Macrobenthic invertebrates are important sources of food for many estuarine resident and marine transient fishes and shrimps. Macrobenthos and transient nekton (fishes, shrimps, and crabs) in temperate estuaries display inverse patterns of seasonal abundance, suggesting a link between predation by these transients and summer macrobenthos abundance minima. A three-phase study (field manipulations, laboratory feeding experiments, and modeling simulations) was conducted to determine the impact of predation by white shrimp (Litopenaeus setiferus) on the density and spatial distribution of estuarine subtidal macrobenthos. Long-term abundance data for transient nekton and subtidal benthic invertebrates in the North Inlet Estuary, SC, were used for hypothesis generation and eventual creation and validation of a dynamic simulation model.

Compared to controls, macrobenthos densities decreased significantly within field enclosure cages containing 12 or 36 shrimp m-2. In laboratory feeding experiments, shrimp predation significantly reduced macrobenthos densities, while shrimp disturbance and macrobenthos emigration did not. Although the impacts of white shrimp predation on the spatial distribution of macrobenthos remain unclear, GIS interpolation suggests dynamic changes in patchiness did occur. These changes, however, were undetectable using traditional indices of dispersion.

Functional response experiments of white shrimp feeding on macrobenthos were conducted to determine the effects of variable macrobenthos density on predation rates. A simulation model was developed using these data to determine the effects of white shrimp predation on seasonal macrobenthos abundance cycles. Predictions of macrobenthos densities from model experiments were compared with observed data in low, medium, and high density shrimp years. Macrobenthos abundance predictions were within the range of the observed data, although the timing of the predicted macrobenthic decline lagged behind the observations. The greatest reductions in macrobenthos densities were predicted and observed in years of high white shrimp density. This integrated modeling study demonstrated that white shrimp predation can play an important role in seasonal macrobenthos abundance cycles.

This study suggests that predation has primacy in determining macrobenthos seasonal cycles. The results provide evidence that white shrimp can significantly reduce macrobenthos densities and may have contributed to regular seasonal declines observed in the macrobenthos community over the last 25 years.