Rates of uptake of organic and inorganic suspended particulate material by suspension feeding bivalve molluscs have been studied since the nineteenth century (see Viallanes, 1892) . Studies have investigated molluscan feeding mechanisms, filtration capabilities, food assimilation and metabolism. The bulk of this work has been directed towards the mussel Mytilus edulis Linnaeus and the oyster Crassostrea virginica Gmelin (see reviews by Galtsoff, 1964; Ali, 1970; Jorgensen, 1975; 1976; and Winter, 1978). More recently the growth of mussels, oysters, clams and scallops has been quantitatively studied in controlled systems to assess the biological potential of these molluscs in an aquaculture setting (Hartman et al., 1973; Tenore & Dunstan, 1973; Tenore et al., 1973; Kirby-Smith & Barber, 1975; Walne & Spencer, 1974; Epifanio & Ewart, 1977; Winter, 1978). Direct and indirect methods for estimating filtration rates of molluscs (Ali, 1970) have yielded such a wide range of results that the validity of comparisons between different studies is sometimes questionable . Variables such as the mollusc species and size, as well as the nature and concentration of the test suspension contribute to differences in observed filtration rates. The present study simultaneously examined three mytilid speeies of comparable size (85-125 mm shell length) . Each mussel species was tested under the same conditions for its ability to filter and assimilate the unicellular algae Dunaliella primolecta Butcher at suspensions of 5, 12, 25 and 50 x 106cells/1. Filtration rates and food assimilation were determined in test chambers incorporating a new flow-through design which eliminated the possibility of recirculation of the algae test suspension. In previous studies recirculation of the test suspension has occasionally resulted in the under-estimation of filtration rates. Growth comparisons were made among individuals of each species held under the same set of environmental conditions. Two of the mussel species examined in this study, Mytilus edulis L. and Perna canaliculus Gmelin, are presently under cultivation as a human food source. The third species, Mytilus catifornianus Conrad, may be viewed as a potential candidate for aquaculture due to its size, abundance and value as a source of protein. The California mussel, M. catifornianus, is found along the west coast of North America from the Aleutian Islands to Baja California (Soot-Ryen, 1955). The bay mussel, M. edutis , is widespread in the northern and southern hemispheres (Stubbings, 1954). The green-lipped mussel, P. canaliculus, is found throughout New Zealand waters where it colonizes both exposed rocky coasts and quiet bays (Morton & Miller, 1968; Paine, 1971).

A changing climate has been identified as a major driver of changes in marine species’ distribution, phenology, and habitat selection in recent decades and is expected to continue to influence these traits. These changes are not only happening in our oceans, but within coastal habitats as well, where waters are susceptible to sudden changes in temperature and oxygen levels are influenced by nutrient inputs. These changes which will likely impact fish species that utilize these areas as nurseries, spawning habitat, or foraging grounds. In this dissertation I consider climate impacts on two important predators, the sandbar shark (Carcharhinus plumbeus) and cobia (Rachycentron canadum), both of which rely on coastal habitats like Chesapeake Bay for their survival. I used a series of physiological, survey, tagging, and modeling studies to estimate the current and future impacts of climate change on these two species. Sandbar sharks are unable to handle temperatures as warm as 32°C physiology, but in the wild prefer temperatures between 22-26°C. As a result, I estimate bottom habitat losses in Chesapeake Bay by end-of-century for juvenile sandbar sharks. Although they are relatively intolerant of hypoxia (critical oxygen concentration = 3.5 mg l-1), juvenile sandbar shark appear to prefer areas on the fringes of hypoxic zones to avoid larger sharks and find more abundant prey. Therefore, the continued reduction in oxygen levels throughout the entire water column actually improves juvenile sandbar shark suitable habitat. Being a bottom dwelling species, sandbar shark in Chesapeake Bay may be forced to remain in non-preferred bottom habitat, move up in the water column, or shift to shallower habitats. Cobia are tolerant of high temperatures (32°C) and low oxygen (1.7-2.4 mg/l) which should allow them to withstand the detrimental effects of climate change in Chesapeake Bay, at least through mid-century. Hypoxia and elevated temperatures reduce survival of cobia that are exercised to exhaustion. Although the physiology experiments and habitat models suggest cobia will withstand climate change through mid-century, declines in their suitable habitat in Chesapeake Bay are expected by end-of-century. I project arrival time to occur earlier and departure time to occur later when temperatures are warmer and that by mid- and end-of-century cobia may spend on average up to 30 and 65 more days, respectively, in Chesapeake Bay. As conditions worsen in more southern estuaries, cobia may shift spawning habitat in estuaries and bays further north, such as Delaware Bay, New York/New Jersey Bight, and Long Island Sound, where conditions are more thermally suitable. Over the next 60-80 years, suitable cobia habitat is projected to shift northward from spring to fall and to decrease over the U.S. continental shelf. As cobia shift into new areas, the development of regulations in more northern states will become necessary to promote a sustainable cobia fishery. As species shift their distributions as a result of climate change, it is imperative that we understand why and how these shifts are occurring so that both managers and fishers can ensure important resources continue to be fished sustainably.

