Blue catfish Ictalurus furcatus is an invasive species of great concern in coastal habitats throughout the eastern United States, inclulding the Chesapeake Bay and its tributaries. In this dissertation, I use field surveys, laboratory experiments and quantitative modeling to provide insights into several aspects of blue catfish biology at the individual level. In chapter 1, I characterize and compare patterns in growth and body condition in blue catfish populations in the James and York river subestuaries during two stages of invasion. Both the mean growth rate and mean body condition of blue catfish declined in the recent period in response to increases in population abundance. In chapter 2, I uncover life-history plasticity in the reproductive biology of the species: blue catfish in the James River mature at a smaller mean size but provision a greater amount of energy into reproduction than York River fish, which exhibit lower densities than James River fish. In chapter 3, I assess the food demands of blue catfish in a laboratory experiment. I demonstrate that blue catfish have low metabolic demands, as expected for a relatively sedentary benthic fish. Importantly, blue catfish had high survival and significant growth at food levels as low as one third of the maximum, suggesting that the species has a high tolerance of starvation and that individuals may be able to invade and establish in low food habitats in coastal waters. In chapters 4 and 5, I report the results of two laboratory experiments studying the effects of increased salinity on survival, growth and body condition of blue catfish. Blue catfish, typically considered a freshwater species, was found to have a higher salinity tolerance (72-hour LC50 = 15.7 psu) than many freshwater fishes, suggesting the potential of the species to expand its range into most subestuaries of the Chesapeake Bay particularly during wet seasons. Habitats with salinities around 4 psu seemed particularly suitable for blue catfish as growth and body condition were maximized at this salinity despite the lower mean ingestion rates than fish maintained in freshwater. Finally, in chapter 6, I parameterize a full life-cycle bioenergetics model for female blue catfish using data from the literature and from the other chapters of this dissertation. The model supported the implications from other chapters that blue catfish have low maintenance costs, relatively high resistance to starvation and a plastic ability to fuel reproduction even in environments with low food availability. The model, together with results from other chapters, also opened up avenues for further research on characterization of the energetic basis for the observed phenotypic plasticity, identification of physiological modes of action by which salinity might limit survival, growth and reproduction of blue catfish, and ultimately the identification of coastal habitats that might support self-sustaining populations of this invasive fish. This research highlights the need for management efforts to control blue catfish populations in subestuaries where they are already established and to limit the range expansion into novel habitats. Towards this end, this dissertation provides important information on vital rates of blue catfish needed for population models that can be used for management strategy evaluations.

To protect and manage ecosystems over large spatial scales, repeated mapping with remote sensing, such as aerial photography, is valuable, but several potential problems need to be overcome to generate accurate maps. For instance, to monitor submerged aquatic vegetation (SAV), such as seagrass, satellite imagery must often capture seasonal and interannual variation as well as disturbances. We used a model system, SAV and the blue crab Callinectes sapidus in the lower Chesapeake Bay, to examine (i) if Planet Lab (PL) satellite imagery can be used to accurately estimate SAV coverage by comparing PL images coincident with those of the VIMS SAV survey; (ii) if PL imagery can capture seasonal and episodic changes in SAV accurately; and (iii) if PL and VIMS SAV survey imagery can be integrated to assess the relationship between SAV nursery habitat and recruitment of young juvenile blue crabs in mid-summer through early fall. To do so, we analyzed data from six selected sites with high salinity in lower Chesapeake Bay. Our findings were (i) PL satellite imagery was a suitable surrogate for VIMS aerial surveys of SAV conducted annually at the selected sites, with the caveat that PL imagery is at a lower resolution (3 m) than the VIMS SAV survey (24 cm), which could affect the utility of PL imagery for some goals; (ii) PL imagery was able to capture seasonal and episodic changes in SAV cover in the Bay; and (iii) remote sensing imagery taken in late spring and early summer was not representative of SAV cover available to the blue crab during the recruitment period in mid-summer through fall. Consequently, PL imagery can be used to estimate SAV bed area over time scales that are relevant to recruitment of the blue crab in lower Chesapeake Bay. Understanding SAV dynamics and future effects of climate change on SAV can be improved with broad-scale data from remote sensing techniques, such as aerial photography and satellite imagery. However, new platforms such as Planet Lab can provide accurate spatial and temporal distribution patterns for SAV beds relative to abundance of the blue crab during critical phases in its life history. At two locations in the York River, lower Chesapeake Bay, we conducted a mensurative field experiment by sampling percent cover of SAV (eelgrass Zostera marina, widgeon grass Ruppia maritima) and algae (mostly Gracilaria vermiculophylla), density of blue crab juveniles, bed area by Planet Lab, and select independent variables bimonthly over two years. The main findings were: (i) juvenile blue crab density was inversely related to SAV bed area, but reductions in crab density as bed area increased were more than offset by higher total abundance of crabs as bed area enlarged; (ii) crab density was positively related to percent cover of algae (Gracilaria), Ruppia and Zostera; (iii) location, year, season and water depth were not significant predictors of crab density in SAV beds after accounting for the effects of bed area and SAV percent cover; and (iv) potential loss of Zostera in the lower Chesapeake Bay due to global warming was projected to cause either only a modest reduction in crab density if other SAV species do not compensate and bed area remains constant, or crab density could even increase if algae and Ruppia were to compensate for the loss of Zostera.

