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Niche segregation among 4 species of sculpins (Myoxocephalus quadricornis, M. scorpius, M. scorpioides and Gymnocanthus tricuspis) inhabiting the east coast of James bay was studied along estuarine and depth gradients at different times of year between 1987 and 1990. A high degree of habitat overlap and absence of feeding segregation among sculpins was observed. M. quadricornis and M. scorpius dominated catch in the estuary and in the coastal zone, respectively. M. scorpioides and G. tricuspis were less abundant and generally avoided the estuary. G. tricuspis was the only cottid which seemed to migrate. Significant differences in the diets were observed at different sites, seasons and years, but not along depth gradients (2 a 20 m). The distribution and abundance of sculpins appeared to be regulated by physical (salinity and temperature) and biological (competition) factors.

Due to accelerated climatic warming during the past fifty years, interest and concerns have been growing about changes in the ecological integrity of shallow freshwater ponds that dominate the landscape of the Hudson Bay Lowlands (HBL). Climatic warming is altering the hydrological processes that influence the water balances in these ponds, but knowledge remains insufficient to determine the effects these changes have on ecological conditions in the ponds. To address this knowledge gap, this study examines the relations between current hydrological and limnological conditions and recently deposited sedimentary assemblages of diatoms and photosynthetic pigments in 23 shallow ponds in the HBL. The knowledge from the contemporary studies will be used to inform paleolimnological reconstructions using multiple proxies at two ponds to assess how hydroecological conditions have changed during the past several centuries in response to climatic variations. Water samples were collected three times in 2010 to explore the relations between current hydrological and limnological conditions. The climatic conditions in 2010 provided an excellent opportunity to assess the effects that continued climate warming may exert on hydrolimnological conditions in the study ponds as the warm, dry conditions during the early thaw-season (May- mid-July) followed by extremely wet conditions for the remainder of the thaw-season are likely representative of future climate scenarios. The analysis revealed that the water chemistry in the ponds evolved along one of four different ‘trajectories’ throughout the thaw-season in 2010. These seasonal patterns of limnological conditions closely aligned with similar patterns identified in a study of contemporary hydrological conditions (Light, 2011; Wolfe et al., 2011). The patterns identified in both the hydrological and limnological studies were attributed to differences among ponds in catchment characteristics and hydrological connectivity with adjacent basins. Surface sediment samples were collected in 2010 to determine if hydrolimnological conditions are reflected in the distribution of recently deposited diatom and pigment communities. It was determined that diatom community composition was most highly influenced by the availability of microhabitat in the ponds which did not appear to be controlled by hydrological conditions. Nitrogen availability was determined to be indirectly influencing diatom community composition as the nitrogen-limited conditions in the ponds favoured the proliferation of N2-fixing cyanobacterial mats that provided a large amount of epiphytic habitat in the majority of the study ponds. This resulted in the complete domination of diatom assemblages by one diatom specie that was closely associated with these algal mats in the surface sediments of most ponds. Aphanizophyll, a photosynthetic pigment representative of nitrogen-fixing cyanobacteria, was also in the highest concentration in most of the study ponds as a result of the nitrogen-limiting conditions that allowed these organisms to dominate. Ponds located in the tundra ecozone were also found to have the highest overall pigment concentration which was related to a longer growing season due to the small size of these ponds that resulted in earlier ice-off conditions. The longer growing season of ponds in the tundra ecozone may also be due to high winds that cause a decrease in snow cover, lower surface albedos and an earlier onset of the spring thaw. The paleolimnological reconstruction of two of the ponds revealed similar shifts in diatom community composition in the stratigraphic record even though patterns of past change in their basin hydrology, as explored though the analysis of the δ18OPW record archived in the aquatic cellulose contained in the pond sediments, was very different. The water balance of “Left Lake” was found to be highly influenced by increased evaporation associated with recent warming trends as it is a relatively small basin that becomes hydrologically isolated after the melt period. However, “Erin Lake” was not as susceptible to evaporation during the recent warming trend due to its larger catchment and hydrological connections to other ponds. Both of these ponds experienced marked changes in the diatom assemblages. The changes were characterized by a shift from assemblages containing both small, adnate, benthic taxa that prefer mineral grain substrates and epiphytic taxa that are associated with the cyanobacterial mats covering the pond bottoms to assemblages entirely dominated by epiphytic taxa. The shift in diatom community composition occurred ~1820 in Left Lake, but the timing cannot be determined with any degree of confidence in Erin Lake as no diatoms are observed in the sediment record during the period when the change occurred (~1550 to 1850) due to preservation issues. Analysis of fossil pigments indicates that nitrogen-fixing cyanobacteria have been important to the ecology of the ponds over the entire sediment record. However, there is a trend towards lower concentrations of pigments representative of N2-fixing cyanobacteria in the most recent sediments. The trend in cyanobacterial pigment concentrations coincides with inferred changes in nitrogen availability from the geochemical analysis of the pond sediments by Light (2011). This recent shift in nutrient status may be the result of a number of factors including the increased atmospheric deposition of anthropogenically-derived nitrogen or changes in biogeochemical cycling in the ponds.

