No description available.

No description available.

The geographical distributions and seasonal occurrences of decapod larvae and pelagic post-larvae in continuous plankton recorder (CPR) samples over a 3-year period were analysed and described. During this period, the survey covered large areas of the north-eastern Atlantic Ocean and adjacent continental shelf waters, including the English Channel and the North, Irish and Celtic Seas. Multivariate analysis provided the basis for classifying the distributions of 36 of the most abundant taxa (species, genera or subfamily) into groups. These groupings demonstrated the significance of bathymetry and temperature in limiting distributions. Larvae of 3 species were shown to disperse during development from areas where the earliest larvae occurred into areas that were presumably unsuitable for successful reproduction. Geographical variations in the seasonal timing of occurrence in the plankton of larvae of benthic decapods were correlated with parameters of temperature. Analysis of decapods from CPR samples in a subsequent anomalously warm year ( 1989) demonstrated that these correlations also applied to interannual variations within areas. Samples taken using the Longhurst-Hardy Plankton Recorder (LHPR) were analysed to describe vertical distributions of pelagic stages of decapods. Stratification of temperature, salinity and abundance of chlorophyll influenced the vertical distributions and die migrations of decapod larvae. The nature and extent of that influence varied between taxa. For example Pagurus bernhardus zoeas were concentrated near the surface around the thermocline or below the thermocline according to conditions but Liocarcinus spp. zoeas were most abundant above or at the thermocline in all the profiles in which they occurred. Where ontogenetic variation was observed, later developmental stages generally occurred at greater depth than earlier stages. Some of the observed features of vertical distributions were consistent with aspects of results from the single depth CPR samples. The lengths of carapaces of specimens sorted live from the plankton were measured and dry weights, carbon content and nitrogen content of individual larvae were determined. Regressions of dry weight on carapace length, carbon weight on dry weight and nitrogen weight on dry weight were calculated and found to be comparable in most cases with published data on laboratory reared larvae. Regressions of development times on temperature for each stage of selected taxa with fixed numbers of developmental stages were derived from the literature. A method was developed for estimating biomass and production of planktonic larvae, including fluxes between the benthos and plankton at hatching and settlement, from the results of plankton surveys using the regressions of dry weight on carapace length and development times on temperature. Decapoda usually comprised 1-8% of the dry weight biomass of zooplankton retained by a 200µm mesh from samples in the Irish Sea and North Sea in the spring.

Long term data on the North Sea ecosystem are available for phytoplanktonic, zooplanktonic, berithic, fish, and seabird communities. Temporal changes in these have been examined by numerous researchers over the course of the 20th century, their main objective being to determine how the interannual dynamics of these communities are regulated. This study considers the long term ecosystem dynamics, and the mechanisms behind these dynamics, for the North Sea over the latter half of the 20th century, although it focuses upon the time series operated by the Dove Marine Laboratory, and the Continuous Plankton Recorder (CPR) survey in the central-west North Sea region. A review of the literature suggests that long term changes across the North Sea are ultimately driven by two processes. In the northern, western and central areas of the North Sea, the ecosystem is climatically driven, whilst in the southern and eastern regions, the signal of climate is masked by the large arithropogenic nutrient inputs into these regions. A comparison of the Dove and CPR zooplankton time series for the central-west North Sea area found that although their relative year to year fluctuations were similar, large differences were present in the absolute abundances recorded. Model derived catching efficiencies for the two sampling devices suggested that differences in absolute abundances were mainly due in some zooplankton taxa to a greater degree of active avoidance of the CPR sampling device. Further examination of these two series found that the long term zooplankton trends in the central-west North Sea were dissimilar to those observed for other North Sea regions. Inverse relationships between zooplankton abundance, and the position of the Gulf Stream North Wall, and with air temperatures were also observed. These dissimilar trends and inverse relationships were ultimately found to be due to the presence of an internal predation based mechanism. Cmatic influences were also found to indirectly influence the long term dynamics of the benthos in the central-west North Sea The primary factor influencing interannual variation in benthic abundance was phytoplankton productivity (Le. food), which in turn was related to climatic factors. However, at a second central-west North Sea benthic station, situated within a Nephmps norvegicus fishing ground, constant trawling disturbance of the benthos was the primary factor influencing both benthic abundance and species composition. Over the latter half of the 2O1 century, air temperatures and daily sunshine durations have increased in the central-west North Sea region, alongside changes in climatic proxy variables (e.g. NAO index). However, similar trends were not always observed in the biota. Ultimately, the long term dynamics of taxa, communities and ecosystems may be due to direct or indirect factors, yet interactions between a diversiy of internal and external factors, results in the complex behaviour of biological systems over time. This study shows that, a though the centralwest North Sea ecosystem is climatically driven, similar trends between climate and ecosystem components do not necessarily exist, and nor considenng the high comp exity of the ecosystem, should they be expected.

No description available.

The role of crustacean zooplankton in changing the size structure of phytoplankton communities was examined in Lake Memphremagog, Quebec. The hypothesis that zooplankton have a selective effect on various algal size classes, within the net- and nannoplankton, was tested during different periods of the growing season in controlled field experiments. Depending on the pattern of loss rates imposed by zooplankton on different algal size fractions, it is shown that zooplankton can both accelerate and decelerate successional events in the phytoplankton. Manipulation of zooplankton biomass produced significant changes in algal phosphorus demand, estimated from observations on the short-term dynamics of orthophosphorus. It is shown that the presence of zooplankton reduces the phosphorus deficiency of the phytoplankton in early periods of the season. Empirical relationships are also presented, based on literature observations, to predict variation in feeding selectivity of cladocerans and variation in the biomass of zooplankton among lake ecosystems.

Grazing rates of several abundant zooplankters in Kaneohe Bay, Hawaii were measured at different concentrations of natural phytoplankton. The concentration by volume of suspended particles, as determined with an electronic particle counter, was used as the estimate of food concentration. The relationship between grazing rate per animal and concentration of particulate food conformed closely to a hyperbolic model widely used to describe an organism's rate of uptake of food or other needed substrate as a function of the concentration of the substrate. Maximum observed grazing rates in the eutrophic south sector of the bay are near the maximum rates predicted by the model. The concentrations of particles in other areas of Kaneohe Bay do not appear to be high enough to permit grazing rates to approach their maximum levels. There appears to be no preference by the grazers for particles of a size other than the size most abundant in the environment. / Typescript. Bibliography: leaves 23-26.

Typescript. Bibliography: leaves 89-91.

Thesis (Ph. D.)--University of Adelaide, 1986. / Includes bibliographical references (leaves 145-168).

Thesis (M.S.)--Missouri State University, 2008. / "May 2008." Includes bibliographical references (leaves 94-107). Also available online.