COS 142-5
Habitat fragmentation alters predation rates and prey behavior in seagrass
As habitat loss progresses, continuous habitat is fragmented into smaller patches which can affect biological interactions, including predator-prey relationships. Fragmentation has been show to alter predation rates, predator behavior, and prey behavior. Most research on the effect of habitat fragmentation is limited to terrestrial landscapes, and examples in marine systems are often restricted to one trophic level. Seagrass is being lost at a rate of 110 km2/yr, leading to the emergence of fragmented seagrass seascapes. Utilizing the trophic relationship between the blue crab (Callinectes sapidus) and hard clam (Mercenaria mercenaria), where adult blue crabs prey on juvenile blue crabs, and both adult and juvenile blue crabs prey on hard clams, we examined whether predation rates and prey behavior differed between continuous and fragmented seagrass habitat in a multi-trophic context at two sites in Barnegat Bay, NJ. Fragmented seagrass may be a poor prey refuge and therefore we hypothesized that blue crab predation rates and foraging will increase in fragmented seascapes, reducing survival rates of juvenile blue crabs and hard clams. We further expected hard clams to exhibit stronger predator avoidance behavior in fragmented seascapes.
Results/Conclusions
In contrast to our hypothesis, we found that predation on clams was significantly higher in continuous habitats than in fragmented habitats. Densities of blue crabs, the primary predator of hard clams, were higher in continuous habitats at both sites. Clams also buried deeper in continuous habitats to avoid predators. Predation on juvenile blue crabs was significantly higher in fragmented seagrass at one site. Our results suggest that hard clams can experience higher predation in continuous habitats, potentially due to a greater density of blue crabs. In fragmented seascapes, juvenile blue crabs can experience higher predation and densities are lower. Subsequently, survivorship of hard clams can be higher and the use of predator avoidance mechanisms lower in fragmented habitats. This result demonstrates the importance of examining the effects of fragmentation on predator-prey relationships in a multi-trophic context. The impact of fragmentation on higher trophic level predators may drive predation rates and prey responses across the seascape.