<p>This dissertation investigated spawning biology of female blue crabs, <italic>Callinectes sapidus</italic>. Females mate following the terminal molt and undertake a spawning migration seaward, producing multiple clutches of larvae. To examine lifetime reproductive potential of female crabs, individual crabs were confined in the field from terminal molt to death. Crabs produced up to 7 clutches over 1-2 spawning seasons and survived up to 394 d after the terminal molt. Time to first clutch and time between clutches were positively correlated with carapace width and best described by degree-days. Size at maturity was negatively correlated with water temperature on the day of the terminal molt. Most measurements of clutch quality and larval fitness were similar for all clutches. The percentage of embryos developing normally decreased 40% from clutch 1 to clutch 4 and clutch volume decreased 50% from clutch 1 to clutch 5. Thus, most of a crab's reproductive output is from the first few clutches. </p><p>Using swimming and abdominal pumping assays, the roles of pheromones in larval release and migratory behavior were investigated. Following delivery of egg extract, bradykinin (a pheromone mimic), and trypsin (an enzyme that generates peptide pheromones), ovigerous crabs responded with increased abdominal pumping, indicating that peptide pheromones stimulate larval release in blue crabs. Ovigerous crabs responded with increased swimming following delivery of egg extract, but not following delivery of a peptide pheromone mimic or an enzyme that produces peptide pheromones. These results suggest that some substance generated from the egg mass stimulates vertical swimming, but that peptides alone do not stimulate swimming. A blend of molecules, possibly including sugars, may be the cue that stimulates swimming behavior. </p><p>Endogenous rhythms in vertical swimming, a mechanism underlying migration in tidal estuaries, were examined in the laboratory under constant conditions in juvenile females, recently-molted females, and females with mature ovaries from Beaufort, NC. Rhythms were variable in each stage, though circatidal rhythms consistent with ebb tide transport were observed in juvenile females and recently-molted females. Crabs with mature ovaries typically swam around the time of high tide. Rhythms were also examined for ovigerous females collected from estuaries with three different tidal regimes: semi-diurnal, diurnal, and non-tidal. Crabs from the tidal estuaries had circatidal or circalunidian swimming rhythms with period lengths corresponding to the tidal period of their home estuary. Swimming occurred primarily on ebb tide. Crabs from the non-tidal estuary had a circadian rhythm of vertical swimming around the time of sunset. Such a rhythm has no obvious migratory significance and migration likely takes place though another mechanism.</p><p>Swimming behavior was also examined in the field in one non-tidal site and three tidal sites. Crabs were tethered in the field and swimming was monitored using archival pressure tags. Crabs tethered in the non-tidal site did not swim, possibly due to the lack of necessary environmental cues. Crabs at the tidal sites swam primarily on ebb tides. Swimming was greatest at the deepest site, which also had the strongest currents. This site is known to be a migratory area for spawning blue crabs. Decreased swimming behavior was observed at the two shallower sites, including one site that is known to be habitat for all stages of blue crabs. These results indicate that swimming behavior is variable among different areas in a single estuary. In areas where swimming is reduced, crabs may continue migrating seaward by walking or may spend additional time in that area to forage. Within each site, peak swimming generally occurred during the time of the most rapid decrease in water level, suggesting that hydrostatic pressure may serve as a cue for swimming. </p><p>Mark-recapture studies were conducted in three rivers (North River, South River, Adams Creek) in eastern North Carolina, and recently-molted female crabs were tagged to ensure a relatively constant time since molting. Most crabs traveled relatively short distances and were recaptured before producing a clutch of eggs. Individuals that moved substantial distances typically moved down-estuary. The Adams Creek canal, connecting Adams Creek with the Newport River estuary, functioned as a migratory corridor, as crabs from both Adams Creek and South River migrated down the canal, presumably using ebb tide transport. Many of the crabs that migrated down the canal into the Newport River were recaptured while ovigerous. Results of this study support the hypothesis that rapid long-distance migratory movements do not begin until production of the first clutch of eggs, though some down-estuary movement takes place by prior to production of the first clutch of eggs.</p><p>Female blue crabs mate following the terminal molt and begin moving seaward soon thereafter by walking and swimming. Once the appropriate salinity (> 22 ppt) is reached, the first clutch of eggs is produced and migration rate rapidly increases. Blue crab spawning biology should be similar throughout the range of the species. After taking latitudinal temperature variation and other local variables into account, results presented here should be applicable not only to blue crabs in North Carolina, but in other areas as well.</p> / Dissertation

