Final Report Summary - LINKFISH (Invetigating the link between sub-littoral algae habitats and fish communities in the Mediterranean Sea)
General introduction to the Project - Linkfish
Whilst the importance of phytoplankton as a primary producer for coastal ecosystems and thus fish production is well documented, the importance of macroalgae and seaweed in the preservation of fish stocks remains obscure. The project LINKFISH aimed to increase our understanding of how specific characteristics of macroalgae habitats in the Mediterranean can help populations of juvenile fish to thrive.
Macroalgae are predominantly found in the coastal rocky shores. Due to their proximity to human activities, they are under increased anthropogenic pressure and thus more likely to be affected by environmental changes. Some algae, such as the algae of the genus Cystoseira, are in decline and have disappeared from many coasts of the Mediterranean as a result of reduced water quality most likely linked to the increasing urbanisation of coastal areas. Furthermore, algae communities are under pressure from the introduction of alien species in the Mediterranean. For example the rabbit fish, a herbivore fish with a huge appetite for algae, is able to transform areas of previously healthy algae cover into barren rock with only a thin layer of turf, with obvious consequences for other fish. The introduction of alien algae species also has consequences for the overall native composition of algae communities, with as yet unknown consequences for other ecosystem components. To increase our understanding of the functional role algae habitats occupy with respect to coastal fish populations the LINKFISH project conducted intense scuba-diving surveys to study macroalgae habitats, their composition, their communities of associated benthic fauna and their link with juvenile fish fauna.
Completed in May 2015, the project focused on a shallow water system habitats (Cystoseira) for its experimental work, due to its traceability, but also investigated two deep water systems (Osmundaria — Phyllophora and Peyssonnalia) that occur widely in the Mediterranean.
Work carried out, preliminary results up to date
The main objective of the work was to determine the importance of macroalgae habitats for juvenile fish that are known to prey on small size micro-crustaceans associated with macroalgae. Algae habitats can vary considerably in their species composition related to environmental and anthropogenic conditions. Each algae type may harbour their own specific fauna and some may contain more productive prey communities that contribute more to sustaining juvenile fish compared to others. Thus the main research objective of the study was to determine the abundance, biomass and size structure of prey communities inhabiting algae habitats and to relate this back to the juvenile fish present. The study thus aimed to discover which algae compositions contain the most prey and investigate the effect on juvenile fish abundances and fish condition i.e. we expected to find more fish and fish in better condition at sites with an algae composition which harboured high numbers of potential prey.
Different algae habitats were therefore sampled during four field surveys .Two surveys were conducted in spring 2015, one in Mallorca and the other in Menorca. The two locations were subsequently resurveyed in late summer (September) i.e. to obtain temporal variations in algae cover and to sample different juvenile fish communities. In total 8 sites were visited in both locations and season (see Figure 1). At each of the eight sites, six dive transects were conducted to record fish abundances via visual census techniques. Furthermore algae cover and morphological characteristics of the habitat i.e. physical complexities were recorded per transect. Algae samples of the most dominant algae species were obtain by placing a fine mesh bag (55 µm) over the algae and cutting it from the rock at its stem. The bag was reinforced at the bottom via a plastic ring with a diameter of 12cm to cover the same surface area. The alga samples were later processed in the laboratory to separate, quantify and measure the size distribution of the associated fauna. In total 384 algae samples were processed and over 15.000 algae associated fauna measured. Additionally samples of juvenile fish were taken at each site for later analysis of stomach content and condition. Approximately 30-50 individuals of fish were caught at each site using hand nets. Fish ranged in size from 1.5-6cm. Following species of juvenile fish were sampled Diplodus vulgaris, Coris julis, Symphodus rostratus, Thalassoma pavo.
Thus far sample processing and preliminary analysis have been conducted on the algae faunal data. Data of the visual census are currently being analysed. Stomach samples and body condition of juvenile fish caught will be processed in the near future. The project has been extended internally within the host institution IEO and the Marie Curie fellow Hilmar Hinz has gained a Ramón y Cajal contract which will allow him to continue this work despite the financial end of the official Marie Curie project.
The algae data clearly indicates that each algae morphotye identified during the surveys (Figure 2) contains its own specific fauna. Abundances of associated fauna per algae type varied considerably between the two survey areas Mallorca and Menorca and between seasons (see Figure 3). Also the size frequency of fauna associated with different types of algae varied although the peak abundances in all algae species were relatively equal (Figure 4.). The main prey groups associated with algae habitats were harpacticoids and amphipods. The project now needs to link these prey abundances to fish via the data from the visual censuses and the data on fish condition and growth.
Conclusion and future perspective
Hopefully this study will be able to highlight the importance of certain algae habitats for juvenile fish. On the basis of this work, we might be able to classify coastal habitat quality for juvenile fish on a larger scale and incorporate this into spatial management plans. Through the promotion of this knowledge, we hope to be able to sensitise marine stakeholders and the general public to the value of these habitats and hopefully initiate conservation efforts that would help preserve these ecosystems and secure future fish production.
