THE SEDIMENTARY PROCESSES AND GEOMORPHIC HISTORY OF WRECK SHOAL, AN OYSTER REEF OF THE JAMES RIVER, VIRGINIA

Wreck Shoal is a subtidal oyster reef area located in the James River, Virginia. Two significantly different types of oyster reefs are found in adjacent areas on Wreck Shoal. Hard-rock reefs are characterized by a relatively thick oyster shell layer, higher densities of live oysters, a coarser interstitial sediment, and a negligible sediment cover. In contrast, mud-shell reefs are characterized by a very thin osyter shell layer, considerably lower densities of live oysters, a finer interstitial sediment, and a 1-2 cm layer of very fine sediments covering the reef. The contemporary sedimentation processes operating on the hard-rock and mud-shell oyster reefs are distinctly different. The hard-rock oyster reefs are in shallower water, experience stronger bottom currents, and present a hydraulically rougher surface to the flow. The mud-shell oyster reefs are in deeper water, experience weaker bottom currents, and present a hydraulically smoother surface to the flow. These factors result in substantially different bottom shear stresses at the fluid-bed interface. The hard-rock oyster reef, with the high bottom shear stress is rarely depositional with respect to fine sediments. In contrast, the mud-shell oyster reef with the low bottom shear stresses is rarely erosional with respect to fine sediments. The James River estuary has evolved, moving upstream and landward in response to a rising sea level. The Wreck Shoal oyster reefs have developed on the ridge and swale topography of a point-bar formed during the late Pliestocene Epoch. From the 1550\u27s to the 1850\u27s the oyster reef developed vertically almost 1.5 m. From the 1850\u27s to present the oyster reefs have lost more than 1.0 m of elevation due to intense harvesting activity. Conceptual models of subtidal oyster reef dynamics and development are proposed and verified based on field observations. The management implications of the results of the study are presented and recommendations are made for the rational exploitation and management of the resource

Evaluation of a Pound Net Leader Designed to Reduce Sea Turtle Bycatch

Offshore pound net leaders in the southern portion of Chesapeake Bay in Virginia waters were documented to incidentally take protected loggerhead, Caretta caretta, and Kemp’s ridley, Lepidochelys kempii, sea turtles. Because of these losses, NOAA’s National Marine Fisheries Service (NMFS) in 2004 closed the area to offshore pound net leaders annually from 6 May to 15 July and initiated a study of an experimental leader design that replaced the top two-thirds of the traditional mesh panel leader with vertical ropes (0.95 cm) spaced 61 cm apart. This experimental leader was tested on four pound net sites on the eastern shore of Chesapeake Bay in 2004 and 2005. During the 2 trial periods, 21 loggerhead and Kemp’s ridley sea turtles were found interacting with the control leader and 1 leatherback turtle, Dermochelys coriacea, was found interacting with the experimental leader. Results of a negative binomial regression analysis comparing the two leader designs found the experimental leader significantly reduced sea turtle interactions (p=0.03). Finfish were sampled from the pound nets in the study to assess finfish catch performance differences between the two leader designs. Although the conclusions from this element of the experiment are not robust, paired t-test and Wilcoxon signed rank test results determined no significant harvest weight difference between the two leaders. Kolmogorov-Smirnov tests did not reveal any substantive size selectivity differences between the two leaders

Physiological response of scup, stenotomus chrysops, to a simulated trawl capture and escape event

