Predation on marine bryozoan colonies: taxa, traits and trophic groups

While bryozoans are important components of marine benthic ecosystems, their significance as food has scarcely been considered in any comparative study. An analysis of the phylogenetic range of predators on bryozoan colonies was undertaken to elucidate relationships among different consumers. Functional feeding traits and diet categories were determined from literature sources and observations for 399 predator species. Multivariate analyses were used to identify groups of species that consume similar food resources and have related functional traits corresponding to finding, acquiring and ingesting prey. These analyses distinguished gradients among trophic groups based on dissimilar feeding mechanisms, body sizes, types of locomotion and dietary breadths. Co-occurrences of certain diet categories also emerged as important factors. Trophic groups were largely consistent with species clusters at different taxonomic ranks among the predator phyla. At one extreme, fishes and decapod crustaceans with large dietary breadths and body sizes, and crushing or tearing feeding mechanisms, appear to consume bryozoans as minor or even incidental parts of their diets. At another extreme, species of nudibranchs, pycnogonids, turbellarians, and certain polychaetes, small arthropods and nematodes that consume bryozoans do so primarily or exclusively. Their body sizes are comparatively smaller and they often have piercing and suctorial feeding mechanisms. These differences are associated by inference with different probabilities of antagonistic encounters and likelihoods of lethal or sublethal predation. The analyses provide a baseline for ecological and evolutionary comparisons, and a broader context for the questions, 'Who eats bryozoans, how, and how frequently?'.