METABOLISM AND FEEDING OF MESOZOOPLANKTON IN THE EASTERN MEDITERRANEAN (HELLENIC COASTAL WATERS)

Respiration, ammonium and phosphate excretions and phytoplankton consumption of mesozooplankton were examined biweekly in a coastal area of the eastern Mediterranean from January 1989 to January 1990. Taking into account the ambient temperature, the metabolic rates estimated (4 to 31.2 mu l O-2 mg(-1) dw h(-1), 0.4 to 3.5 mu g NH4-N mg(-1) dw h(-1) and 0.1 to 0.6 mu g PO4-P mg(-1) dw h(-1)) were lower than those reported for the western Mediterranean, which might be related to the higher oligotrophy in the eastern Mediterranean. Maxima for these metabolic rates and that for zooplankton community respiration (7 mg O-2 m(-3) d(-1)) were all observed during the period of higher temperatures; some degree of acclimation was also inferred and this may be attributed to the high abundance of cladocerans in the summer. Simple and multiple regression models, the latter based on stepwise variable selection, suggested that temperature was the most significant variable affecting zooplankton metabolism. Body weight and population composition were also important variables. Feeding activity, sometimes showing an increase with food concentration, seemed to increase metabolic rate, but temperature may mask this effect. The low O:N ratio indicated a protein-oriented metabolism. Furthermore, the O:N, N:P and O:P fluctuations indicated a dissimilarity in zooplankton dietary pattern, probably due to the low phytoplankton levels and differing exploitation of other supplementary food sources. The results stress the importance of temperature, rather than food or other factors, for zooplankton metabolism in coastal areas of the oligotrophic eastern Mediterranean, which during summer is comparable to oligotrophic tropical seas.