In 2002, a proposal was submitted to divert water from the confluence of the Guadalupe and San Antonio Rivers to San Antonio, Texas. To investigate the potential impacts of diverting water from the Guadalupe Estuary, my research focused on the foraging ecology of the crane and population ecology of the blue crab, a documented crane food. During winters 2004-2005 and 2005-2006, I examined diets and optimal foraging patterns of territorial adult cranes at Aransas National Wildlife Refuge, Texas. To identify foods of greatest benefit to cranes, I used currencies of optimization to evaluate foraging gain, cost, and efficiency. Foraging benefit differed among foods, depending on the foraging currency used and resource targeted (e.g., energy). Wolfberry fruit, snails, and insects were consumed in the highest quantities, required the least foraging effort, and were generally associated with the highest foraging efficiency. Blue crabs and clams were important sources of protein and biomass. During September 2003-October 2005, I used novel artificial settlement substrates and modified methods of standard deployment to investigate the spatio-temporal patterns of blue crab terminal settlement and recruitment rates. Monitoring rates in shallow bay habitat and ponds of the interior salt-marsh revealed megalopal crabs were developmentally advanced when arriving to study sites and the extent to which young crabs infiltrated the salt-marsh increased with age. Such findings suggested sites represented optimal terminal settlement habitat and consequently critical nursery habitat. Model selection indicated water temperature before and during embryonic development was the best predictor of megalopal settlement, whereas juvenile recruitment was most influenced by recent precipitation. I studied the size-specific abundance patterns of blue crabs in and around mature salt-marsh. Using drop-trapping and throw-trapping methods, I collected monthly samples in several habitats during October 2004-March 2006. Interior-marsh habitats contained fewer but larger crabs than bay habitat. Crabs contributing greatest to biomass were smallest (11-30 mm carapace-width) in bay habitat, larger (31-80 mm) along interior-marsh pond edges, and largest (41-130 mm) in interior-marsh open water. Model selection revealed crab density was most influenced by micro-site characteristics (habitat, water column structure type and structural complexity). Overall, shallow bay provided important nursery habitat for young blue crabs and interior marsh ponds were important for dispersing juvenile and adult crabs.

The blue crab, Callinectes sapidus, represents an ecologically and economically important component of marine and estuarine ecosystems. In Florida, blue crab landings accounted for $9.6 million dollars during the 2010 fishing season. Accurate stock assessments for this valuable fishery are essential. Age is a critical biological component of accurate stock assessments; however, blue crabs and other crustaceans are especially difficult to age because of the complex nature of discrete growth. Biochemical extraction of an aging pigment, lipofuscin, was developed using blue crab eyestalks. The current study investigated the effects of freezing preservation on lipofuscin extracts and examined whether the extraction methodology, developed by Chesapeake Bay researchers, was useful for aging Tampa Bay blue crabs populations. Significant differences in lipofuscin index were found between samples frozen (2 weeks at -80°C) prior to analysis and those processed and assayed immediately (p < 0.001). Quarterly assays of the cohort of known-age individuals revealed a negative linear trend (y = -0.12x + 0.49, p < 0.001) in lipofuscin index over a 12-month period. This result suggests that extraction of lipofuscin is not appropriate for age determination of Florida blue crabs. Investigations into possible causes of the negative trend in lipofuscin suggest this method deserves further examination and refinement before it is acceptable as a reliable method for age determination in Florida blue crabs. Growth data of the known-age population collected during this study revealed that blue crabs in Tampa Bay can reach exploitable size in under sixth months and female crabs can reach sexual maturity within seven months of hatching. These growth patterns have the potential to enhance future Florida stock assessments.