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No description available.

The soft-shell clam, Mya arenaria, is a benthic, filter-feeding, infaunal clam typically found in intertidal and shallow subtidal waters. Chesapeake Bay stocks of M. arenaria have been depleted since the 1960s due to various factors including predation, temperature, low recruitment, habitat loss, disease mortalities, and commercial harvest. As an important prey item for many commercial species, low abundances of these clams are mostly the result of the voracious appetite of the blue crab, Callinectes sapidus. In addition to predation, summer water temperatures in the Chesapeake Bay are likely driving the low abundances of M. arenaria, as water temperatures commonly surpass the optimal thermal range for this species (2 – 28 C). This study addresses several gaps in our understanding of M. arenaria, and the conditions required for an aquaculture industry for this species to be successful in the Chesapeake Bay. A series of caging experiments and mesh experiments were conducted over two years (2018 and 2019) and at two tidal zones (intertidal and subtidal) in Timberneck Creek and Catlett Islands, VA to examine the recruitment and survival of M. arenaria. In 2018, cages were constructed of ¼” (0.63 cm) VEXAR mesh and cut-off 5-gallon buckets and compared to open plots in two seasons, spring and fall. In 2019, cages were constructed of perforated aquatic plant pots with one of two mesh types, netting or VEXAR, and one of two mesh sizes, ¼” or ½”, cable tied over the top of each cage. One open cage (no mesh covering cage) treatment served as a control at each of the tidal zones at each site. There were two replicates of each caging treatment at each site and tidal zone. Each cage was filled with sediment and 10 marked and measured M. arenaria were planted ~2.5 cm in sediment. One cage of each treatment at each site and tidal zone was collected and examined 6 months from deployment date (and the remaining cages one of each treatment) were collected and examined 12 months from deployment date. At each tidal zone, “iButtons” (temperature loggers) were deployed to collect continuous water temperature measurements. In the lab, clams were identified, counted, measured, and analyzed for organic content using standard ash-free dry-weight (AFDW) measurements. The presence of crabs that had entered into cages made a significant difference in the survival of outplanted clams across all treatments for both tidal zones. Net treatments yielded significantly greater densities of recruits as compared to open and VEXAR treatments in both tidal zones. Overall, the presence of caging and netting increased Mya arenaria survival and recruitment. Netting offered enough protection from predators to allow clams to grow to harvestable sizes within six months. Caging mesh type and size played a role in M. arenaria recruitment and survival, with recruits tending to be more abundant in the ¼” net treatments. This study provides evidence that protection by caging and netting increases survival and recruitment of Mya arenaria – indicating that it is possible to have a successful soft-shell clam aquaculture operation developed in the Chesapeake Bay.

<p>Rainbow trout took up Zn from both the diet and the water. Trout on a low Zn diet became Zn-deficient, based upon mortality, lack of growth, and depressed plasma protein and hematocrit. Both plasma and whole body [Zn] were also depressed. Elevated [Zn], in either diet or water, reversed all symptoms of Zn deficiency. At high [Zn], Zn was taken up in excess of requirements, but in an attenuated fashion. These results support a relative homeostasis for Zn for both plasma and whole body, but also indicated that Zn uptake from water and diet were partially independent. There was no overt toxicity. Metal-binding proteins, important in mineral metabolism, were induced by this exposure in gill and intestine but not in liver.</p> <p>The gill was identified as the major site of Zn uptake from the water by the use of an in vitro preparation which directly measured flux rates. Pre-exposure of trout to soft water for 5 days gave considerably higher influx rates than occurred in tapwater-acclimated trout, probably by stimulating proliferation of gill chloride cells. Zn influx in soft water, studied from 0.4 to 7.5 mg Zn/L followed saturable, first-order kinetics, suggesting a restricting pore or carrier mediation. Influx was studied in vivo for 24 h using a novel technique which overcame the limitations of non-specific adsorption found with traditional methods. Influx rates measured with this technique confirmed the saturable nature of influx, but were much higher. Waterbone Ca interacted with Zn influx in two separate ways. Acute increases in [Ca] up to 5 fold showed a competitive interaction, suggesting that Zn and Ca compete for the same mechanism of branchial entry. Acute removal of Ca however revealed in addition, a large influx with increasing [Zn], indicative of opening of a paracellular leak pathway across the gill.</p> / Doctor of Philosophy (PhD)

