KANDID A T UPPSA TS
Naturvård och artmångfald 180hp
A study on the Construction and Ecological succession of two Small Artificial Reefs on the Swedish West Coast
Malin Forsberg och Joakim Järlind
Biologi 22,5hp
Halmstad 2014-10-13
A study on the Construction and Ecological succession of two Small Artificial Reefs on
the Swedish West Coast
Bachelor´s thesis in Biology Halmstad University, Sweden . 2014
Malin Forsberg & Joakim Järlind
Abstract
Artificial reefs are being built in most parts of the world for a wide variety of purposes
.
Diving tourism is a common motivator for the construction of many reefs, particularly in the tropics, although the most widely used purpose is to improve or reconstruct hard bottom habitats and increase the yield from fisheries.
There are two main reasons for why aquatic life is attracted to artificial reefs.
They provide excellent protection by often being hollow or filled with crevices and cavities and increasing opportunities for improved foraging through accumulating biomass and extending the foraging range of an organism by acting like stepping stones.
Sweden is a coastal country with few artificial reefs.
In this study, two reefs were constructed in the sea off the coast of Halmstad, Sweden to test small scale artificial reef production, marine organism colonisation of the reefs during the first year, and to increase the local marine life diversity.
Many marine organisms that would not normally occur in the sites where the reefs were constructed were observed, such as Symphodus melops and Anguilla anguilla
.
The reefs also provided a new “clean slate” substrate for the settling of sessile organisms such as Urticina felina or partially sessile organisms (i.
e.
during a certain stage of their life-cycle) such as some species of Cnidaria polyps.
The tested method to construct these reefs was relatively cost effective for its purpose.
However a few minor but vital improvements, such as better binding materials, are needed.
Local marine life in the area has become more diverse during the experiment and that alone is enough reason to motivate construction of similar reefs along the Swedish coast. Sammanfattning
Artificiella rev anläggs runt om i världen med en mängd olika syften
.
Det är vanligt att dykturism används som anledning för att bygga artificiella rev, speciellt i tropikerna.
Restaurering avhårdbottenrev och mål att öka kommersiella fiskebestånd är dock de största motiveringarna
.
Det finns två huvudsakliga orsaker till varför akvatiskt liv attraheras av konstgjorda rev.
De erbjuder utmärkt skydd i form av håligheter och sprickor, samt att de ökar möjligheterna för födosök genom att ackumulera biomassa och fungera som ”stepping stones”, det vill säga utöka födosökningsområdet.
Sverige är ett kustland med få artificiella rev.
Två rev anlades i Laholmsbukten, Kattegatt, just utanför Tjuvahålan i Halmstad med syftet att undersökaeffektiviteten och nyttan av småskaliga rev, att studera marina organismers kolonisering av reven och att öka den lokala biodiversiteten
.
Många marina organismer som inte borde förkommit i området där reven anlagts tidigare observerades.
Ett par exempel är Symphodus melops) och (Anguilla anguilla).
Reven fungerade även som rena underlag för sessila organismer att fästa på.
Djur som till exempel havsros (Urticina felina) och Cnidariapolyper noterades
.
Metoden för att konstruera reven visade sig vara kostnadseffektiv i förhållande till syftet, men några viktiga steg, bland annat fästmaterialet, behöver förbättras.
Den lokala artmångfalden ökade efteranläggningen av reven och borde vara nog motivering för att fortsätta bygga liknande rev längs den svenska kusten
.
Introduction
It was well-known even before the 1800's that new structures introduced into seas or lakes were advantageous for aquatic life
.
In the 1830's, timber houses in South Carolina, USA were sunk in the North Atlantic to promote the fish stock (Gulf States Marine Fisheries Commission 2004).
In Italy, official work with the establishment of artificial reefs has been ongoing since the 1970's (Relini et al.
2007), and in Florida, USA it's common practice for fishermen to sink varying objects on their own accord in their fishing areas (University of Florida n.
d.
).
