The biology of Chaetogammarus marinus (Leach) and Eulimnogammarus obtusatus (Dahl) with some notes on other intertidal gammarid species (Crustacea, Amphipoda)

The reproductive cycles of Chaetogammarus marinus and Eulimnogammarus obtusatus in northern Brittany are compared, as well as the environmental conditions under which these gammarids live. Both species show reproductive activity throughout the year. The maximum rate of ovigerous ♀ ♀ was established for E. obtusatus in the months of February-March (the coldest period of the year), for Ch. marinus in December. The former species showed the lowest rate in August (the warmest month of the year) and the latter species in March. Eulimnogammarus obtusatus lives in the lower half of more exposed beaches and was rarely found on a substrate containing mud, contrary to Chaetogammarus marinus. It was established that the southern distribution limit of E. obtusatus lies in Brittany. Ecological data are given on a number of other gammarid species from the tidal zone of the Atlantic coast of France.