The objectives of my research were to test the hypothesis that compensatory (density-dependent) growth of sandbar shark (Carcharhinus plumbeus) occurred after severe population reduction, to describe the juvenile sandbar shark fauna present in the Chesapeake Bay during 1980-81 and 1990-93, and to perform demographic analyses to examine potential population growth. Age and growth of sandbar sharks were investigated by counting rings in vertebral samples collected in 1980-81 and 1991-92. Age at maturity was 15-16 years for both sample periods and both sexes. For sexes combined, the von Bertalanffy growth parameters were L&\sb{lcub}\infty{rcub}& = 199 cm precaudal length (PCL), K = 0.057, t&\sb{lcub}\rm o{rcub}& = &-&4.9 years for the 1980-81 sample and L&\sb{lcub}\infty{rcub}& = 164 cm PCL, K = 0.089, t&\sb{lcub}\rm o{rcub}& = &-&3.8 years for the 1991-92 sample. Significant differences in size at age and annual incremental growth of juveniles suggest a small increase in juvenile sandbar shark growth rate between the two sampling periods. Annual catches of sharks &>&105 cm PCL declined substantially between survey periods. Males and females were present in a 1:1 ratio. During 1980-81 juveniles ranged in age from 0-7 yr, but in 1990-93 few sandbar sharks over age 4 were taken. Based on the best estimate of fishing mortality the population ranged from 10,087 to 8509 sharks from 1989-1993. Annual year-class size was variable but all estimates were within one order of magnitude. Juvenile sandbar sharks declined in abundance by approximately 15% between 1989 and 1993. The annual population growth rate was highest under a scenario of natural mortality (M) = 0.05 and maximum age of 30 yr, but was only 11.9%/yr. at higher juvenile mortality rates and adult M fixed at 0.10, the best estimate of M for sandbar sharks, population growth rate was only 2.6%/yr. Adding fishing mortality (F) at immature ages caused the population to decline unless F levels were &<&0.10 and 0.05 at maximum age = 30 and 60 yr, respectively. It is apparent that sandbar shark populations will decline under any substantial fishing mortality on immature ages, and mature fish can only be exploited at very low levels of fishing mortality.

Recent studies have demonstrated that the morphologically similar white marlin (Kajikia albida) and roundscale spearfish (Tetrapturus georgii) co-occur in the western North Atlantic, including the U.S. Mid‐Atlantic Bight. Differences in scale morphology have been proposed as one morphological character to discriminate these species, but a thorough analysis of scale morphology is lacking. Because the validity of the roundscale spearfish was not established until 2006, much of the biological information previously collected for “white marlin” may include data for both white marlin and roundscale spearfish. The objectives of this study were to obtain a better understanding of the movements and habitat utilization of positively identified white marlin that inhabit the U.S. Mid-­‐Atlantic Bight during summer months, and to describe the morphological variation of white marlin and roundscale spearfish scales. Eleven long‐term (6 or 12 month) pop-up satellite archival tags were placed on white marlin that were caught and released in the U.S. recreational fishery. Nine tags reported information on temperature, pressure (depth), and light levels for light‐based geolocation for periods of 8 days to 12 months. Most fish moved out of the Mid-Atlantic Bight in September, and overwintered in areas ranging from east of the Gulf Stream off the Carolinas to the Caribbean, and as far south as northern Brazil. of the seven fish that retained tags for more than 40 days, five spent time in known spawning grounds in waters of the Dominican Republic leading up to the spring spawning season. These data demonstrate a large degree of connectivity among white marlin in the western North Atlantic. as noted in previous studies, individuals spent a large proportion of their time in the surface waters (0-10m; 75% across all white marlin pooled), the vast majority of their time in the top 100 m of the water column (97%), and within eight degrees of sea surface temperature (98%), although definite shifts in habitat utilization were evident as fish departed coastal offshore waters of the Mid‐Atlantic Bight. Diel habitat utilization varied greatly, with white marlin spending 81% of total nighttime in the surface waters (0‐10m), and only 26% of total daytime in surface waters. Past studies have characterized the scales of white marlin and roundscale spearfish as being morphologically distinct, but little effort has been made to describe variation within an individual, among individuals, or between species. to better understand morphological variation of scales and squamation patterns of distinct body regions of these two species, individual scales were collected from 11 specific anatomical regions, and scale patches were collected from 3 specific regions of each white marlin and roundscale spearfish brought into marlin tournament weigh stations in the Mid-Atlantic Bight during 2012 and 2013. Scales were measured and described, and scale patches were cleared and stained to examine the level of imbrication of the scales, as well as the overall squamation patterns. In addition to the scales, denticular plates, ossified formations occurring on the surface layer of the dermis, were measured and described. Although considable morphological variation was observed among scales from different anatomical regions of individuals of both species, white marlin scales generally have pointed anterior ends, fewer posterior points, and are more heavily imbricated than those of roundscale spearfish, which are frequently rounded anteriorly, but often have many posterior points and are farther separated within the skin. Over all areas and individuals, roundscale spearfish scales were significantly wider and had a lower length-­‐to-­‐width aspect ratio than those of white marlin. Detailed scale descriptions allow for a more accurate characterization of the variation within and differences between these two species, and could potentially be a valuable tool for investigating istiophorid systematics.

