SW Mediterranean Sea Research Articles

Identifying epibenthic habitats on the Seco de los Olivos Seamount: Species assemblages and environmental characteristics

High habitat diversity was observed on the Seco de los Olivos Seamount (SW Mediterranean Sea), a Site of Community Importance belonging to the Spanish marine Natura 2000 Network. Thirteen epibenthic habitats were identified by analysing 55 Remotely Operated Vehicle (ROV) transects from 76 m to 700 m depth and derived data from multibeam bathymetry and high resolution seismic profiles. Habitat identification was based on a combination of assemblages of habitat-forming species and the environmental characteristics supporting their distribution. Depth and slope were identified as the main significant factors structuring epibenthic assemblages. The high diversity and patchiness of habitats found on the Seco de los Olivos Seamount can be explained by the high environmental variability resulting from its wide geomorphologic diversity, where flat summits, steep flanks, rocky outcrops and sedimentary moats are combined. The distribution of benthic habitats at this seamount is likely a combination of suitable ecological conditions, local recruitment, feeding strategies and attachment mechanisms. Knowledge on the occurrence of habitats in areas of natural importance is crucial to species and habitats conservation and to develop proper monitoring and management programs aimed at fulfilling European regulation requirements.

Isopods of the genus Astacilla (Valvifera, Arcturidae) from the LIFE + INDEMARES project off Alborán Island (S Spain), with the description of a rare species A. carlosoteroi (Reboreda, Wägele & Garmendia, 1994)

Three species of the isopod genus Astacilla were collected off Alborán Island (SW Mediterranean Sea) within the LIFE + INDEMARES project. Twelve specimens of the rare species Astacilla carlosteroi (Reboreda, Wägele & Garmendia, 1994) were found; this species is only known as a single incomplete female from Galicia (NW Spain, Atlantic). Males, reported for the first time, are described, as well as morphological details provided for two additional species, A. dilatata (G.O. Sars, 1883) and A. mediterranea Koehler, 1911.

Plankton food-web functioning in anthropogenically impacted coastal waters (SW Mediterranean Sea): An ecological network analysis

The study is the first attempt to (i) model spring food webs in three SW Mediterranean ecosystems which are under different anthropogenic pressures and (ii) to project the consequence of this stress on their function. Linear inverse models were built using the Monte Carlo method coupled with Markov Chains to characterize the food-web status of the Lagoon, the Channel (inshore waters under high eutrophication and chemical contamination) and the Bay of Bizerte (offshore waters under less anthropogenic pressure). Ecological network analysis was used for the description of structural and functional properties of each food web and for inter-ecosystem comparisons. Our results showed that more carbon was produced by phytoplankton in the inshore waters (966–1234 mg C m−2 d−1) compared to the Bay (727 mg C m−2 d−1). The total ecosystem carbon inputs into the three food webs was supported by high primary production, which was mainly due to >10 µm algae. However, the three carbon pathways were characterized by low detritivory and a high herbivory which was mainly assigned to protozooplankton. This latter was efficient in channelling biogenic carbon. In the Lagoon and the Channel, foods webs acted almost as a multivorous structure with a tendency towards herbivorous one, whereas in the Bay the herbivorous pathway was more dominant. Ecological indices revealed that the Lagoon and the Channel food webs/systems had high total system throughput and thus were more active than the Bay. The Bay food web, which had a high relative ascendency value, was more organized and specialized. This inter–ecosystem difference could be due to the varying levels of anthropogenic impact among sites. Indeed, the low value of Finn’s cycling index indicated that the three systems are disturbed, but the Lagoon and the Channel, with low average path lengths, appeared to be more stressed, as both sites have undergone higher chemical pollution and nutrient loading. This study shows that ecosystem models combined with ecological indices provide a powerful approach to detect change in environmental status and anthropogenic impacts.

