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Harmful algal blooms (HABs) are thought to be increasing in coastal waters worldwide. Anthropogenic nutrient enrichment has been proposed as a principal causative factor of this increase through elevated inorganic and/or organic nutrient concentrations and modified nutrient ratios. We assess: 1) the level of understanding of the link between the amount, form and ratio of anthropogenic nutrients and HABs; 2) the evidence for a link between anthropogenically generated HABs and negative impacts on human health; and 3) the economic implications of anthropogenic nutrient/HAB interactions. We demonstrate that an anthropogenic nutrient-HAB link is far from universal, and where it has been demonstrated, it is most frequently associated with high biomass rather than low biomass (biotoxin producing) HABs. While organic nutrients have been shown to support the growth of a range of HAB species, insufficient evidence exists to clearly establish if these nutrients specifically promote the growth of harmful species in preference to benign ones, or if/how they influence toxicity of harmful species. We conclude that the role of anthropogenic nutrients in promoting HABs is site-specific, with hydrodynamic processes often determining whether blooms occur. We also find a lack of evidence of widespread significant adverse health impacts from anthropogenic nutrient-generated HABs, although this may be partly due to a lack of human/animal health and HAB monitoring. Detailed economic evaluation and cost/benefit analysis of the impact of anthropogenically generated HABs, or nutrient reduction schemes to alleviate them, is also frequently lacking.

Although the terms 'health' and 'healthy' are often applied to marine ecosystems and communicate information about holistic condition (e.g. as required by the Ecosystem Approach), their meaning is unclear. Ecosystems have been understood in various ways, from non-interacting populations of species to complex integrated systems. Health has been seen as a metaphor, an indicator that aggregates over system components, or a non-localized emergent system property. After a review, we define good ecosystem health as: 'the condition of a system that is self-maintaining, vigorous, resilient to externally imposed pressures, and able to sustain services to humans. It contains healthy organisms and populations, and adequate functional diversity and functional response diversity. All expected trophic levels are present and well interconnected, and there is good spatial connectivity amongst subsystems.' We equate this condition with good ecological or environmental status, e.g. as referred to by recent EU Directives. Resilience is central to health, but difficult to measure directly. Ecosystems under anthropogenic pressure are at risk of losing resilience, and thus of suffering regime shifts and loss of services. For monitoring whole ecosystems, we propose an approach based on 'trajectories in ecosystem state space', illustrated with time-series from the northwestern North Sea. Change is visualized as Euclidian distance from an arbitrary reference state. Variability about a trend in distance is used as a proxy for inverse resilience. We identify the need for institutional support for long time-series to underpin this approach, and for research to establish state space co-ordinates for systems in good health. Changes in the northern North Sea, 1958-2008, plotted in a state space defined by the breeding success of kittiwakes, abundance of copepods Calanus spp., and simulated annual primary production.© Inter-Research 2013. www.int-res.com.

Dissolved organic nitrogen (DON) is recognised as an important N source for phytoplankton. However, its relative importance for phytoplankton nutrition and community composition has not been studied comprehensively. This study, conducted in a typical Scottish fjord, representative of near-pristine coastal environments, evaluates the utilisation of DON and dissolved inorganic nitrogen (DIN) by different microbial size fractions and the relationship of phytoplankton community composition with DON and other parameters. The study demonstrated that DON was important in supporting phytoplankton throughout the yearly production cycle. The higher-than-expected urea uptake rates and large fraction of the spring bloom production supported by DON suggested that organic N not only contributes to regenerated production and to the nutrition of the small phytoplankton fraction, but can also contribute substantially to new production of the larger phytoplankton in coastal waters. Multivariate statistical techniques revealed two phytoplankton assemblages with peaks in abundance at different times of the year: a spring group dominated by Skeletonema spp., Thalassiosira spp., and Pseudo-nitzschia spp. group delicatissima; and a summer/autumn group dominated by Chaetoceros spp., Scrippsiella spp., and Pseudo-nitzschia spp. group seriata. The multivariate pattern in community composition and abundance of these taxa was significantly correlated with the multivariate pattern of DON, urea, dissolved free amino acids, DIN, temperature, salinity, and daylength, with daylength and urea being particularly important, suggesting both physical and chemical controls on community composition.

