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Recurrent fish kills in the Spanish Alfacs Bay (NW Mediterranean) have been detected during winter seasons since 1994, and were attributed to an unarmored, ichthyotoxic, dinoflagellate, initially identified as Gyrodinium corsicum Paulmier, Berland, Billard, & Nezan. Several strains were isolated from the bay and their clonal cultures were compared by combined techniques, including light and electron microscopy, internal transcribed spacer and 5.8S rDNA nucleotide sequencing, and HPLC pigment analyses, together with studies of their photochemical performance, growth rates, and toxicity. Using phylogenetic analyses, all strains were identified as members of the genus Karlodinium, but they were separated into two genetically distinct groups. These groups, identified as Karlodinium veneficum (Ballantine) J. Larsen and K. armiger Bergholtz, Daugbjerg et. Moestrup, were also supported by the other techniques used. Detailed analyses of fine structural characteristics (including plug-like structures in amphiesma and a possible layer of semi-opaque material beneath the outer membrane) allowed discrimination of the mentioned two species. Specific differences in pigment patterns coincided with that expected for low-(K. veneficum) and high-light (K. armiger) adapted relatives. The higher photosynthetic efficiency of K. veneficum and the longer reactivation times of the PSII reaction centers observed for K. armiger were in agreement with this hypothesis. The two species differed in toxicity, but the strains used always induced mortality when incubated with bivalves, rotifers, and finfish. Compared with K. armiger, strains of K. veneficum yielded higher cell densities, but had lower growth rates.

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Bacterial biomass, bacterial production and the quantitative importance of the heterotrophic assimilation of photosynthetically produced dissolved organic carbon (PDOC) were examined in relation to the hydrodynamical and biological conditions in the Almeria-Oran front area (Alboran Sea, Western Mediterranean). Although, including all data, bacterial abundance correlated with chlorophyll a (r = 0.49), the bacteria/phytoplankton carbon ratio decreased in the core of the Atlantic jet. Bacterial integrated secondary production ranged from 124 to 199 mg C m-2 d-~. Bacterial generation times averaged 3.2 d (S.D. = 1.3) in frontal sites above the pycnocline and 25 d (S.D. = 11) under the pycnocline. In the adjacent Mediterranean waters, bacterial generation times displayed homogenous values from the surface to 150 m (mean 2.7 d; S.D. = 1.5). An isolated Atlantic water mass, at the right side of the jet, showed the longest average bacterial generation times (9.5 d). In the chlorophyll maximum layers, percent extracellular release represented 23.5% of total net primary production in the oligotrophic sites and only 6.5% in the core of the Atlantic jet. The contribution of PDOC to bacterial production exhibited large variations (17-100%). Dissimilarities among sites and hydrodynamical structures of the water masses were mostly observed in bacterial generation times and phytoplankton extracellular release.