Factors driving the seasonal dynamics of Pseudo-nitzschia species and domoic acid at mussel farming in the SW Mediterranean Sea

ABSTRACT

The seasonal variations in Pseudo-nitzschia species and domoic acid (DA) concentration were investigated, at three shellfish farms in SW coastal Mediterranean. In parallel, the toxicity of mussels was tested. Two distinct groups of species were enumerated according to morphology and size (Pseudo-nizschia delicatissima and P. seriata groups). DA was detected over a nine-week period from July to October 2012 in the Lagoon, with a maximum concentration recorded in July (12.71?ng?DA?L^?1). DA was positively correlated with the presence of P. seriata-group and P. delicatissima-group and was mostly occurred during P limitation period in seawater. No DA was found in mussels that were collected during the period of DA absence in seawater. Our results suggest that temperature, salinity, inorganic and organic nutrients were significant for the seasonal dynamics of P. seriata and P. delicatissima groups, but that the P limitation was the most driving factor for DA production in these areas. The relative influence of environmental factors should be further studied to better understand the recent surfacing of massive blooms of toxigenic Pseudo-nitzschia in SW Mediterranean coast.     

Evolutionary relationships of deep-sea mussels inferred by mitochondrial DNA sequences

In order to elucidate the evolutionary process of deep-sea Bathymodiolus mussels, we investigated the phylogenetic relationships of 16 species worldwide by analyzing nucleotide sequences of the mitochondrial COI and ND4 genes. Deep-sea mussels were clustered into three groups by basal trichotomous divergence. The first was composed of four species found in Japanese waters and one species from the Gulf of Mexico, which contain methanotrophic endosymbiotic bacteria. The second included nine species distributed in the West and East Pacific, Indian, and Atlantic Oceans. Members of the second group were trichotomously divided into the Indo-West Pacific, Atlantic, and East Pacific subclusters. The Indo-West Pacific subcluster was composed of three very closely related species with mutual genetic distances at the intraspecific level (av. 0.019 in COI and 0.009 in ND4 relative to av. 0.156 in COI and 0.265 in ND4 among Bathymodiolus species other than Cluster A species), suggesting some gene flow among these species. The third consisted of two West Pacific species. Species in the second and third groups contain mainly thioautotrophic endosymbionts, including some species harboring both methanotrophs and thioautotrophs.     

Population genetics of the swimming crab<Emphasis Type="Italic"> Callinectes bellicosus</Emphasis> (Brachyura: Portunidae) from the eastern Pacific Ocean

The population genetics and historical demography of the swimming crab Callinectes bellicosus from the eastern Pacific were assessed using mitochondrial DNA (mtDNA) sequences from portions of the cytochrome c oxidase subunit I (COI) and cytochrome b (Cytb) genes. Analysis of molecular variance of sequence data from crabs collected from nine localities, ranging from the upper to lower Gulf of California and the outer coast of the Baja California peninsula, revealed an absence of population structure, suggesting a high level of gene flow over a wide geographic area. Maximum-likelihood estimates of long-term effective population size obtained with the program FLUCTUATE, in addition to highly significant values obtained from neutrality tests (Tajimas D, Fu and Lis D, and Fus F_S) and mismatch analysis, are consistent with a population expansion dating to the Pleistocene epoch. Phylogenetic analysis of C. bellicosus sequences using both neighbor-joining and Bayesian methods revealed a widely distributed subclade (clade II) cryptically embedded at low frequency in the main (clade I) population. Although sequence divergence between the two clades was low (1.1% COI; 0.6% Cytb), statistical support for the split was high. The Kimura-2-parameter genetic distance between C. bellicosus and the sympatric and morphologically similar C. arcuatus was high (d=0.17) and similar to the genetic distance between C. bellicosus and the allopatric C. sapidus from the western Atlantic (d=0.18), suggesting an ancient (Miocene) divergence of C. bellicosus and C. arcuatus.Communicated by P.W. Sammarco, Chauvin     

Variation in protein patterns within and among polychaete sibling species of the genus<Emphasis Type="Italic"> Marenzelleria</Emphasis> (Spionidae): a preliminary survey