Episodic turbulence is a short-lived, high-intensity phenomenon in marine environments produced by both anthropogenic and natural causes, such as boat propellers, strong winds, and breaking waves. Episodic turbulence has been shown to cause mortality in zooplankton, but its effects on marine phytoplankton have rarely been investigated. This study focused on two diatoms: Thalassiosira weissflogii and Skeletonema costatum. I found that exposure for 45 s to turbulence intensities above 2.5 cm2 s-3 caused 24-32% reduction in diatom abundance and increased the amount of intact dead cells to 22%. Turbulence also caused extracellular release of optically reactive DOM. At a turbulence level of 4.0 cm2 s-3, photosynthetic efficiency (Fv/Fm) decreased from 0.51 to 0.38 and 0.55 to 0.50 in T. weissflogii and S. costatum respectively. These turbulence levels are comparable to those under breaking surface waves and are much smaller than those generated by boat propellers. Despite its relatively short duration, episodic turbulence has the potential to affect phytoplankton via lethal and sublethal effects. An improved technique using the Evans Blue stain was developed to enable visual live/dead plankton cell determinations. When used in conjunction with preservation and flow cytometry, this staining method allows the study of phytoplankton mortality due to turbulence and other environmental stresses.

Epibiosis is a common phenomenon in aquatic environments. The chitinous exoskeletons of crustaceans provide stable surfaces for attachment and growth of epibiotic microorganisms. Epibiont ciliate colonization on copepods is commonly recorded but has rarely been studied in Chesapeake Bay; also, little is known about the life cycles of epibiont ciliates in the bay. The present work focuses on the life cycle of Zoothamnium intermedium in Chesapeake Bay. A peritrich ciliate belonging to the genus Zoothamnium was found as an epibiont on the calanoid copepods Acartia tonsa and Pseudodiaptomus pelagicus during the summer in the York River, a tributary of the lower Chesapeake Bay. By using primers conservative for the genus Zoothamnium, two almost identical (99.8% similarity) 2171-bp ribosomal DNA (rDNA) sequences containing the complete small subunit (SSU) and partial internal transcribed spacer (ITS) rDNA regions were obtained from epibiont ciliates on the two hosts, indicating that they were the same ciliate species. Based on phylogenetic analysis and morphological characteristics, the epibiont was presumptively identified as Z. intermedium. In winter, Z. intermedium was only found on P. pelagicus, never on A. tonsa or A. clausi. The continuous presence of Z. intermedium on P. pelagicus during the winter suggests that it used P. pelagicus as its primary host for overwintering. PCR assays specific to Z. intermedium were designed to detect this ciliate in the environment. Positive PCR results were obtained from some sediment samples, potentially implicating the existence of a benthic cyst stage as another possible overwintering strategy. In the laboratory, formation of cyst-like cells from detached zooids was observed at 5°C. In detachment-recolonization trials, colonization of telotrochs to the same host species was higher than across host species, indicating a certain seasonal host specificity.