There is a perception that anthropogenically-driven changes in nutrient supply to coastal waters influences the abundance, frequency and toxicity of harmful algal blooms (HABs) through a change in the form or ratio of nutrient that limits phytoplankton growth. If nutrient concentrations are not limiting for growth, then ratios do not influence floristic composition. At non-limiting concentrations, evidence that alteration of nitrogen: phosphorus (N:P) ratios has stimulated HABs is limited, and primarily based on hypothesised relationships in relatively few locations (in particular: Tolo Harbour Hong Kong and Dutch Coastal Waters). In all cases, an unequivocal causal link between an increase in HABs (frequency, magnitude or duration) and change in N or P as the limiting nutrient is difficult to establish. The silicon (Si) limitation hypothesis is generally supported by experimental evidence and field data on the nuisance flagellate Phaeocystis. We found little evidence that high N:Si ratios preferentially promote harmful dinoflagellates over benign species. Laboratory studies demonstrate that nutrient ratios can influence toxin production, but genus and species specific differences and environmental control make extrapolation of these data to the field difficult. Studies of the role of dissolved and particulate organic nutrients in the growth of HAB species, while limited, demonstrate the potential for organic nutrients (especially organic N) to support the growth of a range of HAB species. There is a clear need for better understanding of the role of mixotrophy in the formation of HABs and for studies of HAB and non-HAB species in competition for environmentally realistic concentrations of organic nutrients.

Recent European Court rulings in the context of eutrophication viewed proliferation of a particular species of algae as a disturbance to the balance of aquatic ecosystems and the proliferation of one or more species as a cause of a reduction in other species. We discuss the scientific basis for this opinion in relation to the growth of marine primary producers and current debates about ecosystem stability. Opposing views in this debate are those of (a) the ‘balance of nature’ paradigm, in which communities of organisms tend towards a stable climax composition, and (b) communities as dynamic systems that may be governed by ‘basins of attraction’ in state space. We use data from the Irish Sea and Narragansett Bay, together with a review of the literature, to show that: the dynamics of temperate marine phytoplankton, with seasonal successions, corresponds more to (b) than to (a); the temporary dominance of any one species of micro-alga or cyanobacterium is part of the natural dynamics of phytoplankton communities and does not permanently impact on other species. Understanding the phytoplankton as a dynamic system suggests its status should not be assessed against a 'climax' model and that eutrophication should be diagnosed from fundamental (nutrient-induced) perturbations of ecosystem state and function rather than from changes in fixed assemblages of species and thresholds of abundance.

The dinoflagellate Noctiluca scintillans is one of the most important and abundant red tide organisms and it is distributed world-wide. It occurs in two forms. Red Noctiluca is heterotrophic and fills the role of one of the microzooplankton grazers in the foodweb. In contrast, green Noctiluca contains a photosynthetic symbiont Pedinomonas noctilucae (a prasinophyte), but it also feeds on other plankton when the food supply is abundant. In this review, we document the global distribution of these two forms and include the first maps of their global distribution. Red Noctiluca occurs widely in the temperate to sub-tropical coastal regions of the world. It occurs over a wide temperature range of about 10°C to 25°C and at higher salinities (generally not in estuaries). It is particularly abundant in high productivity areas such as upwelling or eutrophic areas where diatoms dominate since they are its preferred food source. Green Noctiluca is much more restricted to a temperature range of 25°C–30°C and mainly occurs in tropical waters of Southeast Asia, Bay of Bengal (east coast of India), in the eastern, western and northern Arabian Sea, the Red Sea, and recently it has become very abundant in the Gulf of Oman. Red and green Noctiluca do overlap in their distribution in the eastern, northern and western Arabian Sea with a seasonal shift from green Noctiluca in the cooler winter convective mixing, higher productivity season, to red Noctiluca in the more oligotrophic warmer summer season.

