Maria Mercurio

Distribution, persistence and change in the macrobenthos of the lagoon of Lesina (Apulia, southern Adriatic Sea)

The benthic community of the lagoon of Lesina was studied from July 2000 to June 2001. The distribution of the main macrophytobenthic species was recorded by visual census at 24 stations in July 2000. The macrofauna, from both hard and soft substrates, was analyzed at five stations with seasonal frequency; in addition, the main hydrologic parameters were recorded monthly. The lagoon was mainly characterized by brackish water, with salinity values decreasing from west to east (annual mean: 23.3 psu). It showed mild water temperatures throughout the year (annual mean: 19.8 °C) and moderately high values of dissolved oxygen (annual mean: 9.9 ppm). No dystrophic crises were observed during the period of study. In the eastern basin, Zostera noltii Hornemann, Lissara and Ruppia cirrhosa (Patagna) Grande were the most abundant species of macrophytobenthos. Their distributional pattern was coherent with literature data. Soft bottoms of the western basin were largely occupied by the benthopleustophytic alga Valonia aegagropila C. Agardh, which during the last decade had almost completely replaced Cladophora prolifera (Roth) Kutzing and Gracilaria confervoides Greville, the latter of which was previously very abundant in the lagoon. Macrozoobenthos consisted of 53 species (1 sponge, 2 cnidarians, 11 molluscs, 14 annelids, 21 crustaceans, 1 insect, 1 bryozoan, 1 echinoderm, 1 tunicate), most of which are typical of brackish water. Highest abundances were found in the eastern area of the basin. Some marine species were recorded in the western area. In contrast with the dramatic changes observed in the floral assemblage, a large amount of species had already been recorded in the lagoon during the last 10 years, pointing out the persistence of the macrozoobenthic community. Nevertheless, the distribution of benthic macrofauna seemed to be greatly influenced by the presence of Valonia aegagropila, as shown in an ordination model, where station-points were segregated by the presence of the alga rather than by hydrologic parameters. The impact of biotic factors on the community, such as non-indigenous species invasions, was suggested as constraints inducing the temporal variations of benthos.

Porifera and Bryozoa on artificial hard bottoms in the Venice Lagoon: Spatial distribution and temporal changes in the northern basin

The spatial distribution and temporal changes of demosponges and bryozoans in the northern basin of the Venice Lagoon were studied from samples collected from wooden piles and artificial rocks in June and October 2001. Twenty species of demosponges and 18 species of bryozoans were recorded. Sponges were found at 10 out of 11 sampling stations, while bryozoans were found at all 11 sampling stations. The studied taxocoenoses showed a high percentage cover of the lagoon hard bottoms. Eleven out of the 20 detected species of sponges were reported in a previous study on this taxocoenosis carried out on material collected in 1954–1955. Moreover, the most abundant species were also recorded during a study in 1989. These observations suggest a remarkable degree of persistence of the sponge community. Among bryozoans, the comparison with literature data showed a wider variation in species composition, with the occurrence of five new species in the studied area. The Indo‐Pacific invasive Tricellaria inopinata replaced the native Bugula spp. in the role of dominant species. Finally, a significant increase in species richness along the salinity gradient, more evident for sponges than for bryozoans, was identified.

Inventory and distribution of hard bottom fauna from the marine protected area of Porto Cesareo (Ionian Sea): Porifera and Polychaeta

Abstract The hard bottom fauna of the marine protected area of Porto Cesareo (Salento Peninsula) was examined considering two representative benthic groups, Porifera and Polychaeta. Sampling was performed by SCUBA divers from the surface to a depth of 25 m in a variety of environments. Sponge and polychaete assemblages were rich and diversified, with a total of 160 taxa collected (66 and 94, respectively), representing the first large contribution to the knowledge of the two groups in the marine protected area. This was particularly true for polychaetes, 80% of which had not been previously reported in the literature for this area. The distribution of the species in the examined environments is also given.

Evaluation of microbiological accumulation capability of the commercial sponge Spongia officinalis var. adriatica (Schmidt) (Porifera, Demospongiae).

This study was carried out to evaluate the microbiological accumulation capability of the demosponge Spongia officinalis var. adriatica. Six microbiological parameters were researched in two sampling periods in the water and in reared sponge samples coming from sites with different degrees of microbial contamination: an off-shore fish farm displaced off the Apulian coast (Southern Adriatic Sea) and a no-impacted area displaced into the Marine Protected Area of Porto Cesareo (Apulian coast-Ionian Sea). We detected the density of culturable heterotrophic bacteria by spread plate on marine agar, total culturable bacteria at 37 degrees C on Plate Count Agar and vibrios on thiosulphate-citrate-bile-sucrose-salt (TCBS) agar. Total and fecal coliforms as well as fecal streptococci concentrations were detected by the MPN method. Bacterial densities were always higher in the sponge homogenates compared with the corresponding seawater in the sampling points and in both sampling periods. As regard vibrios, total culturable bacteria at 37 degrees C and fecal streptococci concentrations, the highest values were observed in the sponge samples coming from the off-shore fish farm during the summer period. The ability of Spongia officinalis var. adriatica to accumulate the microbial pollution indicators suggests that this species can be employed as a bioindicator for monitoring water quality.

