Lidia Yebra

Lethal and sublethal effects of naphthalene and 1,2-dimethylnaphthalene on naupliar and adult stages of the marine cyclopoid copepod Oithona davisae

Short-term (24h) exposure experiments have been conducted to determine the effects of two environmental relevant polycyclic aromatic hydrocarbons (PAHs), naphthalene (NAPH) and dimethylnaphthalene (C2-NAPH), on the naupliar and adult stages of the marine cyclopoid copepod Oithona davisae. To resemble more realistic conditions, those exposure experiments were conducted under the presence of food. The naupliar stages evidenced lower tolerance to PAH exposure regarding narcotic and lethal effects than adults. Copepod feeding activity showed to be very sensitive to the presence of the studied PAHs, detrimental effects occurring at toxic concentrations ca. 2-3 fold lower than for narcotic effects. In addition we report PAH-mediated changes in cell size and growth rate of the prey item, the heterotrophic dinoflagellate Oxyrrhis marina, that could indirectly affect copepod feeding and help explain hormesis-like responses in our feeding experiments.

Metabolism and biomass vertical distribution of zooplankton in the Bransfield Strait during the austral summer of 2000

The vertical distribution (0–550 m) of zooplankton biomass, and indices of respiration (electron transfer system [ETS]) and structural growth (aminoacyltRNA synthetases activity [AARS]), were studied in waters off the Antarctic Peninsula during the austral summer of 2000. The dominant species were the copepod Metridia gerlachei and the euphausiid Euphausia superba. We observed a vertical krill/copepod substitution in the water column. The zooplankton biomass in the layer at a depth of 200–500 m was of the same magnitude as the biomass in the layer at a depth of 0–200 m, indicating that biomass in the mesopelagic zone is an important fraction of the total zooplankton in Antarctic waters. The metabolic rates of the zooplankton community were sustained by less than 0.5% of the primary production in the area, suggesting that microplankton or small copepods are the main food source. Neither food availability nor predation seemed to control mesozooplankton biomass. The wide time lag between the abundance peak of the dominant copepod (M. gerlachei) and the phytoplankton bloom is suggested to be the main explanation for the low summer zooplankton biomass observed in these waters.

A new regional algorithm for estimating chlorophyll-a in the Alboran Sea Mediterranean Sea from MODIS-Aqua satellite imagery

ABSTRACT The utility of three different algorithms for retrieving surface chlorophyll-a values from satellite images of MODIS-Aqua is tested in the northern Alboran Sea. The available global algorithm to calculate chlorophyll-a from reflectance of MODIS-Aqua (OC3M) overestimates the surface chlorophyll-a in the study area. Another regional algorithm specifically developed for the Mediterranean Sea (MedOC3) improves the estimates although the best outcome is obtained with OC5, which was developed for Atlantic coastal waters. The three tested algorithms perform worse at in situ chlorophyll-a concentrations higher than 1 mg m−3 and exhibit uncertainty levels higher than 35% for this range of concentrations. A new algorithm (ALBOC3) is proposed which produces a good estimation of the in situ chlorophyll-a for the whole range of concentrations normally registered in the study area (0.1–3.5 mg m−3). We hypothesize that the particular bio-optical features of the northern Alboran Sea phytoplankton explain the poor functioning of the published algorithms that have been tested in this work.

Advances in Biochemical Indices of Zooplankton Production.

Several new approaches for measuring zooplankton growth and production rates have been developed since the publication of the ICES (International Council for the Exploration of the Sea) Zooplankton Methodology Manual (Harris et al., 2000). In this review, we summarize the advances in biochemical methods made in recent years. Our approach explores the rationale behind each method, the design of calibration experiments, the advantages and limitations of each method and their suitability as proxies for in situ rates of zooplankton community growth and production. We also provide detailed protocols for the existing methods and information relevant to scientists wanting to apply, calibrate or develop these biochemical indices for zooplankton production.

New algorithms for estimating chlorophyll-a in the Spanish waters of the Western Mediterranean Sea from multiplatform imagery

ABSTRACT The utility of global and regional algorithms for retrieving surface chlorophyll-a values from satellite images of MODIS (Moderate-Resolution Imaging Spectroradiometer) onboard Aqua and Terra Satellites, SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), MERIS (MEdium Resolution Imaging Spectrometer) and VIIRS (Visible Infrared Imaging Radiometer Suite) is tested in a wide region of the Western Mediterranean Sea, the Spanish Mediterranean. The comparison between chlorophyll-a concentration obtained from samples collected and satellite concentrations calculated with global and regional algorithms for this area demonstrates that satellites overestimate the surface chlorophyll-a. In this work, a set of new algorithms, namely SMED (Spanish MEDiterranean algorithms), are proposed to improve the estimations of surface chlorophyll-a in our study area. The SMED set of algorithms employs the linear function to fit the standard Maximum Band Ratios (MBR) to the in situ surface chlorophyll-a concentration (in logarithmic scale). The implementation of the SMED algorithms is simple, and the accuracy is as good as more complex algorithms like OC5 (5 band algorithms tuned for European Atlantic and tested successfully in the Mediterranean Sea). The improvement of SMED algorithms is important respect to MedOC (built based in data of the Mediterranean Sea) for all sensors, ranging 17%-37% in terms of the coefficient of determination (R2). In the case of OC algorithms (standard global algorithms currently operative for most ocean colour sensors), SMED also improves the estimates in 11%-22%, except in 4% for MERIS. Additionally, when comparing satellite estimates with in situ chlorophyll-a in log-log scale, SMED achieved the best correspondence, even with respect to OC5. During the calibration procedure MERIS remote sensing reflectances (RRS) showed a higher sensitivity to the presence of mineral aerosols, and therefore it is strongly recommended to include the value of Aerosol Optical Thickness (AOT) in the algorithms for chlorophyll in the region under study. A regional algorithm for VIIRS ocean colour sensor is also proposed based on a matchup database built from spatially and temporary distributed SMED chlorophyll-a values of MODIS-Aqua and VIIRS RRS. Our analysis suggests that SeaWiFS, MODIS-Aqua, and VIIRS based SMED algorithms can support generating a multiplatform time series in the region.