Estuaries are important ecosystems which are affected by a large range of environmental factors. It is important to measure, characterise and monitor the ecological status of estuaries, and this is the contribution of this thesis for phytoplankton communities in Southampton Water. The size structure and species composition were investigated during 2002 and 2003, with special attention to nanophytoplankton (cells < 5µm in diameter). The main sampling stations were Empress Dock and NW Netley in both years, and Calshot and Horse Elbow in 2002 only. To aid the interpretation of phytoplankton data, information about prevailing meteorological (air temperature, rainfall, irradiance) and hydrographic (tides, water temperature, salinity, and levels of inorganic nutrients) conditions were also collected. In 2002, Empress Dock was sampled weekly between February and October, and other stations were sampled monthly between May and October. In 2003, Dock and NW Netley were sampled weekly between April and September. Measurements made on the phytoplankton included size fractionated (<2, 2-5, 5-20, >20µm) chlorophyll, photosynthetic pigments by HPLC, cell counts by inverted microscopy, and in year 2003 flow cytometry counts and primary productivity (by oxygen) and Fast Repetition Rate Fluorometer (FRRF). Analyses of the major nanophytoplankton taxa involved oligonucleotide probes using fluorescent in situ hybridization (FISH) techniques. Plymouth Routines in Multivariate Ecological Research (PRIMER) statistical analyses were used to calibrate the environmental parameters and phytoplankton carbon biomass. The phytoplankton populations at the four stations were relatively similar. Maximum values of chlorophyll (chl) and carbon biomass were observed between May and August in both years, with a late diatom bloom in 2002, and a mid summer bloom for various organisms. Phytoplankton (as chl or carbon biomass) distributions for 2002 and 2003 could be divided into four phases associated with irradiance and nutrient level. However, there were rapid chl fluctuations during summer due to different factors, such as water column irradiance, tidal range and flushing rate. PRIMER analyses showed that phytoplankton carbon biomass distribution was associated with seasonal patterns, related to light irradiance water column light attenuation, tidal range and nutrients (N and P). In addition, Si is related to phytoplankton succession, and P to size fraction. The nanophytoplankton generally contributed 35-40% of total chlorophyll and up to 60% in winter at the outer stations. Chlorophyll size fraction measurements at Empress Dock (2002) and NW Netley (2003) showed that increased chlorophyll values are generally associated with fractions greater than 5µm (>5µm) and vice versa, although nanophytoplankton (carbon biomass) size structure was dominated by size 2-5µm followed by picophytoplankton, and flagellates >5µm became important in some samples. Comparison of total and fractionated pigment indicated that chlb and chlc2+3 were highly related to the nanophytoplankton fraction and probably inductive of the importance of Chlorophyta and Chrysophyta.