Artificial reefs are built and deployed for various different projects with varying purposes all over the world, especially in Oceania, the Caribbean and the Americas, although artificial reefs in Scandinavia are uncommon.
In 2011, Spain had 103 artificial reefs, Italy had 70 and the Scandinavian countries had all together only 11 (Fabi et al.
2011).
The purpose of many artificial reefs is to promote commercial fisheries.
Burchmore (1985) reports that despite the disadvantages of artificial reefs compared to natural reefs, the artificial reefs seems to provide a more suitable habitat for economically important fish species.
Studies from Japan (Ogawa 1973), USA (Stone et al.
1979) and Italy (Bombace et al.
1994) report local increases in the rate of colonisation, fish density and catch size in areas with artificial reefs.
However, Huntsman (1981) claims that it is impractical to construct artificial reefs for the promotion of commercial fisheries because of the costs and disproportional effort in relation to the increase in catch size.
It is also difficult to know beforehand if the increased productivity is real or a result of attraction from the nearbyenvironment
.
Where the accumulation of fish is due only to the reefs attractiveness, an increased pressure from commercial fishing could deplete the fish stock at an even higher rate than normal.
Construction of artificial reefs in Scandinavia began in the end of the 20th century (Fabi et al
.
2011)
.
There are examples of artificial reefs at a relatively large scale and with varying purposes from Norway, Denmark, Sweden and neighbouring country Finland.
In 2008, an artificial reef was constructed in Læsø Trindel, Denmark in a Natura 2000 area.
Its purpose was to restore a boulder reef habitat that had been depleted of rocks due to construction of piers and breakwaters (Fabi et al.
2011).
In Norway, there are two examples of artificial reefs constructed to promote fishing.
The first one was constructed in 2002 in Nordfjorden in southern Norway as an attempt to assess the effects on the marine flora and fauna, particularly on certain fish species.
The second one was built 2004 outside of Lofoten in northern Norway to promote fishing (Fabi et al.
2011)
.
The artificial reefs constructed in the Finnish part of the Baltic Sea were created for research purposes, for example a project in the Gulf of Bothnia in1993 that studied the effects of waste from fish farms on filamentous algae and epifauna (Laihonen et al.
1997).
All artificial reefs in Sweden are established along the west coast.
There is a lobster reef project inGothenburg’s archipelago, where seven artificial reefs made from rock fill were laid out with the purpose of promoting the lobster population (County Administration Board of Västra Götaland 2007)
.
Later, reefs were created at two more locations in a similar fashion (Tjörn municipality2013; Sotenäs municipality 2013)
.
Sven Lovén Centre for Marine Sciences on Tjärnö in Strömstad municipality has ongoing research involving artificial reefs and the colonisation of cold water corals (Lophelia pertusa) (L.
Jonsson, Ph.
D.
Principle research engineer.
University of Gothenburg.
pers.
com.
September 2013).
The complex structure of an artificial reef creates more places to hide for prey species that can aggravate predation (Menge 1976; Hixon 1989)
.
Fish species have been observed using shadows formed by reefs to detect predators easier and/or to prey in the sunlit surroundings (Helfman 1979).
Depending on the behaviour of the predator, an artificial reef may have a positive or negative effect on foraging opportunities.
Fish that live in a suitable environment, either a foraging site, a hide or both, will not explore and move around in the surrounding areas as much as a fish that live in a poorer environment.
Fish will therefore accumulate in a high-quality environment and activity will increase (Sale 1969).
An artificial reef that functions as a more suitable living environment for many species will have a higher density of these species than its surroundings.
A new structure in the sea can also infer new possibilities for fish to navigate and not necessarily only provide shelter and foraging opportunities (Bohnsack 1985).
Studies in Puerto Rico (Fast 1974) and California, USA (Matthews 1985; Solonsky 1985) where fish movement patterns were researched, showed a high rate of migration from natural reefs to artificial reefs but not vice versa
.
