University, Diss., 2003--Bremen.

University, Diss., 2001--Bremen.

Thesis (M.A.)--Humboldt State University, 2006. / Includes bibliographical references (leaves 50-53). Also available via Humboldt Digital Scholar.

This thesis investigates sublittoral epibenthic assemblages, the ecological processes associated with distributions of benthic assemblages and potential ecological impacts arising from the de-ployment of tidal energy devices (TEDs) at a key tidal energy development site. An extensive field campaign was undertaken to collect fine-scale, in-situ data for local hydrodynamics, seabed structure and epibenthic assemblages. Data from a two-dimensional hydrodynamic model com- plemented in-situ flow data and provided an insight into possible changes to local tidal patterns after the deployment of a tidal array. The study revealed a highly complex tidal stream structure with maximal velocities reaching 4.2 ms1 during spring tide. The seabed was predominantly formed by scoured bedrock. Deployment of a tidal array was predicted to decrease tidal flow within and downstream of the array by up to 24 % for peak flows, whereas effects on the seabed were thought to be minor. Epibenthic assemblages were typical for tide-swept channels with a fringe of dense kelp forest along the shallow, sheltered waters of the channel, followed by a 'tran- sition zone' dominated by foliose red algae in the mid-depth ranges and animal turf assemblages in the deeper, very tide-swept waters. Multivariate analyses identified depth and bed-shear stress as being strongly associated with the distribution and composition of assemblages. In conjunction with presence-only data for epibenthic species, depth and bed-shear stress were used as predic- tor variables to develop site-specific habitat suitability models (HSMs) for a baseline and TED deployment case. Comparison of probability of occurrence values between the respective HSMs indicated a potential increase of suitable habitat for species inhabiting the deep, very tide-swept circalittoral following the deployment of TEDs, whilst assemblages along the fringes of the channel were mostly unaffected. This is the first attempt of using HSM as a tool for identification of potential changes in distributions of benthic species arising from the deployment of TEDs. The good overall performance of the models shows this tool may be valuable for for impact analysis of tidal energy development projects.

The objectives of this study were to characterise macrozoobenthic community structure of the western sector of Algoa Bay, to identify the drivers of community structure and to develop a long-term monitoring framework. Data were collected from six study sites stratified along-shore. Each site comprised three stations; most sites were located in areas directly influenced by anthropogenic activities such as inflow from storm water drains and areas where dredged spoil was dumped. Other sites included areas in close proximity to estuary mouths. Physico-chemical parameters of the water column were measured with a YSI instrument, sediment for faunal and physico-chemical analyses was sampled with a Van Veen grab, and collected macrofauna were sedated and preserved pending analysis. In the laboratory, macrofauna were identified to finest taxonomic resolution possible under dissecting and compound microscopes, and enumerated. Sediment samples for physico-chemical analyses were kept frozen pending analysis. Up to 187 species belonging to 137 genera and 105 families were identified. Univariate community parameters such as abundance and number of species varied significantly along-shore, generally increasing towards less wave-exposed sites. Multivariate analyses revealed that community assemblages were heterogeneously distributed along-shore, corresponding to areas where anthropogenic influences such as effluent discharge and commercial harbour activities prevailed. During the 2008 survey, species assemblages separated into six groups corresponding to the six sites but xvii during the 2009 survey, species assemblages separated into four groups probably due to changes in environmental parameters such as the hydrodynamic regime. In both surveys the assemblage opposite a drainage canal (Papenkuils outfall) was distinct as it was dissimilar to all other assemblages. This site was also heterogeneous over relatively small spatial scales. Important physico-chemical variables influencing community structures during the 2008 survey included bottom measurements of temperature, salinity, dissolved oxygen, coarse sand and mud. During the 2009 survey, only bottom temperature and mud content were identified as important physico-chemical variables structuring community assemblages. The principal variable was probably the hydrodynamic regime, driving community structure at a larger scale in Algoa Bay. On a localised scale, communities were probably structured by other factors such as effluent discharges, influence of estuary mouths and activities associated with the harbour. With a lack of information on keystone species (regarded as good monitoring species) in Algoa Bay, it was proposed that groups that cumulatively comprise 50–75 percent of total abundance within communities be monitored annually. Included are amphipods, polychaetes, cumaceans, ostracods, tanaids and bivalves. It was also proposed that areas opposite estuary mouths, effluent outfalls and the dredged spoil dumpsite be monitored. This routine monitoring programme should be accompanied by periodic hypothesis driven research to assess the importance of stochastic events (e.g., upwelling) on macrozoobenthic community dynamics. Keywords: macrozoobenthos, soft-bottom, community assemblages, spatial distribution patterns, environmental drivers, long-term monitoring framework.

