Abstract

The response of two different size classes of marine benthos, macrofauna and meiofauna, to manipulation of disturbance/predation and size specific utilization of biogenic structural refuges by each benthic size category were studied in an intertidal sandflat in Virginia. A field investigation was conducted during August and September 1980 in the same Diopatra tube system which Woodin (1978; 1981) previously utilized for macrofauna I experiments. Predator/disturber exclusion cages were employed to experimentally evaluate changes in patterns of abundance of both meiofauna and macrofauna in areas of varying Diopatra tube densities (0, 1, 3 or 6 Diopatra 0.01 m–2). Samples were collected for macrofauna and meiofauna in areas immediately adjacent to tubes (= inner) and in outer areas with no tubes present from all treatment (caged or uncaged) and tube density (0, 1, 3, 6) combinations after 2 and 4 weeks. A significant increase in total macrofaunal polychaetes, nematodes and copepods was recorded inside cages after 2 and 4 weeks. Those species which were numerically abundant in control sites were also dominant inside cages. Adult densities of the bivalve, Gemma gemma increased inside cages after 2 weeks but declined dramatically after 4 weeks. Juvenile Gemma abundances, unlike those of the adults, increased inside enclosures after both 2 and 4 weeks. Along with the density increases noted in cages, a variety of main effects (i.e., tube number or position) and interactions were revealed, but these were not consistent even among benthos of similar sizes. Although densities of both meiofauna and selected macrofauna increased over similar time scales in response to predator/disturber exclusion, their spatial patterns and relationships with tubes were highly variable. Our analyses of spatial patterns of macrofauna and meiofauna in caged and uncaged sites do not fit our a priori predictions necessary to support a refuge hypothesis for all meiofauna and macrofauna by Diopatra tubes. The discrepancies between the findings of this study and earlier reports of macrofaunal utilization of Diopatra tube-caps as refuges may be related to yearly changes in community composition and/or predator/disturber activity or possibly the time scale of experiments reported here. We suggest that simultaneous monitoring of various size classes from soft-bottom communities, coupled with field experimentation, would provide valuable insight into the relative importance of forces organizing soft-bottom assemblages.

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