According to the research the distance between natural reef and artificial reef plays a part in the density of migrating fish, i.
e.
a shorter distance has a higher rate of fish migration to artificial reefs (Matthews 1985; Solonsky 1985; Alevizon 1985).
Thismotivates the placement of an artificial reef in connection to or nearby an already existing natural reef
.
Optimal Foraging Theory (OFT), a model by which an organism strives to consume as much energy as possible through the smallest amount of effort and time, has also been observed in fish (Townsend 1985)
.
Fish can learn to adapt their foraging to variations in their habitat (Hart 1986) and OFT can be applied to movement patterns of fish, particularly when they forage between reefs.
This, together with the accumulation of organisms, i.
e.
the increase in biomass at an artificial reef, shows that artificial reefs can form an optimal foraging area.
With OFT and the tendency of an artificial reef to increase production, it can be concluded that artificial reefs not only benefit fish that seek shelter but also fish that will only use the area to forage.
A study in the Gulf of Mexico showed that grey triggerfish living near oil platforms had a higher growth-rate than individuals in the species’ natural habitat (Nelson 1985).
Although, it is important to note that a species can change habitat preferences during its life span (Starck 1970).
Ergo, an artificial reef will probably not increase the local biomass in an area if a bottle-neck effect for thepopulation growth in the environment outside of and around the reef, occurs (Sale 1969)
.
That is, even if a reef is an ideal habitat for the adults of a species, the production will not increase if the artificial reef or the surrounding habitat cannot support the juvenile population of the same species.
Figure 1
.
Map of the bay of Laholm (left) and of Tjuvahålan (right).
The artificial reefs are located within the green circle.
Source: Google maps ©.
Halmstad municipality, together with Laholm and Båstad municipalities line the shore of the bay of Laholm
.
The bay stretches from Tylösand in the north to Hovs hallar (figure 1) nature reserve in the south and large sand dunes are a characteristic feature of its beaches.
The average water depth in the bay is 15 metres and the bottom is dominated by sand, which is also reflected in the species composition below the water’s surface.
The fauna mainly consists of organisms that rely on a sandy environment; invertebrates, molluscs and fish, like Mya arenaria, Crangon crangon, Cerastoderma edule, Trachius draco and several different species within Pleuronectiformes.
In this environment so called Zostera-fields are vital elements which help to oxygenate the bottom and function as an essential habitat for several species, such as the Syngnathus-species in Kattegatt.
Zostera-fields are threatened in many places in the world, particularly by filamentous algae that are quickly spreading along the Swedish west coast due to eutrophication(Troell et al.
2005)
.
The sandy bottom of the Laholm bay makes it a suitable location for the introduction of an artificial reef where it can form an important and rare habitat and even function as an alternative hide for several species in addition to the dwindling Zostera-fields.
The purpose of this project was to build small scale artificial reefs in the shallow water in the Laholm bay, and study their colonisation by marine organisms during the summer months
.
The aim was also to increase the local biodiversity and hopefully promote diving and snorkelling tourism along the coast of Halmstad.
Which species will colonise the new substrate? Does the construction method and reef design function? Could these methods be used as a model for marine conservation for the coastal municipalities of Sweden?Initially the idea was to follow and document the successive colonisation of two small reefs over the course of a year
.
However, due to delays and difficulties with diving during winter the inventory lasted 3 months.
The reefs will remain in place to allow any follow-up studies and to promote diving tourism in Halmstad.
The reef structures surrounded by sand are a new anddifferent micro-habitat in an otherwise relatively barren and monotonous environment
.
They are located close to pre-existing natural reefs and could possibly benefit the marine fauna in the area by not only functioning as hides, but also by allowing the organisms to use the reefs as stepping stones for spreading and foraging.
These factors, in time, could mean an increased population of some species in the area, perhaps even attract species which are uncommon in the area due to a lack of appropriate habitats.
Materials and methods
An application for “strandskyddsdispans” (exception to the shoreline protection regulation) (reference number BN 2013-001659) was sent to Halmstad municipality and an “anmälan om vattenverksamhet” (notification of activity in water body) (reference number 535-3969-13) was sent to the County Administration Board of Halland
.
