Reconstructing early 17th century estuarine drought conditions from Jamestown oysters.

Oysters (Crassostrea virginica) were a central component of the Chesapeake Bay ecosystem in 1607 when European settlers established Jamestown, VA, the first permanent English settlement in North America. These estuarine bivalves were an important food resource during the early years of the James Fort (Jamestown) settlement while the colonists were struggling to survive in the face of inadequate supplies and a severe regional drought. Although oyster shells were discarded as trash after the oysters were eaten, the environmental and ecological data recorded in the bivalve geochemistry during shell deposition remain intact over centuries, thereby providing a unique window into conditions during the earliest Jamestown years. We compare oxygen isotope data from these 17th century oyster shells with modern shells to quantify and contrast estuarine salinity, season of oyster collection, and shell provenance during Jamestown colonization (1609-1616) and the 21st century. Data show that oysters were collected during an extended drought between fall 1611 and summer 1612. The drought shifted the 14 psu isohaline above Jamestown Island, facilitating individual oyster growth and extension of oyster habitat upriver toward the colony, thereby enhancing local oyster food resources. Data from distinct well layers suggest that the colonists also obtained oysters from reefs near Chesapeake Bay to augment oyster resources near Jamestown Island. The oyster shell season of harvest reconstructions suggest that these data come from either a 1611 well with a very short useful period or an undocumented older well abandoned by late 1611.

Salinity tolerance of larval Rapana venosa: implications for dispersal and establishment of an invading predatory gastropod on the North American Atlantic coast.

The lack of quantitative data on the environmental tolerances of the early life-history stages of invading species hinders estimation of their dispersal rates and establishment ranges in receptor environments. We present data on salinity tolerance for all stages of the ontogenetic larval development of the invading predatory gastropod Rapana venosa, and we propose that salinity tolerance is the dominant response controlling the potential dispersal (=invasion) range of the species into the estuaries of the Atlantic coast of the United States from the current invading epicenter in the southern Chesapeake Bay. All larval stages exhibit 48-h tolerance to salinities as low as 15 ppt with minimal mortality. Below this salinity, survival grades to lower values. Percentage survival of R. venosa veligers was significantly less at 7 ppt than at any other salinity. There were no differences in percentage survival at salinities greater than 16 ppt. We predict that the counterclockwise, gyre-like circulation within the Chesapeake Bay will initially distribute larvae northward along the western side of the DelMarVa peninsula, and eventually to the lower sections of all major subestuaries of the western shore of the Bay. Given the observed salinity tolerances and the potential for dispersal of planktonic larvae by coastal currents, establishment of this animal over a period of decades from Cape Cod to Cape Hatteras is a high probability.