In lower Chesapeake Bay, the spawning season of the bay anchovy Anchoa mitchilli in 1988 was from early May to mid-September. Spawning was temporally synchronized and lasted for about 1.5 h each night. Spawning frequency per individual was every 4 d in early June and 1.3-1.9 d in other months. Batch fecundity was a linear function of fork length and body weight; regression slopes on 6 July and 4 August were significantly higher than those on 6 June and 31 August. Estimated mean total spawnings per female in 1988 was 54. Total egg production for a fish of average size was 45,110, which is equivalent to 346% of body biomass energy. Age determination based on lagenar otoliths showed that some fish spawned when as young as 2.5-3 months. Transport of the adult bay anchovy in darkness was studied in laboratory and field experiments. In a hydraulic flume, 99% of all fish were transported to the end of the flume in darkness at a current speed of 30 cm s&\sp{lcub}-1{rcub}&. In field experiments, fish marked with neutral red dye and released in a creek at flood tide were recaptured 5.1 km upstream 4 h after release at night, and were recaptured within 200 m of the release site 3 h after release in daylight. This nocturnal transport phenomenon may help in understanding behavior and distribution of pelagic estuarine fishes. The standardized CPUE data show long-term population fluctuations on the order of ten fold. The bay anchovy population also has extensive seasonal variations. A Fourier analysis removed the seasonal (short-term) variation from the long-term data series. An autoregressive analysis of the residual series indicated that it contained a significant first-order autoregressive process component (r&\sp2& = 0.26, P &\le& 0.0066), which was interpreted as a spawner-recruit relationship. Cross-correlation analysis indicated that bay anchovy population abundance was positively correlated with winter water temperature (r = 0.663, P &\le& 0.0001) and river flow (r = 0.376, P &\le& 0.027), but negatively correlated with the abundances of white perch (r = &-&0.437, P &\le& 0.011), and the squared function of residual wind speed (r = &-&0.377, P &\le& 0.026). A multiple regression model indicated that temperature, white perch abundance and wind made significant contributions (accounting for 78% of the variation) to the model.

For many shallow water environments, ecosystem function depends on the cycling and flow of materials and energy between benthic and pelagic subsystems. Benthic suspension feeders often are important links between the water column and sediment in coastal ecosystems. Populations of the suspension feeding polychaete Chaetopterus pergamentaceus (previously reported as Chaetopterus variopedatus) are widely distributed along the United States East Coast, ranging from New England to Florida. This species is a structurally and functionally important member of the lower Chesapeake Bay benthic community, where it has maintained stable populations for at least the last 15 years. Little is known regarding the dynamics of this population and its role in benthic-pelagic coupling. For this study, I elucidated demographics, identified the organic matter sources fueling growth and production, determined the in situ behavior, rates and allometry of filtration, and developed an energy budget for this polychaete within the lower Chesapeake Bay estuary. Chaetopterus pergamentaceus exhibited high seasonal and interannual variability in growth, reproduction, and secondary production. High secondary production was mainly due to the rapid growth and maturation of new recruits during summer. Highly variable interannual production was due to inconsistency in recruitment success. Spatial variations in population processes, concordant with major environmental gradients, may influence the population dynamics. Locally produced organic matter, primarily fresh phytoplankton and secondarily recycled material from microbial sources with minimal to no terrestrial input, was utilized for growth and reproduction. Chaetopterus pergamentaceus has a filtration rate comparable to oysters and has the potential to transfer large quantities of matter from the water column to the benthos. This polychaete may filter a large portion of, or an amount equivalent to, the net water column community production on an annual basis. When considered on a daily basis, the potential carbon flux may be greater than net community production. Thus, this organism plays an important role in benthic-pelagic coupling in the lower Chesapeake Bay.