The macroscopic bottom fauna of Marion Lake, British Columbia, was investigated from May, 1963 to September, 1964. The primary object was to document seasonal differences within and between specific populations and to interpret these difference in terms of the life histories of the species and their availability to a predator, rainbow trout. A detailed examination of the 51 species of Chironomidae known to occur in the lake has shown that the ecological characteristics of many of the closely related species are very different. Small species generally fed primarily on phytoplankton while the larger species ate more detritus and organic debris or other invertebrates. Predaceous species had more uniform distributions in the lake than did herbivores or detritus feeders. Most species of the subfamily Orthocladinae emerged in spring or fall and grew rapidly during the winter. The species of Chironominae and Tanypodinae usually emerged during the spring and summer and grew very little during the winter. Summer emerging Chironominae emerged later over deep water whereas the Tanypodinae emerged at much the same time above all depths. Larvae which underwent frequent vertical migrations had a higher mortality rate and were found more frequently in the stomachs of rainbow trout than larvae which rarely or never migrated. Many of the benthic organisms were not effectively utilized by rainbow trout. Organisms which numerically constituted approximately 1.5% of the benthic fauna accounted for more than 50% of the food items found in the trout stomachs. Large forms, such as the Odonata and Trichoptera and species which frequently moved off the bottom, formed the bulk of the food; small species and some of the species which were entirely benthic were rare or absent in the trout stomachs analyzed. This study has shown some of the advantages of working at the species level. Although studies at this level are tedious and often necessitate a time consuming taxonomic study, the additional information is likely to justify the extra effort. The results of ecological investigations that are not carried out at the species level ignore, or at best oversimplify, relationships that exist. Indeed, a comprehensive understanding of, for example, energy transfer within a community, is impossible without a detailed knowledge of the life histories of the species involved. / Science, Faculty of / Zoology, Department of / Graduate

This study focuses on ways that the size distribution of individuals influences the types and intensities of competitive interactions within a population of aquatic arthropod predators. Three field experiments and one laboratory experiment were designed to test for feeding interference, interference mortality, and dispersal effects within and between larval size classes of the primarily semivoltine dragonfly Tetragoneuria cynosura in Bays Mountain Lake. One field experiment documented the temporal pattern of colonization of large-mesh cylinders by the small, first-year-class larvae during a 30-day period; the results are consistent with passive (density-independent) colonization. A second field experiment examined the effect of large, second-year-class larvae at densities of 1 or 3 per cylinder (14 or 42 m-2) on colonization by small larvae; this colonization was inhibited at the high density of large larvae. In the laboratory experiment, when larvae of the two size-classes were together in the same aquarium, small larvae moved around less than when by themselves (dispersal inhibition). Thus the inhibition of colonization observed in the field may result from interference mortality, rather than from a flight response to the presence of larger conspecifics. To evaluate this interpretation, the third field experiment measured the in-situ functional response of large larvae to each other and to their small conspecific prey. Results suggest a type 1 (linear) functional response, with feeding inteference among large larvae. Moreover, the interference mortality inflicted by larger larvae on smaller conspecifics was apparently more intense on larger individuals within the small size-class. Taken together, the three field experiments and a statistical power analysis show how colonization and interference interact to determine the local density of small larvae, and why such interference effects are difficult to detect experimentally in the field.

No description available.

No description available.

Thesis (Ph. D.)--University of Hong Kong, 1981.