SAMS

A mathematical model was developed to represent the dynamics of predation and assimilation of ingested material by heterotrophic marine micro-zooplankton. Predation rate was made a rectangular hyperbolic function of prey carbon (C) concentration modified to simulate the prey selectivity that these organisms have been observed experimentally to exhibit in response to prey nutritional quality. We chose prey N:C ratio as an index of selectivity and related both the maximum predation rate (PM) and the assimilation efficiency (AE) to changes in prey nitrogen:carbon (N:C). Changes in PM simulated the phenomena of "surge feeding" and "prey rejection". Changes in AE simulated sub-optimal assimilation of material from ingested prey, which in turn, served to decrease the ingestion rate on this material. The model was parameterised using laboratory data sets that followed ingestion of non-growing phytoplankton prey of different N:C ratio by a microflagellate predator. Investigative simulations in transient conditions, incorporating growing prey and hence with changing N:C ratio, indicated both PM and AE influenced the quantitative and temporal dynamics of C transfer to the higher trophic level. In particular, we noted that although various model formulations predicted similar trophic transfer of C, this was achieved on very different time scales. The inclusion of heterotrophic micro-zooplankton within food web models is a necessary step in accurate prediction of pelagic nutrient flux but requires physiological models carefully parameterised and tested in both steady state and transient conditions to ensure accurate simulation.

A nutrient-manipulation mesocosm study was conducted in Norwegian coastal waters to determine the effect on a nitrogen-limited microbial food web of changes in the relative concentrations of dissolved organic and inorganic nitrogen (N). Four replicated treatments were studied: no N addition, inorganic N, organic N, or a 50 : 50 mix of inorganic and organic N. Comprehensive abundance, biomass, and rate measurements were made over the 20-d experiment. The form of N available influenced species composition, succession, and the efficiency of carbon (C) incorporation. Inorganic N generated a bloom of the diatom Leptocylindrus danicus, even though silicon concentrations were below 1 mmol L 21 . The c-proteobacteria initially competed effectively with diatoms for inorganic N, exhibiting high productivity and escaping grazing control. Organic N, when available alone, was utilized more slowly by the microbial community, with diatom growth, fueled by regenerated N, achieving a lower peak abundance. A more diverse diatom species assemblage was also evident. The c-proteobacteria were less prevalent and net bacterial productivity was initially lower when the N source was organic and, in contrast to the response following inorganic N addition, the bacterial community was initially grazer controlled. A rapid succession of heterotrophic grazers occurred but with differences in species and their contribution to biomass between treatments. The efficiency of C-biomass production was lower when the N source was purely organic. However, when both inorganic and organic N were available, biomass yield was greater than the mean of the two single N source treatments. 1 Corresponding author ([email protected]).

Phytoplankton underpin the marine food web in shelf seas, with some species having properties that are harmful to human health and coastal aquaculture. Pressures such as climate change and anthropogenic nutrient input are hypothesized to influence phytoplankton community composition and distribution. Yet the primary environmental drivers in shelf seas are poorly understood. To begin to address this in North Western European waters, the phytoplankton community composition was assessed in light of measured physical and chemical drivers during the ''Ellett Line'' cruise of autumn 2001 across the Scottish Continental shelf and into adjacent open Atlantic waters. Spatial variability existed in both phytoplankton and environmental conditions, with clear differences not only between on and off shelf stations but also between different on shelf locations. Temperature/salinity plots demonstrated different water masses existed in the region. In turn, principal component analysis (PCA), of the measured environmental conditions (temperature, salinity, water density and inorganic nutrient concentrations) clearly discriminated between shelf and oceanic stations on the basis of DIN:DSi ratio that was correlated with both salinity and temperature. Discrimination between shelf stations was also related to this ratio, but also the concentration of DIN and DSi. The phytoplankton community was diatom dominated, with multidimensional scaling (MDS) demonstrating spatial variability in its composition. Redundancy analysis (RDA) was used to investigate the link between environment and the phytoplankton community. This demonstrated a significant relationship between community composition and water mass as indexed by salinity (whole community), and both salinity and DIN:DSi (diatoms alone). Diatoms of the Pseudo-nitzschia seriata group occurred at densities potentially harmful to shellfish aquaculture, with the potential for toxicity being elevated by the likelihood of DSi limitation of growth at most stations and depths.