Numbers of sandbar sharks, Carcharhinus plumbeus, in the Northwest Atlantic have experienced drastic declines since the early 1980's reaching their minima during the early 1990's. Catch rates in the early 1990's were a mere 25% of those during the 1980's. Such drastic reductions in other fish stocks have often caused compensatory responses, most notably the cod stocks in the Northwest Atlantic. Compensatory responses in depressed populations may include decreased natural mortality, increased fecundity, or increased growth rates. Compensation for population fluctuations below carrying capacities have been recognized for many terrestrial and oceanic r-selected organisms, but few instances have been noted for K-selected species. Due to slow-growth and late maturity, compensatory responses in K-selected species such as the sandbar shark probably require generation-scale time periods to become evident. A previous age and growth study discovered slight increases in juvenile sandbar shark growth rates when vertebral centra samples obtained in 1980-81 and 1990-1992 were compared. The Virginia Institute of Marine Science shark long-line survey reported the lowest abundance of sandbar sharks in 1992. Animals pupped during this time may display greater differences in growth rates due to drastically reduced population size. Samples obtained over the 2001-2004 time period were compared to the aforementioned time periods to investigate potential compensatory responses in the sandbar shark population in the Northwest Atlantic. Growth estimates for the sandbar shark, Carcharhinus plumbeus, in the Northwestern Atlantic were estimated using a reparameterized von Bertalanffy growth model. Sharks were tagged in Virginia waters with roto-tags and double return nylon dart tags from 1992 to 2006 by the shark longline survey of the Virginia Institute of Marine Science. Captured sharks were measured, tagged, and released by VIMS scientists. Age and growth estimates were determined for the sandbar shark, Carcharhinus plumbeus, from Oahu, Hawaii in the central Pacific Ocean. Age estimates were obtained through vertebral centra analysis of 187 sharks. We verified our age estimates through marginal increment analysis of centra and oxytetracycline marking methods of at-liberty sandbar sharks. Sizes of sampled sharks ranged from 46 cm to 147 cm pre-caudal length. Four growth models were fitted to length-at-age data; two forms of the von Bertalanffy growth model, the Gompertz growth model, and a logistic growth model. Males and females exhibited statistically significant differences in growth, indicating that females grow slower and attain larger sizes than males. Growth parameter estimates revealed slower growth rates than previously estimated (based on captive specimens) for Hawaiian sandbar sharks. The von Bertalanffy growth model using empirical length-at-birth provided the best biological and statistical fit to the data. This model gave parameter estimates of L infinity .=138.5 cm PCL and k=0.12 year-1 for males and Linfinity=152.8 cm PCL, k=0.10 year-1 for females. Male and female sandbar sharks mature at approximately 8 and 10 years of age respectively. The population of sandbar sharks in the Hawaiian Islands is an unfished population. The presents a unique opportunity to conduct demographic analyses on a virgin population of sandbar sharks. Most populations of sandbar sharks have been heavily exploited due to near coastal and estuarine habitat preferences and high demand for fins. Conversely the population of sandbar sharks in the Northwest Atlantic (NWA) has suffered severe declines since the early 1980's. Previous studies have suggested compensatory growth is occurring within this population, but the true effect at the population level has not been estimated. Life history parameters estimated for the Hawaii population, the NWA population in 1980-1981 and 2000-2004 time periods were used in stochastic age-based life tables and Leslie matrices to estimate demographic parameters. Yield recruit-1 relationships were estimated for the Hawaii population to determine optimal harvest strategies that would maintain a population at equilibrium. Population growth for the Hawaii population was estimated to be 1.014 year-1. Yield recruit-1 analyses suggested harvest of sharks 15 years of age and older would provide the greatest yield while not causing population decline. Population growth for sandbar sharks in the NWA was 1.009-1 year for the 1980-1981 time period and 1.030-1 year for the 2000-2004 time period. (Abstract shortened by UMI.).

Coastal seagrass ecosystems are complex habitats that are increasingly influenced by human perturbations. Disturbances that affect the strength of bottom-up (i.e. resource availability) and top-down (i.e. consumer) controls may also influence biomass distribution between trophic levels, sediment biogeochemistry, and seagrass ecosystem metabolism. Here, I experimentally tested how top-down and bottom-up perturbations interact with community structure (diversity, food chain length of epibenthic consumers) to alter sediment biogeochemistry and ecosystem metabolism in an experimental eelgrass (Zostera marina ) system. My data indicated that resource availability influenced SOM composition and ecosystem metabolism. Light availability tended to be a stronger determinant of SOM composition while nutrient enrichment affected secondary production of invertebrate grazers more strongly than primary producers or SOM. Top-down predator effects on SOM composition and ecosystem flux rates tended to be weak. However, the strength of the trophic cascade may partly be a function of grazer community composition and grazer susceptibility to predation. Finally, my results indicated that grazer species identity and community composition strongly influenced SOM composition. In addition to the main effects of light, nutrients, predators, and grazers there were a variety of interactive effects between resources and food web composition. Consequently, the effects of resource availability and food web composition on seagrass ecosystem functioning should not be considered in isolation.

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