Reproduction in the amphipod, Echinogammarus marinus: a comparison between normal and intersex specimens

The fecundity and occurrence of intersexuality in the amphipod, Echinogammarus marinus, collected from populations on the east coast of Scotland are reported. Intersex specimens have significantly smaller mean brood sizes than normal specimens. Embryo survival, as measured by the ratio of eggs/embryos in early and late stages of development, is lower in intersex specimens than normal specimens. Greater differences in the number of early stage eggs compared with late stage eggs in intersex specimens is suggested to arise by the active ejection of non-viable eggs, or from the passive loss of eggs through malformed brood plates in females. An apparent reduction in brood sizes between early and late stages of development in ‘normal’ specimens, emphasizes the importance of quantifying different egg/embryo stages in amphipod toxicology and fecundity studies.