Feeding and reproduction in a small calanoid copepod: Acartia clausi can compensate quality with quantity

Abstract

We analyzed the feeding, egg production rate (EPR), and the egg hatching success (EHS) of resulting eggs of adult Acartia clausi subject to realistic food levels (100 pg C l -1 ) of 7 algae. Feeding was maximum (ca. 20 ml ind. -1 d -1 ) with Thalassiosira weissflogii and minimum (ca. 0 ml ind. -1 d -1 ) with Dunaliella tertiolecta and Prymnesium parvum. EPR was highest with T. weissflogii, Tetraselmis sp., Rhodomonas sp., and Ditylum brightwellii (21 to 26 eggs ind. -1 d -1 ) and moderate with Prorocentrum minimum (15 eggs ind. -1 d -1 ). EHS was highest in P. minimum (84 %), followed by Rhodomonas sp. (80%), D. brightwellii (60%), T. weissflogii (52%) and Tetraselmis sp. (40%). Supplementary nutritional effects (higher EHS and gross growth efficiency) appeared when A. clausi fed on mixtures of algae with contrasting effects on EPR and EHS (T. weissflogii and P. minimum) offered as mixed suspensions, or alternating between unialgal suspensions on a 12:12 h basis. However, realized fecundity (RF) was fairly stable for most single and mixed diets (range 12.3 to 17.3 nauplii female -1 d -1 ), with the exception of Tetraselmis sp. (8.9 nauplii female -1 d -1 ). Such stable RF was attained by compensating low EHS with enhanced feeding and EPR, and consequently lower population growth efficiency. That represents a strategy with a high cost in terms of metabolism and predation risk.