Trends in Shark Abundance from 1974 to 1991 for the Chesapeake Bight Region of the U.S. Mid-Atlantic Coast
John A. Musick, Steven Branstetter, and James A. Colvocoresses
Recent stock assessments indicate that the shark stock of the western North Atlantic is exploited at a rate twice the maximum sustainable yield. This finding is supported by data generated by the Virginia Institute of Marine Science longline program for sharks of the. Chesapeake Bay and adjacent coastal waters. Trends in catch per unit of effort since 1974 indicate 60-80% reductions in population size for the common species - sandbar (Carcharhinus plumbeus) , dusky (C. obscurus) , sand tiger (Odontaspis taurus), and tiger (Galeocerdo cuvier) sharks. Declines include numbers of individuals for all species, size classes within species, and in one case a strong decline in relative abundance. Given the limited ability of sharks to increase their population size, these results suggest that stock recovery will probably require decades.
Central Atlantic Coastal Plain - A Summary of the Geological Evolution of Chesapeake Bay, Eastern United States
Steven M. Colman, Jeffrey P. Halka, and C. Hobbs
The seaward margin of the U.S. Atlantic Coastal Plain has fluctuated through time, from near the Fall Line to near the edge of the present Outer Continental Shelf, owing to changes in relative sea level. The strata that underlie the Coastal Plain were deposited in environments that ranged from fully terrestrial to fully marine. Estuarine environments are critical components of the Coastal Plain; they represent the interface, otherwise known as the shoreline, between the marine and terrestrial depositional systems. The Quaternary evolution of estuaries has important implications for both documenting the history of sea-level changes and interpreting ancient coastal-plain strata. In this paper, we briefly summarize the Quaternary history of the Chesapeake Bay, the largest of the many Coastal Plain estuaries on the Atlantic coast. This summary is based on recent syntheses of a wide variety of data (Colman and others, 1988, 1990; Colman and Mixon, 1988) on the history and evolution of the bay.
Ecological functions and values of nontidal wetlands
Carl H. Hershner
Reviews the current understanding of the functions of nontidal wetlands, assesses the· problems of assigning values to wetland functions, and surveys the use of these functions and values in management programs of the mid-Atlantic states.
Fisheries Assessment and Management Synthesis: Lessons for Chesapeake Bay
William A. Richkus, Steven J. Nelson, and Herbert M. Austin
Describes the basic approaches that are used for stock assessment of the fish and shellfish stocks of the Chesapeake Bay system. The authors summarize the principal methods of stock assessment and fisheries management that have been and are being-applied to Bay fisheries, with particular emphasis on data collection and the use of models. Three case studies of critical species are presented - the striped bass, the blue crab and the Eastern oyster.
Transport of Hypoxic Waters: An Estuary-Subestuary Exchange
A. Y. Kuo and K. Park
Hypoxic or anoxic conditions in the subpycnocline water of Chesapeake Bay persist throughout the summer. The effect on the dissolved oxygen concentration in the deep basin of the lower Rappahannock River, a subestuary on the western side of the bay, was studied with an observational program. The data indicate that in the lower portion of the water column the subtidal (or residual) current was directed into the subestuary most of the time. The mass fluxes of salt and dissolved oxygen into the subestuary through a point near the estuarine bottom at the river mouth were calculated for tidal and subtidal components respectively. From the analyses, we conclude that the mass exchange owing to the tidal component is at least an order of magnitude smaller than that resulting from the subtidal component. Characteristic differences in the properties of water transported into the subestuary were observed. On five occasions, each lasting about two days, during the one month period of field measurements, the imported water was characterized by low dissolved oxygen and high salinity, typically 3 to 4 mg 1−1 lower dissolved oxygen and 2 to 3 psu higher salinity than at other times. The low dissolved oxygen, high salinity water masses were all accompanied by strong subtidal current and southwest wind. During periods of strong wind from the southwest quadrant, the density-driven current near the bottom was enhanced by the wind-driven circulation. Furthermore, the surface set-up favors the transport of the water from the deep portion of the bay resulting from (1) tilting of the pycnocline in the bay and (2) shoreline and bathymétrie configurations around the estuary-subestuary junction.
