Understanding the dynamics of plankton populations is of major importance since plankton form the basis of marine food webs throughout the world's oceans and play a significant role in the global carbon cycle. In this thesis we examine the dynamical behaviour of plankton models, exploring sensitivities to the number of variables explicitly modelled, to the functional forms used to describe interactions, and to the parameter values chosen. The practical difficulties involved in data collection lead to uncertainties in each of these aspects of model formulation. The first model we investigate consists of three coupled ordinary differential equations, which measure changes in the concentrations of nutrient, phytoplankton and zooplankton. Nutrient fuels the growth of the phytoplankton, which are in turn grazed by the zooplankton. The recycling of excretion adds feedback loops to the system. In contrast to a previous hypothesis, the three variables can undergo oscillations when a quadratic function for zooplankton mortality is used. The oscillations arise from Hopf bifurcations, which we track numerically as parameters are varied. The resulting bifurcation diagrams show that the oscillations persist over a wide region of parameter space, and illustrate to which parameters such behaviour is most sensitive. The oscillations have a period of about one month, in agreement with some observational data and with output of larger seven-component models. The model also exhibits fold bifurcations, three-way transcritical bifurcations and Bogdanov-Takens bifurcations, resulting in homo clinic connections and hysteresis. Under different ecological assumptions, zooplankton mortality is expressed by a linear function, rather than the quadratic one. Using the linear function does not greatly affect the nature of the Hopf bifurcations and oscillations, although it does eliminate the homoclinicity and hysteresis. We re-examine the influential paper by Steele and Henderson (1992), in which they considered the linear and quadratic mortality functions. We correct an anomalous normalisation, and then use our bifurcation diagrams to interpret their findings. A fourth variable, explicitly modelling detritus (non-living organic matter), is then added to our original system, giving four coupled ordinary differential equations. The dynamics of the new model are remarkably similar to those of the original model, as demonstrated by the persistence of the oscillations and the similarity of the bifurcation diagrams. A second four-component model is constructed, for which zooplankton can graze on detritus in addition to phytoplankton. The oscillatory behaviour is retained, but with a longer period. Finally, seasonal forcing is introduced to all of the models, demonstrating how our dynamical systems approach aids understanding of model behaviour and can assist with model formulation.

Tintinnids are among the largest and most abundant of the marine cillate microzooplankton but there is very little published information on their feeding rates and abilities. The feeding of Tintinnopsis subacuta (and to a lesser extent, that of 12 other species) was investigated with three methods 1) direct observation 2) counts of accumulated food cells and 3) Coulter Counts of the particles in the experimental medium. There was reasonable qualitative agreement between the results obtained by the three methods but quantitative agreement was poor. Many of the results showed no significant differences due to very great variability in the results for a single tintinnid species within and between experiments. Much of this variability may be due to the methods used but it also reflects the variability of tintinnids in natural populations. A wide variety of items was eaten by tintinnids, including smaller tintinnids; and the maximum food size can be related to tintinnid cell volume over a wide range but is dissimilar in tintinnid species of similar cell size. . Several tintinnid species showed differential predation on various types of laboratory phytoplankton. This differential predation was based upon the ability of the predator to handle prey, or on prey size or prey type depending upon the particular tintinnid species. 'Negative' selection of some types of laboratory phytoplankton in mixed-prey samples was also shown for some tintinnid species, particularly Tintinnopsis subacuta on members of the Cryptophyceae. Feeding rates measured with the accumulation method were equivalent to 0.65% ml/hr/tintinnid for T. subacuta and usually much less. Feeding rates for this species measured with the Coulter Counter technique ranged from 0.33 to 3.8% ml/hr/tintinnid. Very little feeding was observed directly but feeding rates estimated with this method were somewhat higher than those estimated for the same species from accumulation experiments. Tintinnids apparently both consumed, and caused the production of particles during experiments. Correlations between feeding rate and 9 other experimental variables were such that it would be impossible to predict the feeding rate of a tintinnid species using only the size distribution of avaifeble particulate biomass of less than 20 um diameter. There were large differences between the apparent feeding rate asymptotes of T. subacuta and S. ventricosa as measured with the Coulter Counter and the accumulation method. The latter method gave lower asymptotes than did the former. Ivlev electivity indices for T. subacuta were most consistently positive in those middle Coulter size classes which also showed the greatest growth in controls. Increased temperature had little effect on the rate of food accumulation by four tintinnid species, but there was some evidence of a faster rate of disappearance of ingested food at very high temperatures. The relationship between the gain of new food and the loss of old food in individual T. subacuta and Stenosomella ventricosa was highly variable and may strongly reflect the physiological history of the cell. The rate of gain of new food may be largely independent of the amount of old food in a tintinnid, but the average rate of loss of old food is faster in cells given new food than in starved cells. It was shown that natural concentrations of T. sub acuta can apparently control the growth of natural populations of phytoplankton of less than 20 μm dia. in under 24 hours. From a comparison with some other types of microzooplankton it was concluded that the larger species of tintinnid could probably have a potentially predominant effect upon the highly productive phytoplankton of less than 10 um diameter in English Bay and other coastal localities. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Thesis (M.Sc.)--College of William and Mary. / Vita. Includes bibliographical references. Also available via the World Wide Web.