With all necessary permits granted, two small artificial reefs were constructed in Kattegatt in Tjuvahålan outside of Tylösand, Halmstad.
The reefs were constructed by hand out of 26 kg concrete masonry blocks (appendix 1)
.
The placement sites for the reefs were determined after several observation dives two weeks prior to the construction of the reefs.
The blocks were tied to a rubber dinghy, two at a time, together with one large float-buoy per block.
The blocks were then transported to the chosen locations where they were lowered to the bottom.
Each trip took approximately 18 minutes; meaning almost 7 blocks per hour could be moved.
The transport method was later changed and an aluminium boat was loaded with about 20 blocks at a time and towed out to the reef locations using the dinghy.
The blocks were built together into two reefs of 55 blocks per reef
.
The construction was done by hand by two divers; one diver collected and carried the blocks to the other diver who fastened the blocks together using thick cable-ties.
Apart from standard diving equipment, pliers, a laminated blueprint of the construction design and a net for collecting waste were used.
Each reef was completed after two dives at about 60 minutes per dive, which were executed on the 26th and 27th of September 2013.
The finished reefs (appendix 2) weighed approximately 1430 kg each and are one metre tall, one and a half metres wide, placed at 6 metres depth, 80 metres from the nearest shoreline and 44 metres apart.
Inventory method
Inventory took place on 24th of May, 22nd and 29th of June, 6th and 27th of July and 2nd of August 2014
.
One diver always observed and noted mobile organisms.
A scale of “number of specimens per species” was used: 1 being 1 – 5 observations, 2 being 6 – 20 observations, 3 being 21 – 50 observations and 4 being 51 – 100 observations and 5 being over 100 observations.
The other diver photographed organisms for later identification and also noted sessile organisms.
Each reef was studied until both divers were satisfied with the collected data.
Literature used for species identification were Moen, F.
E.
& Svensen, E.
Djurliv i Havet, Nordeuropeisk Marin Fauna.
Temperature and current strength were noted
.
Current strength was noted on an arbitrary scale based on the amount of effort the divers needed to keep stable in the water during the inventory;Easy meaning “no to almost no current”, Medium meaning a little effort was needed to keep stable and Hard meaning a lot of effort was needed to keep stable
.
Equipment used, besides standard diving equipment, was a Suunto ZOOP diving computer for temperature and depth measurements, net-bags, cameras, lamps and underwater writing material.
Results
Reef construction
The concrete masonry blocks used for construction are satisfactory regarding their resistance to saltwater (during the time spectrum of this project) and endurance of harsh handling during the construction period
.
They also function as a good substratum for sessile organisms.
The use of an inflatable dinghy and two large buoys to transport the blocks to each site was an ineffective method, due to the time consuming and unreasonable amount of work needed.
The other method tested, i.
e.
using the dinghy to tow a larger aluminium boat was more effective.
One person managed the boat and one person sat in the aluminium boat and dropped the blocks one by one at each site.
This method allowed this part of the construction work to finish in a three hours.
The electric engine and the battery were powerful enough to operate the inflatable boat while towing the bigger and heavier aluminium boat.
Under water, the blocks were easy to manage and building of the reefs was effective.
However the cable-ties used to bind the blocks together did not work as planned.
The ties held the blocks together a few weeks after the construction was completed in early October 2013, but in May 2014 it was discovered that the ties had snapped and both reefs had collapsed (appendix 3) and a number of blocks had sunk below the sand.
A larger part of reef 2 had sunk beneath the sand compared to reef 1.
Inventory
The current strength varied from easy to hard between the inventory occasions and water
temperature increased throughout the project period from 13 to 22°C
.
In total, 29 fauna taxa and 5 algae taxa were identified.
The numbers of fauna taxa found on reef 1 and reef 2 were 25 and 18 respectively, and both reefs had 5 algae taxa (appendix 4).