The main focus of the current study was to quantify the chemical signals received by a blue crab (Callinectes sapidus) tracking a source in a laboratory flume. To make a direct linkage between tracking behavior and the odorant concentration signal, we developed a measurement system to quantify the instantaneous concentration field surrounding actively tracking blue crabs. A three-dimensional laser-induced fluorescence (3DLIF) system was designed and constructed to measure odorant concentrations around crabs tracking three source types: a continuous release with exit velocity matching the mean local velocity in the flume; a continuous release with a meander created by an upstream cylinder; and a pulsed release switching on and off and with the same mass flow rate as the other two plume types. The meandering and pulsed plumes were introduced to observe the effects of large-scale spatial (meandering) and temporal (pulsed) intermittency on crab tracking. Simultaneous with the chemical concentration measurements, crab position data was recorded for kinematic analysis during post-processing. In addition, concentration measurements were collected for the three plume types without crabs present in order to quantify the statistical characteristics of the plume structure The concentration signals arriving at the antennules and outer chemosensory organs, most notably the legs, were targeted due to the hypotheses that concentration bursts at the antennules mediate upstream movement and that spatial contrast at the leg chemosensors mediates turning. A sampling zone was placed in front of the crab's mouth parts and aligned with the crab carapace orientation to extract odorant bursts at the antennules. The data generally showed an increase in upstream walking speed when high concentration bursts arrive at the antennules location, which agrees with the hypothesis. Measurement of the odorant concentration at the outer chemosensors was less direct and involved placing a box upstream of the crab and sampled earlier in time in order to avoid shadowing interference. Based on the signal at the upstream sampling box, a general bias for turning was observed. Crabs casted transversely in response to the directional bias extracted from the upstream sampling box. A statistical analysis of crab behavioral response to concentrations at the antennules and outer chemosensors can be found in a (future) companion thesis written by Jennifer Page in the School of Biology. Data were also taken for the three plume types in the absence of blue crabs. The continuous plume average statistics displayed Gaussian behavior at nozzle centerline. The meandering plume data conformed to the meandering plume model of Gifford (1959), modified for an induced pseudo-periodic meander. The pulsed plume displayed characteristics intermediate between the cloud dispersion model (Townsend 1951, Chatwin and Sullivan 1979) and the Gaussian dispersion model for a continuous release. For the three plume types, the standard deviation of the concentration fluctuations was greater than the average concentrations, as time records consisted of intermittent high concentrations interspersed with concentrations close to zero.

Thesis (Ph. D.)--Georgia Institute of Technology, 2006. / Title from PDF t.p. (viewed on Oct. 28, 2006). Marc Weissburg, Committee Chair ; Mark Hay, Committee Member ; Lin Jiang, Committee Member ; David Dusenbery, Committee Member ; Don Webster, Committee Member. Includes bibliographical references (p. 115-122).

The world has never been more connected than it is today. While this is true for people, it is also true for Earth's flora and fauna. Unfortunately, this connectedness has contributed to unprecedented invasive species introductions around the world. Most introductions result in an introduced species dying out in the newly invaded territory and never becoming established. Other introduced species establish and persist for years, but never have a noticeable effect on local ecosystems. However, occasionally, an invasive species gets introduced to a new area and has negative impacts on native plant and animal life. The Indo-Pacific swimming crab, Charybdis hellerii, was introduced to the southern Indian River Lagoon (IRL) in the 1990s. Recently, it has been reported to be expanding its non-native range northward up the IRL and into more northerly east coast states. To better understand the ecological role C. hellerii fills in the lagoon and the threat it poses to the economically important and native Callinectes sapidus, this study utilized stable isotope analysis to assess dietary overlap and competition between these species. The results of this study indicate significant overlap in dietary resource usage suggesting C. hellerii is likely feeding on some of the same prey items and competing with native C. sapidus. Based on the increasing numbers of C. hellerii and their reported range expansion, they appear to be establishing populations in the U.S. and will continue to compete with C. sapidus. This could negatively impact C. sapidus populations in the IRL, which is bad for the crab, bad for the fishery, and bad for the lagoon. Further, competition in the IRL is concerning for the rest of the southeastern U.S. states that appear to be in the early stages of a C. hellerii invasion. The findings of this study illuminate the need for further research into the ecological niche C. hellerii is filling in the IRL and the interactions it is having with, as well as the effects it is having on, native species in the lagoon. This study and future research will allow fisheries managers to devise more effective strategies to limit the spread of C. hellerii and minimize the harm it can do in non-native environments.

