Long-term dynamics in a soft-bottom amphipod community and the influence of the pelagic environment.

The processes and patterns seen in coastal benthic communities can be strongly influenced by the overlying pelagic environmental conditions. Integrating long-term biological and environmental data (both benthic and pelagic) can give insight into the specific relationships between key benthic functional groups and natural temporal changes in the marine environment. The identity and abundance of amphipod species found at Station L4 (Western English Channel) were tracked for 7 years (2008-2014), whilst simultaneously, annual changes in phytoplankton biomass, water temperature, salinity and chlorophyll a concentration were also characterized. The main species were persistent and showed little variability along the study period. Overall, however, there were significant changes in the structure of the whole community between sampling times, highlighting the importance of less numerically-dominant species in driving temporal variability. Surprisingly, the current study did not detect a significant influence of the phytoplankton biomass on benthic amphipod dynamics. On the other hand, there was a clear and constant correlation between bottom water temperatures and amphipod abundance. This pattern is different from that observed in other detritivorous species at L4, highlighting the complexity of benthic-pelagic coupling and the high variability of the response to pelagic conditions among different groups. As a result of the biogeographic position of the Western English Channel, the key role of amphipods in benthic communities, the influence of the temperature in their populations dynamics, as well as the solid baseline provided here and in previous studies, the monitoring of long-term amphipod dynamics in the English Channel could be a valuable tool to evaluate the biological effect of climate change over marine benthic communities.