Tiziana Romagnoli

Ostreopsis cf. ovata bloom in the northern Adriatic Sea during summer 2009: Ecology, molecular characterization and toxin profile

Intense blooms of the benthic dinoflagellate Ostreopsis cf. ovata have occurred in the northern Adriatic Sea since 2006. These blooms are associated with noxious effects on human health and with the mortality of benthic organisms because of the production of palytoxin-like compounds. The O. cf. ovata bloom and its relationships with nutrient concentrations at two stations on the Conero Riviera (northern Adriatic Sea) were investigated in the summer of 2009. O. cf. ovata developed from August to November, with the highest abundances in September (1.3×10(6) cells g(-1) fw corresponding to 63.8×10(3) cells cm(-2)). The presence of the single O. cf. ovata genotype was confirmed by a PCR assay. Bloom developed when the seawater temperature was decreasing. Nutrient concentrations did not seem to affect bloom dynamics. Toxin analysis performed by high resolution liquid chromatography-mass spectrometry revealed a high total toxin content (up to 75 pg cell(-1)), including putative palytoxin and all the ovatoxins known so far.

Seasonal variations of epilithic diatoms on different hard substrates, in the northern Adriatic Sea

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 micro-epilithic 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 Ccm -2 . Abundance and biomass values did not present any significant differences for the three substrates examined.

Relationships between benthic diatoms and hydrozoans (Cnidaria)

Some examples of relationships between hydroids and epibionthic diatoms from the Mediterranean Sea are described, verifying the kind of interaction existing between the two partners. The athecate Eudendrium racemosum hosts an extremely rich diatom assemblage, mainly comprising Licmophora spp., Amphora spp. and Cocconeis spp. On the contrary, only adnate growth forms ( Cocconeis pseudonotata , C. dirupta ) were observed in diatom communities growing on the external side of thecate species Campanularia hincksii , Clytia linearis and Synthecium evansi . Some diatom species ( Cocconeis notata , Cylindrotheca sp. and Navicula sp.) are able to survive in the intrathecal microenvironment. They live in the narrow space between hydrotheca and polyp, receiving protection and probably using the nutrients produced by hydroid metabolism. Sunlight can penetrate through transparent thecae and reach the diatom layer, making photosynthesis possible.

Ecology of Ostreopsis cf. ovata Blooms in the Northwestern Adriatic Sea

Abstract The ecology of Ostreopsis cf. ovata blooms was investigated to evaluate the role of environmental factors (temperature, hydrodynamism, nutrient concentrations, depth and substratum) on the bloom dynamics. This paper reports the present knowledge on O. cf. ovata blooms along the Conero Riviera (NW Adriatic Sea), on the basis of samplings carried out from 2006 to 2010. The annual maximum of benthic cell abundance was always observed in late-summer, reaching the order of magnitude of 106 cells g-1 fw (corresponding to 107 cells g-1 dw and 104 cells cm-2) on macrophyte samples. Comparing the mean abundances settled on seaweeds with those growing on hard substrata, significantly higher abundances were observed on the latter. Hydrodynamism plays a major role in Ostreopsis blooms, as significantly higher abundances were observed in sheltered sites compared with exposed ones. The abundances of O. cf. ovata showed a marked decrease with depth. Temperature and nutrients do not seem to play an important effect on the O. cf. ovata blooms. High levels of ovatoxins were recorded in natural samples; episodes of death of both benthic invertebrates (limpets, sea urchins and mussels) and macroalgae were commonly observed during O. cf. ovata blooms.

The ecology of protists epibiontic on marine hydroids

Several hydroid species have an epibiontic lifestyle, living associated with organisms of many different phyla. On the other hand, hydroids can also host dense assemblages of microflora and microfauna, mainly composed of protists and bacteria. Among protists, diatoms are the most abundant and diversified group, followed by foraminifera and sessile ciliata such as Vorticella and suctorians. Regarding the spatial distribution of epibionts, hydroid colonies represent a mosaic of different microhabitats: in some species, each colony portion (base of the stem, branches, pedicels, inner space between the polyp and the theca) hosts different diatom species. Moreover, three foram species have been shown to occupy different positions according to the plasticity of their shell. A host specificity has been also observed: some epibionts are typical of only one or a group of species, such as Vorticella living on the teeth of the Aglaophenia thecae or coralline algae that cover mainly Aglaophenia and Sertularella colonies. The microassemblage associated to Eudendrium racemosum showed a typical seasonal cycle and a vertical distribution which reflects the selective advantage of the different life forms. Experiments with plastic structures miming hydroid colonies demonstrated that the living hydroid affects the assemblage structure. Probably, the perisarc composition and secondary metabolites play a crucial role in the relationships between hydroids and their microassemblage.

Ostreopsis fattorussoi sp. nov. (Dinophyceae), a new benthic toxic Ostreopsis species from the eastern Mediterranean Sea.