Ecological Risk Assessment for Highways in the Chesapeake Bay Watershed
Robert B. Atkinson, J. Cairns Jr., Bruce Wallace, and James E. Perry
The population of coastal counties in the United States is over six-fold higher than non-coastal counties and population density along the Atlantic coast is much greater than all other coasts in the nation. Many areas around the Chesapeake Bay watershed are participating in this growth and extensive interstate construction is planned for this region. A wide array of primary ecological risks to the Chesapeake Bay exists, and may be classified as biological, physical, or chemical. Biological risks range from physical threats to motorists and animals to genetic risks to local flora and fauna populations. Island biogeography theory can be used to predict species losses associated with highway construction and resultant limits to migration. Introduction of exotic species and loss of ecologically significant areas (e.g. wetlands) are included as biological risks. Physical risks are primarily associated with hydrology, erosion, and related water quality considerations. Chemical concerns can be described as either chronic, such as certain airborne pollutants, or acute, such as accidental or illegal discharges. Secondary risks associated with highway construction result from facilitated traffic flow. Included are a variety of effects resulting from urban sprawl, strip development, and economic development of adjacent areas. Some ecological risks have received legislative, and subsequently transportation department attention. However, most ecological risks do not affect the decision-making process.
Groundwater Nutrient Discharge to the Chesapeake Bay: Effects of Near-Shore Land Use Practices
E. Laurence Libelo, William G. MacIntyre, and Gerald H. Johnson
Groundwater discharge supplies a significant portion of the inorganic nutrients entering the Chesapeake Bay. This discharge increases nutrient concentration in surface waters, which may result in increased macrophyte growth, reductions in· submerged aquatic vegetation and alteration of habitat. Human activities adjacent to the shoreline greatly increase nutrient concentration in the underlying groundwater, and so affect the overall nutrient input by groundwater seepage. In order to quantify the effect of land use on groundwater nutrient loading in the Virginia coastal plain we have installed monitoring wells in a variety of near shore environments adjacent to the James and York Rivers. Since the Spring of 1988, groundwater nitrogen species concentrations have been monitored beneath agricultural fields planted with corn and soy beans, woodlands, vineyards, and suburban development with septic drain fields. (...)
Hard Clam Mercenaria mercenaria
G. Curtis Roegner and Roger L. Mann
The hard clam is found along the eastern coast of North America from the Gulf of St. Lawrence to Texas. In Chesapeake Bay, the hard clam is restricted to salinities above approximately 12 ppt. An extensive survey of hard clam resources is overdue.
Statements concerning long term trends in populations are not feasible. Hard clams ·grow to a maximum shell length of about 120 mm. There are few documented cases of diseases in wild hard clam populations. Parasitic infestations are also slight. The life cycle of the hard clam includes a pelagic larval phase and a relatively sedentary benthic juvenile and adult phase. In Chesapeake Bay, ripe gametes can be found between May and October, and spawning commences when temperatures rise above 20-23 ·c. The larvae are planktotrophic (feeding). Metamorphosis usually commences at a shell length of 200-210 mm. Predation on new recruits is very high; dense aggregations of hard clams have been found in the absence of predators. Aside from predation and fishing pressure, the natural mortality of larger clams appears very low.
Hard clams are important suspension-feeding infauna, thus they are important in grazing of primary production, transfer of carbon and nitrogen to benthic food chains, and, through excretion, rapid recycling of particulate nitrogen as ammonia. The major food source for hard clams is planktonic microalgae. In Chesapeake Bay, growth occurs in spring and fall, when optimum water temperatures coincide with abundant food.