Introduction. Nematodes are significant pests of bananas and plantains world- wide. Different levels of susceptibility to these pests have been reported. Studies were carried out to investigate differences in root systems and development of Musa clones with different levels of susceptibility and their possible role in the host-parasite relationship. Materials and methods. Five Musa clones, of which four were susceptible and one resistant to the nematode Radopholus similis, were grown in a plot naturally infested by this nematode. Root samples were collected 6 months after planting and measurements were made on the significance of tissue areas in root cross-sections, and the significance of root mass, root development and nematode populations with depth. Results. No significant difference was observed between cultivars in their general structural organisation or the relative significance of the tissue component of the root cross-section. A significantly lower number of air lacunae was found in the resistant acces- sion in comparison with the susceptible ones. All the accessions except Christine (ABB) were comparable in their root development in the soil profile with more than 70% of the total root mass produced above 40 cm. The greatest nematode population and damage on roots were found at depths between (20 and 40) cm. Conclusions. This is the first report on differences in air spaces between Musa cultivars, and their role in the Musa-nematode relationship needs further investigation. Musa / Cameroon / plant nematodes / host resistance to pests / roots / plant morphology / growth

International audience; The basin of Thau in southern France is a shallow, weakly flushed lagoon which is an important location for oyster cultivation. Phytoplankton analyses were carried out in 1975–1976 and then (almost) continuously since 1987. We report an investigation of ‘the balance of organisms’ in phytoplankton in relation to reductions in phosphorus loading, using two new tools based on phytoplankton lifeforms: the Plankton Index for Phytoplankton (PIp); Euclidean distance in state-space. Our results show the utility of the tools for analysing changes in the ‘balance of organisms’ at the level of functional groups (in our study diatoms and dinoflagellates), but also illustrate the difficulties in demonstrating the reversal of human impacts resulting from eutrophication.The comparison between 1987–89 and 1976 showed the expected ‘de-eutrophication’ due to the reduction in dissolved inorganic phosphate (DIP), with a decrease in dinoflagellate abundance. Since 1989, year-to-year variation in annual mean concentrations of DIP may have contributed to inter-annual variability in the balance of the two lifeforms, but the data suggest that the system has remained in a dynamically stable regime because: (1) there was no long-term trend in Euclidean distance from the reference; and (2) there was no increase in inter-annual variability about the time-series mean Euclidean distance suggesting there has been no decrease in resilience which might signal a regime change.Integrated management of human activities will be required to manage (and reduce) total P in the system. Monitoring phytoplankton and nutrients concentrations to determine how primary production and the balance of species respond to further changes in the nutrient status of the lagoon should be an integral part of any management programme.

Fluvial and sewage loading of N and P to Liverpool Bay (England) elevated winter con- centrations of dissolved inorganic N (29.2 µM) and P (1.7 µM) and molar ratios of N:P (17.0) and N:Si (6.0) compared to Irish coastal waters (9.5 µM N, 0.8 µM P; N:P 12.0 N:Si 1.9). At the enriched site in Liverpool Bay, enhanced spring production (up to 3165.8 mg C m -2 d -1 ) summer production (471.8 to 971.5 mg C m -2 d -1 ) and biomass (4.1 to 13.6 mg chorophyll m -3 ) was dominated by diatoms. Annual production at this site was estimated as 182 g C m -2 compared to 97 g C m -2 at the Irish coastal sta- tion. Enrichment and shifts in nutrient ratios did not favour flagellate growth compared to growth of diatoms in Liverpool Bay. Low amounts of sediment phytopigments (9.2 to 26 mg m -2 ), low concen- trations of pore water Si (mean, 9.8 µM), and a negligible summer benthic efflux of Si (1.0 µmol m -2 h -1 ) suggested little phytodetrital input to sediments in Liverpool Bay and that summer diatom pro- duction required an allochthonous supply of Si. At the Irish coastal station, coupling between benthic and water-column processes ensured that benthic efflux of Si was sufficient to support the bulk of summer diatom production. Water-column recycling of N was an order of magnitude greater than sediment recycling of N at both coastal sites.

