1Dept. of Ecology, Environment and Plant Sciences, Stockholm University (DEEP) – Stockholm University, 106 91 Stockholm, Sweden
2 College of Marine Science [St Petersburg, FL] – University of South Florida, Saint Petersburg, Florida, USA, United States
3 Botany Department, University of Dar es Salaam – University Road, Dar es Salaam, Tanzania
4 Swedish University of Agricultural Sciences (SLU) – Department of Aquatic Resources Skolgatan 6 SE-742 42 ¨OREGRUND SWEDEN, Sweden
Distribution of species within the seascape is not random, but rather a function of different seascape attributes. Such seascape characteristics include proximity to adjacent habitats, patch size and within-patch location. Habitat edges alter physical conditions, resource distribution, and interactions between species, and are known to influence species diversity, abundance and distribution in terrestrial systems. However, little is known about the effects of habitat edges in aquatic systems, particularly in macrophyte habitats such as seaweed- and seagrass beds. In this study, we therefore examine the effect of patch edges on the grazing activity of two common herbivorous fish species, Ctenochaetus striatus and Scarus ghobban in Mafia Island, Tanzania.
Behavioural observations were conducted on 12-15 fish of each species in interior and edges of patches in 6 sites (3 seaweed and 3 seagrass) resulting in a total of 312 fish observations. Fish abundances and habitat characteristics such as % habitat cover, macrophyte height and shoot density were estimated by visual census. Results showed higher individual feeding rates (bites minute -1) in seagrass compared to seaweed areas. Also, bite rates for both C. striatus and S.
ghobban were higher along patch edges compared to interior parts. In addition, abundances of the two studied herbivores were higher along edges than in the centre of patches and a higher number of larger individuals were feeding along the edges compared to the interior of patches.
The results suggest that grazing by herbivorous fish is a heterogeneous process, not only affected by habitat type, but also by characteristics of the habitat and that patch edges appear to play a critical role in determining rates of herbivory in tropical seascapes.
Macroalgae habitat complexity underpins tropical fish biodiversity, replenishment and
productivity
Christopher Fulton ∗† 1, Charlotte Berkstr¨ om 2, Shaun Wilson 3
1 The Australian National University – Research School of Biology, The Australian National University, Canberra ACT, Australia
2 Stockholm University – Department of Ecology, Environment Plant Sciences, Stockholm University, Stockholm, Sweden
3 Department of Parks Wildlife WA – Marine Science Program, Department of Parks Wildlife, Kensington WA, Australia
Macroalgae have been cast in a negative light in tropical ecosystems, where they can pose a threat to coral reef biodiversity. However, canopy-forming macroalgae can provide a high complexity habitat for a diverse and productive fish fauna that complement and connect with adjacent tropical habitats such as coral reefs and seagrass beds. We collate evidence from across the Indo-Pacific to examine the structure and function of tropical macroalgae-associated fish communities, the potential for macroalgae to provide fish nursery habitats, and the consequences of macroalgae canopy habitat loss for tropical fish and fisheries. In identifying a number of local and global threats, we highlight priorities for future research that will support the conservation and management of these macroalgae-associated communities as key components of tropical ecosystems.
∗Speaker
†Corresponding author: christopher.fulton@anu.edu.au
Macroalgal identity drives rates of herbivory and the structure of fish assemblages within
a tropical East African seascape
Dinorah Chacin ∗† 1, Christopher Stallings 2, Maria Eggertsen 3, Carolina
˚ akerlund 3, Yessenia Rojas 3, Christina Halling 3, Charlotte Berkstr¨ om 3
1University of South Florida (USF) – 830 1st St SE, St. Petersburg, FL 33701, United States
2University of South Florida (USF) – 830 1st St SE, St. Petersburg, FL 33701, United States
3 Stockholm University (SU) – SE-106 91 Stockholm, Sweden
Algal beds can enhance productivity and provide habitat to numerous organisms. The presence of algae may play important roles within seascapes, but anthropogenic activities may disrupt their natural functional roles. For example, seascapes could be altered due to introduc- tions of non-native algae, which can become invasive, grow faster or be less palatable compared to native algae, resulting in changes in the rates of herbivory and structure of fish assemblages.
Furthermore, it remains unclear how herbivory and fish assemblages can vary between native and introduced algae within the tropical seascape. To address this paucity, we conducted a fully orthogonal field experiment in Mafia Island, Tanzania. Specifically, we measured the rates of herbivory on both native Sargassum spp. and non-native Eucheuma denticulatum in natural macroalgal beds/areas and open-water macroalgal farms of E. denticulatum and at different distances from each habitat. Preliminary results indicateSargassum spp. was grazed more than E. denticulatum in both native and farmed algal habitats. Furthermore, both species were con- sumed at higher rates in farmed habitats. At each experimental site, we also conducted visual surveys to quantify fish assemblages in each habitat. Abundance of fishes was similar among macroalgal habitats and species richness was higher in native algal habitats. However, herbivory and fish assemblage patterns were not consistent across distances from the habitats. Results highlight the importance of macroalgal identity in playing a role in ecological processes such as herbivory in tropical seascapes.
Spatially varying influence of canopy height on the functional role of seaweed and
seagrass beds as nursery habitats
Linda Eggertsen ∗ 1,2
1 Department of Ecology, Environment and Plant Science, Stockholm University (DEEP, Stockholm University) – Stockholm University, 114 18 Stockholm, Sweden, Sweden
2 Reef Systems Ecology and Conservation Lab, University Federal Fluminense (LECAR) – Niter´oi24020141, Brazil, Brazil
Structurally complex habitats in coastal shallow waters serve as nurseries for several species of reef fish, some of which move to different habitats as adults, contributing to nutrient and energy transfer between habitats. Seaweed and seagrass beds constitute important nursery habitats, but few studies have examined them together to assess the common habitat charac- teristics that structure associated fish assemblages along seascape gradients. In doing so, we aim to identify key habitat variables for juvenile fish communities between two different habitat types with similar ecological function. The importance of within-patch and seascape variables for structuring fish assemblages in seaweed and seagrass beds from two different biogeographical domains are discussed. In the southwest Atlantic, fish assemblages were surveyed in shallow seascape along coastal reef areas, inHalodule wrightii seagrass andSargassum-dominated beds.
Seagrass beds contained low abundance and species richness of fish, while seaweed beds con- tained significantly more juveniles than seagrass and reef habitats, including several species that are found in reef habitats as adults. Short-canopy seagrass beds were located very close to reefs in the southwest Atlantic, potentially resulting in reduced quality as refuge from predation. In both regions, seaweed canopy height was one of the most important variables explaining juvenile fish abundances, a pattern not always observed in seagrass beds. These differences might be ex- plained by the importance of canopy height being relative and dependent on the location within the seascape. We suggest that a taller canopy closer to reefs and on reefs, where predation usu- ally is high, provides potentially better shelter when compared to macrophyte beds away from reefs. Anthropogenic stressors and climate change could impact canopy height by trampling, anchoring, changed water quality and upwelling patterns, affecting the ecological function of macrophyte beds. Our work suggests that the extent of that influence could vary with distance to reefs. This may be of critical importance to juvenile reef fish in seaweed beds, especially in locations where alternative complex shallow water habitats are rare or absent.
∗Speaker
Structural connectivity and local habitat quality shape fish community structure
across a patchy tropical seascape