Temporal patterns of gastropod egg mass deposition on southeastern Australian shores

Spawning of marine invertebrates may be affected by environmental factors (e. g. food availability, environmental stress) or intrinsic factors (e. g. phylogenetic constraints, developmental mode); intrinsic factors may obscure environmental effects. Two-year surveys of gastropod egg mass deposition were conducted at two rocky intertidal sites in south-eastern Australia to test the following hypotheses: (1) temporal patterns of spawning are more similar within taxonomic order than across orders; and (2) species with planktotrophic larvae are more likely to spawn in seasons coinciding with maximum food availability. There were no discernible effects of either order or developmental mode on spawning patterns, suggesting that spawning behaviour is unrelated to taxonomic order or larval food availability. Alternatively, low numbers of species in certain groups may have increased the risk of not detecting significant effects (type II error). Comparisons with anecdotal data from other regions suggest that developmental mode may indeed play a role in marine gastropod spawning. Criteria are provided for future comparative studies, including a direct focus on specific families and the inclusion of similar latitudes and habitats to those used here. Such studies will help to determine the roles of developmental mode, food availability and environmental stress in the evolution of egg mass deposition.