Coastal lagoons are habitats of conservation importance. The characteristic fauna of lagoons includes a number of specialist species, some of which are scheduled for protection. Work on the conservation of coastal lagoons has suggested that detailed information on the ecology of lagoon specialist species is essential to ensure management strategies are relevant to the lagoonal species. This study addresses this issue by providing information about the monthly reproductive investment and energy-balance as well as interactions with parasites for the specialist lagoon amphipod, Gammarus insensibilis (Stock). For comparison information is also presented on the reproductive investment of the lagoonal isopod Idotea chelipes (Pallas). Gilkicker lagoon on the south coast of England, UK, from which the majority of samples were taken, demonstrated environmental variability characteristic of coastal lagoons. Annually, temperature varied between 2 and 28 °C and salinity fluctuated between extremes of 24 and 39. The Lymington-Keyhaven lagoons, also on the south coast of England, demonstrated similar variation. This has implications for Gammarus insensibilis, and effects on reproductive investment were evident. The amphipod was shown to employ a continuous reproductive strategy but while the overall investment, expressed as clutch volume, remained relatively stable over the course of the year, the individual components varied. In the summer, when weight-specific embryo number was at its highest with a mean of 13 embryos mg dry wt.-1 the mean size of the individual embryos was small (0.032 mm3). The opposite was true in the winter months, with mean brood sizes as low as 6 embryos mg dry wt.-1 while mean embryo volume was larger, at 0.04 mm3. Idotea chelipes demonstrated a more seasonal reproductive strategy in which winter reproductive output was low. The environmental variability also had effects on the metabolic rates of individual amphipods with temperature related increases in feeding and respiration rates in the summer months. Scope For Growth (SFG), a measure of net energy availability to the organism, was variable during the year and was unrelated to temperature and salinity. Lowest SFG occurred in spring in conjunction with peak reproductive output. This suggested that the amphipods were well adapted to the environmental variation of the lagoon and that it was reproductive investment that represented an important cost to the organism. Eighty four percent of G. insensibilis from Gilkicker were shown to be infected by microphallid trematode parasites. Reproductive investment was negatively affected, with a 36.6 % reduction in weight-specific brood size associated with higher degrees of infection. Respiration rates were also reduced in the infected organisms. The high prevalence of the parasites and the related effects on the host suggest that trematode infection should be considered, alongside the characteristic habitat variability, as an important aspect of the ecology of lagoons.

The effects of variability in the physical environment on the development of the spring phytoplankton bloom are investigated using a physically forced model of the annual plankton cycle in the ocean mixed layer. The model is optimised to fit survey data from the eastern North Atlantic, collected over a 1500 x 1500 km area between 39N and 54N, from April-June 1991, establishing the feasibility of using spatially distributed point-in-time data in model calibration. Measurements made below the seasonal pycnocline show the existence of an empirical relationship between preformed nitrate and salinity in this area, allowing salinity-based estimates of pre-bloom mixed layer nitrate concentration to be made. These estimates provide important additional constraints for the model. The observed spatio-temporal patterns, at scales between 36 km and 1500 km, in nutrients, chlorophyll and measures of bloom progression derived from these data with reference to pre-bloom nitrate are discussed, together with the corresponding patterns in seasonal stratification. During the spring bloom, when biogeochemical concentrations vary rapidly in response to the developing stratification, absence of data defining its history limits the value of comparison between point-in-time observations and model results. Predictions of variation in stratification at the seasonal time-scale from general circulation models (GCMs) can be used in place of observational data to force ecosystem models. However, the degree to which observations are used to constrain the model solutions should allow for both model error in stratification and misrepresentation of the seasonal development of stratification by the observations. The latter occurs due to sampling error associated with short-term fluctuations. It can be corrected for if a suitable contemporary sea surface temperature data set is available to define the variation of mixed layer temperature at the seasonal time-scale. It is shown that the accuracy of the GCM predictions can be improved by the application of meteorology specific to the year of observation. It is also shown that the sensitivity of the ecosystem model predictions to error in the physical forcing can be reduced by matching model and observations by a stratification measure, rather than by time, when comparing fields. The survey data show an important contribution to the stratification arising from the 'tilting' action of vertical shear on pre-existing horizontal buoyancy gradients in the winter¬ time mixed layer. This effect was severely underestimated by the GCM. The discrepancy can be accounted for by the absence of density fronts and mesoscale dynamics in the model. Ecosystem model results suggest that spatial variance in Zooplankton grazing, due to the effect of differences in the depth and duration of winter-time mixing on the over-wintering success of plankton populations, is one of the major factors controlling the spatial and temporal characteristics of the phytoplankton bloom.

No description available.

