Science Wednesday: A Case of Crabs and People

About the author: Steve Jordan’s environmental career is rooted in a childhood spent in the woods and creeks of suburban Maryland and along the shores of Chesapeake Bay. After graduate school and a couple of decades working in Chesapeake Bay science and management, he joined EPA’s Office of Research and Development as a scientist and manager at the Gulf Ecology Division.

Before the 1970s, intense development of our coastal areas was limited mostly to scattered resort cities separated by large areas of sparsely populated or undeveloped land. As population grew and roads improved, coastal development exploded—and sprawled.

Beach front high-rises are the most obvious result of all that coastal development, but the whole complex of barrier islands, back bays, bayous, and tidal rivers along our Atlantic and Gulf coasts is now arrayed with homes, businesses, roads, golf courses, docks, bulkheads, and everything else that comes with development. Gulf of Mexico coastal watersheds lost over 370,000 acres of wetlands from 1998 to 2004, mostly to development (see: U.S. Fish and Wildlife Service).

Except for the occasional hurricane, the coastal zone is wonderful habitat for humans. It is also essential habitat for many kinds of animals and plants, including the fish and shellfish that shore residents cherish.

Do the habitat needs of humans conflict with the habitat needs of other coastal residents? Our research at EPA’s Gulf Ecology Division indicates that they can. With my coauthors, Lisa Smith and Janet Nestlerode, I developed a mathematical model to simulate how loss of seagrasses and salt marshes could affect the important blue crab fishery in the U.S. Gulf of Mexico.

The model used information from many existing small-scale studies of how tiny, young (juvenile) crabs depend on aquatic vegetation until they are large enough to avoid predators. We linked data from these studies to electronic maps of the essential habitats and long-term, Gulf-wide commercial fishery data.

Putting it all together, we were able to predict that minor, local losses of essential habitats, multiplied many times in many places, could have serious negative effects on the future of the crab fishery. The main scientific advance in this work has been to make a connection between small-scale ecological studies and large-scale population modeling as it is used in fishery science.

With colleagues from the Pacific Coast and elsewhere, we are extending this type of research to other species and coastal areas. We hope this research will contribute to better understanding of the cumulative effects of coastal development on ecosystems and valuable ecological resources.

Figure caption: Simulated U. S. Gulf of Mexico hard blue crab landings 2004-2050. The two lower curves show different scenarios of habitat loss: SAV = submersed aquatic vegetation (seagrasses); hardened shore = loss of salt marsh edge to shoreline structures.