Search

The aesthetic appeal of marine reserves and the facilities provided, together with the increased public awareness of nature, all contribute to creating massive tourism in MPAs. Human activities are being changed inside MPAs in two ways: humans as top predators are generally being removed, but in turn they could come back at great numbers as visitors. Many authors have studied the impact of visitors, and the results highlight that the consequences can be very substantial and may represent a severe threat to the overall diversity of marine communities. To date, the documented effects of human recreational activities on natural communities are restricted to assessing the consequences of trampling over intertidal and upper infralittoral areas, boat anchoring in seagrass meadows and tropical reefs, or SCUB A-diving. In this paper we review the available literature world-wide on the effects of human recreational activities in marine communities. The objective is to address the extent of these impacts and to highlight the gaps of knowledge to be filled in order to optimise decision making on research, monitoring, and management of Mediterranean MPAs. A specific plan for managing tourism use in each Mediterranean MPA should be designated. These strategies should be implemented through education, training, and changes in legislation and policy.

Mollusc assemblages of three concrete artificial reefs (ARs) in the Gulf of Castellammare were compared with those of two nearby natural reefs (NRs). The reefs were located in areas characterized by different degrees of water transparency, with average annual Secchi disk visibility ranging from clear (>20 m) to turbid waters (

Developing embryos and sexually mature follicles of the male portion of ovotestis proved to be a suitable material as a source of cleaving cells for advanced cytological investigations on the sacoglossan species Oxynoe olivacea Rafinesque, 1819 (Mollusca: Opisthobranchia). O. olivacea has a diploid chromosomal number of 30 made up of 15 pairs of which six are metacentric/submetacentric (M/SM), four subtelocentric (ST) and five on the borderline between SM and ST. Correspondingly, 15 bivalents occur in spermatocytes at Metaphase I. Constitutive heterochromatin is scarce and restricted to small C-bands seen in five pachytene bivalents. The use of combined silver staining and fluorescent in situ hybridization (FISH) with a Paracentrotus lividus (Echinodermata) 4.3 kilobase (kb) rDNA probe (prR14) consisting of sequences from the 3′ end of 18S rDNA to the 3′ end of 26S rDNA, revealed that nucleolus organizer regions (NORs) are situated terminally on one arm of a small metacentric pair. The telomeric (TTAGGG) n sequence did not hybridize with termini of O. olivacea chromosomes.

Recent ecological studies have shown a strong relation between temperature, echinoids and their grazing effects on macro-algal communities. In this study, we speculate that climate warming may result in an increasingly favourable environment for the reproduction and development of the sea urchin Arbacia lixula. The relationship between increased A. lixula density and the extent of barren grounds in the Mediterranean Sea is also discussed.

In the Mediterranean, fishing bans generally allow the recovery of populations of sea urchin predators, such as the seabreams Diplodus sargus and D. vulgaris, promoting the transformation of overgrazed communities into ones dominated by erect macroalgae. However, in the marine reserve on Ustica Island (SW Italy) the opposite trend has occurred in the upper infralittoral community, and urchin barrens formed after the cessation of fishing activities. We hypothesized that (1) the natural scarcity of the 2 seabream species leads to a low predation rate on sea urchins at Ustica, and (2) predation rate varies with depth, due to differences in the predator assemblages. Tethering experiments were conducted to test these hypotheses by comparing the predation rates at different depths at Ustica and 2 other locations in Sicily characterized by erect macroalgae communities and low urchin densities. Differences in the assemblages of predators, relative vulnerability of the 2 species of sea urchin present (Paracentrotus lividus and Arbacia lixula), and sea urchin density were also assessed. Despite large variation in predator abundance among locations, there was no difference in predation rate on tethered urchins. Predation by fish was found to be higher in locations where seabreams were abundant, while predation by the starfish Marthasterias glacialis, usually considered a minor sea urchin predator, was found to be the major source of mortality at Ustica. The paucity of predatory fish at Ustica was consistent with the high abundances of urchins and persistence of barrens habitat. The high predation rate on urchins by M. glacialis at Ustica suggests that. this species might play an important role in controlling urchin populations in the future.

