. 13.

(34) Methodological considerations and the use of functional groups There are difficulties with long-term comparisons between different studies of macroalgal vegetation that have to be considered. Macroalgae fluctuate on three different temporal scales, short-lived ephemeral species mainly on an intra- or interannual scale and perennial species mainly on a decadal scale. Some ephemerals are highly seasonal and can be grouped into spring, summer and autumn species. Other ephemerals occur more or less in the same proportions over the year, but vary extensively between years. Perennial species seem to be relatively stable in occurrence but trends and regeneration processes over the course of several years have been observed (Rönnberg et al. 1985). Thus, it is difficult to separate species’ natural fluctuations from persistent trends when continuous time series of the macroalgal vegetation are lacking. In paper I we therefore focused on perennial brown algal belts’ depth distributions which should be relatively stable in their occurrences over time. We also had access to data both from 1943-44 and 1984, which provided a limited control of the persistence of temporal trends. In paper II and III, we used the functional group approach to avoid relying on single species in our conclusions. The rationale of this approach is that macroalgal species’ functional characteristics are related to form and life-history characteristics and thereby can be expected to respond similarly to the environment (Littler & Littler 1980, Littler et al. 1983, Steneck & Dethier 1994). Numerous experimental studies have provided strong evidence of the generality of these assumptions regarding algal form and the productivity potential of the environment (mostly defined as light or nutrient availability, see Padilla & Allen 2000 and references therein). We analysed temporal trends in functional groups based on size (length of the thallus), thallus shape (functional form groups modified from Littler et al. 1983) and longevity (only in paper III). FIELD EXPERIMENTS ON EFFECTS OF SEDIMENTATION Study site and species The field experiments were carried out on a submerged stone reef 60 m offshore at Näskubben on Björkö Island (59°53Ń, 19°05É, Sweden), close to the border between the Bothnian Sea and the Baltic Sea proper (Fig. 2). The reef consists of gently descending solid rock with terraces and scattered boulders that provides abundant substrate for a well-developed macroalgal vegetation from 4 down to 16.5 m depth. Fucus vesiculosus is the only fucoid present and forms a belt of vegetation (> 50 % cover) from 4 to 5.5 m depth. The Fucus plants gradually decrease in size from ca 50 cm where it grows most vigorously, to ca 10 cm small, dwarf-like and non-fertile individuals at the lower limit of occurrence (6.5 m depth). Below the Fucus belt, red algae dominate the vegetation down to 11-12 m (mainly Furcellaria lumbricalis, Polysiphonia fucoides and Rhodomela confervoides), while the small brown alga Sphacelaria arctica dominates from 10 to 16.5 m depth. Different ephemeral algae peak in cover during the year and co-occur epiphytically and epilithically with the. 14.

(35) perennial vegetation (mainly Ceramium tenuicorne, Cladophora glomerata and Pilayella littoralis). Björkö Island is sparsely populated (mostly summerhouses) and free from major local sources of eutrophication. The salinity is rather stable at 5.3-6 psu (practical salinity units), while water temperature ranges between 12-17˚C in summer and 0-3˚C in winter. The study area is well-exposed but protected from the open sea by a thin fringe of small islands and skerries. Outside the island fringe, water depth rapidly increases below 100 m depth. Sedimentation based on yearly averages at ca 100 m depth ranged between 2.4 g·m-2·d-1 (dw) (59°52Ń, 19°19É, Broman 1990, pers. com.) and 8.5 g·m-2·d-1 (dw) (59°55Ń, 19°11É, Strandberg et al. 1998), at two different sampling stations within 15 km of the experimental site. General methods We examined effects of sedimentation on the macroalgal vegetation by quantifying macroalgal colonisation and development on artificial substrate exposed to different sediment loads. As artificial substrate we used clay bricks (15x30 cm). The natural depositional environment in near-shore areas is highly variable depending on weather conditions and water movement. Thus, it is difficult to model natural sediment additions both regarding the amount of sediment settled and small-scale fluctuations in deposition and erosion. Since our prime interest in the two field-experiments was to investigate if the existing sediment load actually had an effect on the vegetation, we therefore manipulated the depositional environment by manually removing loose sediment from the bricks; the bricks were held upside-down and the sediment was carefully shaken off. In both experiments, half the number of bricks was cleaned from sediment every 3-4 weeks (sediment removal treatment) and the other half was exposed to the natural sediment load (natural sedimentation treatment). Experimental set-up In paper IV we focused on the recruitment success of Fucus vesiculosus in a shortterm experiment. We recorded the effect of the sediment treatments on the establishment of Fucus juveniles on bricks that were exposed to Fucus settlements during one reproductive season (experimental time was from April to October 2001). The main reproductive period of F. vesiculosus in the northern Baltic Sea is in June-July (Bäck et al. 1991, Andersson et al. 1994). In order to mimic natural settlement conditions and to account for the effect of filamentous vegetation on sediment deposition, we used bricks with an already well-developed filamentous perennial vegetation. The bricks were introduced 3 years prior to the experiment at 8 to 9 m depth and moved to the lower fringe of the Fucus vegetation at 6 m depth at the start of the experiment. In paper V we recorded effects of the sediment treatments on the colonisation and development of all macroalgal species present and compared effects of the sediment treatments on species with different reproductive strategies. In October 1997, we started a long-term experiment by introducing bricks into the water at 8 and 15 m depth. Bricks were thereafter sampled in an irregular time series over 4.5 years.. 15.