Seasonal variability in diversity and abundance of the free-living pelagic copepod community of the Algerian coasts (SW Mediterranean Sea)

Abstract Investigations on the free-living, pelagic copepod community of the Algerian coasts were performed at the Habibas Islands and in Bou Ismail Bay (Sidi Fredj coast) between 0 and 100 meter depth during various seasons of the year 2012-2013. Seventy-seven taxa at species level have been identified, belonging to 47 genera and 24 families. The distribution of the copepod community revealed seasonal variability; high abundance and species richness (greater than 20 species) characterized winter and spring, while the summer period was characterized by low abundance and species richness. The spatial distribution showed high abundance and species richness on the Sidi Fredj coast (the respective mean abundances along the Sidi Fredj coast and at the Habibas Islands were 253.71 ind.m−3 and 109.77 ind.m−3, respectively). Analysis of the samples showed the presence of seven abundant and frequent species: Centropages typicus, Eucalanus elongatus, Pleuromamma abdominalis, Paracalanus parvus, Paracalanus nanus, Calanus helgolandicus, and Temora stylifera. Multivariate analysis (ascending hierarchical classification and non-metric multidimensional scaling) enabled us to group the stations according to the composition in the copepod species, and the influence of seasonal changes was well observed. A dominance of herbivorous behaviour, followed by an omnivorous feeding strategy, was observed in the two studied areas. A dominance of epipelagic and epi-mesopelagic species was observed during all seasons, reflecting a neritic character of both study areas.

Temporal variation and structure of macro-epifauna associated with macrophytes in the Bizerte lagoon (Tunisia, SW Mediterranean Sea)

ABSTRACTThe temporal variation in composition and abundance of the macro-epifauna associated with seaweeds (Ulva lactuca, Cladophora sp., Gracilariopsis longissima and Gracilaria bursa-pastoris) and seagrass (Cymodocea nodosa) was investigated at Menzel Jemil station in the Bizerte lagoon. Twelve replicate samples (25 x 25 cm frame) were collected monthly from October 2009 to September 2010. Sampling data yielded 21,575 invertebrate specimens from floating seaweeds and the seagrass, belonging to 40 taxa, of which 18 species were arthropods, 13 molluscs, three echinoderms, three fishes, two polychaetes and one cnidarian. Crustaceans were the most dominant and the most species-rich group and Idotea balthica basteri the most abundant species, accounting for 28.94% of the total abundance. Minimum (9.25 ± 5.56 species) and maximum (19.75 ± 3.2 species) values of mean species richness were observed in December and June, respectively. Species richness and density of macro-epifauna showed similar trends to plant biomass and the highest values of both indices coincided with periods of maximal plant biomass. Mean values of Shannon’s index H′ and evenness J′ were low, ranging from 0.34 ± 0.02 bit to 1.08 ± 0.06 bit, and from 0.23 ± 0.03 to 0.52 ± 0.07, respectively. The high dominance of herbivores and detritivores highlighted the substantial role played by macrophytes as food source for associated macro-epifauna species. Multivariate analyses also indicated significant seasonal differences for the macro-epifauna assemblage and revealed significant relationships with environmental variables. According to the canonical correspondence analysis, concentrations of phosphates and nitrites, and temperature were the variables that explained the variation of the macro-epifauna abundance in the Bizerte lagoon.

On the role of turf species as refuge in disturbed environments: A case study with polychaetes (Annelida: Polychaeta) in SW Mediterranean Sea

During the summer of 2014, a field survey was conducted in several littoral rocky sites on the southeastern coast of Spain. In this area, dense canopies of Cystoseira mediterranea characterize undisturbed locations and cover most of the available infralittoral fringe. Turfs composed mainly of the coralline algae Ellisolandia elongata replace the canopy in locations where some kind of anthropogenic disturbance has occurred. The main goal of this study was to compare the polychaete fauna dwelling within the two types of phytal substratum, and several univariate and multivariate analyses were performed to detect significant differences between the two assemblages. The analyses showed that the assemblage inhabiting E. elongata was characterized by a higher population density of polychaetes and was dominated by herbivores and filter-feeders, especially Fabricia stellaris and Amphiglena mediterranea. Polychaetes were less abundant in pristine sites covered by Cystoseira mediterranea, although a-diversity was slightly higher. This assemblage was characterized by a predominance of omnivores followed by herbivores, and by high relative abundances of Syllis prolifera and Salvatoria clavata. However, none of the detected differences was statistically significant and site to site comparison showed that differences between locations with the same phytal cover were similarly deep. Our data point out that the assemblage inhabiting turf algae in the region studied is not substantially different to that found in pristine areas and that this type of phytal covering can act as effective refuge for polychaetes under moderately disturbed condition.

