Spatiotemporal dynamics of nearshore fish communities in Casco Bay, Maine

Nearshore regions in the Gulf of Maine are highly variable habitats acted upon by processes operating on multiple spatial scales and levels of biological organization. As such, they facilitate the reproduction, growth, and migration of many fish species, and are particularly tied to the life histories of many forage fishes. Temperatures in the Gulf of Maine have rapidly increased in recent decades, which may be driving changes in nearshore ecosystems. Here, we use 11 years of summer beach seine survey data within Casco Bay, Maine, to illustrate temperature-related changes to community structure. Further, we use Atlantic herring ( Clupea harengus ) and Atlantic silversides ( Menidia menidia ) as focal species to describe the effects of temperature on individual growth rates and relative abundance. The progression of seasonal use patterns and relative abundance in the nearshore with seasonal warming is evident; species that have cooler preferred temperatures are caught less frequently in the nearshore regions in late summer, when temperatures are highest. Increased temperatures were associated with significantly higher silverside growth rates and community compositions dominated by silverside. Temperature alone did not explain interannual variation in herring growth rates or predict herring-dominated nearshore community composition, and there is evidence that density-dependence may be more important to herring population dynamics. Monitoring nearshore ecosystems could provide critical insight into the dynamics of species that use these areas to facilitate reproduction, growth, and migration, and could therefore be used to identify potential changes to Gulf of Maine community and trophic ecology.