Seasonal Abundance of the CtenophoreMnemiopsis leidyiin Relation to Water Temperature and Other Zooplankton in the Thames River Estuary, Connecticut

Abstract

I examined seasonal patterns in the abundance of the ctenophore Mnemiopsis leidyi (Atlantic Comb Jelly) to determine whether unusually early ctenophore blooms occur outside the range in which they were originally reported (Narragansett Bay, RI) and whether ctenophore abundance is correlated with sea surface temperature (SST) or with declines in zooplankton prey. Sampling was conducted from 23 April to 16 November 2004 in the Thames River Estuary, CT. Adult (≥1 cm) ctenophores first appeared in the estuary on 20 May 2004, with a seasonal peak in mean (± SD) density (9.9 ± 2.5 individuals m-3, n = 7 stations) and biovolume (26.6 ± 9.9 ml m-3, n = 7 stations) on 9 July 2004. Adult Atlantic Comb Jelly abundance was positively correlated with SST, but only during the spring and early summer. Food availability also likely played an important role in ctenophore-population growth early in the year. However, I observed a delay between copepod density and ctenophore biovolume, possibly due to unusually cold winter temperatures that reduced ctenophore survivorship in the months preceding the study. Ctenophore diets in 2004 consisted primarily of copepods. I observed an inverse correlation between ctenophore biovolume and copepod density, but my data suggest that adult Atlantic Comb Jellies consumed only 0.0–2.2% of the copepod standing stock per day. Overall, my results are consistent with the hypothesis that early summer ctenophore blooms occured over a relatively large spatial scale; however, trophic impacts in the Thames River Estuary in 2004 appeared to be relatively low.