Species that were not observed during previous inventory occasions were recorded during each subsequent occasion (appendix 5).
The amount of observed species generally increased between the first and last inventory occasion (figure 2).
Carcinus maenas, Asterias rubens, Nassarius reticulatus, Pomatoschistus minute and Cnidaria polyps were found at each reef on each dive.
Asterias rubens, Nassarius reticulatus, Aphya minuta and fish spawn were the taxa with the most observed specimens, while Macropodia rostrata, Anguilla Anguilla and Sygnathus typhle were observed only once on reef 2, as were Pagurus bernhardus, Spinachia spinachia, Myoxocephalus scorpius, Agonuscataphractus, Pholis gunnellus, Zoarces viviparus and Callionymus lyra on reef 1
.
The sea anemone Urticina felina was observed on reef 1 during the first dive on the 24th of May and it remained intact during the whole inventory period.
During the second dive on the 22nd of June, on reef 2, one species of the taxa Ascidiacea was found and remained intact during the whole inventory period.
Figure 2
.
Curves illustrating the changes in number of species observed at each reef at each inventory occasion.
Discussion
As hoped, we found that the reefs attracted fauna that normally would not inhabit the immediate area
.
According to Moen & Svensen (2009) species such as Cerastoderma edule, Mya arenaria, Arenicola marina, Limanda limanda, Solea vulgaris, Scophthalmus rhombus, pomatoschistus minutes, Crangon crangon, which were common around the reef area, are dependent on a sand bottom habitat, like that of the bay of Laholm.
On or directly adjacent to the artificial reefs we observed a variety of taxa that requires a hard bottom habitat with cavities for hiding from predators and for hunting.
The most gratifying find was the one specimen of Anguilla anguilla, observed at reef 2 on the 2nd of August.
Anguilla anguilla is classified as a critically endangered (CR) species based on the IUCN Red List's criteria (Jacoby & Gollock 2014).
It is not yet fully understood why the global population of Anguilla anguilla is decreasing (Dekker 2012), and even though some major threats have been identified it is not clear how significant each of thesethreats are in reality
.
Degradation and loss of suitable habitat occur all over the species range, and are often caused by flood control and water-level management, abstraction and transport of ground and surface water and sea bottom gravel extraction for both domestic and commercial use (Jacoby & Gollock 2014).
This project is small-scale but the appearance of Anguilla anguilla in one of the reefs is a positive indication that the hard bottom artificial reefs can function assuitable habitats for the species to reside, in an otherwise bare sandy bottom environment
.
This is one example of the importance of these reefs as microhabitats in a larger area.
The reefs function both as islands and as stepping stones for the dispersion of different species by offering anReef 1
Reef 2
0 2 4 6 8 10 12 14 16 18
24-May 22-June 29-June 06-July 27-July 02-August
Number of observed species
Date of inventory
alternative environment and thus provide opportunities for a wider variety of fauna
.
It is also likely that the presence of these reefs increases the chance of successful settling by the pelagic plankton-stage juveniles of sessile organisms (Holst & Jarms 2007).
Several Cnidaria polyps were observed on both reefs although, along with other organisms such as algae and under- developed organisms such as the observed specimens of the Balanus genus, which were not prioritised for species identification.
During the last two inventory occasions we observed a notable decrease in the amount of Asteria rubens and Carcinus maenas
.
This decrease may be factual or caused by live and dead loose filamentous and macro-algae that drifted in with the currents covering both reefs.
This accumulation of algae debris did however vary, seemingly depending on the current strength.
Reef 2 was more covered by algae and sometimes only a few points of the reef protruded above the carpet of algae
.
This collection of algae could also have hidden new unobserved species and might explain the difference between the two reefs in the amount of observed species.
Several juvenile Syngnathus sp
.
were observed and juveniles can be hard to differentiate between the species.
Another species that may have been under-observed is Myoxocephalus scorpius which can sometimes be confused with Taurulus bubalis (Moen & Svensen 2009).
