Several south-western Cape Ecklonia maxima communities were examined to determine their basic demography and the effects of substrate selection. Overall percentage substrate composition, stipe lengths and substrate attachment for all kelps were recorded at four sites off the Cape Peninsula. Strength of attachment to different substrates was measured. Selection for substrate type was analysed using Jacobs' index. A substrate of Pyura stolonifera was the most common for juveniles, whereas substrates of rock and conspecific holdfasts were dominant in the larger individuals. No significant difference in strength of attachment was found for kelps less than 50 cm. An analysis of the frequency of single- and multi-stiped holdfasts indicates that survival on rock is greater than on that of holdfasts. Size-class distributions indicate that E. maxima is a shade-tolerant species showing advanced regeneration. Establishment on rock may occur through episodic recruitment escaping grazing pressure. In areas with low grazing intensity, recovery from catastrophic storms may be limited by competition with understorey algae.

A study has been made of a select group of marine zooplankton - the Chaetognatha. The analysis was done from a community viewpoint, that is, an objective technique was used to identify related groups of the Chaetognatha and these groups were then correlated with the distribution, abundance and fecundity of the individual species and with the existing hydrographical conditions. Competitive relationships among the species for habitats and niches were also examined.

Seaweed extracts are known to have a stimulatory effect on the growth and development of plants. This study investigated the effect of applying a commercial seaweed concentrate (kelpak) on rhizobia growth (Bradyrhizobium strain CB756 and Bradyrhizobium japonicum strain CB 1809) and nitrogen fixation in cowpea ( Vigna ungulata L. Walp.) and soybean (Glycine ma.x L. Merr.) plants. Two concentrations of Kelpak (1:100 v/v and 1:500 v/v seaweed concentrate dilutions) were applied to pots with seeds or seedlings at sowing and after every 14 days (1:l00A; 1:500A), at sowing and after every 7 days (1:100B; 1:500B) or after germination and after every 14 days (1: l00C; 1:500C). From the first experiment, cowpea plants in the various treatments showed no change in shoot biomass. The root biomass was significantly inhibited in treatment 1:100B relative to the control. The nodule dry matter of cowpea was reduced in 1:100A, 1:100B and 1:100C Kelpak concentrations compared to control, with a significant increase only in 1:100B Kelpak concentration. As a result, cowpea plants showed the highest total biomass in 1:500B treatment. Although shoot N in cowpea plants remained unchanged under the various kelpak treatments, root N was significantly reduced. Soybean plants showed a significant decrease in shoot and root biomass compared to the control. Nodule dry matter was lowest for soybean plants in Kelpak treatments 1:500B, 1:100B and 1:100C. As a result, there was a decrease in soybean total growth in treatment 1:500B compared to the control. Total N in shoots and roots was highest in soybean plants growing in 1:500A relative to the control. Culturing cells of Bradyrhizobium strain CB756 with Kelpak showed a significant increase in growth at 1:100 and 1:500 dilutions compared to the control. However, over the 93 h period with sterile Kelpak culture there was an inhibition in growth of strain CB756 relative to the control. Beyond the 93 h there was a significant increase in growth of Bradyrhizobium japonicum strain CB 1809 in all Kelpak treatments. The 1:100 concentration showed the highest bacterial growth compared to the control and the other treatments. These data suggests the presence of an active molecule in Kelpak that stimulates rhizobial growth and its symbiotic interaction with legumes.

Coccolithophores are a biogeochemically important phytoplankton group, fulfilling an important role in the global carbon cycle through primary production and the formation and export of calcium carbonate. Despite this biogeochemical importance, relatively little is known about their ecophysiology, for example their response to nutrient availability in terms of both macronutrient (nitrate, phosphate) and micronutrient (trace metal) or how this impacts on their competition with other phytoplankton groups (e.g. diatoms, Synechococcus). Hence, this study investigated the response of coccolithophores to trace metal (iron, zinc and cobalt) additions in the high latitude North Atlantic (Iceland and Irminger basins) and the Southern Ocean (Great Calcite Belt, Scotia Sea). The response of coccolithophores to environmental conditions was investigated by examining distribution patterns in situ and in targeted bioassays where natural communities were incubated with elevated levels of trace metal concentration. The wide range of initial conditions for these bioassays (e.g. temperature, macro- and micro-nutrient availability and phytoplankton community composition), provided valuable insights into coccolithophore responses to trace metal addition across a range of different biogeographic regions. These responses were investigated in terms of coccolithophore cell abundances, species composition, calcite production and growth rates, and were contrasted with responses of the total phytoplankton community (chlorophyll α) and abundances of diatoms and other phytoplankton groups (e.g. Synechococcus). The major finding of this thesis is that iron addition positively enhances coccolithophore growth rates and calcite production in both the Northern and Southern subpolar oceans. Another significant finding was that zinc addition also positively enhanced growth rates of coccolithophores (and diatoms) in a number of bioassays across the Great Calcite Belt (Southern Ocean). Thus, the trace metals iron and zinc are important micronutrients to consider in regulating coccolithophore growth and calcite production. As climate change potentially altering the flux of such trace metals to the ocean it is therefore important to further investigate the role of these micronutrients in regulating coccolithophore communities and their biogeochemical impact.

