Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Foraging values of Mulinia lateralis and Ischadium recurvum: energetics effects of surf scoters wintering in the Chesapeake Bay.(2008-03-26) Berlin, Alicia; Ottinger, Mary Ann; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Surf scoter (Melanitta perspicillata) populations wintering in the Chesapeake Bay primarily prey on two food items, the hooked mussel (Ischadium recurvum) and dwarf surfclam (Mulinia lateralis). The decline of oyster reefs (Crassostrea virginica) has decreased availability of mussels inducing surf scoters to switch to a more opportune food item, the dwarf surfclam. The objectives of this study were: 1) to determine the comparative nutrient composition of these prey items; 2) to evaluate the energy assimilated by surf scoters from these prey items; 3) to determine the functional responses of scoters foraging on four different ecologically relevant densities (30, 100, 1000, and 3000 m-2) of each prey item; and 4) to model the foraging value (costs - benefits) of both prey items for surf scoters. I. recurvum contained higher ash, protein, lipid, and energy per item than M. lateralis. Metabolizable energy from each prey item by surf scoters was 83% for M. lateralis and 87% for I. recurvum. The shell strength of I. recurvum was significantly stronger than M. lateralis. For scoters foraging in a large diving tank 2 m deep, intake (# s-1) for M. lateralis was significantly higher than I. recurvum at high densities, but lower at the low densities. Gross energy intake (kJ s-1) and metabolized energy intake (kJ s-1) were significantly greater for I. recurvum than M. lateralis. Based on nutrient content, metabolizability, behavior and intake rates, and energy expenditure at naturally occurring densities, the foraging value for M. lateralis was significantly lower than I. recurvum. Despite higher ash content and harder shell, which would partly offset the apparent energetic advantages of I. recurvum, greater foraging value of I. recurvum than M. lateralis provides a more beneficial prey item for wintering surf scoters. Therefore, wintering surf scoters must adapt in order to maintain their daily energy requirement. If surf scoters are forced to feed primarily on M. lateralis, the most advantageous and available prey in the Chesapeake Bay, instead of I. recurvum; there may be insufficient energy for them to build fat reserves needed to make migration.Item Habitat use of surf scoters wintering in the mesohaline region of the mainstem Chesapeake Bay, Maryland(2007-12-11) Kidwell, David M.; Adams, Lowell W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Surf scoters (Melanitta perspicillata) are common in coastal waters during winter, but remain one of the least studied waterfowl in North America despite indications of a declining population. Surf scoter foraging was investigated in the mesohaline region of the Chesapeake Bay during 2004-2005. The study compared biological and physical characteristics of benthic habitats among scoter feeding and non-feeding sites. Benthic samples were taken seasonally via a Peterson grab. Surf scoters foraged over oyster bar, packed clay and sand habitats, but avoided mud habitats. Clam densities varied seasonally, increasing over winter regardless of scoter foraging activity. Foraging activity appeared to influence hooked mussel densities on hard bottoms. Lack of foraging over mud habitats, where visibility can be limited, suggests that surf scoters may be visual predators and may have been impacted by habitat sedimentation The correlation of hooked mussel with oyster bars suggests that oyster restoration efforts may positively impact surf scoters.Item THE BEHAVIOR OF THE SCYPHOMEDUSAE CHRYSAORA QUINQUECIRRHA AND AURELIA AURITA AND ITS ECOLOGICAL IMPORTANCE(2004-11-23) Matanoski, Joseph Carroll; Hood, Raleigh R; Purcell, Jennifer E; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Scyphomedusae are important components in trophic and community structures of marine and estuarine systems worldwide. Behavior likely has a significant influence on medusa population dynamics and growing evidence points to the disproportionate effect individual behavior has on population responses, yet there are few quantitative studies of medusa behavior and no method for quantifying the behavior of individual pelagic organisms. A numerical model of medusa swimming behavior would be an important tool for assessing its effect on spatial patterns and foraging efficiency. An approach was developed that uses a suite of statistical techniques to quantitatively describe time-dependent changes in behavior of pelagic organisms and tested on the swimming behavior of Aurelia aurita and the foraging behavior of Chrysaora quinquecirrha. An individual-based model of medusa swimming behavior was formulated as a correlated random walk of velocity vectors in three dimensions. Each A. aurita medusa exhibited a unique swimming behavior, including varying swimming bell pulsations, speed, and turning at characteristic frequencies. C. quinquecirrha swam in mostly linear trajectories that alternated between periods of slow and fast swimming while searching for prey, but swam at a constant moderate rate with increased anisotropic turning while feeding. Foraging behavior by medusa groups depended on interindividual and intraindividual variability in medusa behavior, including deterministic changes in swimming pulsation strength and turning. Empirical and model results showed that variability of behavior among medusae and by individual medusae over time are integral components determining the aggregated population response. Medusa foraging behavior appears adapted for patchily distributed prey. Alternating between slow and fast swimming while searching for prey may minimize energy expended while periodically generating prey-entraining currents. Increased turning in the presence of prey increases the likelihood of remaining in prey patches. Anisotropic turning created vertically spiraling paths, well suited to horizontally compressed prey patches. Model results demonstrated that medusae tend to swim toward and accumulate at the surface, avoid direct contact with the bottom, orient search patterns to long-range stimuli (e.g. gravity) and feeding patterns to local stimuli (e.g. prey contact), and exhibit periodicities of velocity outside prey patches and turning within patches that result from deterministic behavior.