Differences in protein patterns of the soluble protein fraction among the sibling species Marenzelleria viridis (formerly type I) and M. neglecta (formerly type II) were investigated under common environmental conditions using two-dimensional gel electrophoresis (2D-PAGE). Protein expression was determined using general protein staining with Coomassie-blue and compared with radioactive labeling of proteins. In the well-resolved region of stained gels an average of 319 protein spots for M. viridis and 241 spots for M. neglecta could be detected. High sensitivity of radiolabeling allowed separation of an average of 517 and 496 spots for M. viridis and for M. neglecta, respectively. Differences in protein expression between both species could be attributed mainly to qualitative differences in protein patterns. Triplet pattern was used to calculate the genetic similarity of the two species. Thus, 373 protein spots were scored for this analysis; whereas 304 spots were invariant, 36 spots were specific for M. viridis, while 33 spots were specific for M. neglecta. The genetic similarity (F) of the two Marenzelleria sibling species was 0.815. Apart from presence and absence, differences between both species resulted either from slight changes in the isoelectric point or from molecular weight, but rarely from both. Genetic variability was found only among specimens of M. viridis. The experimental conditions to perform two-dimensional electrophoresis for these polychaete species were established for subsequent investigations on a proteomic level. Using 2D-PAGE we expect further insight into the evolutionary adaptation in Marenzelleria spp.Communicated by O. Kinne, Oldendorf/Luhe     

Seasonal variations in distribution patterns of sympagic meiofauna in Arctic pack ice

During two expeditions of the R.V. Polarstern to the Arctic Ocean, pack ice and under-ice water samples were collected during two different seasons: late summer (September 2002) and late winter (March/April 2003). Physical and biological properties of the ice were investigated to explain seasonal differences in species composition, abundance and distribution patterns of sympagic meiofauna (in this case: heterotrophs >20 µm). In winter, the ice near the surface was characterized by extreme physical conditions (minimum ice temperature: –22°C, maximum brine salinity: 223, brine volume: 5%) and more moderate conditions in summer (minimum ice temperature: –5.6°C, maximum brine salinity: 94, most brine volumes: 5%). Conditions in the lowermost part of the ice did not differ to a high degree between summer and winter. Chlorophyll a concentrations (chl a) showed significant differences between summer and winter: during winter, concentrations were mostly <1.0 µg chl a l^–1, while chl a concentrations of up to 67.4 µmol l^–1 were measured during summer. The median of depth-integrated chl a concentration in summer was significantly higher than in winter. Integrated abundances of sympagic meiofauna were within the same range for both seasons and varied between 0.6 and 34.1×10³ organisms m^–2 in summer and between 3.7 and 24.8×10³ organisms m^–2 in winter. With regard to species composition, a comparison between the two seasons showed distinct differences: while copepods (42.7%) and rotifers (33.4%) were the most abundant sea-ice meiofaunal taxa during summer, copepod nauplii dominated the community, comprising 92.9% of the fauna, in winter. Low species abundances were found in the under-ice water, indicating that overwintering of the other sympagic organisms did not take place there, either. Therefore, their survival strategy over the polar winter remains unclear.Communicated by O. Kinne, Oldendorf/Luhe     

Interspecific differences in the photosynthetic carbon metabolism of marine phytoplankton

Six species of marine phytoplankton of different sizes and taxonomic categories were grown in microcosms under identical experimental conditions; the species cultured were: Pavlova lutheri (Prymnesiophyceae), Dunaliella tertiolecta (Chlorophyceae), Phaeodactylum tricornutum (Baciollariophyceae), Eutreptiella sp. (Euglenophyceae), Alexandrium tamarense (Dinophyceae), and Phaeocystis pouchetii (Prymnesiophyceae). The photosynthetic carbon metabolism of these phytoplankton was studied throughout the exponential and lag phases of growth after nutrient depletion. The relative incorporation of carbon into protein was positively correlated with phytoplankton growth, while carbon assimilation into low molecular weight metabolites (LMWM) and storage products, i.e., lipid and polysaccharides, generally increased under nutrient-limiting conditions. Clear taxonspecific differences were observed in the proportions of carbon incorporated into cell constituents. A significant linear relationship was consistently found between the relative synthesis of protein to LMWM, and both the production normalised to chlorophyll (P:B) and the phytoplankton growth rate. However, ANCOVA revealed significant, interspecific differences in these relationships.