Viability of subitaneous copepod eggs following fish predation on egg-carrying calanoids

Abstract

The viability of subitaneous eggs of the eggcarrying calanoid copepod Euryternora herdmani was examined following fish ingestion and evacuation. More than 90% of the copepod embryos recovered intact in the fecal material of Atlantic silversides Menidia rnenjdja hatched within 3 d of incubation at 12 C in both light/dark and completely dark regimes. Percentage hatch was comparable to that for uningested embryos removed from eggsacs and for uningested embryos within eggsacs both attached to, and excised from, maternal copepods. For E. herdmani, selective silvers~de predation on ovigerous females is countered by the capacity of their subitaneous eggs to resist digestion. Zooplankton features that influence prey selection by planktivorous fish include prey size (Ivlev 1961, Brooks 1968, Werner & Hall 1974, O'Bnen et al. 1976), pigmentation (Zaret & Kerfoot 1975, Hairston 1979a, b) and, in some egg-carrying copepods and cladocerans, the presence of highly visible eggs (Mellors 1975, Hairston et al. 1983). Prior to periods of intense fish predation, many crustaceans produce diapause eggs that are thick-walled, highly pigmented and digestion resistant (Proctor et al. 1967, Mellors 1975). It has been suggested that the production of diapause eggs acts as a survival strategy to offset the costs of selective feeding on egg-bearing females (Hairston & Munns 1984) and ultimately aids in the perpetuation of endemic populations (Uye 1985). There has been only one account of digestion resistance in nondiapause copepod eggs. Marcus (1984) showed that both subitaneous ('quick-hatch') and diapause eggs released by the marine copepod Labidocera aestiva are capable of surviving passage through the gut tracts of 2 benthic polychaete species. Egg mortality during gut transport however, was higher for ingested subitaneous embryos. Many other copepod Present address: Ocean Sciences Centre. Memorial University of Newfoundland, St. John's, Newfoundland, Canada