Clams are capable of living in a variety of sediment types, but higher abundances are found in coarse-grained sediments. Hard clam stocks are susceptible to overfishing. Recruitment rates are poorly understood, as are possible reestablishment periods if areas are depleted through commercial harvesting, and factors influencing larval settlement rates. Hard clam mariculture is well established and could easily be expanded into sites within the Bay. Given the ability of clams to bioaccumulate toxic substances, adequate monitoring should be maintained. The sub lethal effects of toxic material readily found in the lower James River should be examined
Hypothetical Northern Spawning Limit and Larval Transport of Spot
Brenda L. Norcross and Deborah A. Bodolus
The exact northern limit of the spawning grounds of spot (Leiostomus xanthurus) has not been determined. Previous reports of spot spawning during the winter/spring in the Middle Atlantic Bight (MAB) are refuted based on the presence of low bottom-water temperatures at that time. Analyses of historic bottom isotherms in the MAB during winter/spring show that the most northerly occurrence of required 17° C bottom temperatures from December to May is on the outer continental shelf off North Carolina near the Gulf Stream. It is therefore suggested that spot recruiting to Chesapeake Bay are spawned near Cape Hatteras at the shelf break in winter. (more ...)
Long Term Culture of Hepatocytes of Some Fish Species of the Chesapeake Bay
M. Faisal, N. Youssef, and R. Huggett
The liver is an important site of metabolism and effects of toxic chemicals. This makes it an important organ for tumorigenesis studies. This study was aimed at investigating the optimal culture characteristics of liver cells derived from some indigenous Chesapeake Bay fish species. Hepatocytes from Atlantic -menhaden (Brevootia tyraMus), toadfish (Opsanus tau), croaker (Micropogonius undulatus), and hogchocker (Trinectes maculatus) were isolated using an enzymatic dispersion technique. The highest yield was obtained from toadfish livers (14.9±5. lx 1 o5 cells/g oflive weight) and the lowest was from the croaker (5.9±3. lx 1 o5 cells/g of live body weight). The percentage of hepatocytes in cell preparations exceeded 90% except for the toadfish liver cells preparation (82.3%). Freshly isolated hepatocytes were globular with irregular contour and occurred as individual cells or small clusters of 2-30 cells. A confluent monolayer of attached cells was obtained after two weeks of incubation. An osmolality of 325 m Osm/kg best supported the multiplication of hepatocytes of the four fish species. While the optimum temperature for hogchocker and toadfish hepatocytes appeared to be 33oC; it ranged from 21-27oC for menhaden and croaker. The medium that best supported the growth of culture
The potential of long term hepatocyte culture using fish of Chesapeake Bay will enable further studies on the activation and detoxification processes of xenobiotics and, therefore, help in understanding pollution related neoplasia and diseases
Prototype for a Regional Online Toxics Database
Charles A. Lunsford and Craig L. Smith
An interactive online computerized database for retrieval of chemical analytical information on volatile and extractable organic compounds, and the priority pollutant metals has been developed. Current information about samples from the Chesapeake Bay region in Virginia and Maryland are available. This database stores information on organic compounds in effluent, water, tissue, and sediment in a format which does place restrictions on the number of compounds per sample. It includes various QA/QC items as well as the analyst's assessment of the validity of the data. A variety of keyed retrieval options permits selection of reporting format, and flagging of items exceeding selected limits of concentration. Application includes retrievals for use by managers, and by researchers in planning and interpreting environmental studies related to toxic chemicals.
Soft Shell Clam Mya arenaria
Patrick K. Baker and Roger L. Mann
Large populations of soft shell clams persist only in relatively shallow, sandy, mesohaline portions of the Chesapeake Bay. These areas are mostly in Maryland, but also occur in the Rappahannock River, Virginia. In some other portions of the Bay, especially polyhaline portions, low populations of soft shell clams persist subtidally. Restricted populations persist intertidally.
