Silvia Tazioli

Antipathella subpinnata (Antipatharia, Myriopathidae) in Italian seas

The distribution of Antipathella subpinnata in Italian seas is herein given and discussed. A. subpinnata is a large, white, branched antipatharian with an Atlanto‐Mediterranean distribution. It is probably the most commonly observed black coral in this basin and it is possible to find large populations of this species at diving depths. Personal records of the occurrence of the species in the Strait of Messina, together with a wide census involving diving centres along all the Italian coasts, have been used to create a distribution data set. A description of the species, including in vivo measurements of the polyps, is given. Information concerning the habitat, the population density, the substrate, the epibionts and the environmental conditions of the sites where the species was found are also included. This study confirms the importance of A. subpinnata as a common component of the lower fringe of the circalittoral twilight environment, below 50 m depth, in localities where hard substrata are available.

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.

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.

Ecological and morphological characteristics of Ephelota gemmipara (Ciliophora, Suctoria), epibiontic on Eudendrium racemosum (Cnidaria, Hydrozoa) from the Adriatic Sea

The relationship between the suctorian Ephelota gemmipara and the large hydroid Eudendrium racemosum from the North Adriatic Sea has been studied over its full annual cycle. Ephelota gemmipara settles on the perisarc of the hydroid, usually close to the hydranths in order to exploit the hydroids food discharges. The life cycle of E. gemmipara is influenced by temperature variations and by its relationship with the host. The hydroid shows an active phase in the summer, and it gets through the adverse winter season forming resting stages. In April, when temperature increases, the hydroid starts its active phase and it is colonized by suctorians. From May to September the suctorians produce multiple buds (swarmers) that detach from the parental cells to settle on an Eudendrium colony. The abundance of the suctorian peaks in September, with more than 1.2 million ind. m(-2). Their proliferation coincides with the maximal abundance of their host and the highest water temperatures. On the contrary, sexual reproduction and the encystment occur when the temperature and the abundance of E. racemosum decrease. Lastly, we also report the presence of symbionts such as bacteria and the parasitic protozoans Tachyblaston ephelotensis and Enigmocoma acinetarum.

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.

The epibiontic assemblage of Geryon longipes (Crustacea: Decapoda: Geryonidae) from the Southern Adriatic Sea

The crab Geryon longipes lives in muddy bottoms of bathyal environments. Its epibiontic assemblage was studied in a population from the Southern Adriatic Sea. Four species of invertebrates were observed on the crab exoskeleton. The most abundant was the hydroid Leuckartiara cf. octona; the bryozoan Triticella flava was also quite frequent, while another hydroid, Hydractinia sp., and a bryozoan, Arachnoidea sp. were only occasionally observed. The study of the abundance and the distribution of the two most common epibionts in relation to the crab revealed a different spatio‐temporal pattern of colonisation between the hydroid and the bryozoan.

A marine biological underwater depuration system (MUDS) to process waste waters

An underwater device, able to favour the sea auto-cleaning capacities, is herein described. This system, called MUDS (marine underwater depuration system), consists of a percolating filter and is placed at sea over an urban sewage outflow of a submarine pipeline. Due to the density difference, the water effluent flows through the percolating filter: this favours the mixing and a prompt recycling of organic matter, activating a marine trophic web. Rich microbenthic communities develop on the MUDS, both interstitially, inside the filter, and on the structure. The community mainly consists of ciliates, nematodes, harpacticoid copepods and polychaetes, all of which being organisms that increase the depuration efficiency by consumption of organic matter. This structure acts also as a deterrent for the illegal trawling activity in the area, and attracts large numbers of several finfish species, thus working as a fish aggregating device (FAD). It is possible to utilise this underwater device for medium littoral towns with strong differences in effluent discharges during the year, where the use of land-built effluent treatment plants is too expensive.

The cnidome of Carybdea marsupialis (Cnidaria: Cubomedusae) from the Adriatic Sea

Kinds and distribution of nematocysts of the cubomedusa Carybdea marsupialis were described by light and scanning electron microscopy. Three kinds of nematocysts were found in tentacles: heterotrichous microbasic euryteles, flattened holotrichous isorhizas and subspherical holotrichous isorhizas. The microbasic euryteles of the tentacles show a characteristic detachable multilayered lancet, already described in the euryteles of Carybdea alata . A possible explanation of the function of the lancet is proposed. The pedalia and the umbrella are armoured by holotrichous isorhizas together with an unidentified kind of small, drop-shaped nematocysts. Gastric cirri, characterized by a rough and ciliated surface, contain heterotrichous microbasic euryteles.

First evidence of a specific association between a stylasterid coral (Cnidaria: Hydrozoa: Stylasteridae) and a boring cyanobacterium

The association between living Stylasteridae and boring organisms have been hypothesized since 1942, when Broch (1942) observed in Distichopora borealis forma japonica and in Distichopora foliacea ‘‘numerous, streak-like, straight canals crossing the skeletal substance in all directions...much narrower than the normal coenenchym canals of the coenosteum’’ suggesting that these canals are probably due to some parasitic micro-boring organisms. Subsequently, Cairns (1988) hypothesized that the rose-violet colour of the Australian Stylaster tenisonwoodsi was due to an encrusting or a boring alga. These observations are now confirmed by the study of numerous specimens of Stylaster sp. collected in the Bunaken Marine Park (North Sulawesi, Indonesia) from 10 to 70 m depth. The colonies showed two colours, white and pink, and lived in groups inside caves and crevices (Fig. 1a). The colour of the pink specimens was distributed mainly on the side of the colony exposed to light. The analysis at the microscope of branches partially decalcified with HCl 4% revealed the presence of a boring pink cyanobacterium producing a net of filaments that was especially dense around the cyclosystems (Fig. 1b). The scanning electron microscope showed the arrangement of the net of the cyanobacterium filaments and the existence of thin canals, about 5 lm in diameter, inside the coenosteum (Fig. 1c). The canals were present in the entire transversal section of the branches, although their abundance was greater in the portions more exposed to light. Except for the colour, the colonies hosting the cyanobacterium were identical in size and morphology to the white specimens and showed no sign of disease or necrosis. The occurrence of cyanobacteria was very frequent in this species but was never observed in the coenosteum of other stylasterid corals living in the same habitat. These findings point towards the existence of a highly specific association between Stylaster sp. and a boring cyanobacterium. The higher concentration of the cyanobacterium filaments around the polyps is suggestive of a functional relationship between the two organisms that deserves further attention.

Nematocyst arrangement on the tentacles of the polyps of Eudendrium (Cnidaria, Hydrozoa)

Abstract The nematocyst arrangement on the tentacles of seven Mediterranean species of the genus Eudendrium is described. This character is different in each studied species and therefore may be fruitfully used as a diagnostic tool in this complex genus. The ne‐matocysts of Eudendrium tentacles are always microbasic euryte‐les arranged in more or less tidy bands along the tentacle length. Generally, the proximal portion of the tentacle has a lower amount of capsules or, sometimes, nematocysts are completely lacking in this zone. Differences in nematocyst arrangement are highlighted at three levels: the distribution of capsules along the tentacle; the distribution of capsules in each band; and the orientation of the axis of capsules with respect to the tentacle axis, giving the tentacle surface a smooth or spiny appearance.