We investigated, with a series of field and laboratory observations, the possible effect of the starfish Marthasteria glacialis predation on the operational sex ratio (OSR), i.e. the number of sexually mature males divided by the total number of sexually mature adults of both sexes at any one time, of the edible sea urchin Paracentrotus lividus. The OSR was estimated three times during the sea urchin summer spawning period (July 2004, June 2005 and July 2006) on barren substrates of Ustica Island Marine Protected Area (Southern Tyrrhenian Sea, Italy). Four sites were selected: two characterized by high M. glacialis density (take zone C) and two controls with low starfish density (no-take zone A). Mature sea urchins were independently collected by SCUBA diving and sexed. The adult sex ratio was skewed towards males at high M. glacialis density sites, whereas it was balanced (1:1) at predator low-density sites. Results of sex-selective feeding experiments in the laboratory showed that females of P. lividus were more vulnerable to M. glacialis predation. These outcomes underline the possible importance of M. glacialis in regulating the OSR of P. lividus populations.

Seagrass colonise new areas via the dispersion of seeds or vegetative fragments. Independent of the manner of colonization, habitat requirements need to be met for the successful establishment of seagrasses. Here we report on the colonization process of Posidonia oceanica in a highly disturbed area: a gas pipeline trench at Capo Feto (SW Sicily, Italy). A trench dredged through a P. oceanica bed was back-filled with rubble added from dump barges leading to the formation of a series of rubble mounds on the seabed. Over time, these mounds became colonised with P. oceanica. In order to understand the pattern of P. oceanica colonization, shoot density was quantified over 3 years (2001-2003) on different mound locations (crests, sides, valleys). Seagrass coalescence was observed only in valleys between mounds where shoot density averaged 133 +/- 50 shoots m(-2), while values for sides and crests were significantly lower (30.5 +/- 14 and 5.8 +/- 2.6 shoots m(-2), respectively). Although sediment accumulated on both crests and valleys, a significantly thicker sediment layer was recorded in the valleys (9.8 +/- 0.4 cm) than on crests (1.1 +/- 0.2). Plaster dissolution rate (an indicator of the hydrodynamic regime) tended to decrease from crests to valleys but even in the valleys, the currents were still higher than in the adjacent vegetated control location. This pattern was constant over time and depths. This is the first study to report on P. oceanica vegetative recruitment on artificial rubble after a disturbance event. It appears that the valleys between the rubble mounds are suitable for seagrass recruitment as sediment deposited between the rubble provides the necessary resources for plant settlement and growth. Once the seagrass patches are established, they may start a positive feedback of attenuation of currents, sediment accumulation and seagrass patch expansion.

This paper provides information on spawn morphology and egg features of the stenophagous planktotrophic Mediterranean sacoglossan Oxynoe olivacea. Smith and Fretwell’s hypothesis, predicting that individuals of the same population growing in the same environmental conditions and varying in size should spawn eggs of a constant size, was tested in a population of O. olivacea living in the Straits of Messina. To determine whether (a) spawn mass size, (b) total egg number per spawn, and (c) egg size were related to parent size of O. olivacea, 21 egg masses (seven egg masses deposited by seven different 20 mm animals, seven egg masses deposited by seven different 25 mm animals and seven egg masses by seven different 30 mm animals) were randomly chosen and examined. Results showed that both spawn mass width and number of eggs per spawn mass increased across O. olivacea body size and apart from the significant variation of the short capsule diameter, there was no consistent variation of egg features in O. olivacea. In conclusion the species allocates constant amounts of energy to individual embryos and thus supports the prediction designed by Smith and Fretwell.

