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The spatial and temporal distribution of the toxic benthic dinoflagellate Ostreopsis ovata was investigated along the Conero Riviera (northern Adriatic Sea) during summer 2007 to evaluate the role of substratum, depth and hydrodynamic conditions on bloom dynamics. Sampling was carried out from April to November on different substrata (seaweeds, mollusc shells and rocks) and in the water column. O. ovata bloom started in September, reaching maximum values in the first week of October (1.7 × 106 cells g−1 fw corresponding to 21.0 × 106 cells g−1 dw and 6.2 × 104 cells cm−2) and completely disappearing at the beginning of November. On average, the abundances of O. ovata on rocks were significantly higher than those on seaweeds. Seaweeds with branched thalli supported higher values of epiphytes than non-branched ones. The abundances of O. ovata were significantly higher in sheltered than in exposed sites indicating a major role of hydrodynamism in regulating bloom dynamics. O. ovata abundances showed a marked decrease with depth with significantly lower values at depths >3 m. In the northern Adriatic, bloom development did not show any relationship with temperature, as the peak occurred when temperature values were decreasing.

The colonization of epilithic diatoms on artificial hard substrates (marble, quartzite and slate) was investigated on a seasonal basis in a subtidal site of the northern Adriatic Sea to determine if substrate-dependent differences in colonization occurs and to define the seasonal variations of microepilithic communities in terms of abundance, biomass and community structure. Artificial substrates (smoothed small discs mounted on a Plexiglas sheet) were placed at a depth of 8 m in April 2003, July 2003, January 2004 and February 2004. The discs were collected after 6–7 weeks for counting and taxonomic identification of the diatoms. The community structure of epilithic diatoms showed a dominance of motile species over the entire study period, followed by erect, adnate and tube-dwelling diatoms. Diatom density showed a marked seasonal variability, ranging from 365±407 (winter 2004) to 557156±82602 cells cm-2 (spring 2004). Biomass ranged from 0.02±0.01 to 17.53±3.20 μg C cm-2. Abundance and biomass values did not present any significant differences for the three substrates examined.

Special issue Phytoplankton Life-Cycles and Their Impacts on the Ecology of Harmful Algal Bloom.-- 13 pages, 4 figures, 6 tables, A PCR-based assay was developed and applied to sediment and sediment trap samples for the detection of different cysts belonging to dinoflagellates and raphidophytes in European coastal areas. Oligonucleotide primers were designed based on the ITS-5.8S and LSU ribosomal gene sequences. The specificity and sensitivity of the PCR assay were assessed using genomic DNA from clonal cultures, plasmid copy number of cloned target sequences, as well as from sediment samples. Qualitative PCR determinations of different cysts in sediment and sediment trap samples were compared to taxonomic examinations by light microscopy. This molecular methodology permitted a fast and specific detection of target cysts in sediment samples. We also detected dinoflagellate and raphidophyte cysts at concentrations not detectable by microscopic methods or that are difficult to identify. The results given by molecular and microscopic methods were comparable. However, higher values of positive detection for target cysts were obtained by PCR than with microscopy. Some taxa were detected in 100% of the samples using PCR, while others were only found in 10% of the samples. The data obtained in this study showed that the PCR-based method is a valid tool for cyst identification in marine sediments, This study was financed by the EU funded Research Project SEED (GOCE-CT-2005-003875). E. Garcés was sustained by a Ramon y Cajal contract from the Spanish Ministry of Science and Education

The microalgal community associated with Eudendrium racemosum, a marine hydroid widely distributed in the Mediterranean Sea, was studied during an annual cycle, at monthly frequency, in a coastal station of the Ligurian Sea. Microalgae were represented mainly by diatoms, which exhibited higher abundance and biomass values between autumn and spring (max 46,752 cells mm-2 and 1.94 μg C mm-2, respectively), while during summer a significant decrease was observed (min 917 cells mm-2 and 0.013 μg C mm-2). High levels of abundance of filamentous cyanobacteria were observed in summer. Spatial distribution of epibiontic microalgae showed a markedly increasing gradient from the basal to the apical part of hydroid colonies. Considering the growth forms of diatom communities, motile diatoms (mainly small naviculoid taxa) were the most abundant in all the periods. Adnate (Amphora and Cocconeis spp.) were distributed mainly in the basal and central part of hydroid colonies and showed two peaks (autumn and summer). Erect forms (mainly Tabularia tabulata, Licmophora spp., Cyclophora tenuis) were mainly distributed in the apical part of the colonies and showed their maximum densities in spring-summer. Tube-dwelling (Berkeleya rutilans, Parlibellus sp.) were observed at low densities throughout the study period, without any significant temporal or spatial variability. Comparing the microalgal communities on marine hydroid to those grown on mimic substrata placed in the sampling station during summer, significantly higher values of abundance were observed in the hydroid, suggesting that microalgae may benefit from the polyp catabolites. This fact was particularly evident for the adnate diatoms, whose temporal trend paralleled the cycle of hydroid host. © 2006 Springer-Verlag.

Living diatoms are commonly found within Antarctic Porifera, and generally interpreted as additional food source, or as mutualists or parasites of sponge tissues. However, no data are available about temporal variations of the abundance of diatoms inside sponges especially during the winter period. In this paper we analysed the amount of diatom frustules and chlorophaeopigment concentration in six species of Antarctic sponges (Dendrilla antarctica, Homaxinella flagelliformis, Kirkpatrickia variolosa, Suberites montiniger, Haliclona dancoi, Haliclona penicillata) sampled weekly from November 2001 - before the ice melting - to February 2002. Frustule concentration in the sponge tissues was very low at the beginning of November in all the sponge species, and increased between 9 and 22 January, to reach maximum values between 29 January and 7 February. Diatom abundances were significantly higher in H. dancoi tissues, comparing to the other sponge species, reaching values up to 1217′178 cells *10 g - 1 dw at the end of January. Chlorophaeopigments, very low at the beginning of November, increased between 5 and 19 December, before the peak of diatoms. Maximum chlphaeo values (650.5 ′ 5.9 μg g - 1 dw) were observed in D. antarctica. The planktonic Fragilariopsis curta was the most common diatom species recorded inside sponges. These data clearly indicate that diatom concentration inside the sponge tissues is related to the summer phytoplankton bloom. The shift between the pigment and frustule peaks strongly suggests that diatoms are used as a food source by sponges and that their frustules are accumulated inside the sponge body. The lack of frustules at the beginning of summer indicates that diatom frustules are expelled or dissolved during the cold season.