The effect of a biologically produced structure on the benthic copepods of a deep-sea site

Abstract

In deep-sea soft bottoms, a variety of organisms produce structures that persist for long periods, even after the structures are vacated. It has been hypothesized that these structures are a major source of patchiness in these communities and are important in maintaining the high diversities that characterize the deep sea. Although several studies have shown species' abundances to be correlated with structures, the mechanisms underlying the associations are not known. We attempted to discover these mechanisms, focusing on the responses of benthic copepods to mudballs made by the polychaete Tharyx luticastellus at a site at 1050 m depth in San Diego Trough (32° 52.4′N, 117°45.5′W). It was found that seven out of 40 species responded. Four were more abundant around the structure only when the worm was in residence. These species apparently benefit from some consequences of the worm's presence. Given that bacterial abundance is higher about occupied Tharyx mudballs than nearby controls, it may be that the attractiveness occupied Tharyx mudballs arises from the provision of food. Three species responded to unoccupied mudballs. We measured responses to various types of mudball mimics to determine whether responses were to a habitat provided by the mudball, to a refuge from predation in its vicinity, or to hydrodynamically mediated increases in local food availability. Two of the species appeared to use the mudball as a habitat, the third as a refuge from infaunal predators. The results indicate that biologically produced structures can persist long enough to be viewed as habitat heterogeneity by other species in the community and that this source of patchiness is important to deep-sea species.