Experimental evidence of subsurface feeding by the burrowing ophiuroid Amphipholis gracillima (Echinodermata)

Knowledge of the feeding habits of infaunal deposit-feeders is essential to understand their role in the movement of sediment-bound material and nutri ents and in trophic transfer. Deposit-feeding ophiuroids are abundant in th e world's oceans but many details of their intricate feeding behaviors are unknown. We used fluorescent polystyrene microspheres in a subsurface food layer to demonstrate that Amphipholis gracillima, an infaunal ophiuroid kno wn to feed on surface particles, is also capable of consuming subsurface pa rticles in the laboratory. Although physical conditions varied only slightl y during experiments there was a significant effect of temperature on the n umber of microspheres consumed. Additional experiments using layers of micr ospheres with and without food demonstrated that food layers significantly influenced the disc depth of A. gracillima, whereas layers without food did not. Utilizing subsurface sources of food might give burrowing organisms a ccess to more sources of nutrients, decrease sublethal predation and lead t o more stable populations over time.