Journal of the Marine Biological Association of the United Kingdom, 2005
ABSTRACT Sphaeroylus antarchcus is a common Antarctic sponge characterized by a dense spicule fur... more ABSTRACT Sphaeroylus antarchcus is a common Antarctic sponge characterized by a dense spicule fur that covers its surface. This sponge has been sampled at Terra Nova Bay from 22 November 2001 to 29 January 2002 at weekly intervals. On its spicules, a rich assemblage of benthic diatoms has been observed, mainly composed of Hyalodiscus sp., a centric sessile diatom, forming short colonies. The temporal trend of the abundances of these diatoms showed a maximum of 115x10(6) cells g(-1) dry weight (dw) at the end of December. Almost all the diatom frustules observed in the sponge choanosome belonged to the planktonic species Fragilarlopsis curta, which displayed a peak (50x10(6) cells g(-1) dw) in the second half of January. Diatoms that were observed in the choanosome were of a size comparable to that of the inhalant pores, suggesting that sponges actively engulf diatoms, due to the pumping activity of their choanocyte chambers. Sponges, as active filter feeders, therefore represent one important vector in the transfer of energy from planktonic to benthic trophic chains in Antarctic habitats.
ABSTRACT In the last few years, intense blooms of the toxic benthic dinoflagellate Ostreopsis cf.... more ABSTRACT In the last few years, intense blooms of the toxic benthic dinoflagellate Ostreopsis cf. ovata have been a recurrent phenomenon along several Mediterranean coasts during summer. Blooms are associated with noxious effect for humans and death of benthic invertebrates. Monitoring activities on the Conero Riviera (N Adriatic Sea) highlighted that O. cf. ovata colonizes several substrata, such as rocky bottom, pebbles, macrophytes, and invertebrates (molluscs, hydrozoans, echinoderms). The highest abundances of O. cf. ovata (106 cells / gram of fresh weight, i.e. 105 cells / square cm) were recorded at the end of summer, with significantly higher abundances on abiotic substrata than on macrophytes, suggesting that allelopathic interactions between epibionts and their host may occur. This study investigated the interactions between epiphytic O. cf. ovata and macroalgal hosts under experimental conditions. Macroalgae were chosen among the most common species in the Conero Riviera, Dictyota dichotoma (brown algae), Rhodymenia pseudopalmata (red algae) and Ulva rigida (green algae). Three different experiments were set up: O. cf. ovata was incubated (i) with fresh macroalgal tissues, (ii) with filtered culture media in which macroalgae were previously grown, and (iii) with dry macroalgal powder added at different concentrations. The results of coexistence assays showed that the growth of O. cf. ovata was inhibited by fresh tissue (U. rigida and D. dichotoma), by filtered culture media (D. dichotoma) and by dry macroalgal powder (all species). D. dichotoma had the highest inhibiting effect, causing growth decrease of O. cf. ovata under all the experimental conditions tested. Exposed cultures showed the presence of cysts.
During 2004 an artificial barrier area has been sampled monthly to investigate the seasonal cycle... more During 2004 an artificial barrier area has been sampled monthly to investigate the seasonal cycle of phytoplankton assemblages and estimate the downward flux of dinoflagellate cysts by the deployment of a sediment trap. Phytoplankton polpulations showed a regular annual cycle with a spring bloom of Ceratau-lina pelagica. Calcareous walled cysts represented the most abundant morphotype and cyst fluxes showed a good relation with the organic fraction of the settling particles. A few HAB species have been detected in the water column, but in low abundances. Cysts of Lingulodinium polyedrum have been detected. Introduzione Il lavoro, svolto nell'ambito del Programma per la tutela ambientale della Regione del Veneto "Intervento 72 – Campo sperimentale in mare", coordinato dall'Osservatorio Alto Adriatico di ARPAV, ha lo scopo di studiare i popola-menti fitoplanctonici, da un punto di vista sia quantitativo (densità cellulare e numero di specie) sia qualitativo (dinamica...
