Stability of spatial pattern of fish species diversity in the Strait of Sicily (central Mediterranean)

In this paper, species diversity of demersal fish communities was analysed over an area covering about 45,000 km² of the Italian side of the Strait of Sicily (central Mediterranean). Fish abundance data come from a 10-year series (1994–2003) of experimental bottom trawl surveys carried out within the framework of the international program MEDITS. A simple GIS-based method was proposed to identify areas supporting high or low values of diversity and evaluate their temporal stability. A well-defined spatio-temporal pattern in diversity emerged from the analysis, with some areas of great ecological relevance being identified. Importantly, the greatest diversity within the fish communities was consistently seen at the offshore bank on the western part of the south Sicilian shelf (Adventure Bank). The site also supports high total biomass of demersal resources and shows the presence of species of great concern to fisheries. Results suggest that Adventure Bank represents a priority site for investigating the possibility of innovative management of marine ecosystems and demersal fisheries in offshore zones.     

Spread of Microcosmus squamiger (Ascidiacea: Pyuridae) in the Mediterranean Sea and adjacent waters

The Mediterranean Sea is subject to an ever-increasing arrival of non-indigenous marine organisms. Microcosmus squamiger is a solitary ascidian that inhabits shallow rocky littoral habitats. It probably originated in Australia and it has shown great invasive potential in other parts of the world. In the Mediterranean, M. squamiger has only been reported at a few sites in Spain and Italy. However, the closely related species Microcosmus exasperatus has been reported in several areas of the western Mediterranean. As these species can be easily confused, we re-examined most of the material from previous studies and our personal collections. In addition, sampling was done at several sites along the western Mediterranean and Atlantic coasts. The results showed that the majority of the M. exasperatus reports correspond to M. squamiger, and that M. squamiger is common on the Atlantic shores. This suggests that M. squamiger has entered the Mediterranean through the Gibraltar Strait, while the restricted distribution in the eastern Mediterranean of M. exasperatus suggests that this species is probably a Lessepsian migrant. In the Mediterranean Sea, M. squamiger has the ability to occupy extensive areas of hard substrata and to outcompete native species. Further studies are necessary to assess what impacts this invasive species have on native communities.     

Anchovy egg and larval distribution in relation to biological and physical oceanography in the Strait of Sicily

The European Anchovy (Engraulis encrasicolus, Linnaeus, 1758) represents one of the most important fishery resources in some areas of the Mediterranean. This short-lived, small pelagic fish is characterized by large interannual fluctuations, probably as a result of environmental variability. As part of the European Project Med 98-070, the main aim of which was the study of the anchovy population in the Strait of Sicily, icthyoplankton surveys were carried out between 1999 and 2001, during the peak spawning season for anchovy. Present work reports the relationship between meso-zooplankton biomass and the abundance of anchovy eggs and larvae in the Strait of Sicily. Data on anchovy egg abundance showed that the main spawning area was located in the north-western region of the study area. The branch of the Atlantic Ionian Stream, running parallel to the southern Sicilian coast, acts as a transport mechanism for anchovy eggs and larvae towards the southernmost end of the island, off Cape Passero. Observed distributions were largely consistent with local hydrographic features, which allow larvae to be retained in areas providing the necessary feeding conditions for recruitment success.     

Effect of spawning ground location on the transport and growth of chub mackerel (Scomber japonicus) eggs and larvae in the East China Sea

