MEPS 222:131-141 (2001)  -  doi:10.3354/meps222131

ABSTRACT: Laboratory experiments were performed on the amphipods Monoporeia affinis and Pontoporeia femorata in order to test the hypotheses that specific reproductive variables are affected by moderate hypoxia and/or slightly increased temperature. These reproductive variables include unfertilised/undeveloped eggs, dead eggs and females carrying a dead brood. In a series of experiments, amphipods were exposed to increased temperature during different parts of the reproduction cycle. Exposure prior to mating caused an increased number of dead eggs and a higher percentage of females carrying dead broods. Furthermore, the effects of low oxygen concentrations (2 to 6 mg O₂ l^-1), solely and in combination with contaminated sediments, heavy metals and hydrophobic organic contaminants (polycyclic aromatic hydrocarbons and polychlorinated biphenyls), were tested during the reproduction cycle. Exposure to low oxygen concentrations induced a higher frequency of females carrying dead broods, and females exposed to hypoxia or contaminants had a lower fertility rate compared to controls. Our results show that oxygen concentrations and temperature conditions normally occurring in the Baltic Sea and that are not otherwise detrimental to adults could severely affect the gonads and the embryos. Females with dead broods, undeveloped/unfertilised eggs and dead eggs are proposed as tools for use in monitoring non-contaminant stressors.

KEY WORDS: Reproduction · Temperature · Hypoxia · Monitoring · Amphipods · Monoporeia affinis · Pontoporeia femorata