1 Department of Ecology, Environment and Plant Sciences (DEEP) – Stockholm University SE-10691 Stockholm, Sweden
2College of Marine Science, University of South Florida – 140 7th Avenue South St. Petersburg, FL 33701, United States
3Botany Department, University of Dar es Salaam – University of Dar es Salaam P.O. BOX 35060, Dar es Salaam, Tanzania, Tanzania
4Stockholm University (SU) – Stockholm University SE-10691 Stockholm, Sweden
5 Department of Aquatic Resources, Swedish University of Agricultural Sciences – Skolgatan 6, SE-742 42 ¨OREGRUND, Sweden
Consumer-producer dynamics are important forces in the marine environment, shaping ecosystems by structuring benthic communities and transferring energy to higher trophic levels.
Within the tropical seascape, herbivorous fish are among the most important consumers, forming a heterogeneous community which is functionally diverse and often species-specific. Among the producers, algal communities play a prominent and highly dynamic role as different functional groups and species of algae sustain different species or life stages of consumers/herbivorous fish.
Grazing pressure distribution across the shallow seascape and the responsible factors for ob- served patterns are complex processes which have mainly been studied in coral reef habitats in East Africa. Therefore, we adopt an across-habitat view and investigate grazing pressure on algal resources in three common habitats; coral reefs, seagrass- and macroalgal beds, by different functional groups of fish. Grazing pressure was investigated by 1) video-recorded experiments with tethered macroalgae, 2) recording of bite rates and feeding choice, and 3) inventories of feeding scars by excavating/scraping parrotfish. Herbivore surveys were performed in all three shallow-water habitats and fish communities were documented by underwater visual census (UVC). Herbivorous fish communities differed among habitats, and herbivores from all func- tional groups (browsers, grazers, scrapers, excavators) were generally most abundant on coral reefs. Macroalgal consumption was density-dependent, and grazing intensity (bites minute -1) was highest on coral reefs. Also, food choice was strongly dependent on available resources.
Several herbivorous species within the same functional group was observed to consume algae, suggesting a high redundancy within reef habitats. Results illustrate how dynamic ecological processes can be, even over smaller scales (1-10 km) and the importance of including habitat, functional groups, and densities of both consumers and producers to better understand herbivory patterns in tropical seascapes.
∗Speaker
Edge effects on seaweed- and seagrass browsing within a tropical seascape
Charlotte Berkstr¨ om ∗ 1,2, Carolina ˚ akerlund 1, Maria Eggertsen 1, Dinorah Chacin 3, Amelia Buriyo 4, Christina Halling 1
1Dept. of Ecology, Environment and Plant Sciences, Stockholm University (DEEP) – Stockholm University, 106 91 Stockholm, Sweden
2 Swedish University of Agricultural Sciences (SLU) – Department of Aquatic Resources Skolgatan 6 SE-742 42 ¨OREGRUND SWEDEN, Sweden
3 College of Marine Science [St Petersburg, FL] – University of South Florida, Saint Petersburg, Florida, USA, United States
4 Botany Department, University of Dar es Salaam – University Road, Dar es Salaam, Tanzania
With increasing anthropogenic pressure from eutrophication, dredging and CO2-emission, coastal ecosystems are subjected to habitat loss and fragmentation. Hence the understanding of seascape- and patch dynamics are urging. Previous studies have focused on how seascape at- tributes and edge effects influence species abundance and richness in seagrass meadows, and how species are distributed within and between patches. However, research on the effects of seascape variables and edge on seaweed patches is lacking. Furthermore, the effect of patch edges on important ecological functions such as herbivory and predation are non-existent. In the present study we therefore investigated browsing by fishes along edges and the interior parts of seaweed- and seagrass patches through a combination of tethering experiments, browsing estimations and visual census in Mafia Island, Tanzania. Biomass loss of tethered Sargassum aquifolium was higher in the centre of seaweed patches than along edges, although no differences were found in seagrass areas. On the contrary, there were higher number of bites onThalassodendron ciliatum shoots along seagrass patch edges compared to the interior parts. The abundance and diversity of browsing herbivores was higher in seagrass patches than seaweed patches, although there was no difference between the interior and edge of patches in either habitat. Macrophyte cover (%) was significantly higher in the middle than along the edges of seaweed areas. However, there were no differences in mean canopy height. The opposite pattern was found in seagrass patches where there were no differences in shoot density between interior and edge of seagrass beds but shoots in the middle were significantly higher than shoots at the edges of seagrass patches. Our results suggest that both habitat type and seascape characteristics like patch edges can influ- ence important ecological functions such as herbivory. This information is crucial for proper management, especially with the alarming increase of habitat loss and fragmentation in shallow coastal areas worldwide.
