Simona Bussotti

Fish fauna of a mixed meadow composed by the seagrasses Cymodocea nodosa and Zostera noltii in the Western Mediterranean

The fish fauna of a shallow meadow composed by the seagrasses Cymodocea nodosa and Zostera noltii was studied in the Gulf of Olbia (NE Sardinia, Italy; Western Mediterranean). Visual censuses were conducted monthly from August 1995 to August 1996. Environmental variables for water temperature, salinity and seagrass shoot density were collected on each sampling occasion. A total of 23 fish species from eight families were recorded. Planktivorous species (Atherinids) numerically dominated the fish community, followed by necto-benthic fish, chiefly Labrids and Sparids. There was no discernible trend in total fish density. Species richness, diversity, evenness and density of necto-benthic species, instead, displayed a distinct seasonal pattern, higher Values occurring from late spring to early autumn. All community variables, except total fish density, were positively related to water temperature and shoot density, but not to salinity. Multivariate analysis revealed variation in species composition and relative abundances of the fish community throughout the year. The most common fish species displayed different seasonal patterns of density throughout the year. Differences were also found in the relationships between the relative abundances of each species with the environmental variables (water temperature, salinity) and the seagrass shoot density. The data show that the fish fauna of the meadow of Olbia was characterised by a distinct seasonal variation of the community structure, probably influenced by the fluctuations of both environmental variables and habitat complexity. Since seasonal variations in fish density were due to the contribution of juvenile, sub-adult and adult specimens, the data presented here imply both recruitment and migration phenomena from and towards adjacent habitats in the colonisation of the bed during warmer months...

Study of the coastal fish assemblage in the marine reserve of the Ustica Island (southern Tyrrhenian Sea)

Abstract The coastal fish assemblage in the marine park of the Ustica Island was studied using underwater visual census. Seasonal surveys were conducted from May 1996 to March 1997 at several sites located within three zones of the reserve, each characterized by different levels of protection (integral reserve, general reserve and partial reserve). Visual strip transects were conducted using SCUBA at three different depth (3–5 m; 10–15 m; 25–30 m). Species richness and diversity indices were better correlated to depth than to protection level. Oppositely, size and/or abundance of some vulnerable species (e.g., Epinephelus marginatus, Labnis me‐rula, Labrus viridis) were positively correlated with degree of protection and the so‐called ‘reserve effect’. These observations stress the importance of protection measures for littoral fish assemblages and represent the only available data for an Italian marine park of considerable extent.

Invertebrate borers in Posidonia oceanica scales: relationship between their distribution and lepidochronological parameters

The occurrence and pattern of distribution of invertebrate borers in the scales (remains of leaf bases still connected to the rhizome) of the seagrass Posidonia oceanica was studied in two meadows of the Mediterranean Sea. At Noli (Ligurian Sea), Posidonia shoots were sampled at 1, 5, 10 and 15 m depths, while at cape Coda Cavallo (Northern Sardinia) samples were collected only at 6 m depth. The lepidochronology technique (based on the annual cycle variation in the scale thickness) was employed in order to study the relationship between plant and borers and to characterize their microhabitat in the stem. Borers belong to Polychaeta and Crustacea Isopoda. Three species of polychaetes belonging to the family Eunicidae (Lysidice ninetta Audouin and M. Edwards, Lvsidice collaris (Grube) and Nematonereis unicornis (Grube)) and one species of isopod of the family Limnoriidae (Limnoria tuberculata (Sowinski)) were responsible for burrowing within Posidonia scales. Estimated density of borers reached in some instances values as high as 278 individuals m 2. Isopods occurred in younger scales, whereas polychaetes inhabited older scales. A positive trend was observed between polychaete width (3rd body segment) and scale thickness; however, both Spearman rank correlation and linear regression coefficients showed quite low significant values. In some instances polychaetes burrowed also into the living tissues of the shoots. Borers have been recorded also in several other Posidonia beds along the Italian

Differences in escape response of fish in protected and fished Mediterranean rocky reefs

In both protected and fished rocky reefs in the southern Adriatic Sea, the behaviour of the sea breams Diplodus sargus and D. vulgaris (both targeted by spear-fishing) in the presence of divers was found to be mostly negative (i.e. escape response). However, at protected reefs sea breams frequently swam into the closest shelters, whereas in fished reefs they mostly escaped in open water. This study suggests that spear-fishing may alter the escape response of fish from natural predators and that marine reserves may re-establish natural behaviour patterns.

