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.

Benthic communities on the outer continental shelf of the Middle Atlantic Bight are characterized by abundant populations of amphipods in the families Ampeliscidae and Corophiidae. Members of these families occupy tubes at or near the sediment surface and, thus, potentially compete with each other for spatial and trophic resources. This study examines the spatial, temporal and trophic resource use of six numerically dominant species in these families as a means of assessing the relative importance of competition as a structuring force in outer shelf benthic communities. Analysis of abundance data and the use of discriminant analysis to relate abundance to measured environmental parameters indicated that habitat partitioning was of major importance within the ampeliscid group. Spatial partitioning appeared to be of little importance within the corophiid group. Between group patterns suggest that only one species, the corophiid Unciola irrorata, was able to coexist in deep swales with the ampeliscid Ampelisca agassizi. Seasonal abundance patterns were exhibited by all corophiids, but the high degree of temporal overlap in abundance suggests that this was not an important partitioning mechanism. Similarly, persistent abundances over· time (!. agassizi) or variation in a non-seasonal manner suggests that temporal partitioning of resources was not important within the ampeliscid group. Differences in body size which might facilitate differential spatial or trophic resource use among species were observed. These differences were most strongly pronounced in closely related species which frequently co-occured. The use of trophic resources was indirectly assessed by comparing mouthpart morphologies and known feeding behaviors of each species. Quantitative morphological differences among species were evident which relate well to observed habitat preferences. A complex set of physical and biological factors were found to govern the distribution and abundance of these species within the outer shelf zone. In outer shelf swale habitats the ampeliscid, A. agassizi, effectively excludes the other members of this family. This may be the result of the species superior abilities to utilize spatial or trophic resources. Outside . of swale habitats the abundances of Ampelisca vadorum and Byblis serrata may be limited by the availability of trophic resources. The corophiids show little evidence of resource partitioning, although some differences in microhabitat distribution may facilitate coexistence among ·the species in this family, as well as between families. Populations · of these species may be held below the levels at which competitive interactions become important by benthic predators. The corophiids are known to comprise a major portion of the diet of benthic fishes on the outer shelf.

The purpose of this study is to examine the feeding ecology and trophic role/importance of the northern pipefish, Syngnathus fuscus, in a lower Chesapeake Bay seagrass community. The study incorporates; 1) examination of stomach contents in conjunction with prey abundance data, inorder to arrive at conclusions concerning the food preferences of S· fuscus, 2) determination of daily feeding periodicities and stomach evacuation parameters, thus allowing for the determination of a daily ration for S· fuscus, 3) examination of size relationships between S. fuscus and it's major prey species, 4) estimation of pipefish densities at the study site, and 5) examination of the trophic importance of S. fuscus via estimation of the annual quantities of specific prey species consumed at the study site, and comparison of these values with estimated production values for the prey populations. It is suggested, that while S. fuscus consumes only moderate portions of the annual production of it's prey species, it may serve to modulate the production of these prey species by feeding predominantly upon small individuals, thus effectively altering the age-class structure of the prey population, and assumably the production charactoristics as well.

Hypoxia and anoxia have significant deleterious ecological effects on living resources throughout many estuarine and marine ecosystems worldwide. Brief periods of low oxygen facilitate transfer of benthic production to higher trophic levels as many benthic infaunal species have shallower sediment depth distributions during hypoxic events. A baited time-lapse camera equipped with a water quality datalogger was used to document in situ exploitation of oxygen-stressed benthic invertebrate prey organisms by mobile fish and crustacean predators during alternating normoxia-hypoxia cycles in the York River. Based on photographic and diver observations, this hypoxiainduced benthic-pelagic transfer of production is more likely to occur when environmental dissolved oxygen concentrations rise above an apparent threshold between 1 and 2 ml/1. When oxygen concentrations decline below 2 ml/1, the functional response of the predator to increased prey availability is interrupted. There is no energy gain by the predator until oxygen concentrations rise above this critical level when predators return to affected areas and resume feeding activity.

Long chain n-3 polyunsaturated fatty acids (LCn-3 PUFAs) such as EPA and DHA are important biomolecules regulating production in marine ecosystems. This study examined how the interaction at the phytoplankton-zooplankton interface affected the transfer of LCn-3 PUFAs to higher trophic levels. Heterotrophic dinoflagellates contained higher levels of EPA and DHA than their algal prey, suggesting heterotrophic dinoflagellates enhanced the nutritional value of poor quality algae and subsequent transfer to the next trophic level. Formation of EPA and DHA in the dinoflagellates appears to be achieved by the elongation and desaturation of shorter fatty acid chains rather than through de novo synthesis. Fatty acid content in the copepod Acartia tonsa resembled the fatty acid signature of its prey, further supporting the idea that heterotrophs depend on their diet to obtain these nutrients, and their nutritional value is subject to the type of food consumed. Transfer of DHA to A. tonsa, was improved by feeding on a heterotrophic dinoflagellate grown on a poor quality algae, versus feeding on the algae itself. Thus omnivorous copepods may compensate dietary deficiencies by feeding on a variety of prey items. The presence of EPA and DHA can be used as a proxy for the nutritional value of copepods. A. tonsa fed nutritiously poor algae also affected the fatty acid content of its predator. Pseudopleuronectes americanus fed low quality copepods, had lower levels of EPA and DHA than those fed copepods with higher levels of these fatty acids. However, content of these fatty acids did not have a direct effect on the growth rate of the fish. The finding herein does not support consumption of LCn-3 PUFAs as important factors regulating growth in juvenile fish. These results, albeit discouraging, are by no means comprehensive in elucidating the role of n-3 PUFAs for fish health. It is possible that due to food limitation, the effect of food quality was confounded. Field collected data in a nursery ground for juvenile P. americanus showed that the quantity of EPA and DHA in the prey for the fish at the time of sampling was low. The low availability of these fatty acids in the plankton suggests this estuary is at times suboptimal for the growth and development of P. americanus. EPA and DHA are critical for P. americanus growth; however, the low availability of LCn-3 PUFAs does not by itself explain differences in growth rates. It is clear that further field studies should combine physical, biological and chemical factors in order to evaluate the nutritional status of the nursery ground.