Feeding and growth by ephyrae of scyphomedusae Chrysaora quinquecirrha

Abstract

Clearance rates of Chrysaora quinquecirrha ephyrae were quantified in the laboratory using monocultures of different plankton organisms as prey, as well as mixed natural zooplankton assemblages. Further, growth of ephyrae was measured at different densities of rotifers or ctenophores as prey. The ciliate Strobilidium sp. (strain CRE) and the rotifer Brachionus plicatilis were cleared in monocultures at medium rates: 4 ml h-1 ind.-1 and 1 ml h-1 ind.-1 respectively. Clearance of copepod nauplii was low (0.5 ml h-1 ind.-1) and the dinoflagellates Gymnodinium sanguineum were not eaten by the ephyrae. In a mixed zooplankton assemblage, rotifers and copepod nauplii were cleared at rates similar to those obtained in monocultures, and tintinnids also were eaten. In contrast, larvae of the etenophore Mnemiopsis leidyi were cleared at a much higher rate (30 ml h-1 ind.-1) than microzooplankton. When the rotifer B. plicatilis were offered in excess to ephyrae, a maximum specific growth rate of 0.3 d-1 was measured. Growth rate more than doubled (0.7 d-1) when ctenophore larvae were offered. The growth rate obtained on ctenophore larvae is the highest rate reported so far for any scyphomedusan species. We suggest that M. leidyi may be of critical importance for the high growth of C. quinquecirrha ephyrae in natural populations during springtime in Chesapeake Bay, USA.