(36) Sampled bricks were transported to the laboratory were we visually estimated the algal species’ percentage cover and examined how the species were recruited to the bricks. Throughout the study, we noted findings of spore producing structures (sexual or nonsexual sporangia), fragmented individuals attached with secondary rhizoids or entangled on the bricks, stolon-like rhizoids and persistent resting stages. Furthermore, we compiled published information from the Baltic Sea on the reproduction of the species present.. RESULTS AND DISCUSSION LONG-TERM CHANGES The results of the long-term studies show that the macroalgal vegetation has changed significantly since the 1940s – 1960s in the Öregrund archipelago and in the Gullmar Fjord area. We have documented increasing trends of species with opportunistic functional group characteristics, decreasing trends of large more complex perennial species and declines in species’ depth distributions. These changes are consistent with the predictions made for a general increase in biological production by nutrient enrichment resulting in eutrophication. The opportunistic species-group includes algae with high productivity and the capacity of rapid growth that are common in disturbed environments (Littler & Littler 1980). These functional traits are characteristic for small and thin algae because of their high surface to volume ratio and consequently high nutrient uptake efficiency (Littler & Murray 1975, Littler et al. 1983) and high photosynthetic potential (Johansson & Snoeijs submitted manuscript). Opportunistic species are also predominantly ephemeral since they are adapted to utilise intermittently favourable conditions (‘ruderals’ Grime 1977, Littler & Littler 1980). Thus, because they have a more efficient nutrient uptake, opportunistic species are favoured over large more complex slow-growing species when nutrient availability increases (Thompson & Valiela 1999, Worm et al. 1999, Worm et al. 2000). Most of the ephemeral macroalgae in the Baltic Sea belong to the opportunistic species-group, while species with lower productivity and slow growth rates mainly are perennial (Wallentinus 1984). Macroalgal changes in the Öregrund archipelago – northern Baltic Sea In the Öregrund archipelago, the depth distribution of the Fucus vesiculosus belt decreased significantly between 1943-44 and 1996, both considering average depth and lower distribution limit (with an average of 1.7 and 2.5 m depth respectively, Fig. 3). The study from 1984 documented a similar decline in F. vesiculosus’ general depth distribution (Kautsky et al. 1986) and in our five investigated diving profiles there was no significant change in the lower distribution limit between 1984 and 1996. This confirms that there was a major change in depth distribution of F. vesiculosus between the 1940s and the 1980s and shows that the change is persistent. We found no similar. 16.

(37) (a). (b) 1943-44. Max. depth Mean depth. 1996-98 0. 100%. 100% 1. *. 2 3 4 5. Depth (m). 6 7 8 9 10 11 12. 1943-44 1984 1996. FIG. 3. Changes in the depth distribution of Fucus vesiculosus between the 1940s and the 1980-90s in five diving profiles in the Öregrund archipelago. (a) percentage cover of F. vesiculosus at different depths in 1943-44 and 1996-98 (based on paper I and unpublished data). Mean, minimum and maximum covers in the investigated profiles are indicated. (b) lower distribution limits of F. vesiculosus (Max. depth) in 1943-44, 1984 and 1996 and mean depths in 1943-44 and 1996 (based on paper I and Kautsky et al. 1986). * no data were available for 1984. Error bars indicate one standard deviation of the mean. The depth penetration of F. vesiculosus decreased significantly both expressed as lower distribution limit and as mean depth (t-test, n = 5 sites, p < 0.05).. trend for any of the other perennial species. This is in contrast with the 1984 study that reported that the lowermost growing brown algal belt (dominated by Sphacelaria arctica Harvey) had been replaced by different red algae (Kautsky et al. 1992). The cover of ephemeral algae was significantly higher in 1996 than in 1943-44; the mean maximum cover increased by 48 % (fig. 5 in paper I). There were no signs of detoriation of the Fucus vesiculosus belt at shallower depths, so causes for the decline in depth distribution must be identified among constraints that change with depth. Kautsky et al. (1986) suggested that the declined depth distribution was caused by decreased water transparency due to a large-scale eutrophication. This is supported by the documented decrease in summer Secchi depth in the northern Baltic proper (Sandén & Håkansson 1996). However, other factors that increase with eutrophication by nutrient enrichment may also be involved. Water movement by wave action decreases with depth which creates a depth gradient in sediment cover (Håkansson & Jansson 1983) and affects epiphytic overgrowth (‘the whiplash effect’, Kiirikki 1996). Both these factors influence the amount of available light for Fucus plants and are proposed to interfere with the establishment success of Fucus by pre-emption of available space for settlement (Kangas et al. 1982). In 1996, 17.