The ecological importance of marine algae is widely known but in shallow coastal areas the composition and structure of algal communities may be affected by different human activities. Recovery from different trampling disturbances of two competing morphological groups (i.e. macroalgae and algal turfs) and effects of macroalgal canopy removal on the dominant associated fauna were examined using controlled trampling experiments. Six months after trampling disturbance was removed, the two morphological groups closely resembled control (untrampled) conditions, both in terms of cover and canopy (%). In particular, macroalgal recovery seemed to be very rapid: the higher the impact on the system the more rapid the recovery rate. In the short-term, the removal of macroalgal fronds (i.e. canopy) caused evident changes in invertebrate and crypto-benthic fish densities although these indirect effects were species- specific. Erect macroalgae are very sensitive to disturbance and even relatively low intensities of human use may be non-sustainable for this shallow assemblage. The present findings suggest some interesting options for the management of Mediterranean rocky shallow areas. This is crucial for coastal areas that are intended to be maintained in natural condition for conservation purposes.

Summary 1To better understand the role and importance of body size in hermaphroditic mating system theory, the mating behaviour of the shelled sacoglossan Oxynoe olivacea was studied. This simultaneous hermaphrodite exhibits bilateral and unilateral sperm transfer and thus it is particularly suitable for studies on hermaphrodite sexual conflict. 2In this study three hypotheses on body size were tested: that O. olivacea partner size has an effect on (i) mating mode choice, (ii) duration of mating modes, and (iii) choice of sexual role. Furthermore, we tested Charnov's hypothesis that in O. olivacea, like many simultaneous hermaphrodites, a sexual conflict exists and the male role is preferred. 3A laboratory experiment was done to test the aforementioned hypothesis and to observe the general mating behaviour of O. olivacea. Pairs of similar (S) and different (D) sizes were considered for a total of five different treatments (S1, S2, S3, D1, D2). 4During the five copulatory treatments O. olivacea mated up to 93 times. Specifically, pairs of the same size mated with bilateral sperm transfer while unilateral copulation was common in pairs of slightly differing size. Contrary to predictions, animals of small body size started mating in the female role. O. olivacea showed an active alternation of sexual roles and thus did not specialize in one particular sexual role. 5This study produced evidence of a relationship between mating mode and body size in O. olivacea and highlighted the need for new studies on this simultaneously hermaphroditic species.

Biogeographia vol. XXII - 2001 (Pubblicafo il 1 ottobre 2001) Biogeogratia degli ambienti costieri Distribuzione delle piattaforrne a molluschi Vermetidi nel Mar Mediterraneo TIZIANA DIELL DARIO PELLINO. SILVANO RIGGIO Dzpzrtinzezzro di Biolagizz Arzinzzzle, Uni:/er:it¢‘z a’z' Pd/£77710, Vizz Arc/Jz'mfi, 18 - L90123 Przlemzo (lmlizz) INTRO DUZION E Un tipico reef ‘ e um formazione rocciosa “vivente” formata dalla stretta aggtegazione di organismi animali e Vegetali muniti di rivestirnenti schelem'ci estemi, Che si eleva da un basso fondo marino, :1 volts emergcndo sulla superficie in forma di scogliera. Nel corso della sua crescita, legata allo sviluppo degli organismi costruttori, ogni recfmodjfica progressivamente Fambicnte locale, sia fisicamente, in quanto crea nuovi spazi su scala tridirnensionale, chr: ecologicamente, in virtil della moltitudine di microambienti che si segregano nelle varie parti della struttura e che ospitzmo popolamenti diversi (‘Sage-rstrom, 1987; Bianchi e Morri, 1996). Lungo Yestensione deile scogliere le associazioni biotiche si djstribuiscono e selezionano in Funzione delia distanza relativa dallhcqua, della profondite e/0 deifaltezza relativa sul livello medio del mare, e (161 substrate di impianto. Ogni reef crea nuove nicchie, con l’eiTetto di aumentare sia l’eter0geneit£z spzzzizzle che la liiotliverzvitfz [om/2 Indipendentcmente dalle loro origini e posizioni geografiche, le biocostruzioni mostrano alcune caratteristiche comuni. Quests possono tiassumersi nelle seguenti: rilievo topografico positive; deposizione di mgteriale scheletrico; tasso di crescita piil o meno elevato; erosione Che pub essere pari al tasso di crescita; struttura complessa; profilo orizzontale fittamente dentellato; alto tasso cli formazione di sedirnento detritico; elevata diversite dei popolamenti associati. ‘ In itaiiano tmducibile — anchc se impropriamente » con bnrricrn.