Distinct gelatinous zooplankton communities across a dynamic shelf sea.

Understanding how gelatinous zooplankton communities are structured by local hydrography and physical forcing has important implications for fisheries and higher trophic predators. Although a large body of research has described how fronts, hydrographic boundaries, and different water masses (e.g., mixed vs. stratified) influence phytoplankton and zooplankton communities, comparatively few studies have investigated their influence on gelatinous zooplankton communities. In July 2015, 49 plankton samples were collected from 50 m depth to the surface, across five transects in the Celtic Sea, of which, four crossed the Celtic Sea Front. Two distinct gelatinous communities were found in this dynamic shelf sea: a cold water community in the cooler mixed water that mainly contained neritic taxa and a warm water community in the warmer stratified water that contained a mixture of neritic and oceanic taxa. The gelatinous biomass was 40% greater in the warm water community (∼ 2 mg C m-3) compared with the cold water community (∼ 1.3 mg C m-3). The warm water community was dominated by Aglantha digitale, Lizzia blondina, and Nanomia bijuga, whereas the cold water community was dominated by Clytia hemisphaerica and ctenophores. Physonect siphonophores contributed > 36% to the gelatinous biomass in the warm water community, and their widespread distribution suggests they are ecologically more important than previously thought. A distinct oceanic influence was also recorded in the wider warm water zooplankton community, accounting for a ∼ 20 mg C m-3 increase in biomass in that region.

Distribution, occurrence and biotoxin composition of the main shellfish toxin producing microalgae within European waters: A comparison of methods of analysis.

Harmful algal blooms (HABs) are a natural global phenomena emerging in severity and extent. Incidents have many economic, ecological and human health impacts. Monitoring and providing early warning of toxic HABs are critical for protecting public health. Current monitoring programmes include measuring the number of toxic phytoplankton cells in the water and biotoxin levels in shellfish tissue. As these efforts are demanding and labour intensive, methods which improve the efficiency are essential. This study compares the utilisation of a multitoxin surface plasmon resonance (multitoxin SPR) biosensor with enzyme-linked immunosorbent assay (ELISA) and analytical methods such as high performance liquid chromatography with fluorescence detection (HPLC-FLD) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for toxic HAB monitoring efforts in Europe. Seawater samples (n=256) from European waters, collected 2009-2011, were analysed for biotoxins: saxitoxin and analogues, okadaic acid and dinophysistoxins 1/2 (DTX1/DTX2) and domoic acid responsible for paralytic shellfish poisoning (PSP), diarrheic shellfish poisoning (DSP) and amnesic shellfish poisoning (ASP), respectively. Biotoxins were detected mainly in samples from Spain and Ireland. France and Norway appeared to have the lowest number of toxic samples. Both the multitoxin SPR biosensor and the RNA microarray were more sensitive at detecting toxic HABs than standard light microscopy phytoplankton monitoring. Correlations between each of the detection methods were performed with the overall agreement, based on statistical 2×2 comparison tables, between each testing platform ranging between 32% and 74% for all three toxin families illustrating that one individual testing method may not be an ideal solution. An efficient early warning monitoring system for the detection of toxic HABs could therefore be achieved by combining both the multitoxin SPR biosensor and RNA microarray.

Anthropogenic influence on sediment transport in the Whittard Canyon, NE Atlantic.

Unusual peaks in turbidity were detected in two branches of the Whittard Canyon in June 2013. Enhanced nepheloid layers (ENLs) were defined as layers with concentrations of suspended particulate matter exceeding those of nepheloid layers typically observed in a given region. Here, ENLs had peaks in turbidity and elevated suspended particulate matter concentrations exceeding ~1 mg L(-1) with the largest ENLs measuring between ~2-8 mg L(-1). The ENLs measured ~100-260 m in vertical height and were detected in water depths of between 640 and 2880 m. Vessel Monitoring System data showed that high spatial and temporal activity of potential bottom trawling vessels coincided with the occurrence of the ENLs. Molar C/N ratios of the suspended organic material from the ENLs showed a high degree of degradation. Regular occurrences of such events are likely to have implications for increased sediment fluxes, burial of organic carbon and alteration of benthic and canyon ecosystems.

