Moving From Sea to Land Via the Freshwater Route: Larval Physiology and Mode of Recruitment in a Freshwater Fiddler Crab

University South Carolina Research Foundation, Columbia SC

Investigators

Abstract

In this study, we will develop a molecular method to identify the cryptic larval forms of three fiddler crab species common in salt marsh communities of the southeastern United States. While the adults of these closely related species, Uca minax, Uca pugnax, and Uca pugilator, are among the most studied of salt marsh invertebrates, work on larval and juvenile crabs has been hindered because they are morphologically indistinguishable at these early life stages. Using a fast, inexpensive molecular assay, we will map the distribution of these three species starting in late spring when they begin to enter the mouth of South Carolina's North Inlet estuary after completing larval development in open coastal waters until late fall when the last of the year's young have joined the established adult populations. From this information, we will produce a high-resolution model of the annual invasion of the marsh by Uca crabs. We will determine the timing, position, and degree of penetration by young of the three species into habitats preferentially occupied by their adult counterparts. We will learn if the three species migrate differently, or if their young penetrate all areas equally and differential mortality after settlement determines adult distributions within the estuary. Estimates from the field will be refined with lab-based experiments in which young crabs of the three species will be exposed to sediment from adult habitats under low or high salinity conditions. How young crabs respond to these environmental cues may explain their ability to locate adult habitats. The broader impact of this study lies in the molecular assay that we are developing to differentiate young of these three crab species. Fiddler crabs heavily impact southeastern estuaries by modifying species composition, landscape topography, and water chemistry in areas where they burrow and feed. Also, adult crabs can comprise a large portion of the diets of wetland birds and crab larvae are important prey for small fishes that are eaten by larger fishes exploited by commercial and sport fisheries. Our assay will allow us to assess the stability of marsh ecosystems over time and will be useful in estimating crustacean biodiversity. The development of this assay will eliminate a large hurdle in our understanding of birth, recruitment, and death in the salt marsh by allowing us to investigate the full life cycles of these widely studied crabs in detail for the first time.