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.

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.

No description available.

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / A combination of overexploitation and destructive fishing practices, such as bottom trawling, have depleted native populations of groundfishes in coastal New England and reduced benthic community diversity. The Stellwagen Bank National Marine Sanctuary (SBNMS) in the southern Gulf of Maine is partially overlapped by the Western Gulf of Maine Closed Area (WGMCA). The WGMCA is closed to commercial fishing for groundfishes managed under the Northeast Multispecies complex and the use of bottom trawling fishing gear is prohibited to protect essential fish habitat. This has reduced fishing pressure and benthic disturbance levels. The area of the SBNMS outside of the WGMCA is still disturbed by intensive commercial fishing for much of the year. Key questions for this area are (1) How does the higher level of disturbance in areas outside of the WGMCA affect SBNMS groundfish communities?, (2) Is the WGMCA effective at increasing the diversity, abundance, and biomass of groundfishes in the SBNMS?, and (3) How does the decrease in disturbance impact groundfish trophic ecology? A comparison of the groundfish communities inside and outside of the WGMCA within the SBNMS was carried out via trawl sampling. Results show that groundfish communities are more diverse inside the WGMCA than outside. Additionally, several commercial groundfish species had higher abundance and/or biomass inside the WGMCA. Stable isotope analyses showed that prey items differed for some species inside and outside of the WGMCA, but trophic levels were unaffected. Finally, stable isotope analyses of five groundfish species provide evidence that groundfishes may display a high level of foraging area fidelity. Primary conclusions include: (1) the protection of groundfish habitats from trawling disturbances paired with reduced fishing pressure will result in increases in community diversity and abundances of groundfishes, (2) groundfish ecology should be considered on a small geographic scale due to apparent site fidelity, and (3) if the entire SBNMS were closed to bottom trawling and commercial fishing, it could help to rebuild overexploited groundfish populations in the southern Gulf of Maine and serve as a source population for the remainder of the Gulf of Maine and adjacent shelf environs. / 2999-01-01

The causes of increasing outbreaks of Acanthaster planci on the Great Barrier Reef have been a point of hot debate in recent years. It is unknown whether the increased success is due to nutrient runoff, salinity levels, or a decrease in predation, among other possibilities. In this paper I argue that the primary influence on outbreak status is sea surface temperature. From existing literature, I demonstrate that sea surface temperature in the Great Barrier Reef has increased by 0.4°C per year over the past three decades. I attempt to tie this increase with an increase in frequency of A. planci outbreaks on a selection of reefs throughout the Great Barrier Reef region. Due to the development of A. planci, specifically the fact that it takes them between 2 and 3 years to reach full maturity, I examined the potential relationship between an outbreak and the sea surface temperature 1 and 2 years before the event. Through my exploration of the data and my subsequent data analysis, it is clear that there are no statistically significant results when comparing the three classifications of outbreak (active, incipient, and recovering) and not outbreaking populations with temperature at each of the three time relationships. However, when I considered the three stages of outbreak to be “affected” and those not outbreaking to be “unaffected”, I found a statistically significant relationship. This finding has important implications when looking at the temperature changes that have been predicted for the Great Barrier Reef region due to global climate change. If the water temperature continues to increase, A. planci will more often be living within their optimal temperature range and will be more successful, continue to have major outbreaks that devastate the reef ecosystem, and eventually destroy it all together.

The internal morphology of fixed specimens of Antarctic pycnogonids WDS examined. Theories postulated during the course of these histological studies were then tested and modified by observations on live material and specimens fixed specially for histochemistry on visits both to the Arctic and d Antarctic. Live material was also transported back to Britain from these regions and cultured in refrigerated marine aquaria. The digestive system was studied in considerable detail. It is suggested that digestion is intracellular with gut cells changing their morphology during their lifetime. Embryo cells develop into Absorptive cells which at some stage take up a glandular appearance but not a glandular function. There are therefore two gut cell types, 'Embryo' and 'Absorptive/glandular'; this is in disagreement with some previous authors who separate the latter. The rele of the gut cell in the light of present day lysosome theory is discussed and a re-interpretation of work by previous authors suggested. It is found that the digestive process is slow and the prey tastes of the species studied, catholic. Furthermore, it is found that some species can survive for long periods without appearing to feed. Suggestions are made as to the significance and mechanisms of these phenomena. Mass transport in the body cavities is considered flnd compared with that of Hydra, an animal with which previous authors have made comparisons; - their philosophy is questioned. Blood flow, heartbeat and intestine movements are also considered and suggestions for future studies made. The role of blood itself is studied a possible clotting system described. Preliminary experiments on blood electrophoresis and chromatography indicate that such techniques may be useful in clarifying some complexities of pycnogonid classification and might provide a means by which future workers in the field might better link nutritional state, mass transport, digestion and external environment conditions.