The new benthic toxic dinoflagellate, Ostreopsis fattorussoi sp. nov., is described from the Eastern Mediterranean Sea, Lebanon and Cyprus coasts, and is supported by morphological and molecular data. The plate formula, Po, 3′, 7″, 6c, 7s, 5‴, 2′′′′, is typical for the Ostreopsis genus. It differs from all other Ostreopsis species in that (i) the curved suture between plates 1′ and 3′ makes them approximately hexagonal, (ii) the 1′ plate lies in the left half of the epitheca and is obliquely orientated leading to a characteristic shape of plate 6″. The round thecal pores are bigger than the other two Mediterranean species (O. cf. ovata and O. cf. siamensis). O. fattorussoi is among the smallest species of the genus (DV: 60.07 ± 5.63 μm, AP: 25.66 ± 2.97 μm, W: 39.81 ± 5.05 μm) along with O. ovata. Phylogenetic analyses based on the LSU and internal transcribed spacer rDNA shows that O. fattorussoi belongs to the Atlantic/Mediterranean Ostreopsis spp. clade separated from the other Ostreopsis species. Ostreopsis fattorussoi produces OVTX‐a and structural isomers OVTX‐d and ‐e, O. cf. ovata is the only other species of this genus known to produce these toxins. The Lebanese O. fattorussoi did not produce the new palytoxin‐like compounds (ovatoxin‐i, ovatoxin‐j1, ovatoxin‐j2, and ovatoxin‐k) that were previously found in O. fattorussoi from Cyprus. The toxin content was in the range of 0.28–0.94 pg · cell−1. On the Lebanon coast, O. fattorussoi was recorded throughout the year 2015 (temperature range 18°C–31.5°C), with peaks in June and August.

Coralline algae epibionthic on thecate hydrozoans (Cnidaria)

The relationships between three species of thecate hydrozoans, Sertularella crassicaulis, Sertularella ellisii and Aglaophenia tubiformis with three species of encrusting Corallinales, Pneophyllum fragile, Melobesia membranacea and Hydrolithon cf. farinosum from different locations in the western Mediterranean are described. In Aglaophenia tubiformis, algae were observed on the hydrotheca, while in Sertularella spp. they grew on the stem, the branches and the hydrothecae which became completely covered by encrusting, calcified thalli. The polyps were living in the covered theca. The hydroid species hosting Corallinales were a small fraction of the entire assemblages and this evidence suggests that hydroids cannot be considered as a simple, inert substrate. We hypothesize that this specificity could be explained by a different molecular composition of hydroid exoskeletons, and/or production of secondary metabolites that affect organism settlement. Moreover, perisarcal areas close to hydranths were more abundantly covered by algae, probably due to nutrient emission generated by the metabolism of the hydroid.

Effects of the bloom of harmful benthic dinoflagellate Ostreopsis cf. ovata on the microphytobenthos community in the northern Adriatic Sea

Composition and temporal variation of the microphytobenthos communities of the Conero Riviera (northern Adriatic Sea) were investigated in the course of an annual cycle, focusing on their relationships with blooms of the benthic dinoflagellate Ostreopsis cf. ovata. Sampling was carried out from March 2009 to March 2010 on undisturbed benthic substrata (macroalgae and pebbles). Samples for the study of microphytobenthos were collected with a monthly frequency, while those for the study of Ostreopsis bloom weekly. Benthic diatoms dominated the microphytobenthos communities for most of the annual cycle (except the summer), both in terms of abundance and biomass. In summer, cyanobacteria were dominant (54.04±9.18 and 24.29±11.11% of total abundance and biomass, respectively), while benthic dinoflagellates were an important component of the community in terms of biomass only at the peak of the Ostreopsis bloom in late summer (up to 91% of the total biomass). Among diatoms, the most abundant forms throughout the year were motile species (77.5±3.71% of the population), while erect diatoms formed the majority of the biomass in winter and spring (48.66±16.66 and 48.05±5.56% of total population, respectively). Diatoms were mainly affected by DIN availability, while the patterns of biomass of O. cf. ovata and cyanobacteria were related to salinity and temperature. The biomass of Ostreopsis was also affected by the availability of phosphorus. The results of this study suggest that the proliferation of Ostreopsis affected the structure of the benthic diatom community: motile diatoms were significantly more abundant during the Ostreopsis bloom peak than during the rest of summer, probably because they benefited from the abundant mucilaginous mat covering the benthic substrata. In the course of the O. cf. ovata bloom the diversity of the microphytobenthos was significantly lower than during the rest of the year, suggesting an influence of both the shading produced by the mucous mat and allelopathic compounds possibly produced by O. cf. ovata.

MORPHOLOGICAL STUDIES OF SOME MARINE MASTOGLOIA (BACILLARIOPHYCEAE) BELONGING TO SECTION SULCATAE, INCLUDING THE DESCRIPTION OF NEW SPECIES

Epiphytic diatoms on seagrass and seaweed were collected from tropical (e.g., Siladen Island, Celebes Sea, Indonesia and Phú Bài, China Sea, Vietnam), subtropical (e.g., Sharm el‐Sheikh, Red Sea, Egypt), and temperate regions (e.g., Patmos Island, Greece) in 2000, 2005, and 2006. Eight species of Mastogloia, belonging to the section Sulcatae, are described mainly through scanning electron microscopy, including two new species to science, M. oculoides and M. sergiana. These species show a differently shaped median depression on the external valve face between the raphe‐sternum and the valve margin. Moreover, they lack a developed conopeum or pseudoconopeum, which covers the median depression in other species of the section Sulcatae. This study gives new insights on the ultrastructure of the Mastogloias valves and provides an update of their current geographical distribution.

Diatom assemblages associated with Sphaerotylus antarcticus (Porifera: Demospongiae)

Sphaerotylus antarcticus 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 115×10 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 Fragilariopsis curta , which displayed a peak (50×10 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.