Chub mackerel (Scomber japonicus) are an important pelagic fish species within the China Sea. Annual recruitment of this species is determined primarily by survival in the early life history stages. Minor changes in the physical marine environment can have a significant effect on the growth and survival of eggs and larvae, thereby affecting recruitment of population. To model this interaction, we constructed a bio-physical dynamic model of the early life history of chub mackerel in the East China Sea (ECS). The physical model was based on the unstructured grid Finite Volume Coast and Ocean Model (FVCOM) and simulated the 3-D physical fields. The biological model was based on individual-based models (IBMs) in which the early life stages of chub mackerel were divided into five stages based on age or length. The model was parameterized using functions describing spawning, growth, and survival for chub mackerel in the ECS. Using this coupled physical and biological model, driven by the March–July climatological forcing, we tracked super individuals from spawning grounds to the nursery grounds to evaluate the influence of the physical environment at each of the spawning locations (western, normal, eastern) on the transport and survival of chub mackerel. The model suggests that spawning location has a significant effect on larval transport, although the larvae were generally advected northeastward to enter the Japan/East Sea through the Tsushima/East Strait or southeastward with the Kuroshio Current which then flows along the eastern Japanese coast. Spawning to the west was highly influenced by the Taiwan Warm Current (TWC) during early transport when the larvae were advected northward and then northeastward. The speed of drifting during this period was relatively slow. The model predicted that a large number of eggs and larvae would enter and transit through China’s coastal waters (Changjiang River Estuary, Hangzhou Bay, and the Zhoushan Islands). Under this scenario, the majority of larvae were transported to the northern nursery grounds, 79% to the nursery at Jeju Island and 10% to the nursery at Tsushima Strait. In contrast, only 11% were transported to the southern nursery grounds in the Pacific Ocean and Kyushu. Larvae spawned at the eastern spawning ground were primarily influenced by the Kuroshio Current which transported the larvae southeastward. Kuroshio acts as a barrier, restricting larvae from being advected to the interior of the western Pacific Ocean. Under such circumstances, almost no eggs and larvae were retained in the coastal waters of China. Instead, the larvae were rapidly transported northeastward from the Chinese shelf towards the coast of Japan. The model predicted that a large number of larvae would be transported to the southern nursery grounds in the Pacific Ocean and Kyushu, before entering the Pacific Ocean and Japan Sea. In total, 36% of larvae were transported to the Pacific Ocean nursery, 45% to the northern nursery grounds of Jeju Island and Tsushima Strait, and 27% to the Jeju Island nursery. The three simulations assumed the same number of eggs were spawned (2.17 × 10¹²) and the survival of larvae at the western, normal, and eastern spawning grounds was 0.0306%, 0.0353%, and 0.0234%, respectively. The average length was 123.7, 126.0, and 123.5 mm, respectively. Our results suggest that larvae spawned in different regions encountered different physical environments and were subject to different transport processes. These differences explain the changes in survival and growth observed between larvae from the different areas. Survival and growth was highest for chub mackerel that were spawned at the normal spawning location and subject to suitable water depths and temperatures during transport.     

Congruence in genetic markers used to describe Mediterranean and Atlantic populations of European hake (Merluccius merluccius L. 1758)

Eight samples of the hake, Merluccius merluccius L., from the Mediterranean basin (370 fishes total) and one from the Atlantic ocean (50 fishes) were analysed in order to assess genetic variability and describe genetic population structure. Five polymorphic protein coding loci were scored (ADH*, PGI‐1*, PGI‐2*, PGM* and SOD‐1*) in eight samples, together with a haplotype variation of four samples, obtained from polymerase chain reaction/restriction fragment length polymorphism (PCR–RFLP) analysis on the mitochondrial DNA control region. The average value for observed heterozygosity was typically higher than expected (showing an excess of heterozygotes among the samples) whereas the haplotype diversity at mtDNA was very low. Samples originating from inside the Mediterranean basin appeared genetically homogeneous but the sample originating from the Atlantic was heterogeneous compared with the Mediterranean populations. Nuclear and mitochondrial gene analysis showed similar results supporting that the Strait of Gibraltar may be considered as a breakpoint area to gene flow.     

