Disappearance of the natural emergent 3-dimensional oyster reef system of the James River, Virginia, 1871-1948

Journal of Shellfisheries Research, Jan, 2005 by Helen Woods, William J. Hargis, Jr., Carl H. Hershner, Pam Mason

ABSTRACT Anecdotal reports have long indicated that oysters, Crassostrea virginica (Gmelin), in the Chesapeake Bay once grew in large 3-dimensional reef structures. However, hard evidence of widespread 3-dimensional oyster reefs in the Chesapeake Bay has been scarce. This study uses data collected from historic charts of the James River, one of the most productive oyster producing tributaries of the Chesapeake Bay, to examine the natural occurrence of these reefs as well as their destruction. An early series of charts from the 1870s clearly documents widespread emergent oyster reefs in the James River from Burwell's Bay to Newport News Point. They were long, fairly wide, and shoal-like and oriented at right angles to the current. A 1940s series of charts indicates that by this time nearly all of these reefs had become submerged. Paired t-tests indicate a significant decrease in reef height and volume but not in reef area. This suggests that oysters and shell have been physically removed from the reefs. This likely had a major impact on water circulation patterns over and around the reefs, which may also have further adversely affected oyster populations.

KEY WORDS: oyster reef, Crassostrea virginica, Chesapeake Bay, James River

INTRODUCTION

The Chesapeake Bay, named Chesepiooc, the "great shellfish hay," by the Algonquin speaking Native Americans of the region, was once one of the most productive oyster (Crassostrea virginica) (Gmelin) producing estuaries in the world. With the advent of canning and the development of the railroad system, huge national and international markets were established for Chesapeake Bay oysters (United States Secretary of the Interior 1866,Wennerston 1981). From 1894 to 1912 annual oyster harvests in Virginia alone ranged from 5-7.5 million bushels (Hargis & Haven 1988). Shells from the harvested oysters were not replaced on oyster grounds but removed and sold for a variety of commercial purposes ranging from road projects to chicken feed. This tremendous, largely unregulated harvest of oysters and shells wreaked havoc on the number of living oysters and their habitat (Wennerston 1981, Rothschild et al. 1994).

Throughout the 20th century, despite decades of overharvest and disease, the James River, a southern tributary of the Chesapeake Bay, has remained one of the most important and productive oyster areas in Virginia (Haven et al. 1978). This is mostly attributable to the water quality and hydrographic conditions of the river because circulation patterns in the Lower James trap and enhance residence time of oyster larvae in the river (Ruzecki & Hargis 1989).

Oysters in the James River once grew on large reefs. Many of these reefs were 3-dimensional structures that breached the surface of the water at low tide (Marshall 1954) and provided habitat for a variety of organisms (Harding & Mann 1999). The 3-dimensional structure of these reefs is believed to have favorably altered the environment for oysters by raising oysters off of the bottom into the upper water column. It is also believed that orientation coupled with the 3-dimensional reef structure increased water flow around the reefs, thereby decreasing sedimentation and increasing food availability (Grave 1905, Moore 1907, Masch & Espey 1967, Lenihan 1999).

In the 19th and 20th centuries the James River reefs were heavily harvested, greatly altering the size and structure of the reefs. This study documents the physical changes in the 3-dimensional oyster reef habitat of the James River from the 1870s to the 1940s. Historic hydrographic surveys were used to create and describe images of the bottom of the James River Estuary of 1871-1873 and 1940s. A series of paired t-tests were then performed to examine physical changes in the reefs.

STUDY LOCATION

The James River is a partially-mixed estuary (Pritchard 1953, Nichols 1972) in southeastern Virginia. The study area is that portion of the James from Deep Water Shoals to Newport News Point (Fig. 1). Salinity ranges from 2-18.5 ppt in this area (Stroup & Lynn 1963).

[FIGURE 1 OMITTED]

MATERIALS AND METHODS

Two detailed nineteenth century bathymetric charts and eight detailed twentieth century bathymetric charts of the James River between Hog Island and Newport News Point were used for computer analysis. US Coast Survey charts H01179a and H01179b were in paper format and depicted bathymetric soundings made from 1871 to 1873, as well as the crests of many intertidal oyster reefs. US Coast Survey charts H06682, H06729, H07025, H07087, H07160, H0762, H07174, and H07641 were created during the period from 1941 to 1948 and existed in digital format.

The original 1870s charts were copied to Mylar and registered using ArcInfo, Geographic information system (GIS) software and a Numonics 2200 digitizing tablet. Approximately 30,000 depth soundings, coded to the nearest quarter foot, original shoreline, and mean low-water lines from the 1870s charts were digitized to create GIS data layers. All depths were referenced to mean low water. These data were then translated into a 3-dimensional triangulated irregular network (TIN) model using the ArcView 3D Analist.