(38) a thick overgrowth of epiphytic ephemeral algae and a conspicuous sediment layer covered the lower part of the Fucus vegetation (6-10 m of depth). In 1943-44, the overgrowth was much lower and a conspicuous sediment layer was neither mentioned in Wærn (1952) nor in Wærns original diving protocols. Regardless of the specific causes of the decreased depth distribution of F. vesiculosus, the implications for the Baltic Sea ecosystem should be of serious concern. Generally, shallower depth distributions will make the F. vesiculosus belts more susceptible to severe disturbances, such as ice scouring, low water events and strong wave action. Considering the importance of F. vesiculosus as an ecosystem engineer for other organisms in the Baltic Sea, increased instability of the Fucus belts may have severe effects on general productivity, community structure and biodiversity in coastal areas. Large-scale deterioration and disappearance of Fucus communities have repeatedly been reported from different areas in the Baltic Sea during the last decades (Schramm 1996). In the early 1980s F. vesiculosus had completely vanished from several localities in the Archipelago Sea and strong declines were detected at other sites in Finland (Kangas et al. 1982, Hällfors et al. 1984, Mäkinen et al. 1984, Rönnberg et al.1985). In the late 1980s it had partly re-colonised its former habitats but the decline had continued in other parts of the archipelago (Rönnberg 1991). Drastic declines of F. vesiculosus have also been documented in the Kiel Bay in Germany (Breuer & Schramm 1988, Vogt & Schramm 1991), in the Gulf of Riga (Kukk & Martin 1992, Kukk 1995), along the coast of Lithuania (Olenin & Klovaitơ 1998) and in several sheltered localities close to the mainland of Sweden (Kautsky et al. 1992). Macroalgal changes in the Gullmar Fjord – Skagerrak In the Gullmar Fjord area, the community composition of macroalgae changed considerably both at the threshold of the fjord and Bergsviken between 1960-61 and 1997 (fig. 8 in paper II) and at Bornö inside the fjord between 1941 and 1998 (fig. 2 in paper III). While the changes in total macroalgal cover were contradictory in the two studies, there were obvious similarities in the responses of functional groups. At the threshold of the fjord and in Bergsviken, total macroalgal cover increased between 1960-61 and 1997 (Wilcoxon signed rank test, n = 123 species scores, p < 0.05) (see material and methods and fig. 9 in paper II for an explanation of species scores). This increase was mainly due to significant increases of small (< 10 cm, n = 60 species scores, p < 0.05) and thin filamentous algae (n = 69 species scores, p < 0.001), while large and coarsely branched algae showed no significant changes (Paper II). At Bornö, total macroalgal cover decreased significantly between 1941 and 1998 (Paper III). This decrease was mainly due to significant decreases of large (> 10 cm), coarsely branched and perennial algae, while small, thin filamentous and aseasonal ephemeral algae showed no significant changes in cover. Thus, small (< 10 cm), thin filamentous and persistent ephemerals generally increased in importance (absolute or relative abundance) in the Gullmar Fjord ecosystem between the 1940-60s and the 1990s, whereas large (> 10 cm), coarsely branched and perennial algae decreased (Table 1).. 18.

(39) At Bornö, there was also a significant decrease in the depth distributions of macroalgal species (average decrease = 2.8 m depth) between 1941 and 1998, as well as a dramatic decline in species richness in the lower littoral; below 16 m depth we found 4 species compared to 19 species reported in 1941. TABLE 1. Results from the two studies of long-term changes in macroalgal functional groups between 1960-61 and 1997 (Paper II) and 1941 and 1998 (Paper III) in the Gullmar Fjord area. Percentage values from paper III show the change in representation of the functional group in the total algal cover. FUNCTIONAL GROUPS. Paper II. Paper III. All algae/total cover Size: Small algae (< 10 cm) Large algae (> 10 cm) Thallus form: Thin filamentous Coarsely branched Longevity: Aseasonal ephemerals Perennial algae. Significant increase *. Significant decrease ***. Significant increase * N.s.. N.s. (relative increase 12 %) Significant decrease ***. Significant increase *** N.s.. N.s. (relative increase 14 %) Significant decrease **. Not tested Not tested. N.s. (relative increase 19 %) Significant decrease **. Notes: Paper II – statistical results calculated using Wilcoxon test for dependent samples. Paper III – statistical results calculated using t-test for dependent samples. N.s. = no statistically significant change in absolute abundance between study periods, * P < 0.05, ** P < 0.01, *** P < 0.001.. There are strong indications that the primary production and sedimentation of organic matter have increased in the Gullmar Fjord during the last half of the 20th century. Since the beginning of the 1960s nutrient concentrations showed significantly increasing trends with time, both for phosphorus and nitrogen (Svansson 1984, Paper III). Svansson (1984) and Rosenberg (1990) described significantly declining deepwater oxygen concentrations in the fjord during the same period of time. There were no similar temporal trends in temperature or salinity, suggesting that the oxygen depletion is caused by a rise in the production and sedimentation of organic material in the water column (Rosenberg 1990). Nordberg et al. (2000) also showed that the decline in oxygen concentrations was paralleled by an increase of organic carbon content in the sediment. Our results indicate that the selective conditions in the fjord have changed due to the increased nutrient availability, favouring fast growing ephemeral algae over slow-growing perennial algae. The detoriation of the deeper vegetation at Bornö further indicates that the production of organic material in the water column has increased. The contrasting trends in terms of total macroalgal cover in paper II and III probably depend on the different exposure and water exchange conditions on the threshold compared to the interior of the fjord. At the exposed threshold of the fjord, 19.