Fickle or Faithful: The Roles of Host and Environmental Context in Determining Symbiont Composition in Two Bathymodioline Mussels

The Mediterranean Sea and adjoining East Atlantic Ocean host a diverse array of small-sized mussels that predominantly live on sunken, decomposing organic remains. At least two of these, Idas modiolaeformis and Idas simpsoni, are known to engage in gill-associated symbioses; however, the composition, diversity and variability of these symbioses with changing habitat and location is poorly defined. The current study presents bacterial symbiont assemblage data, derived from 454 pyrosequencing carried out on replicate specimens of these two host species, collected across seven sample sites found in three oceanographic regions in the Mediterranean and East Atlantic. The presence of several bacterial OTUs in both the Mediterranean Sea and eastern Atlantic suggests that similar symbiont candidates occur on both sides of the Strait of Gibraltar. The results reveal markedly different symbiotic modes in the two species. Idas modiolaeformis displays high symbiont diversity and flexibility, with strong variation in symbiont composition from the East Mediterranean to the East Atlantic. Idas simpsoni displays low symbiont diversity but high symbiont fidelity, with a single dominant OTU occurring in all specimens analysed. These differences are argued to be a function of the host species, where subtle differences in host evolution, life-history and behaviour could partially explain the observed patterns. The variability in symbiont compositions, particularly in Idas modiolaeformis, is thought to be a function of the nature, context and location of the habitat from which symbiont candidates are sourced.     

Influence of environmental variability on anchovy early life stages (Engraulis encrasicolus) in two different areas of the Central Mediterranean Sea

The survival of early stages of small pelagic fish species (e.g. Engraulis encrasicolus) is highly dependent on environmental conditions in both spawning and nursery areas. Knowing the relationship between the mortality rates of the early stages and the environment may help to study and model recruitment fluctuations. During the summer of 2006, two consecutive oceanographic cruises were carried out in the Central Mediterranean sea (CMED) in two different areas: the western Libyan waters and the Sicilian?CMaltese waters. For the first time a nearly synoptic comparison between the two border areas of the CMED is performed. In spite of a higher overall egg density in the Sicilian?CMaltese waters, there was a higher density of anchovy larvae in Libyan waters. The comparison between the oceanographic datasets singled out different circulation patterns and different characteristics of water masses, which helped to explain the differences in density of the spawning products in the two areas. A Lagrangian transport model was used to evaluate the effects of major oceanographic features on offshore egg and larval transport. The results of the model simulations and the nutritional conditions, as indicated by lipid, carbohydrate and protein contents, support the hypothesis that the western Libyan waters may represent a more favourable nursery ground compared to the Sicilian?CMaltese waters in terms of environmental conditions and food availability.     

Phylogenetic reconstruction of key traits in the evolution of ivies (Hedera L.)

The Mediterranean harbours the highest number of Hedera (Araliaceae) species, lineages, ploidy levels, and trichome morphologies of any area where the genus occurs. Previous molecular and cytogenetic studies identified two main centres of diversity for Hedera (Araliaceae), the eastern and western parts of the Mediterranean region. An explicit analysis of key traits was performed to investigate geographical patterns and ancestral character states of ivy lineages. Interestingly, the greatest diversity of Hedera was found in the western Mediterranean, including the three species of Macaronesia (H. azorica in the Azores, H. maderensis in Madeira and H. canariensis in the Canary Islands). Phylogenetic and phylogeographical analyses of the nrITS and plastid trnT-L sequences revealed multiple connections between the Mediterranean region and Asia, and suggest recurrent colonization between these two areas. Reconstruction of three important characters long used to distinguish members of the genus (trichome types, ploidy levels, and geographical areas) suggests that a diploid species with scale-like trichomes from the Mediterranean basin was the most recent common ancestor of the extant species of Hedera.     

Occurrence of Diopatra marocensis (Annelida,Onuphidae) in the eastern Mediterranean

The present study deals with the presence of Diopatra marocensis in the eastern Mediterranean. This species is small-sized and inhabited muddy bottom near the opening of rivers or lagoons [salinity range: 33−39‰] in the Aegean and Levantine Seas, and reached a maximum density of 90 ind.m^-2 in Mersin Bay. This species might be an alien species that was introduced from the East Atlantic (near Gibraltar) to the eastern Mediterranean via ballast water of ships, as it has never been reported from the western Mediterranean Sea.     