Soft shell clams grow rapidly in the Chesapeake Bay, reaching commercial size in two years or less. They reproduce twice per year, in spring and fall, but probably only fall spawnings are important in maintaining population levels. Major recruitment events do not occur in most years, despite heavy annual sets. Soft shell clams are important food for many predators. Major predators on juveniles include blue crabs, mud crabs, flatworms, mummichogs, and spot. Major predators on adults include blue crabs, eels, and cownose rays. Some other species that may depend heavily on soft shell clams include ducks, geese, swans, muskrats, and raccoons.
Diseases may play an important role in regulating adult populations of soft shell clams; hydrocarbon pollution is linked to increased frequency of disease. Oil pollution does the most widespread and persistent damage to soft shell clams through toxicity, aside from its role in inducing disease. Heavy metals, pesticides, and similar pollutants can be extremely toxic, but the harmful effects to clams do not last if the pollution abates. The main concern with the latter toxicants is bioaccumulation by soft shell clams, with the potential for passing toxic contaminants on to predators or to humans.
Siltation caused by storm events, dredging operations, or erosion, can smother clam populations. Eutrophication, enhanced by nutrient inputs from sewage or agriculture, is not known to have affected soft shell clam populations.
Acoustic Geology of a Portion of Virginia's Innermost Continental Shelf
Carl H. Hobbs III
Side-scan sonography of the innermost continental shelf between Cape Henry and the Virginia-North Carolina border depicts a relatively typical inner shelf bottom generally characterized by medium density, meso-scale roughness. Subbottom acoustic protiles depict the stratigraphy as a Tertiary age basement separated from Quatenary-age deposits by a regional, angular(?) unconformity. Holocene-age sediments form a discontinuous layer above another unconformity. The area's topography appears to be a function of the presence of the modern sediments.
A Procedure for Assessing Heavy Mineral Resources Potential
Andrew E. Grosz, C. R. Berquist Jr., and C. T. Fischler
Supplies of placer heavy minerals, such as ilmenite, rutile, zircon, and monazite, are anticipated to be in short supply by early in the next century. The depletion of conventional onshore deposits coupled with the declaration of the Exclusive Economic Zone in 1983 have provided the impetus to assess the resource potential of heavy-mineral concentrations in U.S. Continental Shelf sediments as future sources for these mineral commodities.
Mineralogically imprecise assessments of placer resources result from analyses of concentrates derived from small volume samples because of the particle-sparsity effect. The overall low grade of heavy minerals in Atlantic Continental Shelf sediments require the analysis of mineral concentrates from large volumes of bulk sample. A set of procedures to extract and analyze heavy minerals from large-volume samples is presented.
Early Life-History Implications of Selected Carcharhinoid and Lamnoid Sharks of the Northwest Atlantic
The size of most newborn sharks makes them susceptible to predation from their own kind and other large fishes. In the northwestern Atlantic, juvenile nursery grounds can be generally classified according to whether or not the young are exposed to such predatory risk. Several related factors-breeding frequency, litter size, size at birth, early growth rate-may help offset early natural mortality. These factors are counterbalanced by the different species in several different ways, producing numerous early life history strategies. In general, slow growing species are either born at relatively large sizes or use protected nursery grounds, whereas faster growing species tend to rely more on growth rates than the other factors.
Heavy Mineral Concentrations In Sediments Of The Virginia Inner Continental Shelf
C. R. Berquist Jr., C. T. Fischler, L. J. Calliari, and et al
The Virginia Division of Mineral Resources and the Virginia Institute of Marine Science investigated the occurrence of heavy minerals in the offshore sediments of Virginia. We began the project because earlier reconnaissance studies reported high heavy-mineral concentrations from several samples collected off the Eastern Shore of Virginia. Our work confirms the previously reported mineral values and locates additional high concentrations up to 20 nautical miles offshore. Furthermore, we show that potentially economic mineral values are not restricted no surficial sediments, but also are found in the upper 15 to 20 feet of inner continental shelf sediments. Several core samples indicate that potential economic values of heavy minerals are clustered offshore of Hog Island, Smith Island, Virginia Beach, and False Cape. These areas are likely targets for resource assessment studies of heavy minerals and construction or beach nourishment sand. The high heavy-mineral concentrations suggest that further investigations are warranted.