Seed dispersal and seed predation are two important processes in the early life history of plants. The interaction between these two processes influences the population recruitment from a parent plant. These mechanisms have been studied extensively in terrestrial plants and have resulted in various models to describe plant recruitment (e.g. Janzen-Connell, Hubbell, McCanny). However, seed dispersal and predation may also influence the population recruitment of marine angiosperms, such as Zostera marina (eelgrass). The objectives of this study were to determine: 1.) the patterns of seed dispersal as a function of distance from the seed source, 2.) the predation pressure on seeds within and outside the parent bed, 3.) the distribution of seedlings as a function of distance from the parent bed, and to test if this distribution corresponds to the seed dispersal and predation pressure, and 4.) how the observed patterns compare with simulated seedling establishment using a model developed by Nathan and Casagrandi (2004). Seed densities were highest within, and adjacent to, vegetated areas. However, some seeds were found up to 320m from the closest seed source. Seed predation was random throughout the study area; there was no significant difference in predation pressure between vegetated and unvegetated areas. Seedling densities in the spring of 2014 were highly correlated with seed densities found in the previous year, which also suggests that seed predation has a limited impact on population recruitment. The high reproductive output of Z. marina as well as the random distribution of seed predators in both vegetated and unvegetated areas may explain how many seeds are able to escape predation. These results are consistent with the invariant survival model, first described by McCanny, which states that seed predation has no spatial trend. Therefore, a majority of the dispersed seeds remain close to the parent bed, while a small portion of seeds disperse farther from the source. This is the first study of marine angiosperms to address seedling recruitment as a function of dispersal and predation from a parent source and has important implications in recovery and restoration of these systems following disturbances.

Fisheries have become increasingly important to manage and conserve, and this is particularly challenging for data-poor species. Elasmobranchs are commonly considered data-poor or data-limited species. Their life history characteristics make their populations susceptible to depletion from fishing pressures and habitat degradation. Thus, it is important to understand the movement patterns and habitat use of the targeted species as well as the models used in the stock assessment for the species. This thesis involves developing techniques and information for data-poor species, such as elasmobranchs. The objectives of this research were to 1) identify the wintering grounds for the cownose rays (Rhinoptera bonasus) from Chesapeake Bay, 2) determine summer and fall movement patterns for this species, and 3) understand how changes in the data input (i.e., catch and effort) affect the parameter estimates from a simple surplus production model. Cownose rays have received negative attention in Chesapeake Bay for presumably heavy predation on commercial shellfish. Although the population size is unknown, there are concerns about the increase in abundance of this species, resulting in the need for management to control its population size. However, there are many questions regarding the movement patterns and habitat use for cownose rays, particularly for males. A total of 16 cownose rays in Chesapeake Bay were tagged with pop-up satellite archival tags (PSATs) to determine their wintering grounds and summer and fall movement patterns. Six tags (3 on females and 3 on males) were released on the programmed date and contained data on temperature, pressure (for depths) and light-level (for geolocations). The end locations from the satellite tags indicated that both sexes migrated to the coastal waters of central Florida for the winter. Females were exited Chesapeake Bay at the end of September and early October and migrated south to Florida. Males left the bay at the end of July and traveled northward to a second feeding ground in the coastal waters of southern New England. At the end of summer and early fall, the males made the southerly migration down the coast to Florida. There were no diel differences detected; however, male rays occupied a wider depth and temperature range compared to females. Data-poor stocks are often regulated based on surplus production models when only catch and effort data are available. However, reported catch and effort rarely equal the true values. Reported data may not include bycatch, illegal fishing or local consumption, resulting in higher true catch and effort values than that reported. I used ASPIC (A Surplus Production Model Incorporating Covariates) software to examine the viii PREVIEW effects of underestimated catch and effort on parameter and ratio estimates (e.g., MSY, F/Fmsy and B/Bmsy) in a production model. Using three example fisheries, I determined that a fishery with constant underestimation of catch and effort over time can be managed based on the parameter estimates from the production model. The parameter estimates either yielded no errors or were underestimated by the same percentage as the underreported data; however, the ratios of parameter estimates were free of error due to cancellation of errors. Trends in underestimation of catch and effort (e.g., improved reporting rates or increased illegal fishing) caused the errors in the estimates from the production model to be highly variable and scenario-dependent. Consequently, if underreporting of catch and effort is suspected, I would recommend conducting additional simulations specific to the fishery.