<p>The osmorespiratory compromise is the trade-off between high gill permeability for oxygen uptake and low gill permeability for conservation of ions in fish. The fundamental purpose of this study was to examine facets of the osmorespiratory compromise in freshwater fish under conditions of extended exercise and acute hypoxia, in light of previous research identifying very different gill morphometric and ionoregulatory modifications in the hypoxia-tolerant Amazonian oscar (<em>Astronotus ocellatus</em>) and the hypoxia-intolerant rainbow trout (<em>Oncorhynchus mykiss</em>). A technique using [³H]polyethylene-4000 ([³H]PEG-4000) for branchial paracellular permeability measurement was developed, and then applied to investigate the osmorespiratory compromise during extended swimming. Methods were developed to overcome the challenges of renal [³H]PEG-4000 loss, respirometer surface adsorption, and freshwater drinking of the chemical. In both trout and oscar, corrections were employed for these sources of error – leading to findings that in both species, branchial [³H]PEG-4000 permeability was not rectified and freshwater drinking was quite high. In both species, during an 8-h swim (1.2BL/s), oxygen consumption rate increased by 75-90%; drinking rate remained high but did not increase. Branchial paracellular permeability increased by 61% during exercise in trout but remained constant in oscar. The methods developed here can be widely applied to future studies of branchial paracellular permeability.</p> <p>Unidirectional fluxes (by ²²Na) of sodium, and net fluxes of potassium, ammonia, and urea were observed during a 2-h nomoxia:2-h hypoxia (30% O₂ saturation):2-h normoxic recovery protocol – to identify adaptive trends across phylogenies and/or environments in North and South American teleosts. Strategies for coping with hypoxia appeared to be environmentally, rather than phylogenetically linked, since both the oscar (perciform) and the tambaqui (<em>Colossoma macropomum</em> – characiform) displayed characteristic permeability reduction (of apparent transcellular origin); both frequently encounter severe hypoxia in their natural habitat. Two North American perciforms, pumpkinseed (<em>Lepomis gibbosus</em>) and bluegill sunfish (<em>Lepomis macrochirus</em>) which live in less hypoxic environments, increased branchial ion leakage as in the hypoxia-intolerant trout. Four Amazonian tetra species (all characiformes: <em>Paracheirodon axelrodi, Hemigrammus rhodostomus, Moenkausia diktyota,</em> <em>Hyphessobrycon bentosi rosaceus</em>) which experience intermediate hypoxia in their native Rio Negro presented variable responses. Finally, during a 4-h swim at1.2BL/s, branchial ion fluxes were not reduced but elevated in oscar, indicating that ionoregulation in this species occurs primarily transcellularly, and that adaptive strategies to one manifestation of the osmorespiratory compromise (hypoxia) may not apply to another (exercise).</p> / Master of Science (MSc)

Pelagic forage fishes play critical roles in productive marine food webs by providing a link between zooplankton and piscivores and transferring energy from feeding grounds to other ecosystems. The amount of energy moved to higher trophic levels or new systems is directly linked to the consumption rate of pelagic forage fishes. In the Gulf of Maine, Atlantic herring (Clupea harengus) is the dominant forage fish; the purpose of this study is to determine their specific consumption rate (g prey/g fish/day). Using fish collected in autumn 2012 and spring 2013, we applied a mercury mass-balance model to estimate individual and population consumption of Atlantic herring in the Gulf of Maine. Our results suggest that the specific consumption rate increases from age 1.5 until age 6 (years) and then asymptotes. These estimates were contradictory to much of what exists in the literature; for most fishes, specific consumption estimates decrease with age and overall are much lower than our estimates. We looked further into our results to explore the underlying cause of the increase in specific consumption rate. We combined the mercury mass-balance model with a Wisconsin (WI) bioenergetics model and ran several simulations adjusting the most sensitive factors in each--prey mercury in the former and activity in the latter. The results of our simulations showed that an increase in activity relative to age and mass can best explain the increase in the consumption rate of Adult herring. This suggests that an ontogenetic shift to migration in adult Atlantic herring results in increased energy demand with age, and ultimately increased consumption.