Distribution of four isopods (Peracarida: Crustacea) in shallow waters of the Bizerte Lagoon (Tunisia, SW Mediterranean Sea)

The distribution of four isopods – Idotea balthica basteri (Pallas, 1772), Idotea chelipes mediterranea Charfi-Cheikhrouha, 1996, Sphaeroma serratum (Fabricius, 1787), and Paracerceis sculpta (Holmes, 1904) – at Menzel Jemil (Bizerte Lagoon, North Tunisia) was analysed and then related to the variation of temperature, depth and plant biomass. The abundance of isopods showed monthly fluctuations with maxima in August and minima in December 2010. The most dominant species was I. b. basteri followed by S. serratum, with a spatial gradient in the distribution pattern of isopod species in the study area. The high density of juveniles in algae and seagrass highlights the important role played by this habitat as a nursery for species. Both dominant species were tolerant to temperature variations, with some preference values (19.73–27.73°C in I. b. basteri; up to 28°C in S. serratum) and salinity (36.7–38.6 psu in I. b. basteri; 39–39.2 psu in S. serratum). Multiple regression analysis between environmental variables and species abundance showed a positive relationship with biomass of Gracilaria bursa-pastoris and Ulva lactuca for the two species of Idotea and Sphaeroma, respectively, while abundance of P. sculpta was positively related to temperature. Biotic and environmental linking (BIOENV) analysis confirmed the greatest influence of temperature and vegetation biomass on the temporal distribution of these isopod species. A spatial distribution pattern according to successive depths was revealed.

Assessment of surface sediment dynamics and response of benthic macrofauna assemblages in Boughrara Lagoon (SW Mediterranean Sea)

A study was conducted in the spring of 2009, the winters of 2010 and 2013, and in the summer of 2012 at 13 stations in Boughrara Lagoon, Tunisia (southern Mediterranean). The country⿿s largest lagoon, it is considered to be an anthropogenically stressed area, though a major tourist centre⿿Djerba Island⿿is located along its northern shores. The lagoon bottoms were studied via analyses of grain size, surface sediment composition, total organic matter (TOM) and through the trophic and functional organisation of benthic macrofauna. The results indicate that the bottoms are composed of fine, medium or coarse sands and that sediment distribution is controlled by water movement. Estimation of TOM content revealed that the studied samples present both normal and imbalanced sediments. The structure and organisation of the lagoon⿿s benthic macrofauna are dominated by select deposit feeders and underwent significant changes during the period 2010⿿2013.Subjected for decades to increased pollution due to growing human activities in the surrounding area, Boughrara Lagoon now appears to be impacted by certain environmental/anthropogenic stressors, as indicated by the presence of pollution-tolerant bio-indicator species in the imbalanced area. The response of the lagoon ecosystem to changes in benthic sediment deposition provides a potential assessment tool for similar habitats elsewhere.

Effects of nitrogen supply on Pseudo-nitzschia calliantha and Pseudo-nitzschia cf. seriata: field and laboratory experiments.

