Oyster Gardening in Virginia: An Overview of Techniques

This document is intended to respond to a growing demand for information on intensive, off- bottom aquaculture of the eastern oyster, Crassostrea vlrginica, in Virginia and neighboring coastal states and represents an attempt to partially fulfill the requests from oyster gardeners for information on approaches towards culturing oysters

Evaluating and enhancing the success of oyster reef restoration: The effects of habitat complexity on oyster survival

We evaluated the progress of several oyster restoration efforts of varying ages in three tidal tributaries of Chesapeake Bay, the Rappahannock, the Piankatank and Great Wicomoco rivers. In 2003 and 2004, we determined the density, biomass and size frequency distribution of oyster populations on the reefs during spring, summer and fall. Recruitment of oysters to the reefs was quantified using standardized substrates deployed and retrieved from the reef surfaces on a weekly or bi-weekly schedule from May through November. The prevalence and intensity of the oyster pathogens Perkinsus marinus and Haplosporidium nelsoni in oysters on the reefs was determined from samples taken in October 2004 and compared with values taken from another study on the reefs in October 2003. Additionally, the composition and abundance of other epifaunal community constituents associated each of the reefs were enumerated. We characterized the condition of reef base material by measuring the prevalence of present or past damage by boring sponge (Cliona spp.) and by measuring individual particle sizes. Finally, large-scale reef attributes such as slope and water depth were quantified. Oyster population data were then related to epifaunal community metrics and substrate condition with correlation analyses

Evaluation of dredge fishing activity on the seaside of Virginia\u27s Eastern Shore, December 1994 - November 1995

Dredging has a long history in Virginia\u27s commercial fisheries. In general, dredges are scraping or digging apparatuses that harvest as they are towed behind boats under power. Mechanical dredges have been used with sail power to harvest oysters since the mid- l 800\u27s. Crabs have been harvested by power dredges since at least 1900, while dredge fishing of clams, which reside deeper in the substrate, began somewhat later. Individual crab dredges in Virginia can be a maximum of 8 ft wide and are usually pulled in pairs for a maximum total width of 16 ft. The dredge has a scraping or combing forward bar with 4 to 6 inch-long teeth that dig crabs out of the bottom sediment. The crabs then move across the bar into a chain or mesh bag. In the dredging process many materials may become dislodged from the bottom ( e.g. rocks, macroalgae, vascular plants and other shellfish); those greater than the bag mesh will be retained throughout the towing period. Oyster dredges are similar in design to the crab dredge; however, they are usually only 4 ft wide. Clam dredges were originally similar to oyster dredges, but over the years as clam populations have declined, the teeth in the clam dredge have been lengthened to dig deeper, and the bag is sometimes replaced with a heavy metal cage constructed of welded reinforcing bar

Materials Processing by Oysters in Patches: Interactive Roles of Current Speed and Seston Composition

Filtration rates for oysters have typically been measure in still water laboratory experiments and ecosystem-level effects estimated by extrapolation. With the exception of in situ measures of oyster filtration by Dame (1999, Chapter 18, this volume and references cited therein) these estimates have failed to account for the effects of hydrodynamic effects on oyster filtration rates and on physical redistribution of particles. In this chapter we report on a series of experiments conducted in a recirculating seawater flume designed to address the effects of flow speed and seston composition on filtration rates in a bed of oysters. In six separate experiments ninety oysters were arranged in the bed of the flume, flow speed adjusted to one of eight levels (0.65, 1.0, 2.1, 4.2, 6.0, 10.4, 13.7 or 22.0 cm s·1 ), seston added to the flume and particle concentrations upstream and downstream of the oyster bed determined from vertically-arrayed samples. Four experiments investigated the effects of each flow speed on the filtration of a unialgal diet, while two experiments utilized the algal diet in combination with inorganic particles. Control experiments sought to estimate the effects hydrodynamic effects on particle distribution by measuring filtration rates over beds of ninety pairs of empty oyster valves. Our findings reveal effects of flow speed and, less evidently, seston composition on particle filtration by oysters. More importantly, our results point to the importance of hydrodynamically-mediated particle redistribution of particles over patches of oysters, and portend sampling difficulties associated with quantifying oyster filtration rates in the field.https://scholarworks.wm.edu/vimsbooks/1089/thumbnail.jp

An Experimental Evaluation Of The Effects Of Scale On Oyster Reef Restoration

We investigated the effects of spatial scale, ranging from 10’s of meters to several km’s, on the development of oyster populations and other reef-associated organisms during the early stage of reef restoration. Employing a block design, experimental reefs were constructed at four sites in the lower Rappahannock River, VA. We tested the effects of sites (scale ≈ 1 – 10 km), reef sizes (scale ≈ 100 m) and locations within reef (scale ≈ 10 m) on the settlement, survival and growth of oysters and on the abundance, biomass, species richness and diversity of developing communities utilizing the reefs. The project provides descriptive data about the developing reefs, both in terms of their physical characteristics and the early succession of species to colonize the reefs. We test numerous hypotheses related to temporal and spatial development of the reefs, and we explore some of the relationships between the development of oyster populations, the abundance and biomass of other species, and the species richness and diversity of reef- associate fauna. We also pose and test several specific a priori hypotheses related to the effects of scale on the development of oyster populations and reef communitie

Distribution, habitat characteristics, prey abundance and diet of surf scoters (Melanitta perspicillata) and long-tailed ducks (Clangula hyemalis) in polyhaline wintering habitats in the mid-Atlantic region: a comparison of shallow coastal lagoons and Chesapeake Bay environs