Wastewater from the pressure cooking of blue crabs presents a difficult treatment challenge. COD concentrations in the range of 15,000 to 30,000 mg/L are found in this wastewater, with TKN concentrations above 2,000 mg/L. Direct discharge of the wastewater, which is currently allowed, adds nutrients to the Chesapeake Bay, and potentially creates local DO depletion in receiving waters. Anaerobic treatment of this wastewater was studied for the reduction of COD. Nitrification was studied for the conversion of ammonia, present at levels above 1,000 mg/L NH3/NHA4-N, to nitrate for possible denitrification. COD reductions averaging above 11,000 mg/L were found to occur in an upflow anaerobic filter operating with less than a 4 day HRT. Further COD reduction in the aerobic reactor resulted in a final effluent averaging 2,400 to 3,100 mg/L soluble COD with a corresponding BOD₅ of 110 to 340 mg/L. Nitrification proved to be inhibited, perhaps by the high levels of NH₃/NH₄-N in the effluent from the anaerobic stage. Nitrification did occur in a batch study, but only after extended aeration, and depletion of BOD. Non-degradable COD was estimated to be 2,900 mg/L in the anaerobic effluent. Monod model kinetic coefficients for the anaerobic stage were determined on a degradable COD basis to be: k = 0.68 day⁻¹, Ks = 3,500 mg/L (degradable portion), Y = 0.19, and Kd = 0.028 day⁻¹. The effect of the addition of certain trace metals (Fe, Ni, Co, Mo) to the feed was investigated. There was no improvement in COD removal performance, and slight inhibition may have occurred. / Master of Science

The Food and Drug Administration has recently expressed concern for the safety of seafood and seafood products. One of the concerns is the presence of Bacillus cereus in fresh blue crab meat. Bacillus cereus is a spore-forming pathogen whose spores survive the customary thermal treatments applied during cooking and pasteurization; therefore it could potentially present a health concern to consumers as the microorganism could increase to pathogenic levels. The objectives of this study were to evaluate the effects of a post-processing method i.e. high hydrostatic pressure treatment on the quality of fresh crab meat and to evaluate the effectiveness of high pressures on the inactivation of B. cereus spores. Fresh blue crab meat was pressurized at 300 and 550 MPa at 25° C for 5 min and stored at 4° C for 31 days to determine the pressurization effects on the microbiological, physical, and sensory quality of the meat. A pressure of 300 MPa caused a 1 log reduction in total aerobic plate count and a 3 day lag period, whereas 550 MPa inactivated 2 logs in total aerobic plate count with no evident lag phase. Physical and sensory qualities of pressurized crab meat were not statistically different from the untreated crab meat (P>0.05). A pressure of 300 MPa extended the shelf-life from 17 to over 24 days with the prevalence of Carnobacterium piscicola at the time of spoilage. Crab meat treated with 550 MPa was not rejected by sensory panels at day 31 and Enterococcus spp. was identified as the predominant microorganism. High hydrostatic pressure (550 MPa at 40° C for 15 min) inactivated less than 1 log (0.66 log) of B. cereus spores inoculated in fresh crab meat. The meat essentially had a protective effect on pressure inactivation of the spores. During storage (31 days), surviving B. cereus was suppressed and outgrown by the other pressure resistant microflora at a storage temperature of 12° C. At 4° C, B. cereus could compete with the other pressure-resistant microflora and was isolated even at the end of the storage period (day 31); however, diarrheal toxin was not detected in any stored samples. / Ph. D.

The dehydration rates of crabs during low temperature storage and various cooking processes were determined. Season, cooking time, and cooking method significantly affected the weight loss of crabs. The thermal energy (F250 ) crabs received during a commercial cooking process was evaluated by season, cooking method and time, and crab type. The effects of sex, size, and type (sexual maturity) of crab and season on the yields of lump, top flake, bottom flake, and claw and total meat were examined. The effects of cooking time and method and storage time on meat yield was also determined. During summer, male crabs yielded more lump, claw, and total meat than female crabs, and clean female crabs yielded more lump, top flake, and total meat than sponge female crabs when retort cooked for 10 minutes. / Ph. D.

In recent years, the blue crab fishery has become the main source of income for Virginia's watermen. This fact, along with growing concerns of overharvesting and uncertainty about the amount of effort in the fishery, has led to calls for more complete data on the fishery. This study examined the characteristics of Virginia's blue crab fishery, through an extensive survey of crab pot license holders conducted on a monthly basis from March to November of 1992. Along with a description of the people in the fishery, this study also modeled prices, harvest levels, and income levels for the blue crab industry. Because the models were interactive in nature, the effects of various fishery management strategies were also analyzed. The main emphasis of the policy simulations was to discover what impacts the different strategies had on harvest and income levels. The results of the simulations showed that many of the policies currently under consideration will have only a small impact on overall harvest and income levels, but there are some larger distributional effects among different firm classes. The findings of this study suggest that in order to gather accurate and useful data on the fishery, the random surveying techniques of this study should be continued over a period of years. / Master of Science