The effects of inorganic and organic nitrogen supply on the growth and domoic acid (DA) production of Pseudo-nitzschia cf. seriata and Pseudo-nitzschia calliantha from Bizerte Lagoon (SW Mediterranean Sea) were studied during field and laboratory experiments. Nitrogen enrichments (40µM NO3 (-); 10µM NH4 (+); 20µM CH4N2O) and a control, with no added N, were carried out in separate carboys with seawater collected from Bizerte Lagoon. In the field experiments, all N-enrichments resulted in significant increases in chlorophyll a concentration, and maintained exponential growth until the end of the experiment. The initial diatom community was dominated by a bloom of P. cf. seriata (9.3×10(5) cells l(-1)). After 6days of incubation, the abundance of P. cf. seriata was greatest in the urea addition (1.52×10(6) cells l(-1)), compared to the ammonium treatment (0.47×10(6) cells l(-1)), nitrate treatment (0.70×10(6) cells l(-1)) and control (0.36×10(6) cells l(-1)). The specific growth rates, calculated from increases in chlorophyll a and cell abundance, were statistically different across all treatments, with the highest in the urea and nitrate additions. Similar results were obtained from the laboratory experiments. These were carried out with P. calliantha isolated from Bizerte Lagoon and grown in f/2 medium enriched with 40µM nitrate, 10µM ammonium and 20µM urea. The exponential growth rate was significantly faster for the cells cultured with urea (1.50d(-1)) compared to the nitrate (0.90d(-1)) and ammonium (0.80d(-1)) treatments and the control (0.40 d(-1)). Analysis of DA, performed at the beginning and the end of the both experiments in all treatments, revealed very low concentrations (below the limit of quantification, 0.02- 1.310(-7) pg cell(-1), respectively).The field and laboratory experiments demonstrate that P.cf. seriata and P. calliantha are able to grow efficiently on the three forms of N, but with a preference for urea.

Viability, growth and domoic acid toxicity of the diatom Nitzschia bizertensis following filtration by the mussel Mytilus sp.

The diatom Nitzschia bizertensis was recently discovered in Bizerte Lagoon (Tunisia, SW Mediterranean Sea), where it was shown to produce the amnesic shellfish poisoning toxin, domoic acid (DA). This diatom was previously found to be widespread in both time and space throughout the lagoon. The present study was carried out to test the hypothesis that N. bizertensis is able to survive after being filtered and ejected as biodeposits (faeces plus pseudofaeces) by mussels. N. bizertensis cultures (strains BD4 and BD8), at natural bloom concentrations, were fed to mussels (Mytilus sp.). The stomach contents (after 1 h) and biodeposits (after 48 h) were observed for the presence and viability of N. bizertensis cells. Light microscopy revealed intact and partial cells of N. bizertensis in both the stomach contents and biodeposits of the mussels. Incubation of the biodeposits resulted in the regrowth of N. bizertensis. This provides evidence that transplanted mussels have the potential to serve as vectors for the transport of N. bizertensis. Furthermore, cells regrown from the biodeposits contained DA, but at levels lower than those in pre-filtered cells (up to 11.9 fg cell−1). Thus, regrown cells remain toxigenic. The results suggest that one must guard against spreading N. bizertensis and other DA producers via the transfer of shellfish from contaminated to pristine areas.

Trophic and functional organization of the benthic macrofauna in the lagoon of Boughrara – Tunisia (SW Mediterranean Sea)

The lagoon of Boughrara is the largest lagoon in Tunisia. For several decades it has been subject to the impact of increasing anthropogenic activities, and also to environmental stressors due to climate change and the low renewal of its waters. The present work is a contribution to the study of the functional organization of the benthic macrofauna of the lagoon of Boughrara 3 years after the extension of the channel ‘El Kantra’ which connects this lagoon to the open sea. In total, 13 stations facing the main prospective sources of disturbance and in areas likely to be more polluted were seasonally sampled during 2009–2010. Seasonal monitoring of the abiotic parameters shows a spatial heterogeneity linked to environmental and anthropogenic factors, including hydrodynamics, sedimentary texture and anthropogenic activities. The community of benthic macrofauna is generally poorly diversified at lagoonal-marine stations undergoing influences of both the marine and lagoon environment. The extreme seasons in terms of temperature and salinity seem to have an important role in the reduction of biodiversity in the lagoon of Boughrara. The trophic structure of the macrobenthic community is generally dominated by selective deposit feeders, and seems to be linked more to the availability of trophic resources than to disturbance.