Seagrasses modify the coastal areas they occupy by trapping sediments and improving water clarity, providing habitat for marine animals, and cycling nutrients. Populations are in decline worldwide, and in the lower Chesapeake Bay, U.S., Zostera marina populations are decreasing due to poor water quality and high summertime temperatures. Ruppia maritima, a seagrass that is smaller, but has a greater tolerance of high temperatures than Z. marina, is replacing Z. marina in some areas. This study examined bed characteristics and microbial community structures of each seagrass species, as well as mixed assemblages, at three sites in the lower Chesapeake Bay where R. maritima has been replacing Z. marina over recent years. The objective of this study was to determine the potential of R. maritima to ameliorate detrimental effects of Z. marina loss. Samples were taken in June and August of 2013. In contrast to expectations that R. maritima would increase in abundance by August, R. maritima biomass and density decreased. Sediment grain size showed interactions between site and habitat type; two sites of the three showed greater mean fine sediments in Z. marina than R. maritima stands. Where sediment erodibility was measured, eroded mass was greater in the Z. marina sediment compared to the R. maritima sediment in June, while eroded mass was greater in R. maritima sediment in August. This suggests that sediment trapping capabilities may differ seasonally between the two species, with Z. marina generally capable of trapping more fine sediments than R. maritima; however this capability may be affected by location and season. Z. marina provided better quality habitat for epifauna in the early summer, but results from late summer were inconsistent as both species died back. Microbial communities, which affect sediment nutrient cycling, were found to be similar among sediments occupied by both species of seagrass, although the effects of site and month were strong. There was also a greater relative abundance of sulfate reducers in the August samples than the June samples. Overall, the results demonstrate that although the quality of some ecosystem services were greater in Z. marina compared to R. maritima, R. maritima still possessed the ability to provide valuable ecosystem services, and could be considered as a restoration option in the Chesapeake Bay, especially in areas where the potential for Z. marina regrowth is low.

Relative to the rest of the Southern Ocean, the Ross Sea continental shelf experiences very high productivity and phytoplankton biomass, which supports an extensive food web including high concentrations of upper trophic level biomass. Conventional observational methods, including ship-based sampling, instrumented moorings, satellite imagery, and computer-based modelling, have illustrated the seasonal progression of the phytoplankton bloom over the past four decades. While we have been sampling phytoplankton variability in the Ross Sea on a variety of relatively large scales, with observations at specific locations or times, over spans of time, or at specific depths, our understanding of smaller scales of variability (on the order of a few hours or several kilometers) is still poor. Utilizing two seasons (2010-2011 and 2012-2013) of high-resolution autonomous glider deployments in the southwestern Ross Sea, I examined the mechanisms driving both the transitions between stages of the phytoplankton bloom and the short-term perturbations in average 0-50 m chlorophyll. By including the available raw fluorescence data from both glider seasons and three mooring seasons, I determined that the 2012-2013 season had greater than average variability, with greater levels of variability observed in only two other seasons. Differences in the timing of bloom transitions were relatively constrained; the transition from bloom to post-bloom levels occurred within a temporal span of 6 d. These findings were likely the result of the location of the 2012-2013 glider adjacent to Ross Island and the Ross Ice Shelf, where complex bathymetry, turbulent flows, and the presence of an ice field contributed to the greater observed variability. To investigate the mechanisms driving the short-term perturbations in chlorophyll, I examined the relationships between average chlorophyll, average temperature, and mixed layer depth measured by the gliders and wind speed measured by two automatic weather stations atop the Ross Ice Shelf. Over the course of the 2012-2013 season, perturbations or responses in chlorophyll were heavily influenced by the degree of temporal coupling between wind events and the depth of mixing. Longer delays of 12-24 h observed prior to the biomass maximum shortened following the transition to biomass dissipation to 2-12 h. Furthermore, by causing aggregate formation and rapid vertical flux, physical forcing factors contributed to the observed short-term perturbations through reductions in biomass in surface layers and the appearance of chlorophyll in deeper layers. These results suggest that the small-scale observing capabilities of autonomous gliders allow for an improved understanding of the mechanisms that drive variability and short-term perturbations in shallow chlorophyll in the southwestern Ross Sea.

No description available.

A study was made of the intertidal zone of aged wooden pilings from February to June, 1967 at Gloucester Point Virginia,located in the lower York River estuary. Twenty-six species of marine algae were found grouped into three floristic zones. Nine species were limited to below mean low water, whichialL.rlted the lowest cone. In this group there were six Rhodophyta and three Chlorophyta. Seven floral levels comprised the middle floristic zone between mean low water to a height of 74 cm above mean low water. These levels ere based on uppermost range extensions of sixteen species (six Cyanophyta, two Rhodophyta,one Phaeophyta and seven Chlorophyta). The Cyanophyta Calothrix crustacea formed the highest floristic zone attaining a maximum height of 122 cm above mean low water. Collections from acrylic plastic plates showed a change in the floral composition below mean low water during May and June.Six species were found during the study period that were previously unreported from Virginia: Ectocarpus confervoides Enteromorpha compressa, Enteromorpha erecta, Enteromorpha prolifera, Monostroma leptodermum and Ulothrix flacca.