Juliana M. Harding

VEINED RAPA WHELK (RAPANA VENOSA) RANGE EXTENSIONS IN THE VIRGINIA WATERS OF CHESAPEAKE BAY, USA

Abstract Three recent range extensions for the Chesapeake Bay, Virginia, veined rapa whelk (Rapana venosa) population are described. These extensions into Tangier Sound, the mid James River estuary, and to Cape Henry at the Bay mouth extend respectively, the northern, western, and southeastern boundaries of the occupied rapa whelk range in Virginia waters. Salinity and tidal circulation mediate the distribution of adults and larvae of this animal. During dry years (e.g., 2001 and 2002) adult rapa whelks may move up-estuary in western tributaries like the James River, given increased salinity and available habitat and food resources. Declines in salinities (or return to normal salinities) will either kill the rapa whelks in the upriver habitats or force a return to downstream habitats.

NORTHERN QUAHOG (HARD CLAM) MERCENARIA MERCENARIA ABUNDANCE AND HABITAT USE IN CHESAPEAKE BAY

Abstract Recent (2001–2002) surveys of hard clam Mercenaria mercenaria density and distribution, using patent tongs in a stratified random design (n = 7,358 stations) in lower Chesapeake Bay are not consistent with historic descriptions of clam habitats and densities. The highest average densities observed, up to 3.1 clams m−2, were in the lower James River. The highest modern average density observed is half that of clam densities commonly observed in these same habitats during the early 1970s. Current distribution is significantly affected by water depth and substrate composition. Hard clam density in Chesapeake Bay is positively associated with increasing sediment grain size; 78% of all clams collected were found in shell or sand habitats. However, 44% of sand habitats and 54% of shell habitats were unoccupied suggesting that even habitat types that typically support higher clam densities may currently be underused.

Sea turtles as potential dispersal vectors for non-indigenous species: the Veined Rapa Whelk as an epibiont of Loggerhead Sea Turtles.

Abstract We present the first record of Rapana venosa (Veined Rapa Whelk) as an epibiont of Caretta caretta (Loggerhead Sea Turtle) and the first observation of rapa whelks in the South Atlantic Bight, USA. Veined Rapa Whelks are invasive shellfish predators. The only known North American population of Veined Rapa Whelks is in the southern Chesapeake Bay. Collections of Veined Rapa Whelks as epibionts on Loggerhead Sea Turtles from Norfolk, VA and Wassaw Island, GA present a previously undescribed vector for whelk range expansion to widely separated coastal habitats. In October 2008, a live juvenile Loggerhead stranded near Norfolk, VA with a Veined Rapa Whelk attached to its carapace. Since May 2005, a total of eight Loggerheads with Veined Rapa Whelks as epibionts have been observed nesting on Wassaw Island, GA. The shell lengths of the two smallest Wassaw Island whelks (1.9 and 2.6 mm) indicate that the whelks settled from the plankton 24–48 hr immediately prior to collection in Georgia. This time frame is not commensurate with turtle migration from Chesapeake Bay to Wassaw Island and indicates a whelk source that is geographically distinct from the Chesapeake Bay. Rapa whelk use of Loggerhead carapaces as settlement and juvenile habitat is of serious concern given the observed potential for coastal and oceanic migrations by turtles to facilitate Veined Rapa Whelk dispersal.

Comparison of Crassostrea virginica Gmelin (Eastern Oyster) Recruitment on Constructed Reefs and Adjacent Natural Oyster Bars over Decadal Time Scales

Abstract Since 1993, oyster reef replenishment efforts in the Virginia portion of the Chesapeake Bay have relied heavily on construction of oyster shell reefs with enhanced vertical relief. We evaluated the performance of six reefs constructed in proximity to natural subtidal oyster bars by comparing recruit densities (spat m-2, where spat are young-of-the-year oysters with shell heights less than 50 mm) between habitats. Recruitment was higher on the reefs than bars during the first 1–3 yr post-construction, usually by at least an order of magnitude. Within 7 yr, recruitment was similar between reef-bar pairs although both reefs and bars received additions of shell, live oysters, or both during the study period. At decadal time scales, constructed oyster reefs did not show enhanced recruitment relative to adjacent natural oyster bars. The rapid decline in reef recruitment post-construction is likely related to three processes: (i) shell degradation by taphonomic processes, (ii) biofouling that occludes the shell surface to recruitment, and (iii) inability of extant oysters on the reef to produce new shell at a rate commensurate with losses to (i) and (ii). There appears to be a requirement for continued replenishment activity to maintain the shell base on these reefs, contrary to the dynamics of a healthy natural oyster population. The similarity in recruitment between constructed reefs and natural bars at decadal time scales suggests that subtidal shell plants or shell additions to natural bars may be a more cost-effective repletion strategy because they provide equal population enhancement per unit area.