Evolution of the MIDTAL microarray: the adaption and testing of oligonucleotide 18S and 28S rDNA probes and evaluation of subsequent microarray generations with Prymnesium spp. cultures and field samples.

The toxic microalgal species Prymnesium parvum and Prymnesium polylepis are responsible for numerous fish kills causing economic stress on the aquaculture industry and, through the consumption of contaminated shellfish, can potentially impact on human health. Monitoring of toxic phytoplankton is traditionally carried out by light microscopy. However, molecular methods of identification and quantification are becoming more common place. This study documents the optimisation of the novel Microarrays for the Detection of Toxic Algae (MIDTAL) microarray from its initial stages to the final commercial version now available from Microbia Environnement (France). Existing oligonucleotide probes used in whole-cell fluorescent in situ hybridisation (FISH) for Prymnesium species from higher group probes to species-level probes were adapted and tested on the first-generation microarray. The combination and interaction of numerous other probes specific for a whole range of phytoplankton taxa also spotted on the chip surface caused high cross reactivity, resulting in false-positive results on the microarray. The probe sequences were extended for the subsequent second-generation microarray, and further adaptations of the hybridisation protocol and incubation temperatures significantly reduced false-positive readings from the first to the second-generation chip, thereby increasing the specificity of the MIDTAL microarray. Additional refinement of the subsequent third-generation microarray protocols with the addition of a poly-T amino linker to the 5' end of each probe further enhanced the microarray performance but also highlighted the importance of optimising RNA labelling efficiency when testing with natural seawater samples from Killary Harbour, Ireland.

An assessment of RNA content in Prymnesium parvum, Prymnesium polylepis, cf. Chattonella sp. and Karlodinium veneficum under varying environmental conditions for calibrating an RNA microarray for species detection.

Traditional methods of identification and enumeration can be somewhat ambiguous when identifying phytoplankton that requires electron microscopic examination to verify specific morphological features. Members of the genus Prymnesium (division Haptophyta), members of the Raphidophyceae and naked dinoflagellates are examples of such phytoplankton whose identification can be difficult. One alternative to traditional microscopy-based methods of identification is to use molecular protocols to detect target species. Methods that measure cellular DNA and RNA content can be used to estimate the number of cells present in a sample. This study investigated the variation of RNA yields in Prymnesium parvum, P. polylepis, cf. Chattonella sp. and Karlodinium veneficum cells grown under different light, temperature, salinity and inorganic nutrient conditions. This information was used to calibrate the signal intensity of a variety of oligonucleotide probes spotted onto the microarrays for the detection of toxic algae (MIDTAL), which is being developed to aid national monitoring agencies and to provide a faster means of identifying and quantifying harmful phytoplankton in water column samples.

The influence of bloom intensity on the encystment rate and persistence of Alexandrium minutum in Cork Harbor, Ireland.

