Bioenergetics and growth in the ctenophore Pleurobrachia pileus
Knowledge of how energetic parameters relate to fluctuating factors in the natural habitat is necessary when evaluating the role of gelatinous zooplankton in the carbon flow of coastal waters. In laboratory experiments, we assessed feeding, respiration and growth of the ctenophore, Pleurobrachia pileus, and constructed carbon budgets. Clearance rates (F, l d 1) of laboratory reared Acartia tonsa as prey increased as a function of ctenophore polar length (L, mm) as F 0.17L1.9. For ctenophores larger than about 11 mm, clearance rate was depressed in containers of 30 50 l volume. Clearance rates on field collected prey were highest on the copepod, Centropages typicus, intermediate on the cladoceran, Evadnenordmanni and low on the copepods, Acartia clausi and Temora longicornis. Specific growth rates of 8 10 mm P. pileus increased with increasing prey concentrations to a maximum of 0.09 d 1 attained at prey carbon densities of 40 and 100 mg C l 1 of Artemia salina and A. tonsa, respectively. Weight specific respiration rates increased hyperbolically with prey concentration. From experiments in which growth, ingestion and respiration were measured simultaneously, a carbon budget was constructed for individuals growing at maximum rates; from the measured parameters, the assimilation efficiency and net growth efficiency were estimated to be 22 and 37% respectively. We conclude that the predation rates of P. pileus depend on ctenophore size, prey species, prey density and experimental container volume. Because the specific growth rates, respiration, assimilation and net growth efficiencies all were affected by food availability, knowledge of the ambient prey field is critical when evaluating the role of P.pileus in the carbon flow in coastal waters.
Hydrobiologia