Predation by omnivorous copepods on early developmental stages of Calanus finmarchicus and Pseudocalanus spp.

Predation is thought to be an important source of mortality in the early li fe stages of fish and copepods on Georges Bank. Omnivorous copepods may be predators on copepod eggs and nauplii, but data on feeding rates or selecti vity are scarce. As part of the GLOBEC Georges Bank program, we generated f unctional response curves for the omnivorous copepods Metridia lucens, Cent ropages typicus, and Temora longicornis feeding on the eggs and nauplii of Cal anus finmarchicus or Pseudocalanus spp. in shipboard pre dation trials. Neither C. typicus nor M. lucens reached saturation feeding on Calanus egg s until prey concentration was > 400 L-1. Individual M. lucens and C. typic us ingested up to 34 +/- 9 (mean +/- SD, n = 3) and 24 +/- 14 eggs d(-1), r espectively (6 degreesC). T. longicornis was more abundant in late spring, when they ingested Calanus eggs at rates similar to those of C. typicus. At ambient prey concentrations, ingestion rates of Calanus nauplii were highe r than rates of Calanus eggs for the predator M. lucens but were similar fo r C. typicus. Advanced naupliar stages were less susceptible to predation t han young stages. Pseudocalanus nauplii moved faster and were ingested at l ower rates than similarly sized Calanus nauplii. Predation rates increased with increasing temperature for the warm-water species C. typicus but decre ased for the cold-water species M. lucens. These results may contribute to models predicting the development of copepod populations and their availabi lity to larval fish.