Nonnative Oysters in the Chesapeake Bay (2004) / Chapter Skim
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4. Oyster Biology
4. Oyster Biology
Pages 60-99
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From page 60... ...
Some particles, such as microalgae, are sent into the mouth; others, such as sediment, are usually rejected and deposited as "pseudofeces" just outside the shell. Filtration rates are a function of several environmental factors, including temperature, salinity, and suspended particulate concentration.
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From page 61... ...
(1992) reviewed the literature on filtration rates for numerous marine bivalves and found that the relationship between filtration rate and size was similar for all species examined, including several oysters.
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From page 62... ...
, which cause MSX and Dermo diseases, respectively, in the Eastern oyster, C virginica (the host)
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From page 63... ...
While all commercial molluscan species examined so far are infected by some parasites, oysters have more reported lethal diseases than any other commercial species (Bower et al., 1994; Ford, 2001; see Table 4.1~. As a matter of fact, the molluscan diseases listed as "of concern" by the Office International des Epizooties, an international veterinary body concerned with animal health, are primarily those affecting oysters of various species and are all caused by water-borne protozoan parasites that invade through the gut or external epithelium and proliferate inside the soft tissues, killing the oyster when the parasite burden becomes high.
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From page 64... ...
64 ~ ~ ~ ~ ~ ~ ' ~ ==' ~ ~ C ~ ~ 5 ~ =~ ~= ~ ~ 5 ~ ~ C u 'a 1 ~ ~ U ~ C ~ O be ~ ~ ~ ~ O ~ ~ o ~ ~ ~ ~ 3 ~ c ~ ~ ~ ~ c c ~ 5 3 ~ ~ c 3 5 ~ ,,, ~ ~ ~ a in,, ~ 9 ,, ;!
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From page 65... ...
65 C ,U ~ go o ~ ~ ~ ~ ° ~ ~ ~ ~ ~ C ~ ~ ,~ ~ to .
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From page 68... ...
Various bacterial species and the herpes virus are examples of pathogens most commonly associated with disease outbreaks in hatcheries and nurseries (Hine et al., 1998; Renault et al., 2000, 2001; Arzul et al., 2001~. Others are encountered during routine surveys or health examinations required for the shipment of molluscs across governmental boundaries.
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From page 69... ...
The larval stage lasts for about 2 to 3 weeks, depending on food availability and temperature. Larvae appear to migrate vertically, particularly at later stages, tending to concentrate near the bottom during the outgoing tide and rising in the water column during the incoming tide, thus increasing their chance of being retained in the estuary (Kennedy, 1996; Shumway, 1996~.
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From page 70... ...
Grassle, Rutgers University, Port Norris, personal communication, 2003~. Further, there is little evidence for a broodstock size/recruitment relationship for oysters, and very large sets can occur even when the stock of oysters is very low, as occurred in Delaware Bay several years after the MSX disease epizootic and heavy oyster drill predation had severely reduced the Chesapeake Bay population (Fegley et al., 1994~.
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From page 71... ...
estimated that predators annually killed 12 to 18% of oysters more than a year old on lower Delaware Bay leased grounds about half as much as died from other causes, mostly MSX disease. In addition to providing habitat for numerous other species, a principal ecological function provided by oysters is considered to be their ability to remove, or filter, particles from surrounding water (Newell, 1988~.
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From page 72... ...
(1998) subsequently observed that Long Island Sound oysters grew faster than Delaware Bay oysters.
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From page 73... ...
Loss of oysters is generally attributed to overfishing, habitat degradation, disease pressures, and the interaction among these factors, while destruction of reef habitat is the direct result of fishing practices used to harvest the oysters. Habitat and Resource Provision Oyster reefs provide essential habitat for the maintenance of oyster populations through provision of substrate for larval settlement, refuge from predators and near-bottom hypoxia, and vertical relief above the
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From page 74... ...
or microbial biofilms (Fitt et al., 1989, 1990; Weiner et al., 1989) , the consequence of gregarious larval settlement is that oyster reefs develop as multiple generations of oysters settling one upon another (Coen and Luckenbach, 2000~.
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From page 75... ...
and Breitburg and Miller (1999) have characterized the trophic links between oyster reefs and selected fish species in the bay.
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From page 76... ...
for five species in the bay (naked goby, Go biosoma bos c; strip ed blenny, Chasmodes bosqu tan us; feather blenny, Hypsoblennius hentz; skilletfish, Gobiesox strumosus; and oyster toadfish, Opsanus taut. Pelagic-Benthic Coupling and Nutrient Cycling Oysters are active suspension feeders, acquiring food by filtering organic materials from the water column and depositing copious quantities of particulate waste materials on the seafloor.
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From page 77... ...