This study applies a metapopulation dynamics approach to modelling a distribution of plankton by representing a region of ocean as an ensemble of plankton populations interacting through the stirring and mixing eects of the ow. The methods of synchronisation theory are applied within this framework to gain insight into emergent spatial structure in biophysical simulations. The manifestation of synchronisation, including statistically stable local clustering of populations, frequency-locking or phase-locking of the entire ensemble and fully synchronised dynamics, is found to depend upon: the biological model used; the strength of mixing between populations; the number of populations or, equivalently, spatial resolution of the modelled region; the level of mismatch between and spatial arrangement of population natural frequencies; the strength of stirring of the ensemble at spatial scales larger than the grid-cell. The study therefore highlights a number of biophysical modelling parameters determining the properties of emergent spatial structure in simulations of surface ocean biological dynamics. This study shows that persistent spatial heterogeneity (patchiness) can result from what intuitively should be a homogenising in uence: mixing can increase the level of disorder between the plankton populations. Furthermore, the work shows that synchronisation eects occur generically under a range of simulation scenarios, giving condence that synchronisation theory can explain some of the spatial structure, or `patchiness', observed in plankton distributions, and providing one possible answer as to how populations of planktonic organisms maintain coherent spatial structures under the mixing and stirring action of the oceanic flow.

Air bubbles in the ocean, naturally induced by breaking waves or artificially entrained by ships, remain in the water for different periods of time. Knowledge of the factors accounting for the differences in air bubble residence time (BRT) is essential for understanding processes of air sea-gas exchange as well as for the detection of underwater ship wakes in defence applications. Reasons for the differences in BRT have been found mainly with respect to physical and chemical properties of seawater, such as temperature, salinity and gas saturation level. The impact of biological factors on the behaviour of air bubbles in seawater has not previously been investigated. It is hypothesised that phytoplankton influence BRT through the production of dissolved organic material (DOM) and oxygen. Laboratory experiments were carried out in a seawater mesocosm tank system to investigate the influence of phytoplankton growth on the BRT of artificially injected air bubbles of a wide size range (10-1000 µm diameter) using both natural phytoplankton populations from Kiel Firth and phytoplankton monocultures. BRT was determined acoustically and several phytoplankton growth-related parameters (chlorophyll concentration, dissolved inorganic nutrients, dissolved organic carbon (DOC), oxygen saturation, bacteria numbers) as well as physico-chemical parameters (surface tension and viscosity) were monitored. BRT showed statistically significant covariation with oxygen saturation and chlorophyll a concentration during phytoplankton growth periods in the tank. Increases in BRT of a factor of > 2 were found during the chlorophyll maxima, provided that the water was sufficiently supersaturated with oxygen (~>110%). When the seawater was undersaturated with oxygen, BRT changed only marginally regardless of the chlorophyll a concentration. No clear relationship was evident between BRT and measurements of DOC, surface tension and viscosity. Investigations of the influence of dissolved oxygen on BRT through variation of oxygen saturation of deionised water showed that oxygen saturation alone has no apparent effect on BRT. The influence of phytoplankton on the rheological properties of an air/water interface was investigated in small scale experiments using different phytoplankton monocultures. An increase in surface shear viscosity was detected for only one of the four species of microalgae tested, Nitzschia closterium. Dependency of BRT on the combination of oxygen supersaturation and other phytoplankton growth-related parameters are discussed.

Holothurians play an important role in carbon cycling. They dominate the abyssal oceanic megabenthos, reworking large amounts of organic matter. Holothurians require essential organic nutrients, such as carotenoids for their reproduction. Enhanced carotenoid concentration in the ovaries of echinoderms increases reproductive output and larval survival. Carotenoids cannot be synthesised de novo by holothurians, only by phytoplankton. To examine the link between diet and reproduction in deep-sea holothurians, the pigment biochemistry of holothurians, sediment and particulate organic matter from three abyssal sites as investigated. A temporal comparison at the Porcupine Abyssal Plain (PAP), NE Atlantic, has shown 1) the supply of organic material (OM) can affect the diet of holothurians, depending on their feeding adaptations and 2) holothurian reproductive biochemistry can be affected by compositional differences in the OM reaching the seafloor, although the extent of this influence appears to differ between species. Two abyssal sites around the Crozet Islands, Southern Ocean, were investigated to compare contrasting OM supply on the diet and reproductive biochemistry of holothurians. The sites are only 460 km apart, with no topographic boundary to separate them. However, they are subject to differing overlying primary productivity regimes and therefore biochemical differences can be ascribed to the composition and amount of organic matter reaching the sea floor at each site. The results showed that 1) the quantity of OM reaching the seafloor at each site differed, mirroring the overlying primary productivity regimes. This was also reflected in the diet of some holothurian species, depending on their ability to take advantage of the fresh material. 2) The reproductive biochemistry of the holothurians sampled at both sites showed quantitative differences, mirroring the supply of OM to each benthic site. The present study has shown that changes in the composition and quantity of the supply of OM to the deep-sea floor can affect holothurian diet and ovarian biochemistry. This may lead to large community changes as seen at the PAP in the NE Atlantic, which alters the reworking rate of the sediment, ultimately affecting the sequestration of carbon.

