Long-term variability and environmental preferences of calycophoran siphonophores in the Bay of Villefranche (North-Western Mediterranean)

Long-term variability of the main calycophoran siphonophores was investigated between 1974 and 1999 in a coastal station in the north-western Mediterranean. The data were collected at weekly frequency using a macroplankton net (680 μm mesh size) adapted to quantitatively sample delicate gelatinous plankton. A 3-year collection (1967–1969) of siphonophores from offshore waters using the same methodology showed that the patterns of variability observed inshore were representative of siphonophores’ changes at a regional scale. The aims of the study were: (i) to investigate the patterns of variability that characterised the dominant calycophoran species and assemblages; (ii) to identify the environmental optima that were associated with a significant increase in the dominant siphonophore species and (iii) to verify the influence of hydroclimatic variability on long-term changes of siphonophores. Our results showed that during nearly 3 decades the standing stock of calycophoran siphonophores did not show any significant change, with the annual maximum usually recorded in spring as a result of high densities of the dominant species Lensia subtilis, Muggiaea kochi and Muggiaea atlantica. Nevertheless, major changes in community composition occurred within the calycophoran population. Since the middle 1980s, M. kochi, once the most dominant species, started to decrease allowing other species, the congeneric M. atlantica and Chelophyes appendiculata, to increasingly dominate in spring and summer–autumn, respectively. The comparison of environmental and biotic long-term trends suggests that the decrease of M. kochi was triggered by hydrological changes that occurred in the north-western Mediterranean under the forcing of large-scale climate oscillations. Salinity, water stratification and water temperature were the main hydroclimatic factors associated with a significant increase of siphonophores, different species showing different environmental preferences.

Trophodynamics and stability of regional scale ecosystems in the Northeast Atlantic

This study addresses the long-term stability of three trophic groupings in the Northeast Atlantic at regional scales. The most abundant taxa representing phytoplankton, herbivorous copepods, and carnivorous zooplankton were examined from the Continuous Plankton Recorder database. Multivariate control charts using a Bray–Curtis similarity metric were used to assess whether fluctuations within trophic groupings were within or beyond the expected variability. Two evaluation periods were examined: annual changes between 1960 and 1999 (2000–2009 baseline) and recent changes between 2000 and 2009 (1960–1999 baseline). The trends over time in abundance/biomass of trophic levels were region-specific, especially in carnivorous copepods, where abundance did not mirror trends in the overall study area. The stability of phytoplankton was within the expected limits, although not in 2008 and 2009. Higher trophic levels were less stable, perhaps reflecting the added complexity of interactions governing their abundance. In addition, some regions were consistently less stable than others. Correlations in stability between adjacent trophic levels were positive at large marine ecosystem scale but generally non-significant at regional scales. The study suggests that certain regions may be particularly vulnerable to periods of instability in community structure. The benefits of using the control chart method rather than other multivariate measures of plankton dynamics are discussed.

The influence of phytoplankton productivity, temperature and environmental stability on the control of copepod diversity in the North East Atlantic

The patterns of copepod species richness (S) and their relationship with phytoplankton productivity, temperature and environmental stability were investigated at climatological, seasonal and year-to-year time scales as well as scales along latitudinal and oceanic–neritic gradients using monthly time series of the Continuous Plankton Recorder (CPR) Survey collected in the North East Atlantic between 1958 and 2006. Time series analyses confirmed previously described geographic patterns. Equatorward and towards neritic environments, the climatological average of S increases and the variance explained by the seasonal cycle decreases. The bi-modal character of seasonality increases equatorward and the timing of the seasonal cycle takes place progressive earlier equatorward and towards neritic environments. In the long-term, the climatological average of S decreased significantly (p < 0.001) between 1958 and 2006 in the Bay of Biscay and North Iberian shelf at a rate of ca. 0.04 year−1, and increased at the same rate between 1991 and 2006 in the northernmost oceanic location. The climatological averages of S correlate positively with those of the index of seasonality of phytoplankton productivity (ratio between the minimum and maximum monthly values of surface chlorophyll) and sea surface temperature, and negatively with those of the proxy for environmental stability (monthly frequency of occurrence of daily averaged wind speed exceeding 10 m s−1). The seasonal cycles of S and phytoplankton productivity (surface chlorophyll as proxy) exhibit similar features in terms of shape, timing and explained variance, but the relationship between the climatological averages of both variables is non-significant. From year-to-year, the annual averages of S correlate negatively with those of phytoplankton productivity and positively with those of sea surface temperature along the latitudinal gradient, and negatively with those of environmental stability along the oceanic–neritic gradient. The annual anomalies of S (i.e. factoring out geographic variation) show a unimodal relationship with those of sea surface temperature and environmental stability, with S peaking at intermediate values of the anomalies of these variables. The results evidence the role of seasonality of phytoplankton productivity on the control of copepod species richness at seasonal and climatological scales, giving support to the species richness–productivity hypothesis. Although sea surface temperature (SST) is indeed a good predictor of richness along the latitudinal gradient, it is unable to predict the increase of richness form oceanic to neritic environments, thus lessening the generality of the species richness–energy hypothesis. Meteo-hydrographic disturbances (i.e. SST and wind speed anomalies as proxies), presumably through its role on mixed layer depth dynamics and turbulence and hence productivity, maximise local diversity when occurring at intermediate frequency and or intensity, thus providing support to the intermediate disturbance hypothesis on the control of copepod diversity.