Even though some individuals may have been wrongly classified, there is at least one individual from each listed species that is correctly identified.
During the last inventory we noted that one or several individuals seemed to have permanently occupied the reefs, particularly individuals of the species Syngnathus acus, Taurulus bubalis and Gobius niger
.
One individual of Syngnathus acus (appendix 6) was noted as it was a particularly large specimen observed on reef two on several occasions.
Both reefs seemed to have apermanent population of Gobius niger, each of them occupying and protecting its own part of the reef from other individuals of the same species
.
Also a couple of individuals of Taurulus bubalis were observed on several occasions on both reefs, each of them protecting a certain part of the reef.
Homing behaviour and site fidelity has been documented in several fish species where individuals show a tendency to maintain a home range to which they return if displaced (Berti et al.
1994; White & Brown 2013).
This would imply that the artificial reefs are suitable habitats for at least these three species.
All observed taxa, except the species Urticina felina (appendix 7), Ascidiella aspersa, Anguilla anguilla and Callionymus lyra, were also observed in the surrounding environment and in the nearby natural reef
.
However none of these taxa are particularly rare.
Urticina felina is common in the seas off the Swedish west coast and Ascidiella aspersa has been observed in Kattegatt (Moen & Svensen 2009).
Anguilla anguilla, although endangered, is often observed along the coast of Halland (M.
Gren.
Dive instructor, Halmstad Dykarskola AB.
pers.
comm.
August 2013).
Only Callionymus lyra is classified as uncommon in Kattegatt but it is common furthernorth along the Swedish west coast (Axelsson n
.
d.
).
It is expected to find some of these species in the nearby natural reef and therefore they are probably not new to the area.
Worth noting is that organisms observed in and around the artificial reefs, but not observed in the surrounding natural reefs before, do not necessarily have to be new to the area
.
Such observations can however indicate that a better habitat has been created for those specific species.
Oneexplanation and possible conclusion could be that an expansion of an unusual habitat can, in the long run, lead to an increase of species that are rare in the area due to the lack of a suitable habitat
.
The most optimal scenario would have been to be able to use our own specially designed concrete blocks (Appendix 8), although that requires a higher budget
.
The idea of our design is that the blocks are attached to each other and held together by friction and their own weight.
We believe that this type of block enables the building of various structures (Appendix 9) with less or even completely without fixing materials while providing greater stability to the entireconstruction
.
The design would create cavities and crevices which various fish species require in a suitable habitat (Hixon & Beets 1989).
We developed this design after studying a number of designs in other artificial reef projects from around the world.
It is common that the artificial reefs which are made of concrete are created as single large pieces having complex structure, i.
e.
hollow pillars with several openings (Fabi et al
.
2011).
These structures can weigh hundreds and sometimes even thousands of kilograms, which means that the handling requires specialised equipment and training (Naturstyrelsen 2013).
Therefore such reefs are not possible for low budget or non-profit operations.
The concrete masonry blocks were an adequate replacement as they functioned as a prototype for our particular design.
However a much more reliable fixing material is needed since the cable ties failed to hold the reef together.
It was most likely during October 2013 when the storm Simone reached the Swedish west coast that the reefs collapsed.
Simone created wind gusts of up to 42 m/s recorded at Hallands Väderö, an island 24 kilometers south-west of Tjuvahålan, which was an October-record for the Swedish coast while the average wind speed was 31 m/s (SMHI, Swedish Meteorological and Hydrological Institute)
.
Due to the fairly shallow depth we suspect that the currents were too powerful around the reefs and the ties snapped when the pressure became too high.
We are not sure if it had helped to attach more ties to the reefs
.
After a short consultation with marine scientists at Sven Lovén Centre for Marine Sciences on Tjärnö, Strömstad we concluded that cable ties were the best option for the project.
We wanted to minimize the risk ofcontaminating the surroundings with plastic particles, and therefore we opted out polypropylene and nylon ropes since they have a higher probability of the threads being worn out and shed when they scratch against the rough surface of the concrete blocks
.