Hagfishes (Myxinidae) are common in deep waters of the Gulf of Mexico (GOM). Two of the species found in the GOM are endemic to the area and potentially provide key ecosystem services (e.g. generate substrate turnover and recycling of organic matter by consuming carrion falls) to the deep environments of the Gulf. Yet, very little is known about hagfish life histories and ecology. I investigated inter and intraspecific variations in trophic structure of Eptatretus springeri, Eptatretus minor, Myxine mcmillanae, including variations along relevant environmental gradients. At the time of this study, the Gulf of Mexico had recently experienced an environmental disaster with the Deep Water Horizon (DWH) oil spill. As a result, I also investigated the potential effects of the DWH oil spill on hagfish trophic structure, and the potential for higher bioaccumulation of mercury (Hg) in their muscle tissue. Feeding ecology and trophic structure were investigated using nitrogen (δ15N), carbon (δ13C) and sulfur (δ34S) stable isotopes and variability in the lipid content (Δδ13C) of each species was used as an indicator of periods of feeding and fasting. I was able to differentiate the isotopic niche of each of the species and determine the different feeding ecologies of E. springeri and M. mcmillanae. The isotopic niche of E. minor overlaps with that of E. springeri and M. mcmillanae. The most depleted mean δ15N values were observed in E. springeri (12.8‰), followed by E. minor (13.9 ‰) and M. mcmillanae (14.9‰). Eptatretus springeri had the highest (Δδ13C), lowest trophic level (δ15N) and exhibited the most isotopic variation with depth. This could suggest this species is an active predator that feeds regularly, and potentially relies on scavenging only to supplement its diet. Eptatretus minor had slightly higher Δδ13C, intermediate but depleted δ15N, and higher δ15N isotopic diversity. These characteristics suggest a more opportunistic foraging behavior for this species, potentially feeding on prey items from several trophic levels. Myxine mcmillanae had the highest δ15N but lowest Δδ13C, and no variation in δ15N with depth. These trends indicate this species could be experiencing irregular feeding with periods of fasting, potentially due to a mostly scavenging behavior and occasionally feeding on larger but infrequently available carrion falls of large animals. Spatial analysis showed all hagfish species displayed enriched δ15N and δ13C, and depleted δ34S values on the continental slope off Louisiana than along the North Florida Slope and in DeSoto Canyon. These shifts in isotopic signatures could be attributed to influx from riverine sources from the Mississippi River. Temporal variations were also correlated to the seasonality of nutrient discharge from the river. Isotopic shifts seemed to be a consequence of riverine inputs rather than as a result of changing environmental conditions from the DWH oil spill. This study also determined Total Hg (THg) and Hg species (Methyl-Mercury-MeHg, inorganic Hg-IHg) concentrations in hafish muscle tissue. There was significant intra and interspecific variation in THg concentrations of all three hagfish species. Enriched δ15N and much higher THg concentrations were observed in M. mcmillanae (11.9 ppm) when compared to E. minor (2.1 ppm) and E. springeri (1.1 ppm). Mean MeHg concentrations were highest in M. mcmillanae (10.9 ppm), followed by E. minor (1.4 ppm) and E. springeri (0.8 ppm), while mean IHg concentrations were 1.3 ppm, 0.7 ppm, and 0.4 ppm , respectively. However, Hg species displayed a wide range of variation, with IHg concentrations in muscle tissue accounting for up to 75% to 95% of the THg content for some individuals. THg concentrations were studied in relation to several biological and environmental factors (stable isotopes, depth, total, length, body weight and lipid content, spatial and temporal variations) but most of these relationships were not significant for one or more species, which suggests that more than one uptake and depuration pathway or factors could contribute to the bioaccumulation of Hg in hagfishes. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the Master of Science. / Spring Semester 2016. / April 11, 2016. / Bioaccumulation, Diet, Hagfish, Mercury, Stable Isotopes, Trophic Ecology / Includes bibliographical references. / Jeffrey P. Chanton, Professor Co-Directing Thesis; William M. Landing, Committee Member.