The Seascape of Demersal Fish Nursery Areas in the North Mediterranean Sea,a First Step Towards the Implementation of Spatial Planning for Trawl Fisheries

The identification of nursery grounds and other essential fish habitats of exploited stocks is a key requirement for the development of spatial conservation planning aimed at reducing the adverse impact of fishing on the exploited populations and ecosystems. The reduction in juvenile mortality is particularly relevant in the Mediterranean and is considered as one of the main prerequisites for the future sustainability of trawl fisheries. The distribution of nursery areas of 11 important commercial species of demersal fish and shellfish was analysed in the European Union Mediterranean waters using time series of bottom trawl survey data with the aim of identifying the most persistent recruitment areas. A high interspecific spatial overlap between nursery areas was mainly found along the shelf break of many different sectors of the Northern Mediterranean indicating a high potential for the implementation of conservation measures. Overlap of the nursery grounds with existing spatial fisheries management measures and trawl fisheries restricted areas was also investigated. Spatial analyses revealed considerable variation depending on species and associated habitat/depth preferences with increased protection seen in coastal nurseries and minimal protection seen for deeper nurseries (e.g. Parapenaeus longirostris 6%). This is partly attributed to existing environmental policy instruments (e.g. Habitats Directive and Mediterranean Regulation EC 1967/2006) aiming at minimising impacts on coastal priority habitats such as seagrass, coralligenous and maerl beds. The new knowledge on the distribution and persistence of demersal nurseries provided in this study can support the application of spatial conservation measures, such as the designation of no-take Marine Protected Areas in EU Mediterranean waters and their inclusion in a conservation network. The establishment of no-take zones will be consistent with the objectives of the Common Fisheries Policy applying the ecosystem approach to fisheries management and with the requirements of the Marine Strategy Framework Directive to maintain or achieve seafloor integrity and good environmental status.     

Feeding Habits of Percnon gibbesi (H. Milne Edwards, 1853) in the Sicily Strait

The subtropical grapsid crab Percnon gibbesi (H. Milne Edwards, 1853) is one of the most recent alien decapods found in the Mediterranean, where it was discovered at Linosa (Pelagie Islands, Sicily Strait) in summer 1999. At present, the invasion of this species has been recorded in several other insular localities. We studied the feeding habits of the crab in an attempt to understand its success in the Mediterranean. The morphological characteristics of the chela, the feeding adaptations of the gastric mill and the analysis of stomach contents indicate that P. gibbesi is a strictly herbivorous species, a characteristic not shared with any other large-sized infralittoral Mediterranean crab.     

Late Quaternary paleoceanography as recorded by benthonic foraminifera in Strait of Sicily sediment sequences

At specific times during the late Quaternary, a widespread low-salinity surface water layer was produced over the eastern Mediterranean which created stagnant conditions and associated deposition of sapropelic muds in the deep basins. The Strait of Sicily has been positioned above the anoxic deeper water masses and is therefore devoid of sapropel deposits. Sediment sequences in the region contain a valuable record of upper bathyal (200–1000 m) benthonic foraminiferal change during times of deep-basin stagnation.Quantitative examiniation of benthonic foraminiferal assemblages in Strait of Sicily Quaternary cores generally reveals changes coeval with sapropels S1, S2, S4, S5, and S6. The benthonic foraminiferal expression is seen as increases in frequency ofGlobobulimina affinis, Globobulimina pseudospinescens, Chilostomella mediterranensis, Bolivina dilatata, and otherBolivina species during intervals corresponding to the episodic abyssal stagnation events. Some cores also display a decrease inCassidulina carinata and an increase inArticulina tubulosa.Similar assemblage changes have been previously documented to be closely associated with the sapropel layers in the deep basins of the eastern Mediterranean (the actual sapropel layers usually do not contain benthonic foraminifera). However, in the Strait of Sicily area, the species exhibit less drastic changes than in the deep eastern basins because of the less severe anoxic conditions. In the deep eastern basins, benthonic foraminifera almost totally disappeared in sapropel layers; at the same time, there was a general reduction in foraminiferal numbers in the shallower Strait area.     

