Seasonal changes in size frequency distribution and estimated age in the marine copepod Acartia hudsonica during a winter-spring diatom bloom in Narragansett Bay

Abstract

Seasonal changes in length frequency and estimated age distributions indicated that Acartia hudsonica adult females are dominated by successive age groups during the winter–spring bloom in Narragansett Bay. The biomass peak during March and April was composed of over-wintering, late autumn-spawned copepods. Winter-spawned copepods entered the adult population during a brief period in late April to early May, and the influx of spring-spawned copepods began during the second week of May. Concurrent studies of egg production and feeding suggested senescence of the adult population prior to the transition between the autumn-spawned and the winter–spring-spawned copepods. Thus population productivity may reflect not only environmental conditions, but also the age-dependent physiological condition of the adults. Modeling indicated that small interannual variations in temperature (±1°C) will significantly affect development rate and maturation of A. hudsonica during winter and spring. The 2°C temperature range corresponded to a 3-week shift in the timing of peak maturation and could significantly alter the intensity of grazing and degree of coupling between primary producers and herbivores during the spring bloom.