Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
Browse
6 results
Search Results
Item DEVELOPMENT OF A NUCLEIC ACID-BASED SPECIFIC GROWTH MODEL FOR JUVENILE BLUE CRAB, CALLINECTES SAPIDUS(2016) Zaveta, Danielle Rae; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The evaluation and identification of habitats that function as nurseries for marine species has the potential to improve conservation and management. A key assessment of nursery habitat is estimating individual growth. However, the discrete growth of crustaceans presents a challenge for many traditional in situ techniques to accurately estimate growth over a short temporal scale. To evaluate the use of nucleic acid ratios (R:D) for juvenile blue crab (Callinectes sapidus), I developed and validated an R:D-based index of growth in the laboratory. R:D based growth estimates of crabs collected in the Patuxent River, MD indicated growth ranged from 0.8-25.9 (mg·g-1·d-1). Overall, there was no effect of size on growth, whereas there was a weak, but significant effect of date. These data provide insight into patterns of habitat-specific growth. These results highlight the complexity of the biological and physical factors which regulate growth of juvenile blue crabs in the field.Item Influence of environmental conditions on the age, hatch dates, and growth of juvenile Atlantic menhaden in the Choptank River, MD(2016) Atkinson, Alexandra Nicole; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Since 1993 Atlantic menhaden has experienced sustained low juvenile production (recruitment) in the Chesapeake Bay. Factors controlling growth, abundance, and mortality of larval and juvenile menhaden change throughout ontogeny such that larval growth rates could carry over to juvenile growth and survival. The effects of winter thermal conditions on the hatch dates and growth of larval and juvenile Atlantic menhaden in Atlantic shelf and Chesapeake Bay habitats were examined using otolith (ear-stone) increment analyses and growth models. For 2010-2013, truncated hatch-date distributions provided evidence for a winter recruitment bottleneck in Atlantic menhaden caused by cold temperatures. Hatch-dates of surviving juveniles were skewed towards warmer months for years characterized by colder temperatures. Reduced larval growth rates, influenced by reduced temperature and food availability, carried over to juvenile growth rates. A growing degree-day model performed well in simulating observed juvenile growth rates in the Choptank River tributary of Chesapeake Bay.Item Dispersal and Population Ecology of the Red-backed Salamander (Plethodon cinereus)(2015) Hesed, Kyle Miller; Wilkinson, Gerald S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Terrestrial salamanders are major components of ecosystems in eastern North America. One species, the Red-backed Salamander (Plethodon cinereus), may be the most abundant vertebrate throughout its range. Red-backed Salamanders are commonly monitored as indicators of ecosystem health and to assess the effects of forest management practices. In order to address poorly understood aspects of the ecology of Red-backed Salamanders, I conducted a 4-y mark-recapture study of a population in Maryland, resulting in 2,745 records of 752 marked salamanders, along with a complementary genetic analysis of six microsatellite loci. I estimated growth rates and age at sexual maturity using a hierarchical Bayesian model fitted by mark-recapture measurements, then measured home range size and seasonal and annual movement distances by immatures and adults, before and after the experimental removal of 98 conspecifics. Males grow and mature more slowly than females, despite reaching slightly larger asymptotic sizes; they may also face greater competition for space: adult males occupy the largest home ranges and show the largest increase in home range size after the removal of conspecifics. The largest between-year movements were made by individuals as they transitioned from immaturity to maturity. Using mark-recapture population models, I found that estimates of survival, detection, and abundance varied temporally along with the age and sex of the individuals present, both within and among seasons. Encounter probability varied among weekly sampling occasions, and models with separate parameters for each sex were strongly preferred. Survival was approximately the same over winters and summers, and lower for males than for females; this may be an artifact of sex-biased dispersal, as the majority of encountered immature individuals were estimated to be males, with models indicating a pulse of emigration in the fall and an influx of immature males onto the study site in the spring. An FST randomization test of multilocus genotypes showed a significant male bias in dispersal. Of salamanders captured repeatedly as both immatures and adults, males moved significantly farther before maturity than females did. Together, these results provide a comprehensive assessment of sex-biased dispersal at fine spatial and temporal scales in a terrestrial ectothermic vertebrate.Item The effects of co-varying diel-cycling hypoxia and pH on disease susceptibility, growth, and feeding in Crassostrea virginica(2014) Keppel, Andrew George; Breitburg, Denise L; North, Elizabeth W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Diel-cycling hypoxia and pH co-occur in shallow waters world-wide. Eutrophication tends to increase the occurrence and severity of diel cycles. We used laboratory experiments to investigate effects of diel-cycling DO and pH on acquisition and progression of infections by Perkinsus marinus, the protistan parasite which causes Dermo disease, as well as hemocyte activity, growth, and feeding in the eastern oyster, Crassostrea virginica, an important estuarine species. Diel-cycling DO increased P. marinus infection and cycling DO and pH stimulated hemocyte activity and reduced oyster growth. However, ambient environmental conditions and oyster age modulated some of these effects. Co-varying DO and pH cycles sometimes had less severe effects than either cycle independently. Oysters may acclimate to, or compensate for, effects of cycling conditions on growth. Variation in magnitude and spatial extent of cycling conditions is an important consideration when choosing restoration sites, as severe cycling conditions may hinder re-establishment of estuarine populations.Item An RNA:DNA-based index of growth in juvenile Atlantic menhaden (Brevoortia tyrannus): laboratory calibration and field assessment(2009) Edwards, Jason Lee; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atlantic menhaden (Brevoortia tyrannus) is an ecologically and economically important species in the mid-Atlantic coastal ecosystem. Its population dynamics are influenced by growth and survival during juvenile occupancy in estuarine nursery habitats. Therefore, quantifying production of potential nursery areas is important to understanding population processes and defining essential fish habitat for this species. Based on laboratory growth experiments, an RNA:DNA-based growth model was developed for young-of-the-year menhaden. The temporal response of RNA:DNA to changes in feeding condition was also quantified in the laboratory. Results of these investigations indicate RNA:DNA as a reliable tool for estimating recent growth and condition in relation to habitat residency. RNA:DNA-based estimates of growth were combined with site-specific abundance estimates to evaluate the spatiotemporal variability in production of potential menhaden nursery habitats. Site-specific production estimates exhibited high spatiotemporal variability suggesting menhaden utilize a mosaic of habitats to promote production, rather than specific sites consistently generating high levels of production.Item Ecology of Juvenile Bluefish, Pomatomus saltatrix, in Maryland Coastal Waters and Chesapeake Bay(2005-12-12) Callihan, Jody; Secor, David; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Shallow coastal ocean environments may function as important nursery habitats for juvenile bluefish, yet little ecological research has been conducted in ocean habitats. This thesis examines seasonal production, growth rates, and diet composition of juveniles in Maryland's coastal ocean environment and the Chesapeake Bay estuary. Summer-spawned juveniles dominated in ocean habitats and exhibited rapid growth rates, 2.0 - 2.4 mm d-1, which were likely fueled by an abundant forage base of young-of-the-year bay anchovy present in ocean environments during late summer/early fall. This summer cohort was rare in the Chesapeake Bay, where spring-spawned juveniles dominated. These results suggest ocean habitats provide principal nurseries for summer-spawned bluefish, and that the Chesapeake Bay and other estuaries are principal nurseries for spring-spawned juveniles. Accordingly, year class strength is likely shaped by contributions of juveniles from both oceanic and estuarine nursery habitats.