Organic materials like hemp ropes are more susceptible to the mouldering effect of salt water and would fray into fibres, which would probably cause the same problems for marine life as plastic fragments cause until the organic fibres mouldered completely (Boerger et al.
2010; Hoss & Settle 1990).
It’s likely that aneven better material would be thick wire which would most likely cope with very hard currents and high pressure
.
The concern then is the wires poor resistance to salt water and at what rate it would rust.
This would obviously depend on the salinity of the area in question and the type and quality of the wire, however cable-ties were a cheaper and more manageable option compared to metal wire.
Arguably an artificial reef can be seen as an irresponsible and unnatural way of applying conservation principles, since an alien structure and material is added to a natural ecosystem (Meier 1989; Buckley 1989; Polovina 1989)
.
According to Buckley (1989), reefs being deployed by the public/private sectors as a “fun” project with almost no consideration to research or conservation have become a problem.
This means that artificial reefs are a kind of solution for the disposal of solid waste with the added benefit of improved fishing and these reef units are often improperly prepared and/or cleaned or consist of hazardous materials.
Even though there are some bad examples of artificial reefs, Meier (1989) claims that the benefits outweigh the risks of having the private sector create reefs.
The important part is to ensure that the private and public sectors are conscious of the available technology and materials for the construction of artificial reefs, and the public interest and awareness for marine conservation is a positive thing.
Unfortunately our reefs will probably not increase diving tourism in Halmstad since the collapse of the reefs has left them fairly aesthetically unappealing
.
Even though they appear to attract marine fauna anyway and have been successfully colonised by sessile organisms, certainattractiveness is appreciated by divers since artificial reefs as a form of under-water art have been very successful in attracting divers (James 2010)
.
Art in the form of artificial reefs could actually be a concept that municipalities could use to attract diving tourists, particularly as, in our opinion, diving in Sweden is under-appreciated and could be used more in conjunction with marinenational parks and nature reserves
.
Diving tourism can however have a negative impact on underwater ecosystems, especially on coral reefs that are particularly sensitive (Carter, 1990).
In coral reefs, up to 15 broken corals for a 30 min dive were measured although this depends on the experience and skill of the diver (Harriott et al.
1997).
Treeck & Schumacher (1999) believe that 90% of the typical requirements for a satisfying, recreational dive can be met by artificially created scenery.
They also propose that artificially made underwater parks, as substitute attractions for recreational divers, would halt or at least reduce the adverse impact of diving tourism on natural reefs.
This could be a clear motivation for building more artificial reefs in general.
Furthermore, artificial reefs that are man-made structures rather than, e.
g.
boulders dumped in a heap are more attractive to divers as they add a sort of architectural charm.
Conclusions
The answer to the question of whether or not we managed to affect the local fauna is clear: yes
.
Superficially the diversity in and around the reefs seemed to have increased during our project
period and we observed several species that probably would not have been present without the artificial reefs
.
Thus it would appear that the use of even a small artificial reef to boost the local marine life in Swedish waters is possible and recommendable.
Furthermore, small reefs are easy to build and, despite requiring more man hours proportionate to the outcome, are cheaper and need less specialised and expensive equipment.
As well as attracting marine life, structurally complex reefs could also increase diving tourism and even public awareness and interest for marine conservation.
The results from this project show that the original design for the concrete blocks and for the reef would probably have been even more effective.
Use of the original design would simplify construction, be more withstanding to the elements and improve structuralintegrity
.
Acknowledgments
We would like to acknowledge and thank those who in any way supported this project: Lars-Erik Widahl, Bo Gustafsson and Ellinor Waldemarson who provided us with useful information and invaluable help
.
Tulltjänstemännens semesterhems stiftelse via Ulf Ängemo and Halmstads dykarskola AB via Marcus Gren and Annika Blomberg who provided us with help through materials and equipment.
Sandra Åhlén Mulio and Evelina Ohlsson helped us with some of the physical work.
