Copepod egg production in the NW Mediterranean: effects of winter environmental conditions

Abstract

In the NW Mediterranean the highest abundance of phytoplankton is found during late winter, when temperatures are low. During summer, on the other hand, temperatures are high and phytoplankton abundance low, resulting in low copepod egg production rates (EPR). Despite the apparently better food conditions for copepod growth during winter, we lack information on copepod EPR during the cold season and on the possible effect temperature has on inhibiting this metabolic rate. To solve this uncertainty, a study was carried out to assess the effects exerted by the winter envi- ronmental conditions on the EPR of 3 representative planktonic copepod species of the NW Mediter- ranean (Centropages typicus, Clausocalanus lividus, Acartia clausi). The data were collected during 2 oceanographic cruises in March 1999 (Hivern-99) and January-February 2000 (Hivern-00) and the results compared to those of typical summer conditions. During the Hivern-99 cruise the phytoplank- ton abundance was very high (ranging from 1 to 1.5 µg > 5 µm chlorophyll a (chl a) l -1 ), indicating bloom conditions. During the Hivern-00, the phytoplankton bloom had not yet developed, evident by the chl a concentration of ~0.5 µg l -1 . The recorded EPR during Hivern-99 were amongst the highest for the studied species, and the clearance rates deduced from them indicate a shorter (phytoplankton - copepods) food web during the winter phytoplankton bloom than for the rest of the year, when the planktonic trophic interactions take place through a longer microbial food web.