Toxic Alexandrium minutum blooms recur annually in Cork Harbor, Ireland where they initiate in an inlet known as the North Channel. The dynamics of these blooms have been studied since 2003, and a high degree of inter-annual variability in the cell densities has been observed. Two intense blooms, with maximum cell densities >500,000cellsL-1, were observed in the summers of 2004 and 2011. Annual cyst surveys during winter found that cyst densities decreased after the 2004 bloom, and by 2010 an average of ca. 40 cystsg dry wt sediment-1 was recorded. The intensity of blooms was found to be independent of the cyst density measured the previous winter. The cyst input to the sediment during both intense and low density blooms was measured directly through the deployment of sediment traps in the North Channel. The data allowed an estimate of the proportion of the A. minutum vegetative cells that underwent successful encystment, which averaged at 2.5% across a range of cell densities spanning three orders of magnitude. Maturation times of fresh cysts were determined at 5, 10 and 15°C. The maturation time at 15°C was found to be approximately 5 months, a value which increased by two months for a 5° decrease in temperature. A cyst dynamics model was constructed based on the field data to simulate the temporal variation of A. minutum cysts in the oxic layer of sediment. It revealed that a degree of resuspension is required to prevent cyst stocks from becoming exhausted in the thin oxic layer at the surface of the sediment. The model also demonstrated that the cysts supplied by periodic intense blooms, which occur with a frequency of every 7-8 years, are not in themselves enough to allow the population to persist over long time scales (decades). The cyst input from interim blooms of lower density is however enough to ensure the annual inoculation of the water column with A. minutum cells.

Megacities and large urban agglomerations in the coastal zone: interactions between atmosphere, land, and marine ecosystems.

Megacities are not only important drivers for socio-economic development but also sources of environmental challenges. Many megacities and large urban agglomerations are located in the coastal zone where land, atmosphere, and ocean meet, posing multiple environmental challenges which we consider here. The atmospheric flow around megacities is complicated by urban heat island effects and topographic flows and sea breezes and influences air pollution and human health. The outflow of polluted air over the ocean perturbs biogeochemical processes. Contaminant inputs can damage downstream coastal zone ecosystem function and resources including fisheries, induce harmful algal blooms and feedback to the atmosphere via marine emissions. The scale of influence of megacities in the coastal zone is hundreds to thousands of kilometers in the atmosphere and tens to hundreds of kilometers in the ocean. We list research needs to further our understanding of coastal megacities with the ultimate aim to improve their environmental management.

An evaluation of the applicability of microarrays for monitoring toxic algae in Irish coastal waters.

The applicability of microarrays to monitor harmful algae across a broad range of ecological niches and toxic species responsible for harmful algal events has been one of the key tasks in the EU Seventh Framework Programme (FP7)-funded Microarrays for the Detection of Toxic Algae project. The technique has a strong potential for improving speed and accuracy of the identification of harmful algae and their toxins to assist monitoring programmes. Water samples were collected from a number of coastal sites around Ireland, including several that are used in the Irish National Phytoplankton and Biotoxin Monitoring Programme. Ribosomal RNA was extracted from filtered field samples, labelled with a fluorescent dye, and hybridised to probes spotted in a microarray format on a glass slide. The fluorescent signal intensity of the hybridisation to >120 probes on the chip was analysed and compared with actual field counts. There was a general agreement between cell counts and microarray signal. Results are presented for field samples taken from a range of stations along the Irish coastline known for harmful algal events during the first field trial (July 2009-April 2010).

Co-occurrence of the West European (Gr.III) and North American (Gr.I) ribotypes of Alexandrium tamarense (Dinophyceae) in Shetland, Scotland.

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 approximately 10 m depth and extending over 6 km was detected in 'Clift Sound' with concentrations locally reaching approximately 1 x 10(4) cells l(-1). 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 approximately 1.5 x 10(3) cells l(-1) 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.

Evaluation of taxa-specific real-time PCR, whole-cell FISH and morphotaxonomy analyses for the detection and quantification of the toxic microalgae Alexandrium minutum (Dinophyceae), Global Clade ribotype.