Simple models which predict the dispersion and input of organic waste from cage fish farms can be used as management tools for the siting of farms and assessing the potential for enrichment of the benthic ecosystem. A modification of the sediment model originally described by Gowen et al. (1988) is presented. The modifications include: variation in bottom topography; changes in current speed with depth; correction of horizontal current flow in response to changing depth. Data from a fish farm in Chile are used to compare simulations of dispersion and sediment loading from the original and modified models.

Some forms of aquaculture cause significant impact on the natural environment and hence there is considered to be a need to control aquaculture developments. One approach would be to predict the impact prior to development and relate the predictions to predetermined standards. Predicting the otential for eutrophication requires the quantification of the amount of soluble waste being released from fish farms; use of numerical models to predict eutrophication in terms of enhanced phytoplankton biomass; establishment of environmental quality objectives and standards. This paper discusses the second and third requirements. Predictive models ranging from empirical relationships between variables to complex ecosystem models have been developed for managing eutrophication of lakes and coastal waters. The use of different types of model are discussed in the context of aquaculture development and it is concluded that empirical models should be used by regulatory authorities as a screening tool to provide a quantitative prediction of the potential for eutrophication. The establishment of environmental quality objectives and standards should be an integral part of any framework plan for aquaculture development. It is suggested that chlorophyll, rather than dissolved nutrients is a more appropriate variable to use as a standard for eutrophication associated with the growth of phytoplanton. It is concluded that there is a requirement for scientifically based values of standards to be set for coastal waters

Phytoplankton are free-floating plants found in marine and freshwaters that through their photosynthetic growth form the base of the aquatic food chain. A small subset of the phytoplankton may be harmful to human health or to human use of the ecosystem. The species that cause harm are now widely referred to as ‘Harmful Algae’ with the term ‘Harmful Algal Bloom’ (HAB) commonly being used to describe their occurrence and effects. In terms of human health, the most important consequence is the production, by some species, of biotoxins. Typically, biotoxin-producing phytoplankton species exist at relatively low densities (c. few hundred or thousand of cells per litre) with the toxins becoming concentrated in the flesh of organisms (particularly bivalve molluscs) that filter feed on phytoplankton. In most cases, there are no adverse effects to these primary consumers, but this concentrating mechanism creates a risk to health if the shellfish are consumed by humans. In this review, we provide an overview of the mechanisms through which marine phytoplankton may cause harm to humans in terms of heath, and the negative effects on the use of ecosystem services. Subsequently, we consider HAB issues in the area we are most familiar with: UK coastal waters. Finally, the methodologies used to safeguard human health from HAB-generated syndromes are discussed.

The distribution of plankton in relation to physical oceanographic features on the southern Malin Shelf and in the North Channel of the Irish Sea was investigated during August 1996. The near surface 13.5 degrees C isotherm and 35.20 isohaline marked the location of the Islay and Irish coastal fronts, respectively. An additional salinity front was observed to the south-east of Islay. A mergence of the Irish coastal front and the salinity component of the Islay front suggested that, at certain times, a frontal boundary separating coastal and oceanic water may extend from south-west Ireland north along the western Scottish Shelf. The presence of highly saline (>35.35) water on the outer shelf indicated the intrusion of Atlantic water. The frontal boundaries influenced the distribution of plankton on the southern Malin Shelf and in the North Channel. The outer shelf region was characterized by the presence of Chaetoceros atlanticus, Gonyaulax polygramma, Oxytoxum scolopax, Doliolum gegenbauri, Sagitta tasmanica, and S. maxima. Halosphaera minor and Limacina retroversa were distributed between the shelf edge and the Irish coastal and Islay fronts. Gyrodinium aureolum dominated the phytoplankton of the Islay front but in contrast, Ceratium longipes was restricted to the east of the Islay Front. The distinct spatial separation of species suggested that there was no exchange of southern Malin Shelf and North Channel water at the time of the study.