To the best of our knowledge there are no published data on sea duck winter habitat use in the higher salinity portion of the lower Chesapeake Bay or in adjacent coastal bays along the Atlantic margin of the Delmarva (Delaware, Maryland, Virginia) peninsula. Within these regions both SUSC and LTDU have been observed in shallow water environments (Ross, pers. obs.), yet little is known about their habitat use or feeding habits in these areas. Importantly, these two adjacent areas, which are separated by as little as 20 km, differ in several key environmental components. In this study we documented the distribution, habitat use and diet for both surf scoters and long-tailed ducks in these adjacent regions during the winter of 2008-2009. Additionally, we characterized the sediment and quantified infaunal and epifaunal prey species composition and abundances in the shallow water environments used by sea ducks in these areas

Settlement and survival of the oyster Crassostrea virginica on created oyster reef habitats in Chesapeake Bay

Efforts to restore Crassostrea virginica oyster reef habitats in Chesapeake Bay typically begin with the placement of hard substrata, such as oyster shell, in the form ofthreedimensional mounds on the seabed to serve as a base for oyster recruitment and growth. A shortage of sufficient volumes of oyster shell for creating large-scale reefs has led to widespread use of other materials, such as surf clam (Spisula solidissima) shell, as a substitute for oyster shell. We monitored oyster recruitment, survival, and growth on intertidal and subtidal reefs constructed shucked oyster and surf clam shell. Results indicate that oyster settlement occurred on both substrate types throughout the monitoring period but high levels of postsettlement mortality occurred on clam shell mounds. On the subtidal clam shell mound, the quality of the substrate material varied with reef elevation with large shell fragments and intact valves scattered around the reef base and small, tightly packed shell fragments paving the crest and flank of the reef mound. The abundance of oysters on this reef reflected this distribution where oysters were more abundant and larger at the reef base and less abundant and smaller on the crest of the reef. Oyster shell reefs supported greater oyster growth and survival and offered the highest degree of structural complexity. We suggest that the availability of interstitial space and appropriate settlement surfaces account for the observed differences in oyster abundance across the reef systems. The patterns observed give context to the importance of substrate selection in similar restoration activities

Effects of commercial clam aquaculture on biogeochemical cycling in shallow coastal ecosystems

The bivalve aquaculture industry is expanding worldwide; sustainability requires improved understanding of its interactions with the environment. As suspension feeders, bivalves, such as clams, reduce primary production through feeding, and thus dampen eutrophication. Additionally, enhanced rates of denitrification, the microbial removal of reactive nitrogen, have been reported in bivalve sediments due to increased organic matter supply through biodeposition; another potential, yet indirect, control on eutrophication. Simultaneously, bivalves can influence local ‘bottom-up’ effects on production by enhancing nutrient regeneration through excretion and microbial mineralization of biodeposits. At clam aquaculture sediments, respiration and nutrient regeneration rates were significantly higher compared to uncultivated sediments. The enhanced nutrient recycling facilitated by clam aquaculture directly fueled macroalgal production, which proliferate on the shallow predator-exclusion nets commonly used by US aquaculturists. The effect of clams on denitrification and dissimilatory nitrate reduction to ammonium (DNRA), microbial processes that compete for nitrate, was site and season dependent; strongly influenced by nitrate concentrations relative to organic carbon availability. DNRA was favored over denitrification in environments with low nitrate (i.e. Cherrystone Inlet, VA) while denitrification increased above DNRA in high nitrate conditions (i.e. low salinity sites in Sacca di Goro, Italy). As a bioextractive practice, bivalve aquaculture is a net sink for nitrogen via harvest, however, depending on the food source (e.g. external or internal), bivalves may increase nitrogen and subsequently production on a local scale. These results highlight the need to assess both nitrogen removal and regeneration pathways associated with bivalve aquaculture to determine the overall effect on eutrophication

Preliminary evaluation of water quality in tidal creeks of Virginia\u27s Eastern Shore in relation to vegetable cultivation

In response to concerns raised about the impacts of vegetable cultivation using plastic ground covers on water quality, we have initiated a broad-scale, systematic study of water quality in seaside tidal creeks of Virginia\u27 s Eastern Shore. Our objective was to determine if acute toxicity associated with heavy metals or pesticides was more prevalent in tidal creeks with drainage areas which include this agricultural practice than in those which do not. Though such correlations do not confirm cause and effect, they may serve as the basis for future, more targeted investigations and for some immediate changes in land management practices which, regardless of the specific cause, are likely to produce some remediation. Eleven study sites, located in six different watersheds, were selected to evaluate acute toxicity (from heavy metals and organic pesticides. Land use patterns and acreage within each watershed was determined from aerial photographs. The amount of vegetable plasti-culture in the watersheds of the study sites ranged from 0-13% of total acreage. An assay for heavy metals, based upon enzyme inhibition in a bacterial strain, was used to determine if up to seven metals (including copper) were present at acutely toxic levels. Both water samples and aqueous extracts of sediment samples were tested. A continuous series of 96 hr in situ bioassays using the grass shrimp, Palaemonetes pugio, were conducted from Aug. I, 1996 - Sept. 22, 1996 at each station to assay for toxicity from organic pesticides. Grass shrimp are known to be quite sensitive to insecticides and the in situ bioassay approach provides a continuous means of monitoring for toxic events