The egg production of a marine planktonic copepod in relation to its food supply: Laboratory studies1

Abstract

Egg production by Paracalanus parvus, a particle‐grazing copepod, was investigated in relation to its food supply. The concentration of available food (P) and the rates of ingestion (I) and egg production (B) were measured simultaneously at intervals of 6 h to 2 d for periods of 2–10 d. Concentration, chemical composition (carbon and nitrogen), and species of phytoplankton were experimental variables. Egg production was related to the food ingested during the previous day. For one food type, I and B were rectilinear functions of P. The average maximum rates of ingestion and egg production were 1.1 µ g N·female−1·d−1 and 53 eggs·female−1·d−1, equivalent to specific rates of 1.5 and 0.37·d−1. B was proportional to I below a critical ingestion rate, I c, and independent of I above I c. For I <Ic, the gross efficiency of egg production (B ·I−1) in terms of nitrogen was 0.37 while in terms of carbon it was a hyperbolic function of the ratio of C:N in the food, ranging between 0.41 (C:N food = 4.0) and 0.15 (C:N food = 11). For I >I c, B·I−1 declined in terms of both carbon and nitrogen. These results, together with the ratio of C:N in particulate matter in the sea off southern California, suggest that nitrogen (hence protein) potentially limits egg production by adult female Paracalanus and that ingested carbon is used inefficiently.