I present here an investigation of several aspects of the biology of sea turtles in the mid-Atlantic Bight. During 19 years of data collection, included in this study, strandings have increased for all species of sea turtles in Virginia. Most sea turtle strandings occurred during the spring when juvenile turtles migrate into the Bay (Kemp's ridleys had a second significant stranding peak, during fall migration) along the Southern Bay and Virginia Beach Oceanfront. Sea turtles utilize the Chesapeake Bay as a feeding area when the water temperature approaches 20??C, and they leave after the water temperature drops below 20??C. Although some turtles have stranded at much lower temperatures. The number of possible anthropomorphic interactions with turtles has increased as recreational boating & fishing has increased in popularity. The cause of death attributed to the largest number of strandings is boat and propeller damage. Commercial fishery interactions (entanglement) were second in importance, but such interactions, while usually resulting in turtles drowning, were less easily detected. The vast number of the strandings having an unknown cause of death maybe attributed to carcass decomposition and lack of observer training. The VIMS data set provided the basis for morphometric analysis. Regressions calculated from the data often explain more than 90% of the variation in the measurements. These regressions may be used to estimate missing values required by State and Federal management agencies. The carapace morphology of loggerheads and Kemp's ridleys changes as they grow. The carapace flattens out in larger individuals, presumably to maintain a relatively constant amount of lift while swimming at higher cruising velocities. The extra lift may be needed by hatchlings because of their low swimming speed. Using satellite imaging technology and sea turtle abundance and distribution data from coastal aerial surveys, off North Carolina, I confirmed a behavioral temperature range of 13??C to 29??C, which is well within previously established physiological limits and also encompass values recorded in the Chesapeake Bay. Magnetic resonance imaging techniques, were used to image juvenile Kemp's ridley and loggerhead sea turtle heads. The location of magnetic particles in the sea turtle heads appears to be in the ethmoid, in the same region as in birds and fishes. The anomalies were bilaterally paired suggesting a possible use as a sensory system. Results from an oxytetracycline injected adult loggerhead sea turtle show that bone rings are laid down on an annual basis. Examination of whole cross sections of the humerus suggests that the dorsal and ventral regions used for taking bone cores used in previous studies is inappropriate. The failure in other studies to detect growth rings may have been due to samples being taken from the dorsal surface of the bone. The lateral edges of the humerus should be used for future oxytetracycline studies. Growth rates and ring deposition support previous data, supporting the notion that sexual maturity may occur over a very large size range.

No description available.