Timing and habitat preferences for settlement of juvenile fishes in the Marine Protected Area of Torre Guaceto (south-eastern Italy, Adriatic Sea)

Abstract Timing and habitat preferences for settlement of juvenile fishes were investigated at the Marine Protected Area (MPA) of Torre Guaceto (SE Adriatic Sea) from April 2005 to March 2006. Data were obtained by visual census (on a fortnightly basis) in 10 habitat types identified within the depth range 0–6 m. A total of 22 taxa of juvenile fish was recorded: juveniles of 14 taxa were analysed for settlement timing and habitat preferences, whereas the other 8 taxa were only occasionally observed. Diplodus vulgaris and Sarpa salpa showed two settlement peaks, while the other 12 species displayed a single annual peak. Most species (10 out of 14) settled between late spring and early autumn. Juvenile labrids and Oblada melanura were mostly associated with exposed shallow rocks, while Diplodus sargus, D. vulgaris, D. puntazzo and S. salpa chiefly settled in shallow sheltered coves. Juveniles of Chromis chromis were found in sublittoral rocks and Posidonia oceanica beds. Spondilyosoma cantharus, Diplodus annularis and Dicentrarchus labrax mostly associated to P. oceanica and small-sized seagrasses for settlement, while Mullus surmuletus chiefly used sublittoral sands. This study provides evidence of clear coherence during settlement of many fishes in terms of habitat for settlement, while some discrepancy was found in terms of timing across the year. In addition, this study provided suggestive evidence of the potential of the MPA, relative to the habitats included within its borders, in hosting juvenile fish stages and thus contributing to sustain local diversity of the coastal fish fauna. Similar data would deserve to be properly considered to design MPAs and refine conservation targets.

Distribution patterns of the cardinal fish, Apogon imberbis, in shallow marine caves in southern Apulia (SE Italy)

Abstract Distribution patterns of the sciaphilic cardinal fish, Apogon imberbis, were investigated by visual census in southern Apulia (SE Italy, Mediterranean Sea) in three shallow marine caves. Sampling was carried out in four periods, from July 2000 to June 2001 and A. imberbis was always found in large numbers inside all three caves. Density values ranged from a few to more than 1800 individuals 100 m‐2. Great numbers of juveniles, about 1 cm long, with a reddish‐transparent livery and grouped in large schools, were found in July 2000 in the three caves. Adult A. imberbis were fairly evenly distributed in time, among caves, as well as within each cave along the axis; recruitment appeared to be the most important process affecting temporal changes in total abundance of A. imberbis. The present study thus showed that marine caves represent important nurseries for recruiting of A. imberbis, as well as the preferred habitat for adults. The fact that A. imberbis may reach such high densities inside marine caves supports the hypothesis that this fish could play a relevant ecological role in the daily transfer of organic matter into these environments, an issue deserving further research.

Protection effects on Mediterranean fish assemblages associated with different rocky habitats

Rocky banks (i.e. sea mountain-like structures rising from the sea bottom) are hard substrate habitats of high socio-economic value (e.g. for fishermen and divers) and ecological relevance as they often host unusually high density of fish. Here we tested whether the response of fish assemblages to protection (i.e. related to the presence of a Marine Protected Area (MPA)) in rocky banks is comparable with the response of rocky reefs dropping from the coast (hereafter called ‘coastal rocky substrates’), and whether there are differences between fish assemblages associated with protected and unprotected rocky banks. Fish assemblages were assessed in shallow and deep coastal rocky substrates, and in rocky banks, in unprotected and protected conditions at a Mediterranean MPA in north-east Sardinia in August 2007 and 2008. Whole fish assemblage structures (in terms of biomass) differed between protected and unprotected conditions in both study years. Fish assemblages at rocky banks, in addition, differed from those associated with coastal rocky substrates. Total fish biomass (summing contribution of all species) was higher under protected than unprotected condition in 2007, while species richness and total fish density did not demonstrate any significant change related to protection. The responses to protection displayed by the target species Epinephelus marginatus and Diplodus sargus were clear especially in terms of greater frequency of large-sized specimens in both study years. Biomass of E. marginatus in 2007 and density of D. sargus in 2007 and 2008 were significantly higher in protected than unprotected conditions, especially in protected rocky banks. This study emphasizes the ecological and socio-economic role of protection and the potential role of rocky banks within management/conservation programmes in the Mediterranean Sea.

