Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
Browse
8 results
Search Results
Item GEOSTATISTICAL ESTIMATION OF BLUE CRAB CALLINECTES SAPIDUS ABUNDANCE IN CHESAPEAKE BAY AT LOCAL SCALES(2022) Jones, Sarah Ann; Miller, Thomas J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increases in the sizes of container ships due to the expansion of the Panama Canal has increased the need for dredging activities in the Chesapeake Bay. Placement of dredged material in the Bay is restricted to winter months owing to concerns for threatened and endangered species. Placement of dredged material in the lower Chesapeake Bay in Wolf Trap Alternate Open Water Placement Site (WTAPS) overlaps with overwintering locations for mature female blue crab. To estimate the potential magnitude of winter mortality in WTAPS and WTAPS Northern Extension (WTAPSNE) resulting from placement of dredged material, a range of geostatistical tools (e.g., inverse distance weighting and kriging) were used to map the distribution and estimate the abundance of blue crab in Chesapeake Bay, WTAPS, and WTAPSNE (i.e., small-scale estimation) from 1990–2020 using data from the winter dredge survey. These analyses indicated that a low proportion of the age-1+ female blue crab population occurs within WTAPS and WTAPSNE (<1.18% and <1.5% respectively). Variability of abundance estimates was high when female age-1+ abundance was less than 150 million in the Chesapeake Bay. Therefore, we suggest the Port limit placement of dredged materials in WTAPS and WTAPSNE when female age-1+ abundance is less than 150 million; we recommend the Port not undertake placement activities when the stock is declared overfished (i.e., when female age-1+ abundance is less than 72.5 million).Item UNDERSTANDING MOLECULAR MECHANISMS REGULATING THE INITIAL SHELL-HARDENING PROCESS OF THE BLUE CRAB CALLINECTES SAPIDUS: INVOLVEMENT OF PROPHENOLOXIDASE AND THE TANNING HORMONE BURSICON(2015) Alvarez, Javier V.; Chung, J Sook; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Phenoloxidase, the integral enzyme for the prophenoloxidase cascade system in insects and crustaceans is essential in the melanization of pathogens and wound healing. Upon proteolytic activation of the zymogen prophenoloxidase, the active enzyme phenoloxidase catalyzes phenol substrates to sclerotize the protein matrix of arthropod cuticles. The hard exoskeleton protects and supports the body of crustaceans; however, it presents several challenges to continuous growth. To grow, crustaceans must periodically molt by shedding their exoskeletons (ecdysis). Ecdysis is triggered by the action of a set of hormones, which also initiate the previous deposition of a new soft cuticle beneath the hard exoskeleton. The flexible and soft new cuticle is expanded by the isosmotic intake of water during and immediately after ecdysis. Animals can then display their molt-related somatic growth. At the same time the unarmored crustaceans undergo the concurrent shell-hardening process to build a new exoskeleton. In crustaceans, the molecular and physiological mechanisms involved in the initial shell hardening process have been poorly understood compared to the corresponding process in insects. This dissertation addresses the molecular mechanisms which regulate the initial shell-hardening process of crustaceans, using the blue crab Callinectes sapidus as research model. To this end, the research focuses on the hemocyte prophenoloxidase and the neurohormone bursicon to define their roles and interactions in the regulation of the initial shell-hardening. A differential expression of prophenoloxidase in hemocytes is found and the role of prophenoloxidase in the shell-hardening process of crustacean is established. Unraveling the shell-hardening process of C. sapidus will add our understanding of the molt-related somatic growth of this and other economically valuable decapod crustacean species. This knowledge may contribute to increases in productivity of crustacean fisheries and aquaculture by the development of biotechnology to extend or reduce the soft-shell stage of crustaceans.Item The functional importance and significance of ecdysteroids in molt-cycle regulation of the blue crab, Callinectes sapidus(2014) Techa, Sirinart; Chung, Sook J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study aims to expand our understanding of how ecdysteroids and neuropeptide hormones (MIH/CHH) regulate molting in crustaceans using the blue crab Callinectes sapidus as a model animal. The hypothesis of this study is that ecdysteroids have a stimulatory effect on MIH/CHH production in eyestalks while generating both positive and negative feedback on ecdysteroidogenesis in Y-organs. Since ecdysteroids exert their signals through an ecdysteroid receptor complex, composed of an ecdysone receptor (EcR) and its partner, the retinoid-X receptor (RXR), the functional activity of ecdysteroids on tissues of interest is examined through EcR expression. Endogenous levels of ecdysteroids as well as expression in EcR, RXR and MIH/CHH are assayed in both embryonic and juvenile molt cycles. Similar patterns of changes in these two cycles suggest that molting control is driven by the same mechanisms in each. During embryonic molt, the correlation of ecdysteroid levels and MIH/CHH expression suggests that ecdysteroids are involved in MIH/CHH production. Using an in vitro system, stimulation of MIH expression occurs in eyestalks incubated with ponasterone A (PoA) and 20-hydroxyecdysone (20-HE) in the ratio found endogenously (3:1) and in ecdysteroid concentrations of 75 and 150 ng/ml. The in vivo response of MIH expression to depletion of ecdysteroid signals was examined by RNAi knockdown of an ecdysone receptor that was found to reduce the levels of MIH to those found by MIH knockdown, providing support for the hypothesis that ecdysteroids stimulate MIH expression through an ecdysone receptor. This study also found evidence suggesting that crustaceans have long-loop feedback for ecdysteroids in the neuroendocrine axis, which is similar to that found in insects.Item DEVELOPMENT, VALIDATION, AND APPLICATION OF A QUANTITATIVE POLYMERASE