Heavy Mineral Variability And Provenance Of The Virginia Inner Shelf And Lower Chesapeake Bay
L. J. Calliari, C. T. Fischler, and C. R. Berquist Jr.
The mineral composition of the 3- to 4-phi (0.125 to 0.063 mm) size fraction of 49 surficial grab samples,located north and south of the entrance to Chesapeake Bay and of 38 surficial samples, located in the bay mouth, was determined during this study. Although up to 17 minerals were identified, principal components analysis indicated that seven minerals accounted for 96 percent of the composition variance in the bay samples. By using Q-mode factor analysis, three mineral composition end-members (factors) were selected from the sample data and provided an adequate description of the spatial variation in heavy-mineral composition. The end members suggest possible mineral sources.
Monitoring Seagrass Distribution and Abundance Patterns: A Case Study from the Chesapeake Bay
Robert J. Orth, Kenneth A. Moore, and Judith F. Nowak
Seagrasses, or submerged aquatic vegetation (SA V), have been mapped in the Chesapeake Bay five times between 1978 and 1987 with standard aerial photographic techniques, resulting in annual reports on SAV distribution. Acquisition of the vertical photography at a scale of 1:24,000, adhering to strict quality-assurance guidelines based on sun angle, tidal stage, cloud cover, wind speed, and season, has produced excellent, high-contrast imagery delineating beds of SAV from adjacent, unvegetated areas. Ground-truthing data from various State, Federal, and public organizations have corroborated the photographic data base. (more ...)
Persistence of Residual Currents in the James River Estuary and its Implication to Mass Transport
Albert Y. Kuo, John M. Hamrick, and Gamble M. Sisson
The distribution and persistence of Eulerian and Lagrangian residual velocity in a cross sectional transect of the James River estuary, Virginia are analyzed. The Eulerian residual velocity has the characteristic two-layered estuarine circulation in the northern half of the transect, however, the net flow is directed downriver at all depths in the shallower southern half of the transect. In the deep channel, the two-layered Eulerian residual circulation is highly persistent over the six month study duration, with disruptions occurring less than 10% of the time when meteorological forcings are intense. No spring-neap tidal cycle variation is apparent. The magnitude of the long-term advective mass transport (calculated as the lowest order approximation to the Lagrangian residual velocity) is approximately twice that of the Eulerian residual velocity and in the same direction in the deep channel. The Stokes drift velocity contribution to the Lagrangian residual velocity enhances the upriver Eulerian residual velocity transport on the north side of the transect and only slightly increases the downriver transport on the south side.
Quaternary Geology of the Chesapeake Bay
Jeffrey P. Halka, Steven M. Colman, and Carl H. Hobbs III
The Chesapeake Bay, which is a classic coastal plain estuary, is located on a trailing edge continental margin. It has a surface area of nearly 6,000 km2 and ranges in width from 8 to 48 km. The morphology of the bay clearly reflects its formation as a response to fluctuating sea level during and following the last major continental glaciation. The shoreline is highly irregular, the tributaries form an intricate dendritic drainage pattern, and a deep axial channel occurs along much of its length (fig. 1). Water depths commonly exceed 30m in this deep channel, which is flanked by broad shallow benches. Overall, the bay is quite shallow and has an average depth _of only 8 m. more....