On the occurrence of the fireworm Eurythoe?complanata complex (Annelida,Amphinomidae) in the Mediterranean Sea with an updated revision of the alien Mediterranean amphinomids

The presence of two species within the Eurythoe complanata complex in the Mediterranean Sea is reported, as well as their geographical distributions. One species, Eurythoe laevisetis, occurs in the eastern and central Mediterranean, likely constituting the first historical introduction to the Mediterranean Sea and the other, Eurythoe complanata, in both eastern and Levantine basins. Brief notes on their taxonomy are also provided and their potential pathways for introduction to the Mediterranean are discussed. A simplified key to the Mediterranean amphinomid genera and species of Eurythoe and Linopherus is presented plus an updated revision of the alien amphinomid species reported previously from the Mediterranean Sea. A total of five exotic species have been included; information on their location, habitat, date of introduction and other relevant features is also provided.     

When invasion biology meets taxonomy: <Emphasis Type="Italic">Clavelina oblonga</Emphasis> (Ascidiacea) is an old invader in the Mediterranean Sea

Taxonomic issues often confound the study of invasive species, which sometimes are unrecognized as introduced in newly colonized areas. Clavelina oblonga Herdman, 1880 is an abundant ascidian species along the southeastern coast of the United States and the Caribbean Sea. It was introduced into the eastern Atlantic and Brazil decades ago. In the Mediterranean Sea, a similar species had been described as C. phlegraea Salfi 1929 and reported from southern Italy and Corsica. In the last few years a species of Clavelina has proliferated in the embayments of the Ebro Delta (NW Mediterranean), a zone of active bivalve culture industry where it has smothered mussel spat, leading to economic loss. We here report the morphological and genetic identity of this species, synonymizing the Atlantic C. oblonga and the Mediterranean C. phlegraea (the latter therefore is a synonym of the former). Thus, C. oblonga has existed in the Mediterranean for over 80 years, but was known under a different name. We also found this species in natural habitats in the Iberian Atlantic coast close to the Strait of Gibraltar, raising concerns about an ongoing expansion. In order to obtain information relevant for management, we monitored growth, reproductive cycles and settlement patterns of this ascidian on bivalve cultures in the Ebro Delta. Its biological cycles were markedly seasonal, with peak abundance and reproduction during the warmest months, followed by regression during the cold season. The settlement period was short, mostly concentrated in a single month each year. Avoidance of mussel and oyster seeding during late summer and early autumn can readily reduce the damage caused by this species.     

Variability of lichen diversity in a climatically heterogeneous area (Liguria,NW Italy)

Abstract:The influence of environmental variables on epiphytic lichens in Liguria (NW Italy) was examined using two complementary approaches. Firstly, the variability of lichen vegetation in relation to environmental variables was investigated. Secondly, the variability of Lichen Biodiversity (LB) counts, used in biomonitoring studies, was analysed in relation to bioclimatic areas. Geomorphology strongly affects lichen vegetation. The coastal mountain ridge and the Tyrrhenian-Po valley watershed limit the distribution range of three different communities: a Parmelion community with a high frequency of coastal suboceanic species, a Parmelion community rich in oak wood species and the Parmelietum acetabuli association, situated beyond the Po Valley watershed. Substantial differences in the distribution of lichen communities related to a climatic gradient (from humid Mediterranean to dry sub-Mediterranean regions) are not matched by corresponding statistically significant differences in LB counts. More accurate studies are necessary to define homogeneous bioclimatic areas, in which LB values can be compared for biomonitoring purposes.     

