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 nutrients and in trophic transfer. Deposit-feeding ophiuroids are abundant in the 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 known to feed on surface particles, is also capable of consuming subsurface particles in the laboratory. Although physical conditions varied only slightly during experiments there was a significant effect of temperature on the number of microspheres consumed. Additional experiments using layers of microspheres 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 access to more sources of nutrients, decrease sublethal predation and lead to more stable populations over time.