MEPS 333:51-60 (2007)  -  doi:10.3354/meps333051

ABSTRACT: The reproductive success of marine broadcast spawners depends on the concentration of sperm that surrounds eggs. Because sperm quickly dilute in the ocean, spawners must be sufficiently close to one another to ensure high rates of fertilisation. Thus, broadcast spawners can experience Allee effects—decreasing density can result in lower reproductive success because the costs of low fertilisation outweight any benefits of reduced intraspecific competition. Recently, there has been a dramatic increase in the number of studies examining the effects of toxicants on fertilisation success. These studies suggest that fertilisation is a highly sensitive stage and exposure to pollutants could severely reduce reproductive success in the field. However, we remain limited in our ability to predict the effects of toxicants under field conditions because most ecotoxicological studies utilise only a single sperm concentration. Moreover, all ecotoxicological studies of fertilisation to date have been limited to laboratory investigations, and it remains unclear whether the effects of a toxicant are overwhelmed in the dynamic and turbulent environment of the real world. We examined the effects of a common pollutant, copper, on the fertilisation success of the intertidal polychaete Galeolaria caespitosa in the laboratory and the field. In the laboratory, we examined the effects of copper over a range of sperm concentrations and in the field, we developed a new apparatus for examining fertilisation success in intertidal organisms. In the laboratory, copper had much stronger effects on fertilisation at low sperm concentrations than at high concentrations. We suggest that the use of single sperm concentrations in ecotoxicological assays of fertilisation is inappropriate because the magnitude of the effect of the toxicant can be estimated incorrectly. Copper also reduced fertilisation success in the field, with eggs having to be much closer to a sperm source in order to achieve any fertilisation success in the presence of copper. For populations of marine invertebrates in which reproduction is limited by sperm availability, the presence of a toxicant has the potential to dramatically reduce fertilisation success and greatly exacerbate Allee effects.

KEY WORDS: Ecotoxicology · Fertilisation kinetics · Polyspermy · Free-spawner · Pollution