Restoration of oyster reef structures rehabilitates habitats and the multi-level ecological communities built on eastern oysters (Crassostrea virginica), the keystone species. Quantitative descriptions of ecological interactions within a habitat are required to delineate essential fish habitats for management and protection. Parallel development of primary (oysters) and secondary trophic levels (benthic fishes) offer an ecological metric of restoration progress over time. The interaction between larval oysters and larval fishes (e.g., Gobiosoma bosc, Chasmodes bosquianus) is quantitatively examined. Oyster settlement estimates for Palace Bar reef, Piankatank River, Virginia are of the same order of magnitude as field densities of recently settled oysters. Benthic fish settlement estimates are within an order of magnitude of observed adult densities. Zooplankton community composition around the reef is temporally variable and plankton densities range from 10 2--106 animals per m3 across temporal scales. Nocturnal densities of naked goby and striped blenny larvae around Palace Bar reef were 3 to 4 orders of magnitude higher than densities observed during daylight hours. Diurnal changes in larval fish abundance near Palace Bar reef are related to ambient light intensities and diurnal vertical migration by prey species. Naked goby, striped blenny, and feather blenny (Hypsoblennius hentzi) larvae selectively consumed bivalve veligers, in multi-factorial laboratory feeding experiments. Temporal co-occurrence of larval oysters and larval fishes was not observed in 1996 field collections although historic oyster settlement data strongly support the probability of co-occurrence during most years. Two different methods are used to estimate the larval oyster - larval fish interaction in the absence of field data. Given existing oyster and fish demographics on Palace Bar reef, larval fishes have the capacity to drastically reduce, perhaps eliminate, local veliger populations if they co-occur. The strength of this interaction is directly related to oyster demography-fecundity relationships. In the absence of veligers, larval fishes consume other plankton taxa that are abundant around the reef. Naked gobies and striped blennies are generalists. Oyster reefs provide optimal rather than essential habitat. Reef restoration will facilitate development of related ecological communities by providing optimal habitat conditions for these ubiquitous estuarine species.

Monitoring of Bear Lake was conducted in 1981 and 1982 to describe the current limnology and trophic state of the lake. The nutrientt loadings of various parameters were measured from April, 1981 through June, 1982. The rate of coprecipitation of phosphorus was determined for different initial phosphorus concentrations by use of non-algal assays. Algal bioassays with Selenastrum capricornutum were used to determine the reduction in potential algal biomass as a result of the coprecipitation of phosphorus. The lake exhibit-.ed chemical characteristics indicative of mesotrophy or eutrophy. Total phosphorus values averaged 11μg/1 for 1981 and 20 μg/1 for 1982. A hypolimnetic accumulation of phosphorus was also not:ed for the stratified periods. Addittionally, hypolimnetic oxygen deficit values were indicative of mesotrophy in 1981 and eutrophy in 1982. The chlorophyll concentrations were characteristic of oligotrophic conditions during both years however. Phosphorus was found to be limiting production approximately 85% of the year. The Bear River Contributed approximately 60% of the total phosphorus loading to the lake in 1981 and 50% in 1982. Overall, the total phophorus loading increased 195% between the dry year, 1981, and the wet year, 1982. Vollenweider's (1976) phosphorus loading model described the loading to Bear Lake as indicative of mesotrophic conditions in 1981 and eutrophic conditions in 1982. Calcium and magnesium concentrations fluctuated widely throughout the year. The Mg:Ca molar ratio varied from 1:1 in the spring to 3.5:1 in the fall. Total hardness values did not vary in response to the changing ionic concentrations and this was attributed to preferential replacement of precipitated calcium by the Bear River inflow. Non-algal assays quantified the removal of phosphorus by coprecipitation at increasing initial phosphorus by concentration. The rate of removal initial decreased substantially as phosphorus levels increased with a shift in reaction order from second order to first order noted at approximately 50 μg/1. Predictive models were derived from the initial assays and verified with data from a separate experiment which use filtered Bear Lake water. The models accurately predicted the amount of phosphorus removed by coprecipitation at all phosphorus levels. Algal bioassays in synthetic Bear Lake and soft-water media were used to evaluate the efficiency of the coprecipitation mechanism when in competition with algae for phosphorus. An average reduction in biomass of 40% was noted between the media at similar nutrient levels.