First evidence of cell deformation occurrence during a Dinophysis bloom along the shores of the Gulf of Tunis (SW Mediterranean Sea)

Never before observed or cited in Dinophysis studies, deformations in Dinophysis acuminata and Dinophysis sacculus are reported throughout their cellular division phases (cytokinesis, and sulcal list regeneration) in 5 in situ cell cycle studies in the Punic harbors of Carthage (northern Tunisia). Two types of deformation were observed: invaginations in the ventral and dorsal margin and protuberances at the base of the left sulcal list. No virus or bacteria were detected with Syber green stain. In situ division rates (μ) varied among seasons and stations for the same species. D. acuminata exhibited moderate (0.22day−1) to high (0.68day−1) μ rates which were however very low (0.02–0.17day−1) for D. sacculus in autumn and moderate (0.21–0.35day−1) in late spring. In 2009 the seasonal distribution of Dinophysis indicates maximum Dinophysis cf. ovum abundance in March and a high number of D. acuminata in early June, while in 2010 maximum abundance of the same species was found in mid-June.Molecular and genetic studies and staining with specific fluorescent strains should be addressed to hopefully explain these Dinophysis cell deformations during their in situ division.

Population structure of the European anchovy, Engraulis encrasicolus, in the SW Mediterranean Sea, and the Atlantic Ocean: evidence from otolith shape analysis

Abstract Understanding the influence of oceanographic features on the structure of fish population is of basic importance to population dynamics studies and fisheries management. The European anchovy (Engraulis encrasicolus) exhibits a complex population structure which has produced conflicting results in previous genetic studies. This study examines the variability in the shape of the anchovy's otolith as a tool for identifying different stocks, and investigates the effects of oceanographic features on population structure. Anchovies were analysed from seven locations in the SW Mediterranean Sea and Atlantic Ocean along the northwestern African (Morocco) and Portuguese (Bay of Cadiz) coasts. A combination of otolith shape indices and elliptic Fourier descriptors were investigated by multivariate statistical procedures. Within the studied area, three distinct anchovy stocks were identified: the Algero-Provençal Basin, the southern Alboran Sea, and the Atlantic Ocean (Morocco and Gulf of Cadiz). The separation of the stocks was based on non-parametric discriminant analysis returning a classification percentage. Over 81% of the separation of the stocks could be explained by oceanographic features. Shape variability of anchovy otoliths was associated with the presence of the Almeria-Oran front, and the strait of Gibraltar. The Alboran stock was distinct from the Algero-Provençal Basin and from the closest Atlantic stocks (Gulf of Cadiz or Atlantic coast of Morocco). Results are discussed and compared with those previously obtained by genetic studies. This study supports the efficiency of otolith shape analysis for the stock identification of anchovy, and highlights the role of oceanographic features in stock separation.

The GenusOstreopsisalong the Algerian Coastal Waters (SW Mediterranean Sea) Associated with a Human Respiratory Intoxication Episode

This work describes the first toxic event (human intoxications and sea urchin mortality) related to Ostreopsis bloom in Algerian coastal waters. The distribution of Ostreopsis is presented in three rocky beaches of Algiers Wilaya, where several cases of human intoxications were registered during July 2009. The maximum abundances attained by Ostreopsis in other stations of the network established by the Agency for the Protection and Promotion of Algiers Wilaya coasts (APPL) for monitoring HABs species are also presented. We discuss some of the factors that could explain this toxic episode.

BLOOMS OF THE DIATOM GENUS PSEUDO-NITZSCHIA H. PERAGALLO IN BIZERTE LAGOON (TUNISIA, SW MEDITERRANEAN)