From food web to biotic interactions:
positive effects of reef fishes in kelp habitats
Alejandro Perez Matus ∗ 1
1 Subtidal Ecology Laboratory and Marine Conservation Center, Estaci´on Costera de Investigaciones Marinas, Pontificia Universidad Cat´olica de Chile, Santiago, Chile – Alameda 340, Santiago de Chile,
Chile
Understanding the processes that drive kelp forest communities is critical for management and conservation of these productive ecosystems. In temperate regions kelp provide important services (e.g, habitat, food) to a conspicuous number of species, including reef fishes. Mecha- nisms of how links between kelp and the associated reef fishes are structured are not yet fully understood and this becomes increasingly important, as most species are experiencing loss due to human influence and/or environmental disturbances. Here I present several lines of research, from meta-analysis, dietary reviews to field and laboratory experiments that reveals the impor- tance of reef fishes in kelp forest and rocky shore communities. The meta-analysis identified that kelps enhance species abundances and facilitate reef fishes sitting at high trophic levels.
Moreover, the food web topological structure and modularity is represented by numerous reef fish associated species in which its absence (due to intense fishing) may destabilize the entire food web structure. The field-and lab based experiments demonstrate the importance of ma- rine protected areas for reef fish biomass and trophic fish diversity and the experimental work evidenced several positive links between the reef fishes and kelp species by a) trophic-and non- trophic control of major kelp grazers, b) provide nutrients that enhance kelp growth, and c) are important dispersal agents of kelp zoospores. Our results show that losses of reef fishes or kelps have their strongest effects via changes in the biotic interactions within the community. These shifts can have major consequences for the functioning of rocky reef ecosystems.
∗Speaker
Juvenile fish resources and nursery function of macroalgal beds in Hong Kong waters – a
habitat-based study
Priscilla To-Yan Leung ∗† 1,2, Min Liu 3, Tak-Cheung Wai 1,2, Zoe Ho 1, Maggie Au 1, Chary Jia-Rui Gu 2, Meng Yan 1,2, Paul Kwan-Sing Lam‡
1,2,4
1State Key Laboratory in Marine Pollution, City University of Hong Kong – Tat Chee Avenue, Kowloon Tong, Hong Kong, Hong Kong SAR China
2 Shenzhen Key Laboratory for the Sustainable Use of Marine Biodiversity, Research Centre for the Oceans and Human Health, City University of Hong Kong Shenzhen Research Institute – Shenzhen,
China, China
3State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Science, Xiamen University – Fujian, China, China
4 Department of Biology and Chemistry, City University of Hong Kong – Tat Chee Avenue, Kowloon Tong, Hong Kong, Hong Kong SAR China
Understanding the juvenile fish habitats, their contributions to adult recruits, and identifying nursery hot spots are fundamental to management and conservation of marine resources. Littoral vegetated habitats, such as macroalgal bed, seagrass bed and mangrove mudflat are generally believed as important nurseries. In Hong Kong, the complex and biologically diverse coastline supports the existence of these habitats. In particular, theSargassumbeds are signature seasonal algal habitat found along the exposed and semi-exposed shores of Hong Kong, mainly at eastern and southern waters. However, little is known about the association of this macroalgal habitat with local juvenile fish resources. Therefore, we aimed to study the species diversity, abundance, the spatial, vegetation-seasonal and habitat- patterns of the assemblages of juvenile fishes that associated with the localSargassum habitat; and to identify potential biodiversity hot spots for focused conservation and management. Forty-two study sites have been surveyed, covering the littoral areas in the north-eastern, eastern and southern waters of Hong Kong. Samplings were performed using purse seining complemented with cage trapping, and were conducted seasonally during the off season ofSargassum bed (non-peak season i.e., July to October 2016) and during theSargassum growing season (peak season i.e., January to May 2017). DNA barcoding analysis using COI gene was employed to identify species from early juvenile stage. Our current results showed that at least 169 species (47 families) of juvenile fish were collected from the littoral habitats. The overall species number, abundance and biomass were higher in the peak season.
Furthermore, the highest mean number of species (per site and per sampling) was reported in
demonstrate the seasonal, spatial and habitat-based pattern and to evaluate the role of the Sargassum habitat as an important nursery ground for juvenile fishes in Hong Kong.
Living on the edge - grazing activity along macrophyte patches