Fish assemblages of Mediterranean marine caves.

Fish assemblages associated with 14 marine caves and adjacent external rocky reefs were investigated at four Marine Protected Areas (MPAs) along the coasts of Italy. Within the caves sampling was carried out in different sub-habitats: walls, ceilings, bottoms and ends of caves. On the whole, 38 species were recorded inside the 14 caves investigated. Eighteen species were exclusively found inside the caves: they were mainly represented by speleophilic (i.e. species preferentially or exclusively inhabiting caves) gobids (e.g. Didogobius splechtnai) and nocturnal species (e.g. Conger conger). Forty-one species were censused outside, 20 of which were shared with cave habitats. Apogon imberbis was the most common fish found in all 14 caves investigated, followed by Thorogobius ephippiatus (recorded in 13 caves), and Diplodus vulgaris and Scorpaena notata (both censused in 12 caves). Distinct fish assemblages were found between external rocky reefs and the different cave sub-habitats. New data on the distribution of some speleophilic gobids were collected, showing the existence of a pool of species shared by marine caves on a large scale (i.e. hundreds of km). Considering the uniqueness of cave fishes (18 exclusive species and different assemblage structures), the inclusion of marine caves among the habitats routinely investigated for fish biodiversity monitoring could facilitate the achievement of more comprehensive inventories. Due to their contribution to local species diversity and the shelter they provide to species valuable for conservation, marine caves should be prioritized for their inclusion not only within future MPAs through the Mediterranean Sea, but also into larger management spatial planning.

An ecosystem-based approach to assess the status of Mediterranean algae-dominated shallow rocky reefs

A conceptual model was constructed for the functioning the algae-dominated rocky reef ecosystem of the Mediterranean Sea. The Ecosystem-Based Quality Index (reef-EBQI) is based upon this model. This index meets the objectives of the EU Marine Strategy Framework Directive. It is based upon (i) the weighting of each compartment, according to its importance in the functioning of the ecosystem; (ii) biological parameters assessing the state of each compartment; (iii) the aggregation of these parameters, assessing the quality of the ecosystem functioning, for each site; (iv) and a Confidence Index measuring the reliability of the index, for each site. The reef-EBQI was used at 40 sites in the northwestern Mediterranean. It constitutes an efficient tool, because it is based upon a wide set of functional compartments, rather than upon just a few species; it is easy and inexpensive to implement, robust and not redundant with regard to already existing indices.

Rocky reef fish assemblages at six Mediterranean marine protected areas: broad-scale patterns in assemblage structure, species richness and composition

Abstract Fish assemblages inhabiting shallow rocky reefs at six Italian marine protected areas (MPAs) were investigated to assess broad-scale patterns in assemblage structure, species richness and composition, and to evaluate the presence of a latitudinal gradient in the distribution pattern of a thermophilic fish, the ornate wrasse Thalassoma pavo. Fish abundance was estimated by visual censuses carried out within the integral reserve zones, within the 1--7 m depth range and during four sampling periods. Multivariate analyses revealed significant differences in the assemblage structure among MPAs, although patterns of variation changed considerably from time to time and they were not consistent with latitudinal or longitudinal gradient. Fish assemblages of Miramare (northern Adriatic) and those of the other MPAs clearly separated into two groups. Multivariate differences among MPAs mainly relied upon some relatively common species (e.g. Diplodus puntazzo and Muraena helena). Substantial contribution to these differences was also accounted for by T. pavo. Significant differences among MPAs were detected also in species richness and total density of fish, although the effect of MPA on species richness varied significantly from time to time. Both species richness and total density of fish at Miramare were always higher compared to the other MPAs, likely in relation to peculiar habitat characteristics. Density of T. pavo declined significantly from south to north, thus confirming the thermophily of this species. Present data point out the importance of monitoring marine fish diversity through long-term surveys across a wide spatial scale, in order to detect the early effects of water warming and to develop future plans of management and conservation.