Graduation date: 1987

Graduation date: 1983

Graduation date: 1987

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 53-58). / vii, 58 leaves, bound col. ill. 29 cm

A unique opportunity to study both benthic microbial mats and modern stromatolites from a common niche is presented by the hypersaline environment of Hamelin Pool, Shark Bay, Australia. However, prior to this study, the microbial mat communities have not been well characterised. To investigate the taxonomic and functional diversity of Hamelin Pool pustular and smooth mats, and their similarity to Hamelin Pool stromatolites, culturing, culture-independent, and lipid analysis methods were employed. The cultured isolates obtained included heterotrophic bacteria similar to those obtained from other hypersaline environments, and 19 strains of cyanobacteria including potentially novel species. For the first time archaeal isolates were obtained from the pustular and smooth mats, and further characterisation of two strains indicated they might represent novel species of the genus Haloferax. Total DNA was extracted from the mats and 16S rRNA gene clone libraries were generated targeting the bacteria, cyanobacteria, archaea and eukarya. Both the pustular and smooth mat bacterial clone libraries were highly diverse, with 11 bacterial divisions represented, and Chao1 estimates of total species richness indicating ~3000 ??? 6000 species. Cyanobacterial and archaeal clone libraries revealed unique phylotypes associated with sediments of differing morphology. Statistically significant differences between the mat populations and Hamelin Pool stromatolite communities were identified using !-LIBSHUFF, a program designed to compare two 16S rRNA gene libraries. Signature lipid biomarkers were assessed for the pustular and smooth mats and an intertidal stromatolite from Hamelin Pool. Fatty acids (as methyl esters), wax esters, hydrocarbons, ether-bound lipids, hopanoids and sterols indicated the presence of oxygenic phototrophs, anoxygenic phototrophs, sulfate-reducing bacteria, sulfur-oxidising bacteria, heterotrophic bacteria and archaea in each of the sediment types. Limited contributions from diatoms, bivalves and their dinoflagellate symbionts, and from higher plant aerosols were also detected. Significantly, 2-methyl hopanoids and eight pseudohomologous series of branched alkanes with quaternary carbon centers were identified in the mats and stromatolites. Although differing in lithification status and precise microbial composition, the pustular and smooth mats are excellent analogues for the extant stromatolites of Hamelin Pool, and by corollary, provide a fascinating link to Precambrian microbial communities.