The recently completed European Census of Marine Life, conducted within the framework of the global Census of Marine Life programme (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010), markedly enhanced our understanding of marine biodiversity in European Seas, its importance within ecological systems, and the implications for human use. Here we undertake a synthesis of present knowledge of biodiversity in European Seas and identify remaining challenges that prevent sustainable management of marine biodiversity in one of the most exploited continents of the globe. Our analysis demonstrates that changes in faunal standing stock with depth depends on the size of the fauna, with macrofaunal abundance only declining with increasing water depth below 1000 m, whilst there was no obvious decrease in meiofauna with increasing depth. Species richness was highly variable for both deep water macro-and meio-fauna along latitudinal and longitudinal gradients. Nematode biodiversity decreased from the Atlantic into the Mediterranean whilst latitudinal related biodiversity patterns were similar for both faunal groups investigated, suggesting that the same environmental drivers were influencing the fauna. While climate change and habitat degradation are the most frequently implicated stressors affecting biodiversity throughout European Seas, quantitative understanding, both at individual and cumulative/synergistic level, of their influences are often lacking. Full identification and quantification of species, in even a single marine habitat, remains a distant goal, as we lack integrated data-sets to quantify these. While the importance of safeguarding marine biodiversity is recognised by policy makers, the lack of advanced understanding of species diversity and of a full survey of any single habitat raises huge challenges in quantifying change, and facilitating/prioritising habitat/ecosystem protection. Our study highlights a pressing requirement for more complete biodiversity surveys to be undertaken within contrasting habitats, together with investigations in biodiversity-ecosystem functioning links and identification of separate and synergistic/cumulative humaninduced impacts on biodiversity.

An investigation into the diversity of the dinoflagellate Alexandrium was carried out during August 2007 within two fjordic sea lochs in the Shetland Isles, Scotland. The co-occurrence in the water column of the non-toxic West European (W.E. or Gr.III) and the neurotoxic North American (N.A. or Gr.I) ribotypes of A. tamarense was demonstrated using fluorescent in situ hybridisation. A patch of A. tamarense (W.E.) localised at $10 m depth and extending over 6 km was detected in 'Clift Sound' with concentrations locally reaching $1 Â 10 4 cells l À1 . A. tamarense (N.A.) was also observed there but despite the presence of toxins in net haul samples collected locally, concentrations were low and near limits of detection. Alexandrium concentrations were $1.5 Â 10 3 cells l À1 in 'Vaila Sound', where both W.E. and N.A. ribotypes were detected with equal relative abundances in some samples. Given the patchiness of A. tamarense populations and their possible organisation in thin layer structures, better vertical resolution through fine-scale sampling will be necessary for population dynamic studies. Implications for the shellfish industry are substantial since harmful microalgae patches may not be detected during routine monitoring. Moreover, the co-occurrence of morphologically indistinct toxic and non-toxic ribotypes will necessitate implementing molecular methods for their discrimination.

High-biomass harmful algal blooms can kill farmed fish through toxicity, physical effects or de-oxygenation of the water column. These blooms often form over spatially large areas meaning that Earth observation is well placed to monitor and study them. In this letter, we present a statistical-based background subtraction technique that has been modified to detect high-biomass algal blooms. The method builds upon previous work and uses a statistical framework to combine spatial and temporal information to produce maps of bloom extent. Its statistical nature allows the approach to characterize the region of interest meaning that region-specific tuning is not needed. The accuracy of the approach has been evaluated using Moderate Resolution Imaging Spectroradiometer (MODIS) data and an in situ cell concentration dataset, resulting in a correct classification rate of 68.0% with a false alarm rate of 0.24 (n = 25). The method is then used to study the surface coverage of a large high-biomass harmful algal bloom of Karenia mikimotoi. The approach shows promise for the early warning of spatially large high-biomass algal blooms, providing valuable information to support in situ sampling campaigns.

High biomass Harmful Algal Blooms (HABs) such as Karenia mikimotoi and shellfish toxin producing HAB species continue to be observed in UK and Republic of Ireland waters. Regional differences continue to be seen in the distribution of HABs in UK and RoI waters with impacts mainly observed in the south and west coast of Ireland and regions in the UK with a strong Atlantic influence e.g. Regions 1, 3, 4, 6 and 7. There is little monitoring aside from the continuous plankton recorder (CPR) in Region 8. The impacts from HABs in Wales, Northern Ireland and the Isle of Man are generally low.