Coastal Water Mass Replacement: Its Effect on Zooplankton Dynamics and the Predator–Prey Complex Associated with Larval Capelin (Mallotus villosus)

Abstract

We examined the hypothesis that the onshore wind-regulated initiation of larval emergence and drift in capelin (Mallotus villosus) was adaptive. Onshore winds were found to induce rapid water mass exchange in coastal Newfoundland resulting in the replacement of cold, high-saline, predator-laden waters with warmer, less-saline waters in which the abundance of an important fraction of the predator community was reduced 3- to 20-fold and zooplankton densities in the edible size fraction were increased 2- to 3-fold. In situ enclosure experiments indicate that the synchronous emergence of larval capelin during onshore winds, coupled with the reduced predator density at this time, results in predator satiation. Wind-induced elevations of the biomass of the edible zooplankton size fraction can produce fivefold increases in the daily growth rate of larval capelin. Capelin larvae thus initiate their drift and first feeding in a wind-induced "safe site." The abundance of eggs and larvae of 11 other marine fish species were also found to be associated with this "safe site" water mass.Key words: capelin, Mallotus villosus; water mass replacement, predation, feeding, growth, larval fish, survival, wind effects, drift, dispersal, enclosures, zooplankton