Choanocyte chambers in unreleased buds of Tethya seychellensis (Wright, 1881) (Porifera, Demospongiae)

The buds of the sponge Tethya seychellensis, collected in May 2006 from South Male Atoll (Maldives), have been processed for histological and ultrastructural investigations. Buds show three stages, different in morphology and size, reflecting different steps of their differentiation: round‐shaped buds (stage I), cylindrical‐shaped buds (II) and thin‐stalked spear‐shaped buds (III). Cells with inclusions, belonging to the category of spherulous cells, are the main components of these buds. At stage I, some irregularly shaped cells, probably precursors of the choanocytes, are able to engulf and remove portions of the collagen matrix, a feature which could be interpreted as an initial step in choanocyte differentiation. Tethya seychellensis stands out among the other congeneric species owing to the occurrence of choanocyte chambers in the unreleased buds, as observed at stages II and III. The precocious differentiation of the choanocyte chambers allows the detached bud to act as a young functional sponge, thus enhancing the survival chances of these filter‐feeding organisms. The structure of the buds of T. seychellensis stresses once more that in the genus Tethya the organisation of the buds represents a species‐specific process, which varies according to the plasticity and the morphogenetic potentiality expressed by a single species.

Sperm ultrastructure of three Syllinae (Annelida, Phyllodocida) species with considerations on syllid phylogeny and Syllis vittata reproductive biology

Phylogeny of Syllidae is under debate due to new studies based on molecular and morphological data. The noticeable taxonomic diversity of syllids (about 700 listed species) is also mirrored in the array of reproductive strategies as well as in sperm morphology, counting a display of forms already supposed to reflect phylogenetic relationships between the species. The sperm ultrastructure of Syllis gerlachi, S. prolifera and S. vittata is herein presented and compared to the Syllinae species studied previously. Moreover, the egg structure and the gamete allocation within stolons of S. vittata are particularly investigated. Both male germinal cells at different level of maturation and oocytes were found in the same individual of S. vittata, suggesting simultaneous hermaphroditism. The ultrastructural analysis revealed that the observed spermatozoa belong to the ect-aquasperm type resembling those of the similar studied species (Syllis sp., S. pigmentata and S. krohni). Differences in the acrosome structure and nucleus shape are in accordance with a recent phylogenetic reconstruction and suggest a trend in the evolution of spermatozoa in Syllinae toward the development of the apical part. However, further molecular and ultrastructural analyses are needed to support this hypothesis. This is the first record of simultaneous hermaphroditism within Syllinae.

Sponges associated with coralligenous formations along the Apulian coasts

Sponge assemblages associated with coralligenous outcrops were studied with the aim of describing and comparing their composition, morphological features and distribution at different depths (shallow vs. deep) along the Apulian coasts. In addition, image analysis enabled the description of the main features of coralligenous outcrops and the detection of structuring species. The paper provides a significant contribution in terms of supplying new taxa of sponges associated to coralligenous assemblages and emphasising the importance of invertebrates in realising calcareous constructions. Most of the new finding came from deep sites, thus underlining the need to improve taxonomic studies on coralligenous communities at greater depths. A total of 153 taxa of sponges were recorded: 4 Calcarea, 6 Homoscleromorpha and 143 Demospongiae. Two species, Clathria (Microciona) macrochela and Thoosa armata, are new records for the Italian sponge fauna, with C. (M.) macrochela representing a new record for the whole Mediterranean. New findings for the Ionian and Adriatic Seas totalled 25 and 8 species, respectively. Thirty-nine species are endemic for the Mediterranean. Data analyses clustered sites into two groups, separated according to the depth. Deep sites, characterised by animal dominance, exhibit a heterogeneous substrate texture richer in cavities than the shallow and homogeneous algal ones. Differences in sponge species composition also correspond to differences in the distribution of sponge growth forms, with the insinuating cryptic species more abundant in deeper communities. Ten of 15 sponge species included in national and international wildlife protection laws and policy have been detected in the present study.

A study on spermatogenesis of three Mediterranean serpulid species

Abstract Sperm ultrastructure and some steps of spermatogenesis of the serpulids Hydroides dianthus, Serpula vermicularis and Vermiliopsis infundibulum are reported. In all the species examined the germinal cells originated from a germinative epithelium associated to blood vessels in the intersegmental septa. The spermatocytes were irregular in shape with a large nucleus and a thin cytoplasmic layer. In early spermatids in which the nucleus gradually condensed, a developed endoplasmic reticulum and some electron-dense bodies were observed. The nucleus was dehydrated in the late spermatids and assumed a cylindrical shape. In all the examined species, the morphology of the ripe spermatozoa can be ascribed to the ect-aquasperm type. The acrosome had a simple cup shape in V. infundibulum, whilst it was more developed extending laterally to the nucleus in H. dianthus, and cup-shaped with a swelling towards the nucleus in S. vermicularis. When the morphology of the serpulid spermatozoa was superimposed on a phylogenetic scheme, some trends could be highlighted. Although the paucity of data on serpulid spermatozoa ultrastructure at present prevents any phylogenetic inference, the comparison of acrosome ultrastructure within a group having similar reproductive strategies showed an increase in the internal complexity of the acrosome.

Some steps of spermatogenesis in Halichondria semitubulosa (Demospongiae, Halichondriidae)

Spermatogenesis of the marine sponge Halichondria semitubulosa (formerly Pellina semitubulosa) has been investigated at the ultrastructural level. This process can be observed in March when, among the choanocyte chambers of the aquiferous system, spermatic cysts are visible. They are delimited by pinacocyte‐like cells and include elements in progressive development: spermatocytes of the first and second order, spermatids and spermatozoa. The early phase of spermatogenesis was not detected. Spermatocytes of the first order show an elongated shape, several small mitochondria and patched chromatin; spermatocytes of the second order, frequently connected by bridges, show denser chromatin, a single large mitochondrion with numerous tightly adherent cristae, glycogen, and round‐shaped inclusions with a central electron‐dense core. In the spermatids the chromatin tends to be packed in the central region. Spermatozoa have a uniformly dense nucleus in close association with the large mitochondrion. Sperm maturation takes place synchronously within the same cyst but asynchronously within the same specimen.