The phytoplankton composition, including the potentially toxic diatom genus Pseudo-nitzschia, and related physico-chemical water properties were determined at four stations in Bizerte Lagoon (SW Mediterranean Sea) monthly, from March 2004 to March 2005. Total phytoplankton abundance was generally low (1.50–7.12 × 105 cells L−1), but peaked in April 2004 (19.4 ± 2.9 × 105 cells L−1), July 2004 (19.9 ± 11.1 × 105 cells L−1) and March 2005 (12.2 ± 4.8 × 105 cells L−1), and was dominated by Plagioselmis spp., Pseudo-nitzschia spp. and Thalassiosira spp., respectively. The contribution of Pseudo-nitzschia spp. to the total algal community was generally moderate (0.6–8.9%, when detected). The genus Pseudo-nitzschia was detected in 70% of the samples and thus appeared as a regular component of the phytoplankton that develops in the surface waters of Bizerte Lagoon. Distribution patterns of Pseudo-nitzschia species in the “delicatissima” group (< 3 μm in width) showed a strong seasonality and were correlated with summer conditions (when temperature, salinity and silicate concentration increased), although they were present during at least seven months of the year, at all stations. Pseudo-nitzschia species in the “seriata” group (> 3 μm in width), conversely, revealed a narrower spatio-temporal distribution and appeared uncorrelated with the environmental factors measured. The causative species of the July peak was identified by scanning electron microscopy as Pseudo-nitzschia calliantha. Two out of four isolates of P. calliantha from Bizerte Lagoon produced the neurotoxin domoic acid (causative agent of Amnesic Shellfish Poisoning) in batch culture. Our findings suggest the possibility of domoic acid contamination of bivalve molluscs in Bizert Lagoon, one of the main shellfish aquaculture areas in Tunisia, and therefore the need for continued vigilance.

Growth patterns of a proximal terrigenous margin offshore the Guadalfeo River, northern Alboran Sea (SW Mediterranean Sea): glacio-eustatic control and disturbing tectonic factors

The shelf-upper slope stratigraphy offshore and around the Guadalfeo River on the northern continental margin of the Alboran Sea, Western Mediterranean Basin, has been defined through the interpretation of a grid of Sparker seismic profiles. We tried to identify evolutionary trends in shelf growth, as well as to determine the regional/local factors that may modify the influence of glacio-eustatic fluctuations. Four major depositional sequences are identified in the sedimentary record by a detailed seismic interpretation, which defines three significant intervals of shelf-upper slope progradation, dominated by deposition of shelf-margin wedges, which resulted in uniform patterns of shelf-margin growth in response to significant sea-level falls. In contrast, the record of transgressive intervals is more variable, mainly as the result of distinct patterns of regressive-to-transgressive transitions. Major progradational wedges are internally composed of seaward-prograding, landward-thinning wedges, interpreted to represent shelf-margin deltaic deposits. In contrast, the last aggradational interval is composed of shelf-prograding wedges that show distinct characteristics, in terms of seismic facies, morphology and distribution when compared with previous shelf-margin wedges. These shelf wedges are thought to represent the particular case of Regressive Systems or Shelf Margin Systems Tracts, and their development seems to be controlled by a drastic change in main depocenter location, which moved from the upper slope to the shelf during the Pleistocene. The stacking pattern of seismic units, the shallowness of the acoustic basement and the migration of the shelf break are used to infer spatial and temporal changes in tectonic subsidence-uplift rates, which interact with low-order glacio-eustatic changes. For much of the Pliocene-Quaternary, uplifted sectors alternated laterally with sectors experiencing more subsidence. Subsequently, a significant change from lateral outgrowth to vertical accretion is recognised. This stratigraphic change could be related to the combined influence of increased subsidence rates on the shelf and the onset of higher-frequency glacio-eustatic cyclicity after the Mid Pleistocene Revolution that occurred around 1 Ma.