Jonas Rundqvist who helped us with getting in contact with our financers at Almi Företagspartner AB via Conny Nilsson.
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Appendix
Appendix 1
© Finja AB
Appendix 2
Appendix 3
Appendix 4
Species list showing all taxa found on the reefs during inventory between 24th May 2014 and 2nd August 2014
.
Listed in taxonomic order according to Burnie et al.
2011.
Reef 1 Reef 2
Fauna taxa Fauna taxa
Cnidaria (polyps) Cnidaria (polyps) Urticina felina Balanus sp
.
Balanus sp
.
Praunus flexuosusParunus flexuosus Carcinus maenas Carcinus maenas Macropodia rostrata Pagurus bernhardus Nassarius reticulatus Littorina littorea Electra pilosa Nassarius reticulatus Asterias rubens Electra pilosa Ascidiella aspersa Membranipora membranicea Anguilla anguilla Asterias rubens Syngnathus typhle Syngnathus acus Syngnathus acus Syngnathus rostellatus Syngnathus rostellatus Spinachia spinachia Taurulus bubalis Myoxocephalus scorpius Symphodus melops Taurulus bubalis Ctenolabrus rupestris Agonus cataphractus Pomatoschistus minutus Symphodus melops Gobius niger
Ctenolabrus rupestris Pholis gunnellus Zoarces viviparus Aphya minuta
Pomatoschistus minutus Gobius niger
Callionymus lyra
Algae taxa Algae taxa
Clodophora sp
.
Cladophora sp.
Ceramium sp
.
Ceramium sp.
Polysiphonia sp
.
Polysiphonia sp.
Delesseria sanguinea Delesseria sanguinea Entreomorpha intestinalis Enteromorpha intestinalis
Appendix 5
Combined list of species found during each inventory occasion on both reefs
.
* - indicates a new species that was not found during the previous inventory occasion.
May 24th June 22nd June 29th
Urticina felina Cnidaria polyps* Urticina felina
Carcinus maenas Urticina felina Balanus sp
.
Nassarius reticulatus Balanus sp
.
* Parunus flexuosus*Asterias rubens Carcinus maenas Carcinus maenas
Taurulus bubalis Pagarus bernhardus* Nassarius reticulatus Pomatoschistus minutus Littorina littorea* Electra pilosa
Aphya minuta Nassarius reticulatus Membranipora membranicea Electra pilosa* Asterias rubens
Membranipora membranicea* Ascidiella aspersa Asterias rubens Syngnathus rostellatus*
Ascidiella aspersa* Taurulus bubalis Pomatoschistus minutus Pomatoschistus minutus
Fish spawn* Gobius niger*
Fish spawn
July 6th July 27th August 2nd
Urticina felina Urticina felina Urticina felina
Balanus sp
.
Balanus sp.
Balanus sp.
Praunus flexosus Carcinus maenas Carcinus maenas
Carcinus maenas Littorina littorea Littorina littorea Macropodia rostrata* Nassarius reticulatus Nassarius reticulatus Nassarius reticulatus Electra pilosa Electra pilosa
Electra pilosa Membranipora membranicea Membranipora membranicea Membranipora membranicea Asterias rubens Asterias rubens
Asterias rubens Ascidiella aspersa Ascidiella aspersa Ascidiella aspersa Syngnathus typhle* Myoxocephalus scorpius*
Anguilla anguilla* Syngnathus acus Taurulus bubalis Syngnathus acus* Symphodus melops* Symphodus melops Syngnathus rostellatus Ctenolabrus rupestris Ctenolabrus rupestris Spniachia spinachia* Zoarces viviparus* Pholis gunnellus*
Taurulus bubalis Pomatoschistus minutus Pomatoschistus minutus
Agonus cataphractus* Gobius niger Gobius niger
Ctenolabrus rupestris* Callionymus lyra* Fish spawn Aphya minuta
Pomatoschistus minutus Gobius niger
Fish spawn
Appendix 6
Appendix 7
Appendix 8
Appendix 9
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