Scup (Stenotomus chrysops) were severely exercised by manual chasing for 6 min, and the clearance of lactate over a 12 hr period was evaluated. Lactate peaked from 0.5 to 1.0 hr following exercise with concentrations ranging from 61.0 to 126.0 mg/dL and returned to rested concentrations within 4 hr post-exercise. Concentrations of lactate in rested fish ranged from 5.2 to approximately 23.0 mg/dL. Fish were observed for 10 days following exercise for delayed mortality. A 100% survival of scup was observed with no significant difference between control and experimental populations. Swimming performance was evaluated for 14.0 to 15.0 cm fork length scup, with a towed stimulus through a still-water circular swimming channel, at prolonged and burst speeds. A maximum sustainable swimming speed of 2.2 BL/sec was observed. Between the speeds of 3.0 and 3.3 BL/sec and 4.4 BL/sec, endurance time significantly decreased with the increase in swimming speed. Blood lactate concentrations were measured at 0.5 and 4.0 hr post exercise, and were used as an indicator of white muscle recruitment. A significant difference was not found between rested and experimental mean lactate concentrations at the maximum sustainable swimming speed of 2.2 BL/sec. White muscle recruitment indicated by increases in lactic acid, was recorded at speeds above the maximum sustained swimming speed, and mean blood lactate concentrations were significantly different within blood sampling times and between swimming speeds. Based on the results of our investigations of lactate recovery in scup following a simulated trawl capture and escape event, we believe that scup interacting with a bottom trawl and subsequently escaping, are physiologically stressed by the event, but recover in less than 6 hr. All experimentally treated fish survived both exhaustive exercise and prolonged swimming, suggesting encounter mortality is minimal. The results of this study do not address the effects of possible physical damage on escape or the effect of multiple encounters

Recent history and response characteristics of Wachapreague Inlet, Virginia : Final report

Wachapreague Inlet, a large downdrift offset inlet in the barrier island complex of the mid-Atlantic coast (Delmarva peninsula), was studied during the period 1971-1974. The inlet channel width is bout 500 m and the throat cross-sectional is about 4,500 m2 • The inlet channel is about 3 km in length, approximately one-half of which is within the well-developed horseshoe shaped ebb delta complex. The maximum channel depth is 20 rn which occurs at the throat. Elements of the study included: (1) the inlet morphornetric history (120 years), (2) assessment of surficial and sub-bottom sediments within the inlet complex, (3) determination of the distribution of tidal flows within the inlet channel, (4) determination of the zone of influence of inlet hydraulic currents along the face of the updrift barrier island and (5) the determination of the response of the channel cross-sectional area to short-term variations in wave activity and tidal prisms. (more...

Bacterial Community Profiling of the Eastern Oyster (\u3cem\u3eCrassostrea virginica\u3c/em\u3e): Comparison of Culture-Dependent and Culture-Independent Outcomes

Tissue-associated bacterial community profiles generated using a nested polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) approach and culture-dependent and culture-independent isolation techniques were compared. Oyster samples were collected from 2 harvest areas along the coast of Maine, in the United States. Profiles from both isolation strategies were evaluated using Sorensen’s index of similarity and cluster analysis of gel banding patterns. Culture independent profiles were further evaluated using the Shannon diversity index. In general, the culture-dependent strategy resulted in a greater number of bands within a profile. Bacterial DGGE profiles were found to be highly similar within an isolation strategy, with a higher degree of unrelatedness between culture-dependent and -independent techniques. Cluster analysis identified bands present in the culture-dependent strategy and not the total DNA technique, and vice versa. Significant differences in community profiles between oyster-associated and seawater were observed, indicating a diverse group of specialist bacterial species inhabit and are able to proliferate within the oyster

A Comparative Evaluation of the Habitat Value of Shellfish Aquaculture Gear, Submerged Aquatic Vegetation and a Non-Vegetated Seabed