Temporal genetic variation in populations of Diplodus sargus from the SW Mediterranean Sea

Population genetic studies on white sea bream Diplodus sargus have revealed different patterns in the subdivision of populations in the Mediterranean Sea. However, the stability of observed allele frequencies over time remains poorly tested. The aim of this study was to show that the genetic structure of D. sargus could significantly change over time by analysing temporal varia- tions in allozymes. In order to determine temporal variation in the genetic structure of 5 natural D. sargus populations in the SW Mediterranean, we screened 14 allozyme loci. Our main finding was the significant genotypic differentiation among cohorts (year-classes) in the Guardamar (FST = 0.012; p < 0.001) and Cape of Palos (FST = 0.008; p < 0.001) populations. The differentiation observed in the present study when considering pair-wise comparisons between cohorts is similar to that of all popu- lations throughout the Mediterranean Sea. Our results suggest that microgeographical variations, also known as 'chaotic genetic patchiness', could occur in D. sargus populations from the SW Mediterranean. The recruitment of genetically variable cohorts at 1 site each year may account for these variations. We also discussed alternative explanations for this genetic pattern. This study con- firms the importance of understanding the ecology, behaviour and environment of fish populations when investigating population genetic structure. Our results also highlight the importance of incor- porating temporal samples when conducting population structure studies.

Diel and vertical movements of preflexion fish larvae assemblage associated with &lt;i&gt;Posidonia oceanica&lt;/i&gt; beds

Habitat complexity is a strong determinant of fish assemblage structure. Enhanced food resources and protection from predators are generally considered the main benefits of vegetated areas. We investigated the diel and vertical movements of preflexion fish larvae within and above the leaf canopy of Posidonia oceanica to determine if it acts as an important habitat for larval stage fish. Samples were taken with moored plankton nets during the night and day at two depths (13 and 15 m) over five consecutive days in July 2000 in the Marine Protected Area off Tabarca Island (Spain, SW Mediterranean Sea). In total, 353 fish larvae were captured. The most abundant taxa were Sardinella aurita, Sparidae, Engraulis encrasicolus and Gobiidae. Sparidae were more abundant within the leaf canopy during the day but increased in waters 2 m above the canopy at night. In contrast, Sardinella aurita were present throughout the entire water column during both the day and night. We conclude that the P. oceanica leaf canopy is important as a transitional shelter for the early stage larvae of some demersal fish species.

Mitigating human disturbance: can protection influence trajectories of recovery in benthic assemblages?

1. Understanding whether Marine Protected Areas (MPAs) can be considered as a suitable tool for restoring the structure and function of populations and assemblages is urgently needed to achieve an effective policy of mitigation of human impact in coastal management. However, to date, the role played by MPAs in enhancing ecosystems resilience has been more advocated than unambiguously documented. 2. This study was designed to test whether full protection in marine reserves facilitates recovery of benthos impacted by the date mussel Lithophaga lithophaga fishery, one of the most harmful human activities affecting subtidal rocky habitats in the Mediterranean Sea. 3. The effects of this destructive fishery were reproduced at one fully protected location (P) and at two unprotected control locations (Cs) in the SW Mediterranean Sea. At each location, three plots (4 m2) of rocky surface at 4-6 m depth were disturbed experimentally, while another three plots served as reference. In each plot, the species composition and relative cover of the sessile benthic assemblages were sampled photographically on each of five occasions during a period of 20 months. 4. Over and above variation in habitat features among locations, multivariate and univariate analyses revealed significant differences between P-vs.-Cs in patterns of assemblage recovery and showed that, at the fully protected location, recovery was faster than at the unprotected control locations. 5. Our results suggest that MPAs have the potential to change the trajectories of recovery of disturbed assemblages by accelerating the processes of recolonization and call for further investigation to identify the specific mechanisms underlying increased resilience.

Polymorphic microsatellite loci isolated from the Atlanto‐Mediterranean colonial ascidian Pycnoclavella sp. (Ascidiacea, Tunicata)

AbstractEight microsatellite loci were characterized in the colonial ascidian Pycnoclavella sp. from an enriched library of genomic DNA. Most microsatellites were large and compound. Allelic variation was assessed in 30 individuals collected from Cerro Gordo (SW Mediterranean Sea). The number of alleles per locus ranged from one to nine, observed heterozygosity from 0.05 to 0.29 and expected heterozygosity from 0.15 to 0.39. No significant linkage disequilibrium between pairs of loci was detected, but five loci showed significant heterozygote deficiency that may be explained either by inbreeding, population substructure or the presence of null alleles.