The Dynamics of Long-Term Mass Transport in Estuaries
John M. Hamrick
The dynamics of long-term mass transport in estuaries having weakly nonlinear long wave dynamics are investigated. Low pass filtered long-term mass transport equations are derived for conditions of weak and strong vertical stratification. The dynamics of the residual mass transport velocity, or lowest order approximation to the Lagrangian residual velocity, are investigated by perturbation analyses of the hydrodynamics equations. For weak vertical stratification conditions, analytical results showing the influence of topography, the earth's rotation, and channel curvature on the distribution of the residual mass transport velocity field are presented. The calculation of the residual mass transport velocity field from field current meter measurements and numerical hydrodynamic model output is also discussed.
Western North Atlantic Shark-Fishery Management Problems and Informational Requirements
Thomas B. Hoff and John A. Musick
The Mid-Atlantic Fishery Management Council (Council) has primary responsibility for the development ofihe Western North Atlantic Shark Fishery Management Plan (FMP). Currently, there is a consensus among the five East Coast Councils that an FMP for sharks should be prepared. The current concerns focus on many of the same issues that were germane a decade ago when a shark FMP was initiated and then halted mainly because of inadequate information. These issues include 1) an expanded, nondiscriminant, commercial longline fishery ; (2) an existing and rapidly expanding recreational fishery; (3) concern for the extensive waste which occurs from both recreational and commercial activities (especially the rapidly increasing issue of harvesting sharks for the use ofonly fins); (4) the reproductive strategy (few offspring, late maturation , and slow growth rates) of many species; and (5) realization that increased fishing pressure on specific shark species generally results in overfishing. Essential information for stock assessment is lacking for sharks and thus management is severely handicapped. Critical data needs include: valid growth information, stock delineation, documentation of the catch by species, samples of the population size structure, mortality estimates, independent indices of population abundance through time, and documentation of all (U.S. and other nationals) user groups both recreational and commercial . Data are particularly sparse for foreign fisheries which have expanded outside U .S. controlled waters, and which could be harvesting the same stocks of sharks.
Habitat use and population biology of Bahamian spiny lobster
William F. Herrnkind and Romauld N. Lipcius
The spiny lobster Panulirus argus is extremely important both for basic scientific research (Davis, 1980) and the seafood industry. Despite the economic significance of Bahamian lobsters, their ecology has been the subject of limited study. Investigators have recorded fishery information (Smith, 1948, 1951), mass migration (Herrnkind and Kanciruk, 1978; Kanciruk and Hermkind, 1978; Hcrmkind, 1980), autumnal reproduction (Kanciruk and Herrnkind, 1976), commercial size composition (Simpson, 1976), life history and ecology of juveniles, and experimental fishing techniques (Waugh and Waugh, 1977; Waugh, 1980). (...) We report here on a 10-month (Sept, 1979-June, 1980) study of Panulirus argus in the region of Lee Stocking Island, north of Great Exuma Island. Size distribution, habitat, reproduction, and molting cycles are emphasized.
Interaction Between Circulation of the Estuary of the James River and Transport of Oyster Larvae
Evon P. Ruzecki and William J. Hargis Jr.
Hydraulic model dye test results are examined to provide estimates of nontidal horizontal circulation and movement/retention of oyster larvae in the James River Estuary. Test conditions maintained a constant mean tide and average summer low freshwater discharge. It was assumed that movement of dye in the model would approximate movement of the planktonic (larval) stages of oysters (Crassostroa virginica) in the prototype. Test results were used to rank six dye release points (candidate brood stock locations) with respect to relative quantities of dye retained in areas of the model representing commercially important seed oyster beds during the period 20-40 tidal cycles after release (the time, after spawning, when oyster larvae will permanently attach to a suitable substrate). Under the test conditions, nontidal circulation in the model was similar to that found in a weak partially mixed estuary: upstream motion along the bottom and over the right hand shoals (looking upstream) and downstream motion elsewhere. The pattern was modified by cyclonic motion of surface waters in the upstream and downstream reaches which increased residence time of material in the seed oyster bed region. Greatest retention during the 20-40 tidal cycle period was from releases over upstream and right hand side shoals and is reflected in release point ranking.
