Evidence of a naturally occurring inhibitor possibly limiting Dermocystidium marinum in Virginia

Dermocystidium marinum, a fungus parasite common in oysters on the eastern shore of Chesapeake Bay, suddenly dissapeared at the beginning of the marsh and bay system of\u27 the outer Virginia coast. No D. marinum was found on the outer coast (Seaside) although temperatures and salinities seem to be optimal. Introduction of populations of infected oysters seem to lose the dieease, but individuals do not. What seems to be a water derived inhibitor was found in a few water samples collected at Wachapreague on the Seaside. Comparable inhibition was not found in Chesapeake Bay water. The inhibitor is difficult to demonstrate and its nature is uncertain. It is suggested that the inhibitor may keep the disease from invading Virginia\u27s outer bays

Winter mortalities of oysters on the Eastern Shore of Virginia, 1959-1961

During the winter of 1960-61 exceptional mortalities occurred among certain oysters on the Virginia Seaside. These mortalities were greatest among James River oysters held intertidally and South Carolina imports placed below low tide level. Intertidal native oysters suffered small mortalities but among subtidal native or James River oysters only the very oldest, with extensive disease histories, showed any winter mortality. (...

Studies on oyster scavengers and their relation to the fungus disease Dermocystidium marinum

Within the past decade there have been several studies on the biological structure of oyster reefs. These studies, however, gave few insights into the dynamics of oyster communities. The extensive studies of Hedgpeth (1953) , Gunter (1955), and Parker (1955, 1969) in Texas and Korringa (1951) in Holland were largely concerned with sessile forms, and the highly motile fishes went almost unnoticed. While these studies clearly emphasized imrmotile organisms, the present study leans in the opposite direction. This study started from casual observations of oyster fishes, and progressed to comparisons of mortality of oysters with activity of other members in the community

Studies on the Mud Crabs (Xanthidae) of the Eastern Shore of Virginia

Small xanthid crabs are among the most abundant members of estuarine communities, and doubtless they have important influence in several communities. In Chesapeake Bay and environs mud crabs are one of the most conspicious members of the oyster community, and they must comprise a large biomass, despite their small size. Collections and observations were made at 11 localities visited at least once a month on the Eastern Shore of Virginia from August 1959 through November 1960, with some scattered study until August 1961

Will Overfishing and Proposed Mississippi River Diversions Imperil Louisiana Oyster Fisheries? Commentary and Review

Two recent articles based on oyster landings have challenged the prevailing wisdom about the most important factors controlling Louisiana oyster production. One article concludes that the northern Gulf industry (principally Louisiana) will collapse based on overfishing; the second concludes that the addition of freshwater through diversions could be harmful to production. These findings are not supported by the literature or our statistical analysis of the landings data. In an effort to put into perspective the complexity of the factors affecting oyster production in the northern Gulf of Mexico, several areas of the oyster literature are reviewed, including (1) hysteresis, (2) the heterogeneous needs of different oyster ages, and (3) the geographic distribution of Gulf oyster populations (some including statistical interpretations). We conclude that Kirby’s (2004) prediction of failure of the Gulf oyster fishery as a result of the danger of current levels of fishing approaching overfishing is exaggerated. We further conclude that Turner’s (2006) data do not support his thesis that diversions are at least unjustified, if not harmful to overall oyster production

Oyster Mortality Studies in Virginia: Ill. Epizootiology of a Disease Caused by Haplosporidium costale Wood and Andrews

A short, sharp eplzootic disease of oysters on Seaside of Eastern Shore, Virginia, has been associated with a new pathogen, Haplosporidium costale Wood and Andrews. Native oysters in trays have shown closely timed May-June losses for three consecutive years. Losses at other seasons were small. May-June losses ranged from 12 to 14 percent in 1959 to 36 to 44 percent in 1960. James River oysters moved to Seaside showed higher losses than natives after a year of acclimation. Oysters in Bayside creeks revealed late summer losses caused by Dermocystidimn marinmn Mackin, Owens, and Collier rather than May-June deaths. The new pathogen was found in live oysters from March to July, and in a high proportion of gapers in May and June. The epizootiology is well established for these periods but unknown for the rest of the year. Increasing prevalence of another pathogen ( MSX ), causing Delaware Bay disease, has complicated mortality studies. Losses are most serious in older oysters which have been held beyond the usual period of culture. Careful timing of planting and early harvesting permit oystermen to a void serious losses

Effects of Slotted Water Control Structures on Nekton Movement within Salt Marshes

Water control structures (WCSs) restrict hydrological connectivity in salt marshes and thereby impede nekton movement within the greater habitat mosaic. Transient fishery species, which spawn outside salt marshes and must get past these barriers to reach spawning areas or salt-marsh nurseries, are especially vulnerable to these structures. Water control structures incorporating slots (narrow vertical openings spanning most of the water column) are thought to improve nekton passage; however, few studies have directly examined nekton passage through WCS slots. Dual-frequency identification sonar (DIDSON) acoustic imaging was used monthly (April-September 2010) on diurnal flood tides to examine nekton movement through 15-cm-wide slots at two identical WCSs located in Louisiana tidal marsh channels. Nekton behavior was compared between these WCSs and a nearby natural salt-marsh creek. Examination of 12 h of subsampled acoustic data revealed large concentrations of salt-marsh nekton at the WCSs (n = 2,970 individuals total), but passage rates through the slots were low (\u3c= 10% of total observed individuals migrated via the slots). Most migrating fish were observed leaving the managed area and swimming against a flood tide. The mean size of migrating individuals (similar to 25 cm TL) did not differ in relation to swimming direction (going into versus exiting the managed marsh) and was similar to that reported from other studies examining similar slot widths. Nekton formed congregations in the WCS channel, but no congregations were observed in the natural salt-marsh creek, even though nekton species composition and sizes were similar among sites. The WCSs in our study appear to function as ecological hot spots, where large individuals may encounter enhanced foraging opportunities but also fishing mortality and where smaller individuals may experience greater predation rates

Trematodes of the Great Barrier Reef, Australia: emerging patterns of diversity and richness in coral reef fishes

The Great Barrier Reef holds the richest array of marine life found anywhere in Australia, including a diverse and fascinating parasite fauna. Members of one group, the trematodes, occur as sexually mature adult worms in almost all Great Barrier Reef bony fish species. Although the first reports of these parasites were made 100 years ago, the fauna has been studied systematically for only the last 25 years. When the fauna was last reviewed in 1994 there were 94 species known from the Great Barrier Reef and it was predicted that there might be 2,270 in total. There are now 326 species reported for the region, suggesting that we are in a much improved position to make an accurate prediction of true trematode richness. Here we review the current state of knowledge of the fauna and the ways in which our understanding of this fascinating group is changing. Our best estimate of the true richness is now a range, 1,100–1,800 species. However there remains considerable scope for even these figures to be incorrect given that fewer than one-third of the fish species of the region have been examined for trematodes. Our goal is a comprehensive characterisation of this fauna, and we outline what work needs to be done to achieve this and discuss whether this goal is practically achievable or philosophically justifiable