Journal of the Marine Biological Association of the United Kingdom, 2005
ABSTRACT Sphaeroylus antarchcus is a common Antarctic sponge characterized by a dense spicule fur... more ABSTRACT Sphaeroylus antarchcus is a common Antarctic sponge characterized by a dense spicule fur that covers its surface. This sponge has been sampled at Terra Nova Bay from 22 November 2001 to 29 January 2002 at weekly intervals. On its spicules, a rich assemblage of benthic diatoms has been observed, mainly composed of Hyalodiscus sp., a centric sessile diatom, forming short colonies. The temporal trend of the abundances of these diatoms showed a maximum of 115x10(6) cells g(-1) dry weight (dw) at the end of December. Almost all the diatom frustules observed in the sponge choanosome belonged to the planktonic species Fragilarlopsis curta, which displayed a peak (50x10(6) cells g(-1) dw) in the second half of January. Diatoms that were observed in the choanosome were of a size comparable to that of the inhalant pores, suggesting that sponges actively engulf diatoms, due to the pumping activity of their choanocyte chambers. Sponges, as active filter feeders, therefore represent one important vector in the transfer of energy from planktonic to benthic trophic chains in Antarctic habitats.
ABSTRACT In the last few years, intense blooms of the toxic benthic dinoflagellate Ostreopsis cf.... more ABSTRACT In the last few years, intense blooms of the toxic benthic dinoflagellate Ostreopsis cf. ovata have been a recurrent phenomenon along several Mediterranean coasts during summer. Blooms are associated with noxious effect for humans and death of benthic invertebrates. Monitoring activities on the Conero Riviera (N Adriatic Sea) highlighted that O. cf. ovata colonizes several substrata, such as rocky bottom, pebbles, macrophytes, and invertebrates (molluscs, hydrozoans, echinoderms). The highest abundances of O. cf. ovata (106 cells / gram of fresh weight, i.e. 105 cells / square cm) were recorded at the end of summer, with significantly higher abundances on abiotic substrata than on macrophytes, suggesting that allelopathic interactions between epibionts and their host may occur. This study investigated the interactions between epiphytic O. cf. ovata and macroalgal hosts under experimental conditions. Macroalgae were chosen among the most common species in the Conero Riviera, Dictyota dichotoma (brown algae), Rhodymenia pseudopalmata (red algae) and Ulva rigida (green algae). Three different experiments were set up: O. cf. ovata was incubated (i) with fresh macroalgal tissues, (ii) with filtered culture media in which macroalgae were previously grown, and (iii) with dry macroalgal powder added at different concentrations. The results of coexistence assays showed that the growth of O. cf. ovata was inhibited by fresh tissue (U. rigida and D. dichotoma), by filtered culture media (D. dichotoma) and by dry macroalgal powder (all species). D. dichotoma had the highest inhibiting effect, causing growth decrease of O. cf. ovata under all the experimental conditions tested. Exposed cultures showed the presence of cysts.
During 2004 an artificial barrier area has been sampled monthly to investigate the seasonal cycle... more During 2004 an artificial barrier area has been sampled monthly to investigate the seasonal cycle of phytoplankton assemblages and estimate the downward flux of dinoflagellate cysts by the deployment of a sediment trap. Phytoplankton polpulations showed a regular annual cycle with a spring bloom of Ceratau-lina pelagica. Calcareous walled cysts represented the most abundant morphotype and cyst fluxes showed a good relation with the organic fraction of the settling particles. A few HAB species have been detected in the water column, but in low abundances. Cysts of Lingulodinium polyedrum have been detected. Introduzione Il lavoro, svolto nell'ambito del Programma per la tutela ambientale della Regione del Veneto "Intervento 72 – Campo sperimentale in mare", coordinato dall'Osservatorio Alto Adriatico di ARPAV, ha lo scopo di studiare i popola-menti fitoplanctonici, da un punto di vista sia quantitativo (densità cellulare e numero di specie) sia qualitativo (dinamica...
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