The life-cycles of four amphipod species in the Kattegat

Populations of four species of Gammaridae (Crustacea, Amphipoda) were sampled over 15 months in the south-western Kattegat at Sangstrup Klint (Denmark). Chaetogammarus marinus, C. stoerensis and Gammarus oceanicus had annual life-cycles, while G. salinus most likely had two generations per year. Mature C. marinus females were found from March to July, mature C. stoerensis females from March to June, mature G. oceanicus females from December to early June and mature G. salinus females from late November to late July. The theoretical maximum number of clutches were estimated at five for C. marinus , five plus for C. stoerensis , and six for G. oceanicus and both winter and summer reproducing G. salinus . Spring was the period of main recruitment in all populations, with additional recruitment during summer in G. salinus .
The geographical patterns of the reproductive strategies are discussed in relation to environmental factors and interspecific competition.