CHAIN REACTION ASSAY TO ASSESS HEMATODINIUM PEREZI PREVALENCE IN ENVIRONMENTAL SAMPLES(2012) Hanif, Ammar; Schott, Eric J; Jagus, Rosemary; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dinoflagellate parasites in the Hematodinium genus have emerged as important pathogens of economically important crustaceans worldwide, causing significant economic losses to fisheries and aquaculture. An understanding of the routes of infection in blue crab (Callinectes sapidus) populations would be facilitated by an improved knowledge of environmental reservoirs. A previously used PCR assay, based on small subunit rRNA sequences, lacked the specificity needed for Hematodinium perezi detection of environmental samples. Therefore a quantitative PCR assay based on the internal transcribed spacer 2 (ITS2) region of H. perezi rRNA genes was developed, validated, and applied to examine temporal and spatial incidences of environmental reservoirs in Delmarva coastal bays. H. perezi was detected in sediment and water in several Delmarva coastal bays, as well as the host, C. sapidus. Results suggest the existence of localized sediment reservoirs in areas where hydrological and geophysical features allow for the formation of cell deposits.Item ECDYSONE AND RETINOID-X RECEPTORS OF THE BLUE CRAB, Callinectes sapidus: CLONING AND TEMPORAL EXPRESSION PATTERNS IN EYESTALK GANGLIA AND Y-ORGANS DURING THE MOLT CYCLE(2012) Techa, Sirinart; Chung, Jum Sook; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The molt cycle in decapod crustaceans, including the blue crab, Callinectes sapidus, is supressed by the crustacean hyperglycemic hormone (CHH) neuropeptide family and stimulated by ecdysteroids (Ecds). The Ecds are thought to act on both eyestalk ganglia (ES) and Y-organs (YO) where the CHH neuropeptides and Ecds are synthesized, respectively. Since the resultant responses of Ecds are mediated through their nuclear receptors: ecdysone receptor (EcR) and retinoid-X receptor (RXR), the temporal expression of EcR-RXR in ES and YO during the molt cycle may reveal the regulatory role of Ecd on the activity of these two organs. In this study, the full-legnth cDNA sequences of C. sapidus EcR1a and RXR1, and the coding region of three other isoforms of EcR and RXR, were isolated. Moreover, temporal distributions of C. sapidus specific isoforms: CasEcR and CasRXR, were examined in ES and YO at different molt stagesItem Growth and recruitment rates of juvenile blue crabs ( Callinectes sapidus) in Chesapeake Bay(2006-05-25) Puckett, Brandon; Secor, David H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recent marked declines of the commercially and ecologically important blue crab in Chesapeake Bay have prompted requests for improved scientific information on blue crab population dynamics. I evaluated recruitment rates to blue crab fisheries using three independent approaches: direct observations, length-frequency analysis, and lipofuscin-based ageing. Three cohorts of known-age pond-reared blue crabs were sampled monthly, growth rates were modeled and compared to estimates from length-frequency analysis of field-collected crabs. Mean growth rates for juvenile pond-reared and field-collected cohorts ranged from 0.4 to 1.4 mm/day. A temperature-dependent growth model back-calculated settlement dates and predicted partial recruitments of juvenile winter size distributions. Predictions coincided with observations for wild blue crabs. Lipofuscin accumulated exponentially with age. The high growth rates, rapid recruitment rates, and lipofuscin-based age designations suggest that peeler/soft crab fisheries in the summer and hard crab fisheries in the fall/winter are predominately dependent on recruits less than 18 months of age.Item FIBER DIGESTION IN THE JUVENILE BLUE CRAB, CALLINECTES SAPIDUS RATHBUN(2006-01-24) Allman, Andrea Lauren; Place, Allen R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Five experiments were performed to determine the importance of chitin and cellulose in the diet of juvenile <em>C. sapidus</em>. A compartmentalized recirculating system was established to provide optimal conditions, maintaining the animals with little mortality. The appropriate ration, compartment size, and an adequate baseline diet were established. We replaced 20% of a commercial diet with varying amounts of chitin and cellulose. Crabs fed the cellulose-containing diet had higher growth rates, conversion efficiencies, molt increments and frequencies than crabs fed the chitin-containing diet, but were equal to the control diet. We then assayed for chitinase and cellulase in gut tissues. Chitinase had lower specific activity (0.072 + 0.159 mU mg-1min-1) than cellulase (3.52 + 0.16 mU mg-1min-1) in the foregut and hepatopancreas. There was no effect of diet on specific activity. The results show juvenile <em>C. sapidus</em> is capable of utilizing cellulose, but not chitin, when delivered as 20% of a diet.Item SPATIAL ECOLOGY OF BLUE CRAB (CALLINECTES SAPIDUS) IN CHESAPEAKE BAY(2004-11-12) Jensen, Olaf Peter; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Spatial heterogeneity is a striking feature of the blue crab life history and fisheries in Chesapeake Bay. However, a quantitative assessment of their spatial distribution and the factors controlling it has been lacking. Based on 13 years of data from a baywide winter dredge survey, geostatistical and two-stage generalized additive models (GAMs) are used to characterize blue crab distributions and investigate environmental factors responsible for the distribution of mature females, respectively. A landscape-based distance metric, the "Lowest-Cost Path" (LCP) distance, is developed as an alternative to Euclidean distance for kriging in estuaries. Estimates of variogram parameters differed significantly between the two metrics but kriging accuracy did not. Geostatistical abundance estimates show significant declines from 1990 to 2002. The observed relationship between changes in distribution and changes in abundance is suggestive of density-dependent habitat selection. Depth and distance from the Bay mouth were the most important predictors of mature female abundance.