MEES Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/19655

Browse

Subject: search.filters.subject.Biology, Zoology

Search Results

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Assessment of local abundance, demographics, health and exploitation of Chesapeake Bay American eel
    (2009) Fenske, Kari Hammarsten; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Chesapeake Bay supports the largest U.S. harvest of American eel Anguilla rostrata, yet little is known about the underlying production rates sustaining harvests. Demographic attributes were compared between six sub-estuaries and with an unexploited population in the Hudson River. A mark-recapture experiment in the Potomac River yielded growth, abundance, and production estimates. Sub-estuaries characterized by lower salinity had a lower proportion of females, and American eels were older, slower growing and showed increased parasitism. Female American eels were larger, older, and had higher growth rates than other gender types. Local abundances were 10-fold higher in the Potomac River estuary in comparison to the Hudson River, but growth rates were similar. Mortality rates were twice as high as those in the Hudson River estuary. The production model indicated American eel recruitment and biomass decreased substantially during the past 20 years.
  • Thumbnail Image
    Item
    HOW DENDRITIC ECOLOGICAL NETWORKS STRUCTURE THE DISTRIBUTION AND MOVEMENT OF STREAM SALAMANDERS
    (2009) Grant, Evan; Palmer, Margaret A; Nichols, James D; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Research in population biology is concerned with factors affecting the change in a population over time, including births, deaths, immigration and emigration. Despite the potential importance of dispersal, empirical data on movement are lacking in many systems. Hence, there is a large body of theory on dispersal that remains to be tested in real biological systems. In particular, many organisms exist in ecological networks with the complex geometry common to caves, plants and streams. This alternative network topology might influence population and community-level patterns and processes. Chapter 1 introduces the concept of the "dendritic ecological network," highlighting special properties and characteristics useful for understanding community and population-level processes. Of most interest for this dissertation is how the rigid spatial structure and branching topology may have implications for patterns of population distribution and the evolution of movement behaviour in stream organisms. In chapters 2 and 3, I investigate patterns of stream salamander distribution, which may be related to the spatial configuration of stream habitat branches. First, I determined the sampling methods suitable for estimating the probability a site is occupied by one of three stream salamander species. I then applied these methods to investigate occupancy patterns, in relation to stream spatial layout across two mid-Atlantic regions. I found that all three species have higher occupancy in streams with a confluent, firs-order stream, though the strength of this association seems to be related to life history characteristics. Finally, in chapters 4 and 5, I sought to identify movement pathways for larval, juvenile and adult Desmognathus stream salamanders. First, I tested my marking method on larval individuals, and found that the visual implant elastomer marks can be retained through metamorphosis. Then, using individual mark-recapture and multistate modeling, I found that stream salamanders move during the juvenile stage, with both an upstream-biased movement, and a proportionally large probability of moving overland to an adjacent stream reach. The chapters in this dissertation combine empirical investigations of the patterns and pathways of stream salamander movement. Taken together, they elucidate the underlying importance of dendritic ecological networks, and provide direct evidence of dispersal in stream salamanders.
  • Thumbnail Image
    Item
    THE DISTRIBUTION OF CALLINECTES SAPIDUS MEGALOPAE AT THE MOUTHS OF CHESAPEAKE AND DELAWARE BAYS: IMPLICATIONS FOR LARVAL INGRESS