Ecosystem-Level Effects and Trophic Interactions Studies over the past three decades in a number of estuarine and coastal systems strongly suggest that when benthic suspension feeders are sufficiently abundant, their feeding activities regulate the amount of phytoplankton biomass (see Smaal and Prins, 1993; and Dame, 1996, for reviews)
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From page 78... ...
The feeding activities of oysters remove materials in the water column besides phytoplankton that can reduce turbidity and allow more light to reach submerged aquatic plants (e.g., seagrasses, benthic microalgae)
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From page 79... ...
note the lack of historical data on phytoplankton, zooplankton, and benthic faunal abundance to confirm whether there were significant changes in phytoplankton or other factors that could have resulted in trophic restructuring in the bay. Coupled with the 100fold decline in oyster abundance and loss of oyster reef habitat have been dramatic increases in anthropogenic nutrient loading and associated oxygen depletion in the bottom waters during the summer (Seagle et al., 1999~.
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From page 80... ...
The pathogen is now present along the entire East Coast of the United States, although its major impact has been from Virginia north to Maine. The Long Island Sound oyster industry, which had been spared recurrent disease outbreaks, has recently suffered heavy losses, mostly due to MSX disease (Sunila et al., 1999~.
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From page 81... ...
The spore, a life stage common to other members of the same phylogenetic group and one presumed to play a role in transmission, is extremely rare in adult Eastern oysters, although it develops readily in juvenile oysters (Barber et al., 1991; Burreson, 1994~. The scarcity of spores suggests that adult Eastern oysters are a dead-end host for H
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From page 82... ...
Mathematical modeling of H nelsoni infection cycles predicts that several successive cold winters would substantially diminish infection prevalence and suggests that climate warming, with concomitant relaxation of the cold winter effect, may be responsible for some recent disease outbreaks in the northeastern United States (Hofmann et al., 2001)
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From page 83... ...
nelsoni are also at variance with a study in Delaware Bay, which found no difference in the acquisition and intensification of that parasite in oysters suspended in the water column compared to those on the bottom (Ford and Haskin, 1988~. Nor do oysters in intertidal locations have fewer infections than subtidal
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From page 84... ...
nelsoni infection prevalences in native oysters have been very low (<30%) in Delaware Bay, and the parasite has caused essentially no commercially significant oyster mortalities.
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From page 85... ...
nelsoni epizootics, selective breeding programs were begun at Rutgers University and the Virginia Institute of Marine Science (VIMS)
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From page 86... ...
virginica bred for resistance to MSX disease at the Haskin Shellfish Research Laboratory, Rutgers University over five generations of selection, compared to susceptible controls (Generation 0)
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From page 88... ...
Guo, Graduate Institute of Environmental and Occupational Health, Medical College, National Cheng Kung University, Taiwan, personal communication, 2003; S Ford, Haskin Shellfish Research Laboratory, Rutgers University, Port Norris, New Jersey, personal communication, 2002~.
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From page 89... ...
K Allen, Virginia Institute of Marine Science, personal communication, 2003~.
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From page 90... ...
Luckenbach (personal communication, Virginia Institute of Marine Science, Gloucester Point, 2003) has conducted prelimi
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From page 91... ...
Oysters growth relatively quickly in southern Chinese coastal waters and are typically harvested, when raised in extensive aquaculture conditions, within 2 to 3 years (10- to 15-cm shell length) after larval settlement (Guo et al., 1999~.
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From page 92... ...
ariakensis could be found as early as tune in Japan. Preliminary laboratory studies by Luckenbach (personal communication, Virginia Institute of Marine Science, Gloucester Point, 2003)
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From page 93... ...
X Guo (Graduate Institute of Environmental and Occupational Health, Medical College, National Cheng Kung University, personal communication, 2003)
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From page 94... ...
West Coast and north and south China. Cells characterized as "unusual" were found in three oysters from the northern China site.
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From page 95... ...
Reece, Virginia Institute of Marine Science, personal communication, 2002~. It should be noted that herpes virus is already present in the East Coast oyster population, as reported by Farley et al.
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From page 96... ...
Burreson, Virginia Institute of Marine Science, personal communication, 2002~. All evidence to date, then, indicates that even though C
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From page 97... ...
Burreson, Virginia Institute of Marine Science, personal communication, 2002~. SUMMARY · Oysters, like other bivalve filter feeders, feed on microalgae and are capable of removing large quantities of particulate matter from the water; they have a larval stage that allows them to be dispersed from the immediate site of the parental stock; and they require a clean, solid substrate on which the larvae can settle and cement themselves.
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From page 98... ...
Selective breeding has also produced C virginica strains that are highly resistant to MSX disease and moderately resistant to Dermo disease; however, when tested under the same conditions, C
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From page 99... ...
Other parasites, including a putative Rickettsiales-like organism and herpes virus, have been found worldwide in numerous marine bivalves.
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