The community structure and vertical distribution patterns of mesozooplankton in the lower York River, Virginia were examined during August, 1978. Samples were collected in the upper and lower water strata before, during and after destratification of the water column due to tidal mixing. In the stratified pre-mixed water column, distinct zooplankton communities were identified above and below the pycnocline. Pronounced diurnal vertical migrations of Acartia tonsa (all stages) and Pseudodiaptomus coronatus were documented. During the well-mixed hydorgraphic regime, the previously identified communities were not as well defined. There was a greater homogeneity of species assemblages and less pronounced differentiation of the vertical distributions for the dominant species during all light conditions. Following restratification, the species assemblages and diurnal vertical distributions closely resembled those identified in the well-mixed sampling period rather than the communities and patterns observed from the initial stratified environment. The homogeneous nature of the zooplankton communities in the well-mixed environment is attributed to the absence of water column stratification. The inability of the zooplankton to reestablish vertically distinct assemblages following restratification of the water column is proposed to be a result of low oxygen concentrations.

No description available.

No description available.

Surrogate contaminant variables (heavy metals, organics, physical oceanograpic data) can be used to predict the incidence of positive cultures of Acanthamoeba sp. in oceanic sediments. Amoebae data are drawn from five years of study involving stations in Narragansett Bay, Rhode Island, the New York Bight, and the Philadelphia-Camden dumpsite, and associated pollution parameters are drawn from literature sources, computerized marine pollution data bases, and other archives. The Statistics Analysis System (SAS) MAXR('2) improvement technique (stepwise regression) and general linear model procedures are used to generate correlations for surrogate variables and produce final predictive models and tables. Model procedures for the three study areas are most valid for Narragansett Bay and the New York Bight but less valid for the Philadelphia-Camden dumpsite due to the small quantity of relevant data. The Durbin-Watson statistic is used to test for autocorrelation of model residuals and, using this test, the Philadelphia-Camden model is again found to be the least valid, although applicable within limits. The division of contaminant variables into "tactical" (short-term, simple analysis) and "strategic" (long-term, more complex analysis) categories enhances the predictive effort through the introduction of a cost-effective procedure evaluation. Generally, the simple variables predict the incidence of positive Acanthamoeba cultures as well as the more complex data sets. There are sufficient data and applicable computer programs to produce useful results for an investigation involving potentially pathogenic protozoans and public health management decisions may be made using the tables and formulae generated using these procedures.

No description available.

No description available.

This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia. Provisional keys to the marine decapod crustacean zoeae of the Chesapeake Bay are presented. These keys provide distinguishing characters for the specific or generic identification of zoeae of 50 decapod species. Also, provisional classification schemes for the different morphological types of antennae and telsons exhibited by Chesapeake Bay brachyuran larvae are given, and the larval stages of each species or genus considered in the keys are briefly described. The larval development of eight Chesapeake Bay decapod species for which the larvae were previously unknown was studied in detail. All larval stages of ~rides limicola and Libinia dubia and the first zoea of Arenaeus cribrarius are described from laboratory-reared specimens, and four larval stages of Callianassa sp. A (=.Q_. major?), two of Callianassa sp. B (=C. atlantica?), one of Callianassa sp. C, four of Upogebia affinis, and three of Lepidopa websteri (?) are described from specimens taken from the plankton. Previous studies concerning the effects of temperature and salinity on larval development of Chesapeake Bay decapods are reviewed, and the results of an experiment to determine the effects of temperature and salinity on larval development of Palaemonetes vulgaris are presented • .!:• vulgaris larvae were reared in the laboratory in a factorial experiment employing three temperatures (20, 25 and 30 C) and six salinities (5, 10, 15, 20, 25 and 30 0/00). Considering survival, rate of development, and number of instars, optimal conditions for larval development were found to occur at a temperature of about 25 C in salinities of 10 to 30 0/00. Surface and bottom plankton samples taken with a Clarke-Bumpus Quantitative Plankton Sampler at monthly intervals over a two-year period were made available to me by Dr. V. G. Burrell, Jr. These samples were collected at 12 stations spread over a distance of about 80 miles from freshwater in the Pamunkey River, through the meso- and polyhaline York River, to euhaline conditions at the mouth of Chesapeake Bay. Some additional samples were collected with paired BCF Bongo samplers. Planktonic stages representing 37 species and genera of decapods were identified in these zooplankton collections. Decapod larvae were numerous throughout the estuary during the summer. However, larvae of Crangon septemspinosa were abundant in the bay from late winter throughout the spring, and peak numbers were generally of the same order of magnitude as total concentrations of larvae of the other species at the bay stations during summer.

Physoclistic fish, such as Pacific rockfishes (genus Sebastes), have closed swim bladders that help them regulate their buoyancy. When anglers catch these fish and reel them to the surface, gases within their swim bladder expand due to the decrease in pressure. This can cause their swim bladder to over inflate––a condition known as barotrauma. Overly buoyant fish experiencing barotrauma often struggle to swim back to dwelling depth if released at the ocean’s surface. These fish may experience high rates of mortality by thermal shock caused by the warmer surface temperatures, starvation, predation, or vision problems caused by barotrauma. Assisted release methods that recompress fish by returning them to depth prior to release may thus greatly improve survival of fish suffering from barotrauma. In this study, I characterized species-specific responses of four species of nearshore Pacific rockfishes (Canary Rockfish, Sebastes pinniger; Gopher Rockfish, S. carnatus; Deacon Rockfish, S. diaconus; and Blue Rockfish, S. mystinus) to rapid ascent by hook-and-line fishing from shallow depths (<40 m). I videotaped their immediate responses upon recompression using a weighted inverted milk crate to transport fish back to their initial capture depth. Fish were videotaped during their descent, as well as their release from the crate. In some individuals, barotrauma symptoms were reversed and did not show behavioral impairment upon release, indicating that even a simple, inexpensive device can be effective in relieving barotrauma symptoms. Species differences were also observed in the severity of barotrauma observed following the collection of fish from depth. Capture depth was positively correlated with the occurrence of barotrauma for Blue Rockfish and Gopher Rockfish, but not for Canary Rockfish or Deacon Rockfishes. I utilized data over an eight-year period from the California Collaborative Fisheries Research Project (CCFRP) to assess survivorship of rockfish experiencing barotrauma. A total of 20 rockfish (1 Black Rockfish, S. melanops; 2 Blue Rockfish; 12 Gopher Rockfish; 3 Copper Rockfish, S. caurinus; and 2 Kelp Rockfish, S. atrovirens) initially displaying barotrauma signs upon capture were tagged using a T-bar tag and released. It is unknown if these fish were recompressed because the CCFRP did not record this information. These 20 rockfish were recaptured days to 3 years later––indicating rockfish can survive long term after experiencing barotrauma. To minimize mortality of discarded fish in the fishery, fish recompression is recommended.

Calanoid copepods were sampled quantitatively at twelve stations in the York River estuary monthly over a two year period. Twenty-two different calanoid species were identified, with five species, Acartia tonsa, A. clausi, Eurytemora affinis, Pseudocalanus minutus and Pseudodiaptomus coronatus making up 95% of the numbers present. Several factors were investigated to determine their biological influence was the ctenophore, Mnemiopsis leidyi, a predator which reduced copepod numbers logarithmically at stations at which it occurred. Increased river flow was followed by large increases in copepod numbers and was the most important physical influence. Distribution of all calanoid species appearing in the estuary was described. Seasonal copepod abundance and the Acartia tonsa - A. clausi distribution in other North American East Coast and Gulf of Mexico estuaries was compared with that of the York River.

No description available.