The habitat value of modified rack and bag, shellfish aquaculture gear (SAG) used for the grow-out phase of the American oyster, Crassostrea virginica, submerged aquatic vegetation (SAV), Zostera marina, and a shallow nonvegetated seabed (NVSB) was comparatively evaluated over a 1-year period in Pt. Judith Pond, a tidal estuary in Southern Rhode Island. Enclosure gear was used to sample the three ecotypes, and organisms (\u3e5 mm) were identified, enumerated, and measured to the nearest millimeter. Abundances of marine organisms and species diversity indices were used as measures of the habitat value of these ecotypes within each season. Environmental and geological parameters were not significantly different between the habitats. Emergent surface area (cm2 m-2 of seabed) within each ecotype was estimated, and used to evaluate its role in providing habitat. The SAG habitat had a significantly greater surface area than either the SAV or NVSB habitats during all seasons. The physical structure of the SAG habitat protects juvenile fish from predators and provides substrate for sessile invertebrates that serve as forage for fish and invertebrates. The SAG habitat supported a significantly higher abundance of organisms per m of seabed throughout the year. Species richness was also significantly greater in the SAG habitat compared with the SAV and NVSB habitats. A 2-way ANOVA indicated significant differences in species diversity (Shannon-Weiner index) between habitats. Tukey’s HSD test indicated that the SAG habitat had significantly higher species diversity than the NVSB habitat, but no significant difference in species diversity was found between the SAG and SAV habitats. These findings indicate that shellfish aquaculture gear provides habitat for many organisms throughout the year, and is especially beneficial to ecosystems that support native species of recreationally and commercially important fish and invertebrates in their early life history stages. Therefore, we conclude that shellfish aquaculture gear has substantially greater habitat value than a shallow nonvegetated seabed, and has habitat value at least equal to and possibly superior to submerged aquatic vegetation

Rapid growth of a deep-sea wood-boring bivalve

The growth of Xylophaga atlantica Richards, a deep-sea wood-boring bivalve, was studied by recovering a 1-year time series of oak and pine panels deployed at depths of 100 and 200 m at the edge of the continental shelf, south of Cape Cod. Change in shell height between samples was used to assess growth rate. At the 100 m site, the first individuals to settle grew much faster, on average, than those that settled later in the year on the same panels (0.085 mm day-1 vs 0.031 mm day-1, respectively). The growth rate of the maximum sized individuals was 0.027 mm day-1 whereas the modal growth rate was half that at 0.015 mm day-1. The modal growth rate of those recovered from 200 m was much greater at 0.246 mm day-1 and is thought to be due to the warmer average temperatures there. Differences in growth rate due to season, substrate and previous density were also apparent. © 1994

Restoration that targets function as opposed to structure: replacing lost bivalve production and filtration

ABSTRACT: Abundant suspension-feeding bivalves have a dominant organizing role in shallow aquatic systems by filtering overlying waters, affecting biogeochemical processing, and diverting production from the water column to the benthos. In degraded aquatic systems where bivalve populations have been reduced, successful restoration of ecosystem functions may be achieved by targeting the revival of bivalve populations. The ‘North Cape’ oil spill on the coast of Rhode Island (USA) provides an opportunity to demonstrate the feasibility of scaling bivalve restoration to meet quantitative goals of enhanced production. After this oil spill, mortalities of bivalves were estimated by impact assessment modeling of acute toxicity, and results were confirmed by comparisons with counts of dead and moribund animals on local beaches. Computation of lost bivalve production included future production expected from affected animals, had they lived out their expected life spans. This calculation of production forgone required a demographic model that combined age-specific mortality with individual growth. Application of this modeling approach to surf clams Spisula solidissima, the species that comprised 97% of the total loss of bivalve production from the spill, illustrates the detailed implementation of scaling restoration to match estimates of losses. We consider the factors known to limit abundance and production of surf clams and other marine bivalves (hard clams, American oysters and bay scallops) and review the advantages of hatchery stocking, transplantation, habitat restoration, and reduction of fishing pressure in selecting a reliable and efficient restoration action. Age-specific estimates of the scale of population enhancement required to restore production showed that fewer additional animals were needed when larger (older) animals were added, but at the expense of greater grow-out requirements. Relaxation of fishing was most effective for hard clams. Accurate scaling of restoration was most sensitive to mortality rate, and the most efficient restoration involving seeding of small bivalves would be accomplished using surf clams. Monitoring of the restoration option chosen to compensate for the bivalve loss following the ‘North Cape’ oil spill can serve to test the underlying demographic assumptions and accuracy of the restoration scaling