The biology of <i>Gammarus</i> (Crustacea, Amphipoda) in the northwestern Atlantic. I. <i>Gammarus duebeni</i> Lillj.

Abstract

Gammarus duebeni is found as far north as southern Labrador and northern Newfoundland in brackish water habitats, but is absent from fresh water in the northwest Atlantic region. A population at Holyrood, Newfoundland, has been studied from 1962 to 1968. Fifty percent maturity for the females occurs at 11.5 mm in the winter and 10.5 mm in the summer. Embryos increase in size with development but at the same stage are significantly larger in the winter than in the summer. Mature females produce a succession of broods between November and August, at which time they enter the resting stage. The November brood develops slowly at the prevailing winter temperature and the young are released the next March. Fecundity increases with size of female. The winter broods are reduced in size with development which is not true of those produced in the summer. Females have a higher mortality rate than males and survive at the most for 1 year. The males are larger and live longer.