Changes in the lower Chesapeake Bay food chain in presence of the sea nettle Chrysaora quinquecirrha (Scyphomedusa)

Abstract

The abundance of 4 levels of the lower Chesapeake Bay food chain (chlorophyll a, herbivores, ctenophore Mnemiopsis leidyi and Scyphomedusa Chrysaora quinquecirrha) were monitored twice weekly at 4 stations from May 10 to Sept 30, 1982 in the Lafayette and Elizabeth Rivers (Virginia). The herbivore standing stock, largely copepods, declined sharply in late May when M. leidyi appeared, but rebounded a month later when C. quinquecirrha medusae reduced the ctenophore population. Despite the additional presence of Aurelia aurita (Scyphomedusa) from July onward, herbivore abundance remained at moderate levels until the end of the study period. Phytoplankton abundance fluctuated and may have been responsible for brief periods of food shortage; the major periods of low herbivore abundance do not seem to have been kept low by food limitation. M. leidyi made a modest resurgence in late Aug. when the C. quinquecirrha population underwent its seasonal decline. C. quinquecirrha may contribute to the secondary productivity of the lower Chesapeake Bay by controlling M. leidyi during summer.