(40) higher nutrient concentrations probably cause a general increase of opportunistic life forms and increased productivity dominates the temporal trend. This general trend is probably reversed at Bornö, where the influence from land and the enclosed and sheltered environment result in naturally high concentrations of organic material in the water column. Increased primary production will therefore complement an already high load of organic material in the water, causing severe light conditions and degrading substrate availability for the deeper vegetation. In 1997, we found an increase of perennial red algae with delicate leaf-like thalli (Delesseria sanguinea and Phycodrys rubens) at the two localities most exposed to wave action, whereas perennial red algae with tougher leaf-like thalli (Coccotylus truncatus [syn. Phyllophora truncata] and Phyllophora pseudoceranoïdes) prevailed at the more sheltered locality with a heavy sediment load. We hypothesised that increased abundances of delicate species with a large growth potential are caused by eutrophication, but that this effect may be counteracted when eutrophication results in a high load of sedimentation since tougher species should better withstand a thick sediment cover (Daly & Mathieson 1977). Accordingly, perennial red algae with tougher thalli (Chondrus crispus and Furcellaria lumbricalis) decreased at the exposed sites, but not at the site with most sedimentation. In the Bornö study, we tested this hypothesis by correlating the abundance of each species to local sediment cover using direct gradient analysis (Canonical Correspondence Analysis). Species that were negatively correlated with local sediment cover in 1998 decreased significantly in amount between 1941 and 1998 (mean change = -26 %). Species that were positively correlated with local sediment cover in 1998 showed no significant change in cover (mean change = 3 % in cover) but increased in relative abundance with 19 % between 1941 and 1998 (fig. 6e & 10 in paper III). These results suggest that part of the change in species composition in the Gullmar Fjord between the 1940s – 1960s and the 1990s could be related to an increased sediment load. EFFECTS OF SEDIMENTATION The experimental studies clearly demonstrate that variation in the sediment load on rocky-bottoms has major effects on the macroalgal vegetation. Sediment removal significantly favoured macroalgal colonisation and development (Fig. 4 & 5, Paper IV & V). In the long-term experiment (Paper V), there were clearly species-specific responses to the sediment treatments and direct gradient analyses also showed that the sediment treatments had a significant effect on the species composition on the bricks. For example, ephemeral green algae (Cladophora glomerata and Enteromorpha spp.) were highly tolerant to sedimentation, while belt-forming perennial brown algae (Fucus vesiculosus and Sphacelaria arctica) were not. The effect of sedimentation increased with depth (Paper V, for F. vesiculosus see below), which is consistent with the depth gradient in sediment cover present in the study area and suggests that sedimentation is a factor that can limit species’ depth distributions.. 20.

(41) Algal cover (%). 200 160 120 80 40 0 1998. 100. Algal cover (%). (a) 8 m depth. 1999. 2000. 2001. 2002. (b) 15 m depth. 80. Sediment removal treatment. 60. Natural sedimentation treatment. 40 20 0 1998. 1999. 2000. 2001. 2002. Time (years) FIG. 4. Effects of sediment removal on the establishment and development of the total algal cover on artificial substrates (bricks) introduced in the water in October 1997, at (a) 8 m depth and (b) 15 m depth. Data are mean percent cover (± 1 SD, n = 5 bricks). Note that the scales on the y-axes are different.. Sedimentation is expected to be a major factor determining the local distribution of algal assemblages (for example Schiel & Foster 1986, Pedersén & Snoeijs 2001). There are also several studies that have demonstrated changes in macroalgal community composition along depositional gradients (for example Daly & Mathieson 1977, Santos 1993, Saiz Salinas & Isasi Urdangarin 1994). Causal mechanisms that determine the composition of algal communities in different depositional environments are poorly understood, but there are several attributes that are proposed to be advantageous for macroalgae in sediment-rich habitats. These include: tough thalli (Daly & Mathieson 1977, Paper II), vegetative propagation (Norton et al. 1982, Airoldi 1998), temporal cycles of reproduction and/or growth synchronised to fluctuations in sediment cover (Stewart 1983, Kiirikki & Lehvo 1997) and the ability to regenerate from basal thallus parts that can resist burial and abrasion (Daly & Mathiesen 1977, Stewart 1983). However, there are still few experimental studies of sediment effects on macroalgae that have investigated species-specific responses and community composition, comparing the effect of sedimentation between species with different traits (Airoldi & Cinelli 1997, Airoldi 1998, Paper V). 21.

(42) Median no. of juveniles · m -2. Fucus vesiculosus We showed that sedimentation has a major effect on the recruitment success of Fucus vesiculosus. Juvenile density was significantly higher on bricks where sediment was removed compared to bricks exposed to natural sediment conditions, both at 6 and 8 m depth (Paper IV & V, Fig. 5). That recruitment success can be reduced by sedimentation has been shown in both laboratory experiments (Devinny and Volse 1978) and field conditions (Umar et al. 1998) for other species of large brown macroalgae. Although sedimentation has been suggested to interfere with the recruitment of F. vesiculosus in the Baltic Sea (Kangas et al. 1982, Kautsky & Serrão 1997, Kiirikki & Lehvo 1997, Berger et al. 2001, Paper I), our study constitutes the first experimental result demonstrating this effect.. 2500. Natural sedimentation treatment. 2000. Sediment removal treatment. 1500 1000 500 0. 6m. Depth (m). 8m. FIG. 5. Effects of sediment removal on total number of establishments of Fucus vesiculosus on artificial substrates (bricks) in a short-term experiment at 6 m depth (n = 16 bricks, Paper IV) and a long-term experiment at 8 m depth (n = 40 bricks, Paper V). Bars show median number of recruits while the error bars indicate upper and lower quartile ranges.. The relative effect of sediment removal on the recruitment success of Fucus vesiculosus was much higher at 8 than at 6 m depth (Fig. 5). In the long-term experiment at 8 m depth (Paper V) we found Fucus juveniles almost exclusively on bricks where the sediment was removed. That Fucus juveniles established on the bricks at 8 m depth at all was highly unexpected, since the lower visible depth limit of Fucus plants was at 6.5 m depth. These results indicate that the recruitment of F. vesiculosus was limited in depth by sediment deposition in the study area. In the shortterm experiment at 6 m depth (Paper IV), we found many Fucus juveniles that were too large to have been established during experimental time, i.e. juveniles from the reproductive season 2001. These juveniles probably established prior to the 22.

