Anti-predator defenses in western North Atlantic sponges with evidence of enhanced defense through interactions between spicules and chemicals

We examined anti-predator defenses in 4 species of temperate sponge from Long Island Sound using a common hermit crab (Pagurus longicarpus) as predator in pair-wise feeding preference tests comparing palatable control versus treatment food. Only Haliclona loosanoffi failed to deter hermit crab feeding. The other 3 species reduced P. longicarpus feeding rates, although the mechanism of deterrence differed for each sponge. Spicules and crude extracts interacted to enhance deterrence in experiments involving Microciona prolifera because combining spicules and crude extract in artificial food significantly reduced crab feeding rates by 53 %. When added to artificial food in isolation, neither spicules nor crude extract from M. prolifera significantly altered feeding rates of the crabs. Crude extracts, spicules and a combination of spicules and crude extract isolated from Halichondria bowerbanki all significantly reduced crab feeding rates compared to consumption of control food. Structural materials were significantly deterrent in feeding trials involving Cliona celata (32 % reduction in feeding), but artificial food containing either crude extract or crude extract plus spicules was significantly preferred over control food. Both H. bowerbanki and C. celata produce spicules that average >= 285 mu m in length, which is above the threshold length that has been hypothesized to deter predators. The data involving M. prolifera, H. bowerbanki, and C. celata indicate that temperate sponges use chemical and structural defenses against potential predators, and that structural and chemical defenses interact in M. prolifera. Results of this and other studies indicate that it may be fruitful to look for additive and synergistic defenses in other sponge species, especially those found to be chemically undefended when compounds were tested in isolation.