The dinoflagellate genus Alexandrium contains neurotoxin-producing species that have adversely affected the aquaculture industry in many countries. The morphological similarity between Alexandrium species has led to the development of molecular methods for the discrimination, enumeration and monitoring of toxic and nontoxic species. A quantitative real-time PCR assay (qRT-PCR) targeting the internal transcribed spacer 1-5.8S rRNA gene using hybridization probe technology was developed for the potentially toxic species Alexandrium minutum (Global Clade) (GC). The assay was specific with a detection limit of less than one cell equivalent. The assay was used to detect and quantify A. minutum (GC) in seawater samples collected during summer 2007 in Cork Harbour, Ireland. The results were compared with those obtained using whole-cell FISH (WC-FISH) and morphotaxonomy analyses. Alexandrium minutum did not reach high bloom concentrations over the sampling period (maximum of c. 6 x 10(4) cells L(-1)), and the average concentrations determined using qRT-PCR, WC-FISH and morphotaxonomy did not significantly differ in eight of nine comparisons. Regression curves showed positive relationships between the methods; WC-FISH and qRT-PCR slightly under- and overestimated, respectively, the A. minutum concentrations compared with the morphotaxonomy method. The qRT-PCR assay for A. minutum (GC) offers high-throughput sample analysis and may prove suitable for implementation in microalgae monitoring programmes and assist in population dynamics studies of the species.

Ocean urea fertilization for carbon credits poses high ecological risks.

The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.

Influence of inorganic nutrition on growth and PSP toxin production of Alexandrium minutum (Dinophyceae) from Cork Harbour, Ireland.

The physiological response of the PSP toxin producing dinoflagellate Alexandrium minutum isolated from the Irish coast was assessed after modulating the initial concentrations of nitrate and phosphate in batch cultures. The cell growth in cultures of strain CK.A02 was primarily controlled by nitrate availability. In all experiments, only gonyautoxins 2 and 3 (GTX2 and 3) were synthesized along the different growth phases, with GTX3 dominating ( approximately 80%) at all stages, making the GTX2-3 toxin profile a possible population marker of A. minutum in Cork Harbour. The cellular toxin quotas remained low and relatively stable at around 2 pg cell(-1), except when high N:P ratios were initially used for culture inoculations; in these conditions PSP toxins accumulated up to 14 pg cell(-1). Due to the composition of the toxin profile, the toxicity of strain CK.A02 was generally relatively low (from 1.1 to 1.7 pg STX eqcell(-1)) in comparison with strains from other geographic areas except when phosphate limiting culture conditions were applied (maximum of 12.5 pg STX eq cell(-1)). Results showed that sufficient soluble protein quotas were necessary to observe the intra-cellular accumulation of PSP toxins in phosphate limiting conditions, highlighting also the requirement of adequate nitrogen supplies. The possible existence of localized toxicity hot spots in the field, linked to the accumulation of PSP toxins within A. minutum cells as a metabolic response to adverse environmental conditions, could potentially increase risks for shellfish farming operations.

Characterization of nontoxic and toxin-producing strains of Alexandrium minutum (Dinophyceae) in Irish coastal waters.

A comparative analysis of the morphology, toxin composition, and ribosomal DNA (rDNA) sequences was performed on a suite of clonal cultures of the potentially toxic dinoflagellate Alexandrium minutum Halim. These were established from resting cysts or vegetative cells isolated from sediment and water samples taken from the south and west coasts of Ireland. Results revealed that strains were indistinguishable, both morphologically and through the sequencing of the D1-D2 domain of the large subunit and the ITS1-5.8S-ITS2 regions of the rDNA. High-performance liquid chromatography fluorescence detection analysis, however, showed that only strains derived from retentive inlets on the southern Irish coast synthesized paralytic shellfish poisoning (PSP) toxins (GTX2 and GTX3), whereas all strains of A. minutum isolated from the west coast were nontoxic. Toxin analysis of net hauls, taken when A. minutum vegetative cells were in the water column, revealed no PSP toxins in samples from Killary Harbor (western coast), whereas GTX2 and GTX3 were detected in samples from Cork Harbor (southern coast). These results confirm the identity of A. minutum as the most probable causative organism for historical occurrences of contamination of shellfish with PSP toxins in Cork Harbor. Finally, random amplification of polymorphic DNA was carried out to determine the degree of polymorphism among strains. The analysis showed that all toxic strains from Cork Harbor clustered together and that a separate cluster grouped all nontoxic strains from the western coast.