Spatial variation in the recruitment of the intertidal barnacles Chthamalus montagui Southward and Chthamalus stellatus (Poli) (Crustacea: Cirripedia) over an European scale

Spatial variation in the recruitment of the intertidal barnacles Chthamalus montagui and Chthamalus stellatus was examined over an European scale. The study was carried out using standardised protocols at a series of locations. The five locations chosen (SW Ireland, NW Spain, SW Portugal and NW and NE Italy) span a large part of the range of these species in Europe. The spatial scales were location (hundreds of kilometres) and shore (thousands of metres).Estimates of total cumulative recruitment (cyprids and metamorphs) summed over the year (April 1997 to March 1998) showed substantial variation between locations which was dependent on the species. Recruitment was highest in SW Portugal for C. montagui and in SW Ireland and NW Spain for C. stellatus. Overall recruitment of C. montagui was higher than that of C. stellatus at all locations except SW Ireland, where recruitment of the two species was not significantly different. There were significant differences among shores in each location.The recruitment period of both species varied with location, with recruitment beginning earlier further south. In general, recruitment of C. montagui and C. stellatus was recorded in 8 months in NW Spain and NE Italy, while only in 7 months in SW Ireland. Recruitment of C. montagui occurred in 10 months in SW Portugal, but no recruits of C. stellatus were found. In all locations there was at least one distinct peak of recruitment. In SW Ireland both species showed only one peak of recruitment, a month after initiation. At the more southerly Atlantic locations, as well as in the Mediterranean, two unequal peaks of recruitment were generally seen. During recruit census, the number of cyprids, in comparison to metamorphs, found at any location was very low. In SW Ireland and NW Spain cyprids of both species were found, while in SW Portugal and in the Mediterranean, only cyprids of C. montagui were found.     

Are woody seeder plants more prone than resprouter to population genetic differentiation in Mediterranean-type ecosystems?

High diversification of woody seeder lineages is characteristic of the south-western cape floristic region (CFR), South Africa, which has been explained as a consequence of its mild Mediterranean climate and reliable winter rainfall. Such climatic regime reduces the risk of post-fire recruitment failure, acting as an ecological filter that favours seeder populations, thus promoting genetic differentiation and diversification in seeder populations, as previously seen in the South African heath Erica coccinea. To explore this hypothesis further, genetic population structure was investigated in two Mediterranean Erica species, one seeder (Erica umbellata) and the other resprouter (Erica australis), using nuclear microsatellites. These two species are endemic to the western Mediterranean Basin and co-occur in heathlands of the Strait of Gibraltar region. Mean annual rainfall in this region is similar to that from the south-western CFR, but summer stress is more marked and winter rainfall is much less reliable. Contrary to what was found in E. coccinea, average genetic diversity levels were considerably lower in seeder populations (E. umbellata), regardless of an apparently higher gene flow among them. No differences in genetic differentiation among populations were found between the two species. The occurrence of less favourable climatic conditions for post-fire recruitment in the western Mediterranean compared to the south-western CFR may affect seeder populations more strongly than resprouter and may thus account for lower levels of within-population genetic diversity in the seeder E. umbellata. In addition, putatively higher migration rates in the seeder E. umbellata, may contribute to reduce its potential for genetic differentiation. This study provides evidence that high divergence of seeder populations is not a general rule in fire-prone, Mediterranean-type ecosystems.     

Weight‐length relationships and condition factor trends for thirty‐eight fish species in trawled and untrawled areas off the coast of northern Sicily (central Mediterranean Sea)

This paper reports the weight‐length relationship (WLR) for thirty‐eight fish species from the Gulf of Castellammare (NW Sicily, Mediterranean Sea). A total of 59 870 fish were collected and measured during four seasonal trawl surveys carried out in 2005 at 10 to 200 m depth. The b parameter of the WLRs ranged from 1.79 (Cepola macrophthalma) to 3.56 (Conger conger). Significant differences in both a and b values among seasons were detected for eight species. Moreover, the condition factors (as weight‐at‐length) of Merluccius merluccius and Mullus barbatus were compared in different area/year combinations characterized by the presence or absence of trawling impact. While M. barbatus showed a higher condition factor in trawled areas/years, possibly due to density‐dependent factors linked to the increased biomass in the no‐trawl area, no such link was detected in M. merluccius.