(43) experiment. In order to mimic natural conditions, the bricks in this study were placed in advance at 8-9 m depth to gain a cover of filamentous vegetation. Since this was ca 2 m below the lower visible depth limit of Fucus plants we did not expect any colonisation of Fucus juveniles before we moved the bricks to 6 m depth at the start of the experiment. However, the bricks were introduced in the water during spring 3 years earlier and probably provided available substrate for Fucus settlement during the reproductive season that started short thereafter. Furthermore, the sediment treatments in the short-term experiment mainly influenced the smaller juveniles (fig. 2 in paper IV) suggesting that the negative effect of sedimentation mainly was the result of an impairment of settling and establishment of new juveniles, while already established individuals were less affected. Species-specific responses to sediment removal and strategies of propagation In the long-term experiment, species responses to the sediment treatments were closely related to the species’ main reproductive strategies (Fig. 6, Paper V). Cladophora glomerata and Enteromorpha spp. showed no response to the sediment removal treatment at 8 m depth. They had similar life histories with continuous spore production from spring to late summer-early autumn and colonised the bricks with large cohorts early in the succession (characteristics of opportunists, Littler & Littler 1980). After initial spore dispersal they produced large amounts of resting stages on brick surfaces. All other species that colonised the bricks by spore dispersal were highly favoured by sediment removal. This category consisted of Fucus vesiculosus, Pilayella littoralis and Sphacelaria arctica, that all have short peak periods of reproduction (1-2 months) in the Baltic Sea. Regeneration from basal crusts has been suggested to confer tolerance to high sedimentation by releasing the alga from the dependence of spore attachment to substrata that are often buried (Norton et al. 1982, Stewart 1983). Long continuous spore production should likewise be advantageous in temporally unstable sediment environments since establishment success will not be dependent on sediment conditions during a short period of time. Thus, by combining these traits C. glomerata and Enteromorpha spp. seem highly adapted to exploit temporally favourable sediment conditions for both spore attachment and growth, while the species dependent on short periods of spore release suffer from the sediment load. Vegetative propagation by dispersal of fragments was very common in the study area and also seemed to be a successful strategy to tolerate sedimentation. For 7 species we could identify fragmentation as the main (or only) source of dispersal. Three of these species (Polysiphonia fucoides, Rhodomela confervoides and Ceramium tenuicorne) were favoured by sediment removal but not as consistently as the species dependent on short periods of spore dispersal (Fig. 6). This is consistent with results from the Mediterranean Sea, where experimental accretion of sediment influenced the success of sexually dispersing algae but did not affect the vegetatively propagating algal turf (Airoldi 1998). Analogous with long continuous spore production, dispersal by fragments probably increases the likelihood of finding suitable patches of substrate. 23.

(44) in a temporally unstable sediment environment. Loose thallus fragments survive for longer periods in the water than unattached spores and the release of fragments will not be confined to one short period of time. Dispersal by fragments probably also decreases post-settlement mortality, as small sporelings are more easily buried by sediment than larger thallus parts. These results indicate that vegetative propagation is an important means of reproduction for many species in the Baltic Sea and that this provides selective advantages when conditions for establishments fluctuate unpredictably.. Species mainly dependent on short periods of spore dispersal Species mainly dependent on dispersal by fragmentation Species with long continuos periods of spore dispersal. **. 45. **. 0.30. 0.15. n.s.. 30. *. 15. 0.00. Algal cover (%). Fucus vesiculosus cover (%). 0.45. 0. Clad glo. Ente spp. Furc lum. Stic tort. Clad rup. Poly fib. Cera ten. Rhod con. Poly fuc. Spha spp. Pila lit. -15. Fucu ves. -0.15. FIG. 6. Effects of sediment removal on species cover (sediment removal treatment - natural sedimentation treatment) on artificial substrates (bricks) at 8 m depth. For each species the results are calculated from the sample in the time series (1998-2002) where the species showed maximum cover on the bricks (different samples for different species). Values for all samples are presented in paper V. Differences between mean effects of sediment removal and zero were tested with t-tests for dependent samples (n = 5 bricks) (table 2 in paper V; Fucus vesiculosus, Cubic-root transformed, t = 3.87). n.s = no significant effect of the treatment, * p<0.05, ** p<0.01. The cover of F. vesiculosus is given on the left y-axis and the cover of all other species on the right y-axis.. 24.

(45) SYNTHESIS AND CONCLUSIONS In this thesis, I have documented significant and generally similar long-term changes in macroalgal community composition and species’ distributions at three different sites on the Swedish coast. Documented changes were consistent with those expected from eutrophication by increased nutrient availability, including increased abundances of opportunistic ephemeral algae, decreased abundances of large more complex perennial algae and a declined depth distribution of species. In the Baltic Sea area, the nutrient load has increased manifold during the second part of the 20th century and changes in the macroalgal vegetation by locally increased nutrient loads have been reported from different areas around the Swedish coast (reviewed by Jansson & Dahlberg 1999). However, the long-term studies in this thesis were conducted in areas that today are free from major local pollution. This indicates that the general eutrophication of coastal waters around Sweden has large-scale effects on the macroalgal vegetation also outside locally polluted areas. These results are of serious concern and emphasise that eutrophication is a problem and has the potential to change the productivity and function of entire coastal ecosystems. I have also demonstrated that the present sediment load is a significant constraint for the macroalgal vegetation in the Baltic Sea area and that sedimentation affects community composition and species distributions. Increased organic sedimentation is a common component of coastal eutrophication and simultaneously as nutrient load has increased, the organic sedimentation has increased 5-10 fold in the Baltic Sea (Jonsson & Carman 1994). Likewise, indirect evidence indicates that organic sedimentation has increased significantly in the Gullmar Fjord (Rosenberg 1990). The experimental results predict that increased sedimentation should constrain mainly species that are highly dependent on short periods of spore release for propagation (like Fucus vesiculosus), while species that are adapted to exploit temporally favourable conditions for establishment and growth (for example opportunistic species like Cladophora glomerata and Enteromorpha spp.) should be little affected. The experimental results also suggest that increased sedimentation should decrease species’ depth distributions (most notably F. vesiculosus). Thus, the experimental results predict changes in the macroalgal vegetation by increased sedimentation that are similar to the documented changes in our long-term studies, and that are similar to those expected from increased nutrient availability in the Baltic Sea. These changes include an increased abundance of opportunistic fast growing algae (like Cladophora glomerata and Enteromorpha spp.) and a decreased distribution of the large slow-growing perennial F. vesiculosus. To conclude, I therefore suggest that the long-term changes in macroalgal vegetation on the Swedish coast documented in this thesis are a consequence of a large-scale eutrophication and that parts of the changes are direct effects of an increased organic sedimentation in these areas.. 25.