No description available.

No description available.

Global warming and eutrophication are driving an expansion of hypoxia in the World Ocean. This will favour organisms, such as Foraminifera (testate protists), that tolerate low-oxygen conditions and may lead to an overall decline in marine biodiversity. With this in mind, community and trophic responses of benthic Foraminifera were investigated at two contrasting sites in the upper boundary (140 m water depth; bottom-water oxygen concentrations = 2.05 mll-1 during the spring intermonsoon and 0.11 mll-1 during the SW monsoon) and the core (300 m water depth; bottom-water oxygen concentration consistently ~ 0.11 mll-1) of an intense, natural, mid-water oxygen minimum zone (OMZ) on the Pakistan Margin, NE Arabian Sea. Live macrofaunal (>300 µm fraction) Foraminifera (including softwalled species) and metazoans were examined at each site during the 2003 spring intermonsoon (April) and SW monsoon (October) seasons (4 replicate multicores/site/season, 25.5cm2 surface area, 0-5 cm depth). Wet-sorting revealed a low diversity assemblage dominated (> 60 %) by calcareous Foraminifera at both sites. A total of 36 species was recognised and diversity was not greatly affected by water depth or season. At both sites, >86 % of Foraminifera were restricted to the upper 0-1 cm layer of sediment and the Average Living Depth (ALD) decreased from the spring intermonsoon to the SW monsoon (140 m, ALD5 = 0.41 to 0.33; 300 m, ALD5 = 0.65 to 0.44). Foraminifera increased in mean abundance from 124 to 153 individuals per 10 cm2 from the spring intermonsoon to the SW monsoon at 140 m and from 86 to 122 individuals per 10 cm2 at 300 m. The calcareous species Uvigerina ex. gr. semiornata dominated communities and increased in mean abundance from 54 to 118 individuals (140 m) and from 41 to 69 individuals (300 m) per 10 cm2 following the SW monsoon. At 140 m, Foraminifera were 3.6 times more abundant than metazoans during the spring intermonsoon, rising to 13.9 times during the SW monsoon. The corresponding proportions at 300 m, where metazoans were rare, were 12.4 and 14.5. Fatty acid biomarkers suggest that foraminiferal diets vary between species. The calcareous species U. ex. gr. semiornata, Bolivina aff. dilatata and Globobulimina cf. G. pyrula selectively ingested phytodetrital material, whereas the agglutinated species, Ammodiscus aff. cretaceus, Bathysiphon sp. nov. 1, and Reophax dentaliniformis favoured bacteria. Moreover, U. ex. gr. semiornata, rapidly ingested (within two days) 13C-labelled diatoms in shipboard laboratory and in situ pulse-chase experiments at the 140-m site following the SW monsoon. This enabled the uptake and processing of organic matter (OM) to be tracked in the foraminiferal cell into individual fatty acids, using Gas Chromatography - Mass Spectrometry (selective ion scan). These results suggest that calcareous Foraminifera, in particular U. ex. gr. semiornata, play a central role in OM cycling on the sea-floor in the upper part of the Pakistan margin OMZ.