Kepone and the James River
Robert J. Huggett
The James River in Virginia was contaminated by the pesticide kepone when the material entered the river as early as 1968 and continued until its discovery in 1975. The river became so contaminated that commercial fisheries were closed. In 1988, 13 years after closure, all fishing restrictions were lifted. The contaminated sediments have been diluted and covered enough by uncontaminated material that the kepone flux back into the water column has diminished. Kepone concentrations in organisms inhabitating the river are finally below the U.S. Environmental Protection Agency and Food and Drug Administration action levels. Biological, chemical, physical and geological aspects of the contamination indicate that remedial actions to remove kepone would be expensive and environmentally unwise.
The Response of Estuarine Circulation to Local Wind Events
K. P. Kiley and C. S. Welch
An analysis of non-tidal estuarine circulation and local wind events was conducted employing wind and current records taken along the York River. Three distinct response conditions of non-tidal circulation to wind were observed. These conditions exhibited significant temporal and spatial variability. The first was typified by a positive two layer flow response to wind that was significant in the middle section of the York during the first six days of the study. The second exhibited a positive one layer flow response to wind that was significant in the upper section of the York during the last three days of the study, The third exhibited no statistically significant relation between current patterns and wind. This condition occurred near the mouth of the estuary, and it may indicate that the currents near the mouth respond more substantially to conditions in the adjacent· Chesapeake Bay than to those caused by local winds.
Bioavailability of Organic Pollutants to Aquatic Organisms
Robert C. Hale and Robert J. Huggett
Settlement of the Chesapeake Bay region began in earnest in the early 17th century. The native American population and early colonists were impressed by the abundance of fish and shellfish and located their population centers to take advantage of these and other natu!al resources. Introduction of wastes into the bay was coincident with this settlement. As the human population increased, so did the pressure on the ecological system. In the 20th century significant quantities of synthetic chemicals began to be introduced, many of which were toxic and nonbiodegradable [Faust and Hunter 1971]. Today the areas surrounding the bay are experiencing unprecedented development; introduction of toxic organic pollutants has correspondingly increased. Water quality and the abundance of many aquatic organisms have suffered accordingly [O'Connor and Huggett 1988].
Comparison of Sediment Landscapes in Chesapeake Bay as Seen by Surface and Profile Imaging
Robert J. Diaz and Linda C. Schaffner
The sediment-water interface is the boundary layer between the water column and sediments. It is involved in virtually all processes and cycles within aquatic and estuarine ecosystems. Interactions and reactions at the sediment-water interface are of particular importance in regulating processes involving nutrient regeneration-remineralization (Boynton and Kemp 1985), fate of toxicants (Olsen, Cutshall and Larsen 1982), development of hypoxia-anoxia (Garber 1987), sediment mixing (Schaffner et al. 1987a, b), and sediment transport (Wright et al. 1987). Much effort has and is being expended to provide details of these processes which will eventually be used in management plans for water quality, sediment quality, and fisheries resources.
