Impact of Climate Change on Estuarine Zooplankton: Surface Water Warming in Long Island Sound Is Associated with Changes in Copepod Size and Community Structure

In coastal ecosystems with decades of eutrophication and other anthropogenic stressors, the impact of climate change on planktonic communities can be difficult to detect. A time series of monthly water temperatures in the Central Basin of Long Island Sound (LIS) from the late 1940s until 2012 indicates a warming rate of 0.03 degrees C year(-1). Relative to the early 1950s, there has been a concurrent decrease in the mean size of the dominant copepod species Acartia tonsa and Acartia hudsonica, an increase in the proportion of the small copepod Oithona sp., and the disappearance of the two largest-sized copepod genera from the 1950s. These changes are consistent with predictions of the impact of climate change on aquatic ectotherms. This suggests that even in eutrophic systems where food is not limiting, a continued increase in temperature could result in a smaller-sized copepod community. Since copepods dominate the zooplankton, which in turn link primary producers and upper trophic levels, a reduction in mean size could alter food web connectivity, decreasing the efficiency of trophic transfer between phytoplankton and endemic larval fish.