Coccolithophore bloom detection in the north east Atlantic using SeaWiFS: Algorithm description, application and sensitivity analysis

Coccolithophores are the largest source of calcium carbonate in the oceans and are considered to play an important role in oceanic carbon cycles. Current methods to detect the presence of coccolithophore blooms from Earth observation data often produce high numbers of false positives in shelf seas and coastal zones due to the spectral similarity between coccolithophores and other suspended particulates. Current methods are therefore unable to characterise the bloom events in shelf seas and coastal zones, despite the importance of these phytoplankton in the global carbon cycle. A novel approach to detect the presence of coccolithophore blooms from Earth observation data is presented. The method builds upon previous optical work and uses a statistical framework to combine spectral, spatial and temporal information to produce maps of coccolithophore bloom extent. Validation and verification results for an area of the north east Atlantic are presented using an in situ database (N = 432) and all available SeaWiFS data for 2003 and 2004. Verification results show that the approach produces a temporal seasonal signal consistent with biological studies of these phytoplankton. Validation using the in situ coccolithophore cell count database shows a high correct recognition rate of 80% and a low false-positive rate of 0.14 (in comparison to 63% and 0.34 respectively for the established, purely spectral approach). To guide its broader use, a full sensitivity analysis for the algorithm parameters is presented.

Basking sharks and oceanographic fronts: quantifying associations in the north‐east Atlantic

Understanding the mechanisms linking oceanographic processes and marine vertebrate habitat use is critical to effective management of populations of conservation concern. The basking shark Cetorhinus maximus has been shown to associate with oceanographic fronts – physical interfaces at the transitions between water masses – to exploit foraging opportunities resulting from aggregation of zooplankton. However, the scale, significance and variability of these observed associations have not yet been established. Here, we quantify the influence of mesoscale (10s – 100s km) frontal activity on habitat use over timescales of weeks to months. We use animal-mounted archival tracking with composite front mapping via Earth Observation (EO) remote sensing to provide an oceanographic context to individual shark movements. We investigate levels of association with fronts occurring over two spatio-temporal scales, (i) broad-scale seasonally persistent frontal zones and (ii) contemporaneous mesoscale thermal and chl-a fronts. Using random walk simulations and logistic regression within an iterative generalised linear mixed modelling (GLMM) framework, we find that seasonal front frequency is a significant predictor of shark presence. Temporally-matched oceanographic metrics also indicate that sharks demonstrate a preference for productive regions, and associate with contemporaneous thermal and chl-a fronts more frequently than could be expected at random. Moreover, we highlight the importance of cross-frontal temperature change and persistence, which appear to interact to affect the degree of prey aggregation along thermal fronts. These insights have clear implications for understanding the preferred habitats of basking sharks in the context of anthropogenic threat management and marine spatial planning in the northeast Atlantic.

Basking sharks and oceanographic fronts: quantifying associations in the north-east Atlantic

Understanding the mechanisms linking oceanographic processes and marine vertebrate habitat use is critical to effective management of populations of conservation concern. The basking shark Cetorhinus maximus has been shown to associate with oceanographic fronts – physical interfaces at the transitions between water masses – to exploit foraging opportunities resulting from aggregation of zooplankton. However, the scale, significance and variability of these observed associations have not yet been established. Here, we quantify the influence of mesoscale (10s – 100s km) frontal activity on habitat use over timescales of weeks to months. We use animal-mounted archival tracking with composite front mapping via Earth Observation (EO) remote sensing to provide an oceanographic context to individual shark movements. We investigate levels of association with fronts occurring over two spatio-temporal scales, (i) broad-scale seasonally persistent frontal zones and (ii) contemporaneous mesoscale thermal and chl-a fronts. Using random walk simulations and logistic regression within an iterative generalised linear mixed modelling (GLMM) framework, we find that seasonal front frequency is a significant predictor of shark presence. Temporally-matched oceanographic metrics also indicate that sharks demonstrate a preference for productive regions, and associate with contemporaneous thermal and chl-a fronts more frequently than could be expected at random. Moreover, we highlight the importance of cross-frontal temperature change and persistence, which appear to interact to affect the degree of prey aggregation along thermal fronts. These insights have clear implications for understanding the preferred habitats of basking sharks in the context of anthropogenic threat management and marine spatial planning in the northeast Atlantic.

Channel Catchments Cluster. Recent developments in tools and techniques for water quality management in the France (Channel) England region

The Channel Catchments Cluster (3C) aims to capitalise on outputs from some of the recent projects funded through the INTERREG IVa France (Channel) England programme. The river catchment basins draining into the Channel region drain an area of 137,000km2 and support a human population of over 19M. Throughout history, these catchments, rivers and estuaries have been centres of habitation, developed through commerce and industry, providing transport links to hinterland areas. These catchments also provide drinking water and food through provision of agriculture, fisheries and aquaculture. In addition, many parts of the region are also economically important now for the tourism and leisure industries. Consequently, there is a need to manage the balance of these many and varied human activities within the catchments, rivers, estuaries and marine areas to ensure that they are maintained or restored to good environmental condition . This document highlights some of the recent work carried out by projects within the INTERREG IVa programme that provide tools and techniques to assist in the achievement of these goals.