Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item The effects of low dissolved oxygen on predation interactions between Mnemiopsis leidyi ctenophores and larval fish in the Chesapeake Bay ecosystem(2006-11-27) Kolesar, Sarah Elizabeth; Breitburg, Denise L; Boynton, Walter R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Differences in predator and prey tolerances to low dissolved oxygen (DO) concentrations are important to planktonic food webs in seasonally hypoxic environments like Chesapeake Bay. Hypoxia alters field distributions, encounter rates, and predator-prey interactions between hypoxia-tolerant ctenophores, Mnemiopsis leidyi, and less tolerant ichthyoplankton and zooplankton prey. To examine the effect of hypoxia on estuarine food web species' interactions, I conducted medium and small-scale experiments, field sampling, and collaborated on individual-based model development, focusing on ctenophore-larval fish dynamics. Laboratory estimates of clearance rates for ctenophores on bay anchovy (Anchoa mitchilli) eggs and yolk sac larvae, and naked goby (Gobiosoma bosc) feeding larvae were the same at low and high DO. Field sampling for M. leidyi, ichthyoplankton, mesozooplankton, and scyphomedusae (Chrysaora quinquecirrha) during day and night at two sites in the Patuxent River indicated increased abundance of most species in the bottom layer with increasing bottom DO. Vertical overlap between predator and prey pairs also increased with higher bottom DO, increasing potential encounters and predation. Larval fish swimming speeds did not differ significantly with DO, but ctenophores swam significantly faster at intermediate DO (2.5 mg L-1) than at either low or high DO. DO did not significantly affect ingestion. Greater ingestion of fish larvae by ctenophores followed multiple encounters (56%) than initial encounters (10%) at all DO concentrations, highlighting the potential importance of repeated predator-prey interactions. DO did not significantly affect encounter model estimates of ingestion rates. Ingestions averaged 0.4 fish larvae d-1 m-3 for first encounters and 2 fish larvae d-1 m-3 for multiple encounters. Results from laboratory and field studies parameterized a spatially-explicit individual based model of a ctenophore-ichthyoplankton-copepod intraguild predation food web. Ctenophore predation had a bigger effect on survival of modeled ichthyoplankton than did competition between ctenophores and fish larvae for shared zooplankton prey, but competition more strongly affected larval fish growth rates. DO did not alter the relative importance of ctenophore predation and competition, but low DO did decrease larval fish survival and increase growth rates. Results suggest that effects of DO on vertical distribution and species overlap are more important to predation than direct DO effects.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.