The first aim of this thesis was to test the hypothesis that the spatial and food resources in the nearshore waters of a subtropical embayment in Western Australia (Shark Bay) will be partitioned within and amongst the main elasmobranch species that occur in that large water body. The size and age compositions, growth rates and reproductive biology of females and males of the nervous shark Carcharhinus cautus in Shark Bay were then determined to better understand the mode of life of this abundant species in this embayment. The second aim was to determine the species and size compositions of chondrichthyans landed by fisheries employing different methods in south-eastern Indonesia. The implications of these data for management were next determined and aspects of the reproductive biology of the most abundant of those species were explored, in a very preliminary manner. The nearshore, shallow waters of Shark Bay are used as a nursery area by several shark species and the different habitats in those waters are partitioned, to a certain degree, amongst those species. Ten species of shark (5 families), five species of ray (4 families) and twelve species of teleost (10 families) were caught in those waters. Carcharhinus cautus was the most abundant species, contributing 59.9% to the total number of elasmobranchs and 42.3% to all fish caught. This species and Negaprion acutidens were collected mainly or entirely from unvegetated sites, whereas Rhizoprionodon acutus, Carcharhinus brevipinna and Chiloscyllium punctatum were caught largely or exclusively at the seagrass site. The number of elasmobranch species and number of individuals of elasmobranchs were greatest in the seagrass site and least in the unvegetated site where no vegetation was present nearby, and they were significantly less in the latter site than in the one where dense mangroves were present nearby. These two biotic variables were also significantly greater in summer and autumn than in winter when temperatures were lowest. The species composition of elasmobranchs in each habitat type almost invariably differed significantly from that in each of the other habitat types and there was evidence that the species composition of elasmobranchs varied in a similar seasonal manner at the three unvegetated sites. Carcharhinus cautus, and probably also Hemigaleus microstoma and Chiloscyllium punctatum, were the only species that completed their life cycles in the nearshore, shallow waters of Herald Bight. However, the capture of the juveniles of a further four species with umbilical scars emphasises the importance of these waters as a nursery habitat for shark species. The dietary compositions of one ray species (Rhinobatus typus) and three shark species (Carcharhinus cautus, Negaprion acutidens, Rhizoprionodon acutus) undergo size-related changes and differ among these species, thereby reducing the potential for competition for food within and among these four species. Rhinobatus typus fed almost exclusively on penaeid prawns and portunid crabs, which is reflected in its narrow dietary breadth, whereas different species of teleosts constituted a major component of the diets of each size class of the three shark species. The relative contributions of the different species of teleost to the diets of the three shark species varied. The variations in dietary composition among the four species reflect differences in behaviour, modes of feeding and relative mouth sizes. Carcharhinus cautus copulates in late October–early November, shortly followed by ovulation (and thus conception) and parturition occurs about 11 months later. The reproductive cycle of C. cautus is biennial. Female and male C. cautus reached ca 28 and 32% of their lengths at their maximum observed ages, respectively, at the time of parturition. Females and males of C. cautus attained maximum total lengths of 1330 and 1110 mm, respectively, and maximum ages after parturition of 16 and 12 years, respectively. Maturity was attained at about 1010 mm by females and 910 mm by males and at least 50% of females and males had become mature by the end of their sixth and fourth years of life, respectively. The three-parameter von Bertalanffy growth curves provided reasonably good fits to the lengths at age of females and males of C. cautus during just postnatal life and throughout the whole of pre- and postnatal life. However, the four-parameter Schnute growth curve significantly improved the fit to these data for both females and males from conception and for females from birth. The question of when, from a biological view point, it might be appropriate to switch from using a von Bertalanffy growth curve to the more complex Schnute growth curve are discussed. A total of 139 chondrichthyan species, comprising 77 species of shark representing 17 families, 61 species of ray representing 11 families and a single species of holocephalan, were recorded at the ten landing sites surveyed in south-eastern Indonesia. However, it should be recognised that up to 49 of the 139 chondrichthyan species recorded have apparently not yet been described and thus assigned a species name. The most speciose and commonly recorded families were the Dasyatidae and Carcharhinidae, which collectively contributed 84.8%, respectively, to the total number of individuals of all species. The use of MDS ordination demonstrated that the species compositions at the eight main landing sites reflected to a greater extent the fishing methods used rather than the geographical location of those sites. Data on the reproductive biology of males demonstrated that a number of elasmobranch species were fished prior to the time that they attained maturity. The three most abundant chondrichthyan species that were caught both as juveniles and adults were Dasyatis kuhlii, Dasyatis zugei and Himantura walga. Since the reproductive cycle of each of these species did not follow a seasonal pattern, the timing of conception and parturition and the duration of gestation of these species could not be determined. The fecundity of these three species was very low, i.e. maximum of two but usually only a single embryo. The size at maturity of the three species, using data on the prevalence of mature fish, ranged from minima of 163 mm for females and males of H. walga to maxima of 237 mm for females and 239 mm for males of D. kuhlii. The translucent zones on the vertebral centra of D. kuhlii were apparently deposited annually and were thus used to estimate the ages of the individuals of this species. The maximum estimated ages of female and male D. kuhlii were 15 and 10 years, respectively.

Thesis (M. Phil.)--University of Hong Kong, 1992.