The role of temperature in seasonal variation in egg production by the copepod, Tortanus discaudatus (Thompson and Scott), in Narragansett Bay

Abstract

Laboratory egg production of female Tortanus discaudatus (Thompson and Scott) collected between January and September and held at ambient Narragansett Bay temperatures varied significantly, with moderate egg production in January (18.2 eggs·female −1·day −1), a high rate of 51.5 eggs·female −1·day −1 in May, then a low of 4.3 eggs·female −1·day −1 in August. Egg size also changed over the season, with larger eggs produced when daily egg production was low. The rates of egg production of females held under experimental conditions at 2, 5, 10, and 17°C were similarly curvilinearly related to temperature with an estimated maximum at 11.22°C. Temperature effects accounted for 35% of the variance in egg production in the experiment, and individual differences, possibly age-related, accounted for an additional 26%. The experimental 5 and 10°C rates were about half those at the same seasonal temperatures. Food quality differences over the season, or between field and laboratory, may have caused the difference. The females held at 2, 5, and 10°C experimental temperatures achieved stable rates of egg production and prey consumption within 12 days. Those held at 17°C did not stabilize in either egg production or prey consumption in 12 days. High summer temperatures of Narragansett Bay waters do not appear to prevent egg production from occurring in this species but do appear to lower significantly the number of eggs released by females.