The northern Gulf of Mexico (nGOM) is home to one of the largest eutrophication-driven seasonal hypoxic zones in the world. These hypoxic zones are also known as “dead zones” because dissolved oxygen (DO) concentrations of ≤ 2 mg L-1 are inhospitable to economically valuable fisheries. However, microorganisms flourish in “dead zones” because of their ability to utilize diverse metabolic pathways and/or by carrying out metabolic function at low oxygen concentrations. Decades worth of geochemical data has provided fine-scale resolution on nutrient and oxygen dynamics in the nGOM, however little is known about microbial community structure and activity despite the implication that microbial respiration is responsible for forming low DO conditions. To begin to fill this knowledge gap, water column samples collected across the nGOM shelf for two consecutive hypoxic seasons in July 2013 (Y13) and 2014 (Y14) were analyzed using 16S rRNA gene iTag sequencing, quantification of bacterial and thaumarchaeal 16S rRNA genes and archaeal ammonia-monooxygenase (amoA) genes using quantitative polymerase chain reaction (qPCR) assays, as well as shotgun metagenomic and metatranscriptomic sequencing of a subset of Y13 samples. In chapter two of this dissertation, analysis of the microbial community16S rRNA gene sequence data (iTag) in Y13 water column samples showed that ammonia-oxidizing Thaumarchaeota (100% similar to Nitrosopumilus maritimus) abundances were significantly enriched in hypoxic samples and inversely correlated with DO concentrations. In agreement with the iTag data, subsequent analyses of the absolute abundance (qPCR) of Thaumarchaeota 16S rRNA and amoA gene copy numbers revealed these data to be significantly more abundant in hypoxic samples and inversely correlated with DO concentrations. These results of significantly higher Thaumarchaeota abundances and amoA gene copy numbers in hypoxic samples were confirmed with analyses of Y14 data, as shown in chapter three. For both Y13 and Y14 samples, further analysis of thaumarchaeal microdiversity using oligotyping of iTag sequence data showed single nucleotide variation among Nitrosopumilus 16S rRNA gene sequences. One oligotype was significantly more abundant in hypoxic compared to oxic samples and significantly correlated with low DO, revealing a low DO adapted Nitrosopumilus oligotype in the nGOM. To better understand the ecological significance of the high thaumarchaeal abundances in the hypoxic zone shown in chapters two and three, shotgun metagenomic and metatranscriptomic sequencing was carried out on a subset of samples from Y13. Annotation of unassembled metatranscriptomic reads revealed that functional genes involved in nitrification and ammonia assimilation were some of the most abundant transcripts in both hypoxic and oxic samples, with urease enzymes being significantly more abundant in hypoxic samples. Chapter four described the physiological and metabolic activity of two novel Thaumarchaeota metagenome assembled genomes (MAGs) (estimated 79% and 96% complete). The 16S rRNA gene sequence of one MAG had a 98% identity with Nitrosopumilus maritimus SCM1 and was 100% similar to the dominant Thaumarchaeota (OTU4369009) in the Y13 nGOM. Bioinformatic analyses of these MAGs revealed that one contained transcripts coding for urea utilization, consistent with the analysis of unassembled metatranscriptomic sequences. Both MAGs recruited more metatranscriptomic reads derived from hypoxic samples (≤ 2 mg L-1) compared to oxic samples, revealing an active Thaumarchaeota population in the hypoxic zone where archaeal ammonia oxidation may be influenced by local changes in DO concentrations. Collectively, analyses of the datasets in this dissertation that include data from iTag sequencing, qPCR assays, and meta-omics sequencing, found that seasonal hypoxic conditions influenced Thaumarchaeota abundance, activity and diversity, with the annual nGOM “dead zone” emerging as a niche for low DO-adapted, cosmopolitan ammonia-oxidizing archaeal (AOA). Overall, the findings in this dissertation provided significant new insights into the ecology and biogeochemical contributions of marine Archaea, particularly in regards to the nitrogen cycle during a eutrophication-driven hypoxic event. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2019. / April 2, 2019. / Ammonia oxidation, Archaea, Dead zones, Gulf of Mexico, iTag, Metagenomics / Includes bibliographical references. / Olivia U. Mason, Professor Directing Dissertation; Thomas E. (Tom) Miller, University Representative; Jeffrey P. Chanton, Committee Member; Markus Huettel, Committee Member; Angela Knapp, Committee Member.

Bibliography: leaves 92-99. / The community structures of three shore types namely: "mixed shores" (those where rocky and sandy-shore habitats are intermixed), pure rocky shores and pure sandy beaches in False Bay, South Africa are compared in this study. Four habitats were identified - pure rock (unaffected by sand), mixed rock (rock affected by sand), mixed sand (sand between emergent rocks) and pure sand (beaches with no emergent rock) - representing a gradation from pure rock to pure sandy beaches. The specific aims of this study were to: (1) Sample quantitatively and describe macrofaunal communities on mixed shores in False Bay; (2) make direct comparisons among both the four types of habitats and three types of shores; and (3) test the hypothesis that sand inundation increases diversity at both habitat (a-diversity) and shore (diversity) level. The biological communities of mixed shores are described in terms of species composition, trophic organisation and zonation. Mixed-shore zonation patterns are different from those previously described for pure rocky shores in the region. The ability of Charomytilus meridiana/is and inability of patellid limpets and various algae, to withstand sand inundation are largely responsible for these differences.

The species composition, abundance and distribution of intertidal sea anemone assemblages were investigated by means of line-transects at two sites on the Cape Peninsula - Wooley's Pool in False Bay and Blouberg in Table Bay. A single species, Bunodactis reynaudi dominated at Blouberg (average density 901 running m⁻¹). Juveniles < 35mm basal diameter) were particularly abundant in mussel beds. Seven species exhibiting clear vertical zonation were found at Wooley's Pool (average density 658 m⁻¹). High-shore species were Actinia equina and Anthothoe stimpsoni. A. stimpsoni was the smallest (9.1mm mean basal diameter) and most abundant (maximum density 1450. m⁻² ) anemone at Wooley's Pool. Three species were found at mid-shore: of these Anthopleura michaelseni and Bunodosoma capensis had the same vertical distribution and extended to higher tidal levels than Bunodactis reynaudi. Two species of Pseudactinia favoured the sheltered low-shore. P. flagellifera was confined to the subtidal zone and was the largest (60.2mm mean basal diameter) and least abundant of all the species (10. m⁻² ), while P. varia extended into the low intertidal. Although different anemone species exhibit distinct zonation on the shore, they show considerable overlap. Different morphological and behavioural characteristics facilitating this zonation are discussed. Bibliography: pages 86-98.