seasonal changes in phytoplankton availability

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-‘) and clutch size (eggs female-l). 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 phy-toplankton 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. The life history of copepods in the genus Calanus appears to be well suited for effec-tive utilization of the seasonal phytoplank-ton production in temperate oceans. Late preadult stages spend the winter in dia-pause, thus enduring the scarcity of food resources. In most species the overwintering stages molt into adults in late winter or early spring and are ready to take advantage of the vernal increase in algae. The spring in-crease of Calanus and its correlation with the spring bloom of phytoplankton are wel