    (2009) Biermann, Jeffery Lee; North, Elizabeth W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Transport of Callinectes sapidus (blue crab) megalopae from the continental shelf into estuaries may influence recruitment variability of this economically important species. This research seeks to determine the vertical distribution of C. sapidus megalopae near the mouths of Chesapeake and Delaware Bays, and thereby infer swimming behaviors that may influence ingress to these estuaries. Megalopae and physical conditions were sampled at locations from ~10 km inshore of the estuary mouths to ~40 km offshore in coastal shelf waters in September 2005 and 2006. Megalopae were present in greater abundance and at shallower depths during night compared to day at all locations, suggesting a diurnal effect on distribution within the estuary and on the continental shelf. Unlike previous studies, offshore distributions did not indicate surface oriented behavior. Within the mouth of Delaware Bay, limited evidence suggests that megalopae presence in the upper portion of the water column increases in response to nocturnal flood tides. Results suggest photoinhibited swimming near the mouths of Chesapeake and Delaware Bays. In context of previous laboratory studies, these findings indicate that estuarine chemical cues at very low concentrations may induce changes in megalopae behaviors and stimulate molting at least 40 km offshore of estuarine mouths. Results suggest wind-forcing and density-induced subtidal flow are more likely mechanisms for ingress to Chesapeake and Delaware Bays than tidal-transport.
  • Thumbnail Image
    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.
  • Thumbnail Image
    Item
    HABITAT USE AND COHORT RECRUITMENT PATTERNS OF JUVENILE BLUEFISH (POMATOMUS SALTATRIX) IN DIVERSE MARYLAND NURSERY SYSTEMS
    (2004-08-12) Takata, Lynn Tomiye; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A popular recreational species, bluefish (Pomatomus saltatrix) has been declining since the mid-1980s. This thesis examines patterns of juvenile habitat use, growth rate, and cohort recruitment patterns in three Maryland systems: the Chesapeake Bay, the Coastal Bays, and shallow coastal areas (<20>m): potential nursery habitats where little research has been conducted. Notable differences in growth rate were observed among systems, with consistently higher rates in the Chesapeake compared to the Coastal Bays. Juvenile growth was also amongst the highest reported in the literature. Likewise, relative cohort contribution varied between systems suggesting that late spawning groups may not consistently utilize the upper Chesapeake, and a spawning group intervening between the spring and summer cohorts may occasionally appear in the coastal region. Finally, otolith microchemical analysis indicated that juveniles may exclusively use coastal nurseries, adding to evidence that bluefish may not be estuarine dependent.
  • Thumbnail Image
    Item
    Identification, life history, and ecology of peritrich ciliates as epibionts on calanoid copepods in the Chesapeake Bay
    (2004-02-10) Utz, Laura Roberta Pinto; Small, Eugene B.; Marine-Estuarine-Environmental Sciences
    Epibiotic relationships are a widespread phenomenon in marine, estuarine and freshwater environments, and include diverse epibiont organisms such as bacteria, protists, rotifers, and barnacles. Despite its wide occurrence, epibiosis is still poorly known regarding its consequences, advantages, and disadvantages for host and epibiont. Most studies performed about epibiotic communities have focused on the epibionts' effects on host fitness, with few studies emphasizing on the epibiont itself. The present work investigates species composition, spatial and temporal fluctuations, and aspects of the life cycle and attachment preferences of Peritrich epibionts on calanoid copepods in Chesapeake Bay, USA. Two species of Peritrich ciliates (Zoothamnium intermedium Precht, 1935, and Epistylis sp.) were identified to live as epibionts on the two most abundant copepod species (Acartia tonsa and Eurytemora affinis) during spring and summer months in Chesapeake Bay. Infestation prevalence was not significantly correlated with environmental variables or phytoplankton abundance, but displayed a trend following host abundance. Investigation of the life cycle of Z. intermedium suggested that it is an obligate epibiont, being unable to attach to non-living substrates in the laboratory or in the field. Formation of free-swimming stages (telotrochs) occurs as a result of binary fission, as observed for other peritrichs, and is also triggered by death or molt of the crustacean host. Attachment success of dispersal stages decreased as telotroch age increased, suggesting that colonization rates in nature may be strongly dependent on intense production of telotrochs by the epibiont ciliates. Laboratory experiments demonstrated that Z. intermedium colonizes equally adult and copepodite stages of A. tonsa and E. affinis. The epibiont is also able to colonize barnacle nauplii and a harpacticoid copepod, when these were the only living host available, but fails to colonize non-crustacean hosts, such as the rotifer Brachionus calyciflorus or polychaete larvae. When the epibiont could choose between adults of A. tonsa and alternate hosts from the zooplankton community, it always colonized preferentially its primary host, with only a few telotrochs attaching to other crustaceans (barnacle nauplii and harpacticoid copepod), and to rotifer eggs, suggesting that specific cues may be involved in host selection by this epibiotic species.