Relationship of egg production of Calanus pacificus to seasonal changes in phytoplankton availability in Puget Sound, Washington1

Abstract

Two methods of estimating daily, in situ egg production rate for Calanus pacificus, a planktonic marine copepod that releases its eggs directly into the sea, were developed. The model for both methods separates egg production rate into daily frequency of spawning (% day⁻¹) and clutch size (eggs female⁻¹). One method involves direct observations of spawning frequency and clutch size in a random sample of females held in controlled conditions for a 12–24‐h period immediately after capture. The second method involves a visual assessment of the ovaries of live or preserved females and uses the observation that egg laying in Calanus occurs at night to predict daily rates of spawning. The methods were used to examine the relationship between egg production rate and phytoplankton availability in two areas of Puget Sound with different seasonal patterns of phytoplankton abundance and size composition. Egg production rate was hyperbolically related to phytoplankton concentration. The results show the potential for factors influencing phytoplankton standing stock to influence the timing and magnitude of recruitment into Calanus populations.