SynopsisLochs Fyne and Striven are deep-silled fjords opening into the northern Firth of Clyde. They receive relatively little freshwater from local runoff, have a relatively low rate of tidal exchange, and undergo periods of deep water stagnation. Both contain fish farms which have lost stock because of phytoplankton blooms. Loch Striven was investigated in detail in 1980. Observations are also reported for 1979 and 1981, and for Loch Fyne from 1980–1982. Most stratification in Striven is due to salinity layering, but most of the freshwater in the loch probably originates in the Clyde Estuary and is associated with high concentrations of nitrate. Typical phytoplankton biomasses in Striven are the same as those in the western seaboard Loch Creran, but maxima exceed those in Creran. In addition to a red tide of Gyrodinium aureolum in September, 1980, three periods of high biomass seem to be a regular feature of the phytoplankton calendar in Striven. The spring increase takes place in March or early April, is dominated by the diatom Skeletonema costalum, and probably depends on the stabilizing effects of reduced near-surface salinities. A summer flourishing of Leptocylindrus danicus and dinoflagellates is also associated with near-surface salinity layering. A late spring bloom of diatoms, dinoflagellates and small flagellates, some ichthyotoxic, appears to be related to the occurrence of thermohaline stratification and near-surface nutrient depletion; on some occasions lochhead upwelling may also have been involved. Insofar as data are available, the ecology of phytoplankton in Loch Fyne appears similar to that in Loch Striven.

The hydrography and phytoplankton ecology of Loch Ardbhair, a small sea-loch on the northwestern coast of Scotland, was studied between January 1981 and July 1982. Tidal exchange was the dominant hydrographie feature of the loch and the exchange time was estimated to be between 1 and 2 days. In 1981 seasonal changes in phytoplankton biomass and species succession were similar to other sea-lochs, although the spring peak, and summer levels of, phytoplankton biomass (3.0 and 1.0 mg chlorophyll · m−3 respectively) were lower than might have been predicted from winter levels of nitrate. Chlorophyll levels in Ardbhair were much higher in July 1982 (up to 3.5 mg · m−3) compared to July 1981 (0.7 mg · m−3) and the phytoplankton was dominated by dinoflagellates rather than microflagellates and diatoms. It is suggested that rapid exchange limits in situ growth of phytoplankton in Ardbhair and that phytoplankton biomass and species composition in Ardbhair closely resembles that of Eddrachillis Bay with which the loch exchanges. The importance of these results concerning the risk, to loch-based fish farms, from ichthyotoxic blooms is discussed.

14 souches de Nannochloris. Les besoins nutritifs, la forme et les dimensions sont d'importants moyens de discrimination de ces organismes dans la nature

The distributions of water column stratification, phytoplankton and nutrients were investigated in the Sound of Jura, Scotland, during July 1982 and June–July 1983. The amount of stratification was mainly related to variation in tidal currents and bathymetry along the length of the Sound. Frontal zones separated the well-mixed northern Sound, and lateral regions, from thermally stratified water in the middle of the Sound. In the south transitionally stratified water extended into the North Channel of the Irish Sea. The phytoplankton in well-mixed regions was dominated by diatoms, whereas naked dinoflagellates and microflagellates were important in stratified regions. The distribution of phytoplankton biomass, indicated by chlorophyll concentration averaged over the water column, is explained by the effects of vertical mixing on the average illumination experienced by phytoplankton and by the supply of nutrients to the euphotic zone. Highest mean water column chlorophyll was found near Islay, perhaps due to special local input of nutrients into the euphotic zone there. Biomass was also high in the southern region of transitional stratification. The northern and lateral fronts were not clearly associated with high phytoplankton biomass, perhaps because of the small size of the features in relation to the advective field. Phytoplankton biomass was generally low in well-mixed waters, and at the surface in well-stratified regions. It is suggested that transitional stratification may enhance productivity in the southern region to two to three times that in the well stratified and mixed regions of the Sound. The variations in stratification along the Sound may have important implications for primary productivity in the lochs that exchange with it.