Shipworms as a model for competition and coexistence in specialized habitats

Shipworms, a group of marine wood borers (Mollusca: Teredinidae), are a model group with which to examine metacommunities inhabiting patchy, ephemeral habitats. Multiple species and genera typically share and compete for the same discrete substrata, allowing for direct comparisons to be made between competitive strategies, without confounding by extraneous biological differences. Timber recruitment panels were used to quantify 2, 4, 6 and 12 mo abundances of tropical Australian shipworm species, recording 62075 individuals from 6 genera and 19 species. Species exhibit differing peak recruitment seasons and reproductive modes, with free-spawning, short-term brooding and long-term brooding occurring. However, despite a higher diversity of spawning species (58%) overall, abundance was strongly driven by the lower diversity of short-term brooding species (37%), comprising 95.7% of recruitment. Competition for habitat was high, with up to 1200 individuals per panel (~3 ind. cm^–3), and widespread (40 to 90%) mortality in panels over 4 mo old. Results show that reproductive mode is a key contributor to recruitment success, with the constraints of a patchy, ephemeral habitat favoring a ‘middle of the road’ strategy of short duration larval brooding, most effectively balancing fecundity, larval retention, and dispersive ability.