The results of this work will be published in due course after the termination of all outstanding analyses
Whilst the importance of phytoplankton as a primary producer for coastal ecosystems and thus fish production is well documented, the importance of macroalgae and seaweed in the preservation of fish stocks remains obscure. The project LINKFISH aimed to increase our understanding of how specific characteristics of macroalgae habitats in the Mediterranean can help populations of juvenile fish to thrive.
Macroalgae are predominantly found in the coastal rocky shores. Due to their proximity to human activities, they are under increased anthropogenic pressure and thus more likely to be affected by environmental changes. Some algae, such as the algae of the genus Cystoseira, are in decline and have disappeared from many coasts of the Mediterranean as a result of reduced water quality most likely linked to the increasing urbanisation of coastal areas. Furthermore, algae communities are under pressure from the introduction of alien species in the Mediterranean. For example the rabbit fish, a herbivore fish with a huge appetite for algae, is able to transform areas of previously healthy algae cover into barren rock with only a thin layer of turf, with obvious consequences for other fish. The introduction of alien algae species also has consequences for the overall native composition of algae communities, with as yet unknown consequences for other ecosystem components. To increase our understanding of the functional role algae habitats occupy with respect to coastal fish populations the LINKFISH project conducted intense scuba-diving surveys to study macroalgae habitats, their composition, their communities of associated benthic fauna and their link with juvenile fish fauna.
Completed in May 2015, the project focused on a shallow water system habitats (Cystoseira) for its experimental work, due to its traceability, but also investigated two deep water systems (Osmundaria — Phyllophora and Peyssonnalia) that occur widely in the Mediterranean.
Work carried out, preliminary results up to date
The main objective of the work was to determine the importance of macroalgae habitats for juvenile fish that are known to prey on small size micro-crustaceans associated with macroalgae. Algae habitats can vary considerably in their species composition related to environmental and anthropogenic conditions. Each algae type may harbour their own specific fauna and some may contain more productive prey communities that contribute more to sustaining juvenile fish compared to others. Thus the main research objective of the study was to determine the abundance, biomass and size structure of prey communities inhabiting algae habitats and to relate this back to the juvenile fish present. The study thus aimed to discover which algae compositions contain the most prey and investigate the effect on juvenile fish abundances and fish condition i.e. we expected to find more fish and fish in better condition at sites with an algae composition which harboured high numbers of potential prey.
Different algae habitats were therefore sampled during four field surveys .Two surveys were conducted in spring 2015, one in Mallorca and the other in Menorca. The two locations were subsequently resurveyed in late summer (September) i.e. to obtain temporal variations in algae cover and to sample different juvenile fish communities. In total 8 sites were visited in both locations and season (see Figure 1). At each of the eight sites, six dive transects were conducted to record fish abundances via visual census techniques. Furthermore algae cover and morphological characteristics of the habitat i.e. physical complexities were recorded per transect. Algae samples of the most dominant algae species were obtain by placing a fine mesh bag (55 µm) over the algae and cutting it from the rock at its stem. The bag was reinforced at the bottom via a plastic ring with a diameter of 12cm to cover the same surface area. The alga samples were later processed in the laboratory to separate, quantify and measure the size distribution of the associated fauna. In total 384 algae samples were processed and over 15.000 algae associated fauna measured. Additionally samples of juvenile fish were taken at each site for later analysis of stomach content and condition. Approximately 30-50 individuals of fish were caught at each site using hand nets. Fish ranged in size from 1.5-6cm. Following species of juvenile fish were sampled Diplodus vulgaris, Coris julis, Symphodus rostratus, Thalassoma pavo.
Thus far sample processing and preliminary analysis have been conducted on the algae faunal data. Data of the visual census are currently being analysed. Stomach samples and body condition of juvenile fish caught will be processed in the near future. The project has been extended internally within the host institution IEO and the Marie Curie fellow Hilmar Hinz has gained a Ramón y Cajal contract which will allow him to continue this work despite the financial end of the official Marie Curie project.
The algae data clearly indicates that each algae morphotye identified during the surveys (Figure 2) contains its own specific fauna. Abundances of associated fauna per algae type varied considerably between the two survey areas Mallorca and Menorca and between seasons (see Figure 3). Also the size frequency of fauna associated with different types of algae varied although the peak abundances in all algae species were relatively equal (Figure 4.). The main prey groups associated with algae habitats were harpacticoids and amphipods. The project now needs to link these prey abundances to fish via the data from the visual censuses and the data on fish condition and growth.
Conclusion and future perspective
Hopefully this study will be able to highlight the importance of certain algae habitats for juvenile fish. On the basis of this work, we might be able to classify coastal habitat quality for juvenile fish on a larger scale and incorporate this into spatial management plans. Through the promotion of this knowledge, we hope to be able to sensitise marine stakeholders and the general public to the value of these habitats and hopefully initiate conservation efforts that would help preserve these ecosystems and secure future fish production.
The results of this work will be published in due course after the termination of all outstanding analyses