Epizootiology of the disease caused by the oyster pathogen Perkinsus marinus and its effects on the oyster industry
Jay D. Andrews
Perkinsus marinus is a protozoan parasite that causes a major disease of eastern oysters Crassostrea virginica from Chesapeake Bay south along the Atlantic coast of the USA and throughout the Gulf of Mexico. It is a warm-season disease that kills eastern oysters at temperatures above 20°C. The pathogen requires salinities of at least 12-15%0 to be active, but it persists tenaciously when low temperatures and salinities occur during winter and spring. Prolonged droughts that increase salinities cause extensions of the range of disease. In the Chesapeake Bay, mortalities begin in June and end in October, and up to 50% of native susceptible eastern oysters are killed each year. Most infections are acquired by eastern oysters in proximity to disintegrating dead eastern oysters. Massive populations of prezoosporangia are released into marine waters and eventually produce thousands of zoospores, which are infective when ingested by eastern oysters. The disease is controlled by isolating new beds from infected eastern oysters and by early harvest before the pathogen becomes established. Seed areas in low-salinity waters usually provide disease-free eastern oysters, but beds must be monitored regularly to avoid transplanting infected eastern oysters. In the Gulf of Mexico where warm temperatures persist through much of the year, control is much more difficult. Eradication is difficult unless introductions of infected eastern oysters are avoided and summer warm seasons are short and relatively cool to prevent the pathogen from multiplying in eastern oysters. The presence of P. marinus in Chesapeake Bay has been monitored for 37 years; the disease is established in most eastern oyster-growing areas of Virginia and in many tributaries of Maryland. The disease thrives on densely planted private beds of eastern oysters but persists through wet periods of weather on sparsely populated public beds and artificial structures along shores where there is recruitment of eastern oysters. Unfavorable temperatures essentially eradicated it in Delaware Bay after importations of infected seed eastern oysters from Virginia were discontinued
Humoral Defense Factors in Marine Bivalves
Fu-Lin E. Chu
Natural humoral components have been discovered and described in hemolymph from several marine bivalve species including eastern oyster Crassostrea virginica, blue mussel Mitilus edulis, northern quahog Mercenaria mercenaria, softshell Mya arenaria, and Pacific oyster Crassostrea gigas, These hemolymph components are enzymes of lysosomal origin, agglutinins, lectins, hemolysin, and antimicrobial substances, These components are proteins or glycoproteins found in the serum, hemocytes, or both, The exact relationship of these substances to the internal defense of marine bivalves against parasites and pathogenic microorganisms is not known. Lysosomal enzymes seem to have a double role, defense and nutrition. The free- and cell-bound lectins and agglutinins are believed to serve as recognition factors for the attachment of nonself particles to the phagocytes. The nature of bivalve hemolymph components appears to be innate and nonspecific. It has been suggested that the elevation in titer of enzymes of lysosomal origin in bivalve hemocytes and hemolymph after antigenic challenge is the acquired "humoral" protection produced by the animal. As yet, no experimental evidence has been obtained to support this idea. Whether humoral factors can be acquired in oysters and other marine bivalves needs further investigation. The specificity and the function of humoral factors relating to internal defense remain to be determined. Several mechanisms have been hypothesized for humoral defense in invertebrates. In these hypothesized mechanisms, recognition sites presented on the hemocytes are proposed for the events of phagocytosis, encapsulation, hypersynthesis and release of lysosomal enzymes.
Some Histologic Gill Lesions of Several Estuarine Finfishes Related to Exposure to Contaminated Sediments: A Preliminary Report
W. J. Hargis Jr. and D. E. Zwerner
Collections were made during 1983, '84 and '85 in the Elizabeth River, whose sediments are heavily contaminated with PAHs, heavy metals and other anthropogenic materials. Comparison samples were from the "cleaner" Nansemond River, another subestuary feeding into Hampton Roads (the lower James River) nearby. Most samples from all stations included three transient quasi-catadromous nektonic sciaenids, Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus) and weakfish (Cynoscion regalis), and two endemic estuarine benthic fishes, hogchoker (Trinectes maculatus) and oyster toadfish (Opsanus tau).
Structure of Protistan Parasites Found in Bivalve Molluscs
Frank O. Perkins
The literature on the structure of protists parasitizing bivalve molluscs is reviewed, and previously unpublished observations of species of class Perkinsea , phylum Haplosporidia, and class Paramyxea are presented. Descriptions are given of the flagellar apparatus of Perkinsus marinus zoospores, the ultrastructure of Perkinsus sp. from the Baltic macoma Macoma balthica, and the development of haplosporosome-like bodies in Haplosporidium nelsoni. The possible origin of stem cells of Marrteilia sydneyi from the inner two sporoplasms is discussed. New research efforts are suggested which could help elucidate the phylogenetic interrelationships and taxonomic positions of the various taxa and help in efforts to better understand life cycles of selected species.
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