HISTORICAL BASELINES FOR PREDATION IN SALT MARSHES: CONSERVATION IMPLICATIONS

Extensive areas of salt marsh in the southeastern U.S. have recently died off, with physical factors, including drought-induced high soil salinities and acidity, thought to be the primary causal mechanisms. Research by Silliman and Bertness (2002), however, has shown that the common plant-grazing marsh snail, Littoraria irrorata, if left unchecked by predators---such as the blue crab, Callinectes sapidus---can convert one of the most productive ecosystems in the world into a barren mudflat. Given these results and the fact that the blue crab fishery has recently declined due to overfishing practices, it is hypothesized that runaway grazer effects are contributing to the recent die-off of marsh plants in many southern marsh ecosystems.

If there are less crabs around today to keep populations of marsh snails in check, predation by crabs on these snails should be less intense than it was before initiation of intensive fishing by humans. The Holocene relict salt marshes and archaeological sites on St. Catherines Island, Georgia preserve samples of marsh snails 500-5000 years old that are ideal to test this prediction. Marsh snails found in these deposits record the history of crab predation (preserved as healed scars on the snail's shell) in the marsh before intensive modern fishing practices began. Preliminary comparisons of the paleoecological and archaeological data on the frequency of shell repair with modern samples from the island, suggest that the intensity of crab predation on marsh snails has declined since intensive fishing practices by humans began in southern estuaries.

The preliminary results of this study suggest that overfishing practices may have potential primacy in the deterioration of coastal marsh ecosystems. In the conservation of southern salt marshes, a deeper understanding of the ultimate causal factors driving the die-off of marsh plants, rather than merely addressing the most recent symptoms of the problem, is critical because such losses have far-reaching ecological and economic consequences.