Laura Arin

Seasonal changes of water mass structure and shelf slope exchanges at the Ebro Shelf (NW Mediterranean)

Among several field efforts undertaken in the framework of the EU MAST-III FANS project, three oceanographic cruises covering the Ebro shelf and slope regions (NW Mediterranean) were carried out on board R/V Garcia del Cid between November 1996 and July 1997. A major aim of these three cruises was to provide insight into the seasonal variability of the distribution of physico-chemical oceanographic parameters and the shelf/slope circulation. In this paper we discuss the observed changes in the hydrographic structure, the spatial distribution of nutrients, chlorophyll and suspended particulate matter and the local circulation in relationship to the seasonal variability of the Ebro river discharge rates and the water column stratification. The added effects of mesoscale circulation structures and of the exchanges across the shelf edge are also addressed.

Management of Ostreopsis Blooms in Recreational waters along the Catalan Coast (NW Mediterranean Sea): Cooperation between a Research Project and a Monitoring Program

Abstract As shown in this report, the integration of a research project with a monitoring program improves the detection and management of Ostreopsis blooms in Catalonia. The research project benefits from information previously obtained from several localities by the monitoring program, which in turn profits from the specific findings and conclusions contributed by the research project.

Hydrography and biochemical indicators of microplankton biomass in the Bransfield Strait (Antarctica) during January 1994

The relationships between hydrography and spatial distribution of several biochemical indicators of microplankton biomass (chlorophyll, protein and ATP) were studied in an area covering the eastern part of the Bransfield Strait and the northern part of the Weddell Sea, during Antarctic summer (January 1994). Four hydrographic zones were identified: (a) the northern part of the Bransfield Strait, covered by waters of Bellings- hausen Sea origin; (b) a Weddell Sea water mass that affected most of the study area; (c) the Weddell-Scotia Confluence waters, observed north of Elephant Island; and (d) waters influenced by ice melting, found towards the southeastern part of the sampled area. The highest values of biomass indicators (chlorophyll a, ATP and protein) were found in the zones affected by ice-melting processes and in waters from the Bellingshausen Sea. The lowest values of all biochemical parameters were found in the Weddell Sea and in the Weddell-Scotia Confluence waters. A high variability in the hydrographic structure and the distribution of biochemical indicators was observed. The degree of stabilization of the water column, the depth of the upper mixed layer and the grazing pressure of herbivorous zooplankton played a major role in the development, accumulation and spatial variability of microplankton biomass.

DETERMINATION OF RNA AND DNA CONCENTRATIONS IN NATURAL PLANKTON SAMPLES USING THIAZOLE ORANGE IN COMBINATION WITH DNASE AND RNASE DIGESTIONS

A fluorometric technique, based on the combination of RNase and DNase incubation with the use of thiazole orange (RNase/DNase method), was investigated to determine DNA and RNA concentrations in marine plankton. Tests were performed to optimize both RNase and DNase assay conditions. The RNase assay should be conducted at 37° C for 20 min with 0.5 μg·mL−1 of DNase‐free RNase. An incubation at 25° C for 20 min with 10 units ·mL‐1 of RNase‐free DNase were the optimal conditions required for DNA digestion by DNase. The detection limits in terms of minimum biomass for reliable measurements of DNA and RNA were 7.5 and 10 μg of protein · (mL assay)−1, respectively.

Seawater–atmosphere O2 exchange rates in open-top laboratory microcosms: application for continuous estimates of planktonic primary production and respiration

Seawater-atmosphere O(2) exchange rates were experimentally measured in open-top laboratory microcosms. The objective was to establish the relationships between turbulence and oxygen transfer velocity, and thus correct continuously measured day-night changes in dissolved oxygen as estimates of planktonic primary production and respiration. After saturating 15-l sterile seawater microcosms with an oxygen-poor gas mix (4.9% O(2), 95.1% N(2)), the microcosms were left to equilibrate with the atmosphere under different turbulence conditions. The rate of increase in dissolved O(2) was measured at 15-min intervals with polarographic-pulsed electrodes and the corresponding values of the oxygen transfer velocity (the K(O(2)) constant for the different turbulence conditions) were determined. After pooling these and literature data obtained in similar experimental conditions, the relation between epsilon (turbulent kinetic energy dissipation rates) and K(O(2)) was determined. Theoretical K(O(2)) values were also calculated using semi-empirical models in which oxygen transfer velocity (K(O(2))) is related to wind velocity. Theoretical, wind related K(O(2)) values were significantly higher than the experimental ones, and as a consequence overestimate primary production and underestimate respiration rates, even resulting in nocturnal O(2) increase. The magnitude of the differences between experimentally derived and theoretically calculated oxygen transfer velocity, precludes the use of wind-derived equations to calculate K(O(2)) in meso- and microcosms experiments not affected by wind, while the equation obtained relating experimental epsilon and K(O(2)) provides statistically reliable estimations of primary production and respiration.

Pros and Cons of Biological Quality Element Phytoplankton as a Water-Quality Indicator in the NW Mediterranean Sea

The Water Framework Directive (WFD) mandates the use of biological quality element (BQE) phytoplankton to assess the ecological status of coastal and transitional water bodies (WB). Here, we present (i) a critique of the general ecological assumptions of the WFD, (ii) a review of the ecological features of coastal phytoplankton dynamics, (iii) several approaches to establish a methodology to assess water-quality along the Catalan coast (NW Mediterranean Sea) based on BQE phytoplankton, and (iv) a critical examination of the use of phytoplankton as a BQE. Since 2005, we have followed several approaches aimed at assessing water-quality based on BQE phytoplankton and linking this indicator to a proxy to a costal pressure index. We have therefore studied phytoplankton communities at three different levels: as potentially harmful species, as functional or taxonomic groups, and with respect to their bloom frequency. Despite intense efforts, none of these fulfilled the WFD’s management requirements, which in this context were found to contain several inherent flaws. As an alternative, we propose a methodology to assess water-quality based on the use of chlorophyll-a (Chl-a), as a proxy of phytoplankton biomass. The Chl-a concentration offers a very simple and representative measure of the phytoplankton community, and, importantly, it is used worldwide in water-quality studies, thus allowing not only regional but also cross-country comparisons. Moreover, because Chl-a concentrations clearly respond to nutrient enrichment, we were able to establish a BQE-specific typology for water bodies based on salinity, which is linked to nutrient loads. Using a newly developed coastal pressure index (Land Use Simplified Index, LUSI) that also reflects nutrient inputs, we demonstrated a significant pressure–impact relationship, as required by the WFD for management purposes. Based on this relationship, we were able to define reference conditions and water-quality boundaries for each type. We conclude our discussion with a consideration of the pros and cons of the use of phytoplankton as a BQE.