(46) ACKNOWLEDGEMENTS First of all I want to express my gratitude to my mentors, Pauli Snoeijs, Marianne Pedersén and Mats Wærn. Marianne awakened my interest in the marine realm by amazing stories and inspired me to want to become a phycologist. Pauli made me a phycologist by providing me with the opportunity and trust to go underwater and she has guided/supervised me through the mysterious world of science with enthusiasm, care and a great deal of personal commitment. Mats early research effort has made much of the work in this thesis possible and has been a valuable and wealthy source of information throughout my own vista on marine vegetation. Gustav Johansson and I have been partners in algal-crime for a long time, but right now it feels like a much too short time. Together we have excavated the dark and lonely bottoms of the Baltic (in the water only Gustav and Flipper can hear you scream), shared wonderful spring diving below military ship convoys (“just hope there are no submarines in this convoy” – but of course there were), fought furious iron giants (strykjärn – which are attracted to diving flags like flies to a dead corpse), developed the new sports event of 100 m underwater running with 10 kilos of bricks in your lap into a fine art (status of exhibition event in the Olympics 2008?) and pondered over the immense beauty of algal communities in all possible as well as impossible situations (or as Gustav always states when it has been a little too close – “you don’t need as much air as you would think”). Gustav, thanks for all good times, creative thinking and good ideas and for always having some extra air and snus for me. The Department provides a nice atmosphere to work in but it is the people within the walls that matter, and there are many of you that deserve thanks. Ingrid and Lies, “copepoderna i rummet bredvid”, you have made our little aquatic collective a great place to work in. Ingrid, thank you for always being interested in my questions and knowing so much about everything that you can answer them, but most of all for being a wonderful friend. Lies has read this thesis more times than anybody on this earth, including myself, and without your help I would probably still not be finished. Thank you for all the effort and advice, especially in those hard last months. Big thanks to Christel Gustavsson, Micke Niva and Christina Borg for nice companionship, special moments and great laughs at and outside the department, Tord Snäll for joyful statistics and after work beer enthusiasm, Malcolm McCausland, Geir Løe, Emil Nilsson and Svenja Busse for being… just you in your different ways and making working here more interesting, Shamit Ray for all the nice Bollywood singing in the lab, Jon Ågren for reading and improving my manuscripts, Håkan Rydin, Marcos Méndez and Julio Alcantara for interesting discussions about science, Ulla Johansson for taking care of bureaucratic impossibilities, Willy Jungskär for always taking the time to help with computer related problems, the Florø diving and gambling society, Karin Gerardt for taking us on a wonderful journey through the amazing Costa Rica and of course the Costa Rica crew: Arnie, Shadrack, Tesfaye, Micke, Svenja, Christel, Tord, Ingrid and Lutz. Special thanks to Cecilia Dupré and Martin Diekmann for lots. 26.

(47) of help and rewarding discussions, for being great friends and introducing me to the fine art of Italian cooking. At the big collective EBC there are many interesting and special people that also deserve thanks and I have really enjoyed working together with some of you at courses and other occasions. For me, the exchange of thoughts and visions with other departments has been extremely rewarding. Thanks to Bo Tallmark for making all those hours of Klubban teaching such joy and for learning me to love the Sea by explaining its essence, Jobs-Kalle, Karin, Ineke, Markus and Måns for great teaching collaboration and Annika, Christina, Dick, Jesper and Olivier for being great friends to share fun and despair with after work hours. Besides home-base related activities, fieldwork has been a large part of the effort in this thesis. First of all I have to thank all of you that have helped Gustav and me with all kinds of strange, fun, less fun and more or less impossible things. Big thanks to Ellika Alm, Christina Borg, Selina Eriksson, Niklas Gyllenstrand, Mattias Hjällström, Magnus Johansson, Maria Johansson, Lies Van Nieuwerburgh, Erik Norell, Conny Larsson, Geir Løe, Eva Rommel, Andreas Svärdhage, Gunilla Toth, Krister Westerberg, Ingrid Wänstrand, Anna Östlund, Bernt Östlund, Härlins livs, Sjöfartsverket and Dykföreningen Tumlaren, who all have taken part in or helped with field activities in one way or another. Special thanks to Jonas (Flipper) Eriksson, Jonny-Boy and Bonny-Joy, that have been the core-diving buddies and technical advisors of our excavations with special responsibility of checking issues of equipment colours and product updates (how far, how deep and most important of all, how sexy). Jonken has contributed with enthusiasm and ideas on algae, science and life in general that have made being in the water much more bearable and we owe you BIG for always taking the time to help us – it has been great fun!!! Also special thanks to Christina Ritzl for being babysitter in need and for showing us how easy the trunk of the divemobile can be turned into a smaller kindergarten with sleeping possibilities. I am in debt to Lena Bergström for believing in my ideas and joining me on a summer diving adventure, also thanks to you and Jonny for a nice time in Greece. Klubban has been great fun and Klubban Trollet Anna Karlsson is the one to blame most for that. Thank you Anna for introducing me to the three best survival strategies at the station (Jim och Torgny, Torgny och Jim och en Hyvlad Rijojja), for showing me the ten best ways how to fall into the water from land or boat (a manual that includes getting crushed by boats of different sizes in connection with water impact and the famous Modesty Blaise bottom drop) and for becoming a special friend. More Klubban thanks goes to Annika for you’re incredible laugh and the unforgettable Slangen show and Tommy Karlsson for lots of help and patience with us “landkrabbor”. By the time I read this in the printed version I will probably have realised which ones I have forgotten about here. Whoever you are, thank you… Last I want to thank my family. Lennart and Ann-Katrin, although you may not have understood the road of interest I have taken, you have always supported me unconditionally to go on… and than means a lot. Farfar, tack för att du väckte mitt intresse för skogen och träden, visade mig att naturen myllrar i dess oändlighet av. 27.

