Effect of temperature and salinity on the population dynamics of Tisbe holothuriae Humes (Copepoda:Harpacticoida) fed on two different diets

Abstract

The harpacticoid copepod Tisbe holothuriae Humes was reared through a complete life cycle under fixed conditions of temperature (14, 19, and 24°C), salinity (20, 28, 38, and 48 %.), and diet (two synthetic foods, Renutryl and Germalyne). The main population measurements were determined under the different factor combinations. Temperature and salinity affect the duration of the life cycle, independently of diet. The minimum duration and mean generation time were inversely related to temperature and were prolonged in salinity extremes (20 and 48%.). Longevity of adults was inversely related to temperature and directly related to salinity. Type of food was involved in the processes related to reproduction activity. With Germalyne, the number of egg sacs was independent of temperature and salinity; with Renutryl egg sac number depended on both factors, the number of egg sacs being a maximum at 24°C and 38 %. salinity. The production of offspring was significantly affected by temperature (with Germalyne) or salinity (with Renutryl). Sex ratios depended on both physical factors and their interaction, but the observed variations were more marked with Renutryl. Consequently, variations of the net reproductive rate and of the intrinsic rate of natural increase relative to temperature and salinity depended on the diet provided. Maximum values were attained with a Renutryl diet, but only over a narrow range of salinities. The values measured using a Germalyne diet were comparatively less affected by temperature and salinity variations.