by Tang, Kam Wing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 139-149). / Abstract --- p.1 / Acknowledgements --- p.4 / Table of Contents --- p.5 / List of Tables --- p.6 / List of Figures --- p.7 / Chapter Chapter 1 --- General Introduction --- p.11 / Chapter Chapter 2 --- "Diel vertical migration and gut pigment rhythm of marine copepods in Tolo Harbour, Hong Kong" --- p.13 / Chapter 2.1 --- Literature Review --- p.13 / Chapter 2.2 --- Introduction --- p.21 / Chapter 2.3 --- Material and Methods --- p.25 / Chapter 2.4 --- Results --- p.31 / Chapter 2.5 --- Discussion --- p.66 / Chapter 2.6 --- Conclusion --- p.79 / Chapter Chapter 3 --- Distribution and biology of marine cladocerans in the coastal waters of southern China --- p.80 / Chapter 2.1 --- Literature Review --- p.80 / Chapter 2.2 --- Introduction --- p.84 / Chapter 2.3 --- Material and Methods --- p.93 / Chapter 2.4 --- Results --- p.132 / Chapter 2.5 --- Discussion --- p.133 / Chapter 2.6 --- Conclusion / References --- p.139

Thesis (M.S.)--Western Washington University, 2008. / Includes bibliographical references (leaves 56-59). Also issued online.

Thesis (M.S.)--University of North Carolina Wilmington, 2008. / Vita. Title from PDF title page (viewed September 29, 2008) Includes bibliographical references (p. 31-32)

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 185-195).

Mesozooplankton community structure in the vicinity of the Prince Edward Islands (PEIs) was investigated during six surveys conducted in late austral summer (April/May), 1996 to 1999. Each year zooplankton samples were collected with a bongo net (300 µm mesh) at stations upstream (west), between and downstream (east) of the islands. Chlorophyll a concentrations were determined fluorometrically, corresponding with each net tow. The positions of the Subantarctic Front (SAF) and the Antarctic Polar Front (APF), in relation to the islands in the upstream region, were determined by a line of CTD and/or XBT stations. Both the SAF and the APF were characterised by a high degree of meridional variation in position. Changes in position of the fronts were shown to occur very rapidly. In 1999 the APF moved southwards by ~40nm and the SAF northwards by ~60nm in a period of two weeks, while in 1996 the SAF appeared to move ~120nm northwards in a two week period. The positions of the SAF and APF appeared to have a significant impact on phytoplankton biomass in the vicinity of the PEIs, through the alteration of local flow dynamics. Water retention in 1996, associated with the location of the SAF and APF far to the north and south of the PEIs respectively, corresponded with high chlorophyll a concentrations in the inter-island region (reaching 1.54 mg.m^(-3)). When the fronts were close to the islands, in 1997 and 1999, and a flow through environment existed, chlorophyll a concentrations in the inter-island region were comparatively low. Although biomass enhancement was only observed at the SAF in 1996, phytoplankton size structure in 1999 indicated that, when close to the PEIs, frontal production may be transported to the island system. This is potentially an important source of allochthonous input into the island system. Zooplankton assemblages were a mix of sub-Antarctic and Antarctic communities, with a weak presence of sub-tropical species. Cluster analysis showed that during each survey the region in the vicinity of the PEIs was divided into different, spatially separated zooplankton communities, associated with water masses of different origins. These communities were identified by variations in the abundance and biomass of species rather than variation in species composition and, in general, there was a relatively high degree of similarity both within and between surveys. Inter-annual community analysis revealed that, in many cases, there was greater similarity between communities from different years than communities within years, indicating that short-term variability exceeded inter-annual variability. Multiple regression analysis showed that the major correlate with zooplankton community structure during all surveys was sea temperature, accounting for as much as 77% of the variation in community structure. Temperature was indicative of the relative contribution of sub-Antarctic and Antarctic communities, with low temperatures being characterised by an increased predominance of Antarctic communities and vice versa. The differentiation between sub-Antarctic and Antarctic waters, and their respective communities, was particularly pronounced when the SAF and APF were in close proximity to the islands. Surface salinity and sounding had limited effect on community structure. The affect of sounding was intrinsically related to zooplankton interaction with the island ecosystem. Predation by the islands' land based predators and benthic fish appears to decrease zooplankton biomass over the island shelf, particularly the macrozooplankton size fraction. However, this may only be an important factor under conditions of water retention when replenishment of zooplankton stocks is low. The low densities of many macrozooplankton species, and other deep migrators, on the island shelf may be due to their limited advection onto shallow topography. By contrast, there are indications that zooplankton species occurring at shallower depths may be concentrated in the inter-island region by mesoscale flow patterns. Analysis of the population structure of the copepod Calanus simillimus showed that this species occurred at different stages in its life cycle during different years, even though sampling took place in the same calendar months, indicating that there was inter-annual variation in the timing of the biological season. Differences in the population structure of species, and consequently their contribution to abundance and biomass, may therefore have been an important contributor to inter-annual variation in community structure. Evidence is provided for a long-term trend of southward movement of the SAF. This may have a significant affect on the PEI ecosystem, increasing the proportion of allochthonous input and altering the tropho-dynamics of the island ecosystem