(48) levande organismer och lärde mig att respekt dem. Lies, you have widened my view on life and supported me with endless patience and trust, through the most difficult times you believed in me and encouraged me to go on and through the good times you shared my joy. Thank you for allowing me to be much too absent in the world of phycology, for all the Love and Joy and for taking care of Boupa while I have been writing up the thesis.. CITED LITERATURE Abuodha P.A.W., Kairo J.G. (2001) Human-induced stresses on mangrove swamps along the Kenyan coast. Hydrobiologia 458:255-265 Airoldi L. (1998) Roles of disturbance, sediment stress, and substratum retention on spatial dominance in algal turf. Ecology 79:2759-2770 Airoldi L., Cinelli F. (1997) Effects of sedimentation on subtidal macroalgal assemblages: an experimental study from a Mediterranean rocky shore. Journal of Experimental Marine Biology and Ecology 215:269-288 Ambjörn C., Broman B., Peterson C. (1981) Bottniska viken - vattenutbytesprocesser. In: Cederwall, H. (ed.) Andra svensk-finska seminariet om Bottniska viken. Statens naturvårdsverk, Rapport 1984:22-26 Andersson S., Kautsky L., Kalvas A. (1994) Circadian and lunar gamete release in Fucus vesiculosus in the atidal Baltic Sea. Marine Ecology Progress Series 110:195-201 Bäck S., Collins J.C., Russell G. (1991) Aspects of the reproductive biology of Fucus vesiculosus from the coast of SW Finland. Ophelia 34:129-141 Berger R., Malm T., Kautsky, L. (2001) Two reproductive strategies in Baltic Fucus vesiculosus (Phaeophyceae). European Journal of Phycology 36:265-273 Bonsdorff E., Blomqvist E.M., Mattila J., Norkko A. (1997) Coastal eutrophication: causes, consequences and perspectives in the archipelago areas of the northern Baltic Sea. Estuarine, Coastal and Shelf Science 44:63-72 Borum J. (1996) Shallow waters and land/sea boundaries. In: Jørgensen B.B., Richardson K. (eds) Eutrophication in coastal marine ecosystems. American Geophysical Union, Washington DC. pp 179-203 Breuer G., Schramm W. (1988) Changes in macroalgal vegetation of Kiel Bight (Western Baltic Sea) during the past 20 years. Kieler Meeresforschung, Sonderheft 6:241-255 Broman D. (1990) Transport and fate of hydrophobic organic compounds in the Baltic aquatic environment. Doctoral thesis at the Stockholm University, Akademitryck, Edsbruk. pp 1-76 Brown V.B., Davies S.A., Synnot R.N. (1990) Long-term monitoring of the effects of treated sewage effluent on the intertidal macroalgal community near Cape Schank, Victoria, Australia. Botanica Marina 33:85-98 Cloern J.E. (2001) Our evolving conceptual model of the coastal eutrophication problem. Marine Ecology Progress Series 210:223-253 Daly M.A., Mathieson A.C. (1977) The effect of sand movement on intertidal seaweeds and selected invertebrates at Bound Rock, New Hampshire, USA. Marine Biology 43:45-55 Devinny J.S., Volse L.A. (1978) Effects of sediments on the development of Macrocystis pyrifera gametophytes. Marine Biology 48:343-348. 28.

