The production of subitaneous and diapause eggs: a reproductive strategy for Acartia bifilosa (Copepods: Calanoida) in Southampton Water, UK

Abstract

<it>Acartia bifilosa</it> from Southampton Water lays two morphologically distinct types of egg which are described for the first time. Eggs with a smooth surface are considered subitaneous, while eggs covered with thick 'spines' are diapause. During the seasonal occurrence of<it>A.bifilosa</it> in Southampton Water, from November/December to June, subitaneous eggs are laid during the first months of this period. The production of diapause eggs is restricted to a 2 month period before <it>A.bifilosa</it> disappears from the water column. There are significant differences between the response of the eggs produced at seasonal field temperatures (5-12<IMG SRC="/math/deg.gif">C) and those reported for other<it>Acartia</it> species. In particular, the numbers of eggs female^-1 day^-1, both subitaneous and diapause, are lower and typically &lt;4; and the hatching time of subitaneous eggs is longer, at up to 10 days, at optimum temperatures between 15 and 20&deg;C and optimum salinity &gt;20 PSU. Females acclimated to higher laboratory temperature regimes show higher egg production rates at field salinity. A delayed-hatch subitaneous egg is also reported. Results suggest that fecundity in<it>A.bifilosa</it> from Southampton Water might be limited to some degree by temperature and the responses of the eggs produced appear to offer <it>A.bifilosa</it> a reproductive repertoire to ensure its sustained presence in this seasonally influenced environment.