The effect of the Asian grass carp (Ctenopharyngodon idella Val.) and aquatic vegetation upon the zooplankton in four adjacent experimental ponds (0.139 ha each) was studied for one year. Zooplankton were collected with a newly designed shallow-water sampler. Pond 1 contained no aquatic vegetation. Ponds 2, 3, and 4 contained nine species of rooted aquatic plants. Grass carp were stocked into Pond 2 (65 per ha) and Pond 3 (611 per ha). Physicochemical parameters were similar among the ponds. Eighty-eight zooplankton species were enumerated. The abundance of zooplankton groups (Rotifera, Cladocera, and Copepoda) was not significantly different among the ponds containing grass carp. No significant differences existed between Pond 3 (high grass carp stocking rate) and Pond 4 (no carp) for species diversity (d) and species dominance. The number of species and species diversity (d) was found to be significantly different in Pond 2 (low grass carp stocking rate) when compared to Ponds 3 and 4; those differences probably were not due to the grass carp. Grass carp did not appear to affect the water quality of the ponds. In general, it was concluded that grass carp had little, if any, direct or indirect affect upon the zooplankton. Species commonness was greatest among ponds containing vegetation. Rotifers were the dominant zooplankton group in those ponds. Zooplankton ware moat abundant in the pond without vegetation and were dominated by copepods (notably Tropocyclops prasinus). That pond contained the lowest number of species and had the largest species diversity (d) of the ponds. The annual mean for the Simpson Index (species dominance) was highest in Pond 1. The lack of vegetation may have influenced the abundance and diversity of the zooplankton in Pond 1 compared to the other ponds. Those differences also may have been due to selective predation by mosquitofish (Gambusia affinis); that fish was significantly less abundant in Pond 1.

The zooplankton communities off the north east coast of Scotland, Wee Bankie sand-banks, were studied with traditional net samples and for the first time, for this area, with acoustic methods. A series of zooplankton samples were collected during June 2010 and March/June 2011 together with a set of physical parameters of the water column. Taxonomic analysis of the collected samples enabled the characterisation of zooplankton communities. Neritic communities with oceanic influence were found along the north east coast of Scotland and over the Wee Bankie with spatial variability associated with higher densities of zooplankton inshore. Temporal variability was associated with the expected succession of dominant copepods from spring to summer. An appropriate scattering model, Distorted Wave Born Approximation, was used to predict the target strength of the major zooplanktonic groups and so solve the forward problem to verify a plankton separation algorithm. The algorithm isolated weak scattering targets of zooplankton using three frequencies (38, 120 and 200 kHz) and was used to study the zooplankton spatial distribution during June 2008-2011 in relation to the physical characteristics of the water column. Model predicted target strength for the major zooplanktonic groups was sensitive to orientation for large organisms and material properties for both copepods and euphausiids. The Wee Bankie waters were thermally stratified, with June 2011 the least stratified of all years. Depths of observed maximum backscatter varied in relation to the pycnocline depth and tended to be deeper in offshore stations. The estimated biomass from the observed backscatter increased from 2008 to 2011 but spatial patterns varied from year to year. Although, estimated biomass across years reduced with increasing maximum fluorescence and surface to bottom temperature difference, the same relationship was not evident within year.