(49) Duarte C.M. (1995) Submerged aquatic vegetation in relation to different nutrient regimes. Ophelia 41:87-112 Duarte C.M. (2000) Marine biodiversity and ecosystem services: an elusive link. Journal of Experimental Marine Biology and Ecology 250:117-131 Eleanor K., Charles R. (1998) Response of primary producers to nutrient enrichment in a shallow estuary. Marine Ecology Progress Series 163:89-98 Elmgren R. (1989) Man’s impact on the Ecosystem of the Baltic Sea: Energy flows today and at the turn of the century. Ambio 18:326-332 Grime J.P. (1977) Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. American Naturalist 111:1169-1194 Håkansson L., Jansson M. (1983) Principles of lake sedimentology. Springer-Verlag, Berlin. 316 pp Hällfors G., Kangas P., Niemi Å. (1984) Recent changes in the phytal at the south coast of Finland. Ophelia, supplement 3:51-59 Hardy F.G., Evans S.M., Tremayne M.A. (1993) Long-term changes in the marine macroalgae of three polluted estuaries in north-east England. Journal of Experimental Marine Biology and Ecology 172:81-92 Hemmi A., Jormalainen V. (2002) Nutrient enhancement increases performance of a marine herbivore via quality of its food alga. Ecology 83:1052-1064 Hill S.R. (1996) The flora of Latimer point and vincinity, New London County, Conneticut. Rhodora 98:180-216 Ignatius H., Axberg S., Niemistö L., Winterhalter B. (1981) Quaternary geology of the Baltic Sea. In: Voipo A. (ed.) The Baltic Sea. Elsevier Oceanographic Series 30. Elsevier, Amsterdam. pp 54-105 Jansson B-O., Dahlberg K. (1999) The environmental status of the Baltic Sea in the 1940’s, today, and in the future. Ambio 28:312-319 Jones C.G.J.H., Lawton J.H., Shachak M. (1994) Organisms as ecosystem engineers. Oikos 69:373-386 Jonsson P., Carman R., Wulff F. (1990) Laminated sediments in the Baltic - A tool for estimating nutrient mass balance. Ambio 19:152-158 Jonsson P., Carman R. (1994) Changes in deposition of organic matter and nutrients in the Baltic Sea during the Twentieth Century. Marine Pollution Bulletin 28:417-426 Kangas P., Autio H., Hällfors G., Luther H., Niemi Å., Salemaa H. (1982) A general model of the decline of Fucus vesiculosus at Tvärminne, south coast of Finland in 1977-81. Acta Botanica Fennica 118:1-27 Kautsky H., Kautsky L., Kautsky N., Lindblad C. (1992) Studies on the Fucus vesiculosus community in the Baltic sea. Acta Phytogeographica Suecica 78:33-48 Kautsky L., Serrão E.A. (1997) Reproductive ecology in Fucus vesiculosus - a key species on rocky shores in the Baltic Sea. Abstracts of the BMB 15 and ECSA 27 Symposium, Mariehamn, Finland, 9-13 June Kautsky N., Kautsky H., Kautsky U., Wærn M. (1986) Decreased depth penetration of Fucus vesiculosus (L.) since the 1940's indicates eutrophication of the Baltic Sea. Marine Ecology Progress Series 28:1-8 Kelly B.O. (1995) Long-term trends of macroalgae in Hillsborough Bay. Symposium on human impacts of the environment of Tampa Bay, at 57th annual meeting of the Florida Academy of Sciences, St. Petersburg, FL, USA, 25-27/3 1993.. 29.

(50) Kiirikki M. (1996) Experimental evidence that Fucus vesiculosus (Phaeophyta) controls filamentous algae by means of the whiplash effect. European Journal of Phycology 31:61-66 Kiirikki M., Lehvo A. (1997) Life strategies of filamentous algae in the northern Baltic proper. Sarsia 82:259-267 Kukk H. (1995) Phytobenthos. In: Ojaveer, E. (ed.) Ecosystem of the Gulf of Riga. Estonian Academy Publishers, Tallinn. Academia (Estonia) 5:131-138 Kukk H., Martin G. (1992) Long-term dynamics of the phytobenthos in Pärnu Bay, the Baltic Sea. Proceedings of the Estonian Academy of Sciences Ecology 2:110-118 Larsson U., Elmgren R., Wulff F. (1985) Eutrophication and the Baltic Sea: Causes and Consequences. Ambio 14:9-14 Lavery P.S., Lukatelich R.J., Mc Comb A.J. (1991) Changes in the biomass and species composition of macroalgae in a eutrophic estuary. Estuarine Coastal and Shelf Science 33:1-22 Littler M.M., Littler D.S. (1980) The evolution of thallus form and survival strategies in benthic marine macroalgae: field and laboratory tests of a functional form model. American Naturalist 116:25-44 Littler M.M., Littler S.M., Taylor P.R. (1983) Evolutionary strategies in a tropical barrier reef system: functional-form groups of marine macroalgae. Journal of Phycology 19:229-37 Littler M.M., Murray S.N. (1975) Impact of sewage on the distribution, abundance and community structure of rocky intertidal macro-organisms. Marine Biology 30:277-91 Lundälv T., Larsson C.S., Axelsson L. (1986) Long-term trends in algal-dominated rocky subtidal communities on the Swedish west coast - a transitional system? Hydrobiologia 142:81-95 Mäkinen A., Haahtela I., Ilvessalo H., Lehto J., Rönnberg O. (1984) Changes in the littoral rocky-shore vegetation in the Seili area, SW archipelago of Finland. Ophelia, supplement 3:157-166 Mälkki P. (1981) Bottniska vikens hydrografi - en översiktsrapport. In: Cederwall H. (ed.) Andra svensk-finska seminariet om Bottniska viken. Statens naturvårdsverk, Rapport 1984:11-16 Middelboe A.L., Sand-Jensen K. (2000) Long-term changes in macroalgal communities in a Danish estuary. Phycologia 39:245-257 Munda I.M. (1993) Changes and degradation of seaweed stands in the Northern Adriatic. In: Chapman A.R.O., Brown M.T., Lahaye M. (eds) Proceedings of the 14th International Seaweed Symposium. pp 239-253 Munda I.M. (2000) Long-term marine floristic changes around Rovinj (Istian coast, North Adriatic) estimated on the basis of historical data from Paul Kuckuck's field diaries from the end of the 19th century. Nova Hedwigia 71:1-36 Nixon S. (1990) Marine eutrophication: a growing international problem. Ambio 19:101 Nixon S. (1995) Coastal marine eutrophication: a definition, social causes, and future concerns. Ophelia 41:199-219 Nordberg K., Gustavsson M., Kranz A-L. (2000) Decreasing oxygen concentrations in the Gullmar Fjord, Sweden, as confirmed by benthic foraminafera, and the possible association with NAO. Journal of Marine Systems 23:303-316 Norton T.A., Mathieson A.C., Neushul M. (1982) A review of some aspects of form and function in seaweeds. Botanica Marina 25:501-510. 30.

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