Document: DAV-3-52-24

Population consequences of intermediate disturbance: Recruitment, browsing, predation, and geochemistry.

WETHEY, D.S.* ¹, S.M.LINDSAY ², S.A.WOODIN ¹ and R.L.MARINELLI ³

University of South Carolina, Columbia, SC USA ¹
University of Maine, Orono, ME USA ²
Chesapeake Biological Laboratory, Solomons, MD USA ³

Abstract:
Biogenic disturbance is a dominant feature of marine soft-sediments, affecting both sediment chemistry and infaunal abundances. Our goal was to address how predation, disturbance by infauna, and sediment chemistry interact to determine population structure and recruitment. Sediment dwellers, for example, feed and defecate on the surface, thereby causing mortality of larvae and juveniles. Browsing predation on adults can reduce disturbance imposed by adults because individuals feed and defecate less while they regenerate. While consuming adult body parts, browsers themselves disturb the sediments, resulting in changes in the surficial chemical properties, as well as ingestion of larvae. Previous studies suggest that changes in surficial sediment chemistry may result in changes in the acceptability of a site to larvae. Thus there is a potential balance between browsing predation, sediment disturbance, and larval recruitment in marine sedimentary habitats. We used a population model consisting of 4 coupled differential equations to examine the relationship between predation, disturbance, sediment chemistry, and their interactive effects on the population dynamics of adults, recovering individuals and settlers. We parameterized the model using demographic and predation data on the clam Macoma balthica for the Wadden Sea. In the model Macoma shows enhanced recruitment at intermediate browsing intensities in sediments from sands to muds. The enhancement of recruitment by browsing is a function of the ratio of the recovery rate to the browsing rate, and the ratio of the rate of disturbance by intact adults to the rate of consumption of larvae by browsers. This phenomenon is a population-level analog of Connell's enhancement of species diversity at intermediate disturbance rates, in that both the total population abundance and diversity of age classes is maximized at intermediate disturbance rates.

Keywords: recruitment, disturbance, predation, infauna

This abstract is being presented at: 11:00 AM in session:
Oral Session #7: Aquatic Ecology: Shellfish to Snails.