Hydromedusae of the Mediterranean Sea

Mediterranean hydromedusae can be classified in several categories: common species, widely distributed throughout the Mediterranean and rare species reported from the Pacific, Indian or Atlantic Oceans; seasonal species comprising cold-season species with a boreal affinity and warm-season species with a hot to temperate affinity; neritic and mid-ocean species; surface species and meso-, infra-, and bathypelagic species. Holoplanktonic species are known to be associated with stable hydrological conditions (offshore waters, deep waters, summer and winter homothermy), whereas meroplanktonic species are more likely to be found in more disturbed hydrological conditions (coastal waters, surface waters, spring and autumn periods of temperature fluctuation). A general pattern of medusa distribution is established based upon comparative study throughout the Mediterranean.     

Feeding ecology of Mediterranean razorfish Xyrichthys novacula in the Tyrrhenian Sea (Central Mediterranean Sea)

The stomach contents of 196 razorfish ( Xyrichthys novacula ), collected in the Tyrrhenian Sea (Ponza Island, Italy) between July and December 1994, were examined in order to assess the diet and to analyse size-related dietary variation of the species. The diet of X. novacula showed a strict relationship with well-sorted fine sand (SFBC) benthic species, mostly Mollusca and Echinodermata, as pointed out by the analysis at the specific level of the stomach contents. Mollusca Pelecipoda, essentially Acanthocardium tuberculatum and Echinodermata, with Echinocardium cordatum , made up 90% of the volume of prey of X. novacula. Mysidacea and Gastropoda were frequent but volumetrically less important. The study showed that male and female X. novacula were not effectively segregated by trophic dimension in the study area. The niche overlap between males and females in prey composition was pronounced, as evidenced by the significantly high values of Schoener's index with larger males that showed a greater tendency towards predation of large prey. The increment in length (L.I.) in males, despite a decrease in the percentage body weight increment (B.W.I.), could represent the result of a male reproductive feature: the lack of sperm competition allows the males much more energy to devote to growth than do that of the females of this species.     

Plastic Accumulation in the Mediterranean Sea

Concentrations of floating plastic were measured throughout the Mediterranean Sea to assess whether this basin can be regarded as a great accumulation region of plastic debris. We found that the average density of plastic (1 item per 4 m²), as well as its frequency of occurrence (100% of the sites sampled), are comparable to the accumulation zones described for the five subtropical ocean gyres. Plastic debris in the Mediterranean surface waters was dominated by millimeter-sized fragments, but showed a higher proportion of large plastic objects than that present in oceanic gyres, reflecting the closer connection with pollution sources. The accumulation of floating plastic in the Mediterranean Sea (between 1,000 and 3,000 tons) is likely related to the high human pressure together with the hydrodynamics of this semi-enclosed basin, with outflow mainly occurring through a deep water layer. Given the biological richness and concentration of economic activities in the Mediterranean Sea, the affects of plastic pollution on marine and human life are expected to be particularly frequent in this plastic accumulation region.     

A preliminary study of tintinnid diversity in the NW Mediterranean Sea

Tintinnid diversity in surface waters was investigated in the Bay of Villefranche in March, before the formation of the seasonal thermocline, and in May, following water column stratification. Tintinnid abundance was much greater in March (500 cells l^-1), corresponding to a bloom of Stensomella nivalis compared to May (30 cells l^-1). Nonetheless, high numbers of species were encountered on both dates: 32 in March and 39 in May, respectively. Diversity was higher (H2.5) for the May date with low tintinnid concentrations. We examined taxonomic diversity and morphological diversity. Variance of lorica length was correlated with taxonomic diversity, in contrast to variance of lorica diameter, which was nearly invariant. We suggest that either species with similar lorica diameters exploit different prey items or competition for prey items is not the dominant factor in structuring tintinnid communities.      

Advancing marine conservation planning in the Mediterranean Sea

Twenty leading scientists in the field of marine conservation planning attended the first international workshop on conservation planning in the Mediterranean Sea. This globally significant biodiversity hotspot has been subjected to human exploitation and degradation for 1,000s of years. Recently, several initiatives have tried to identify priority areas for conservation across the Mediterranean Sea. However, none of these efforts have led to large-scale actions yet. The aim of the workshop was to establish a network of scientists who are involved in large-scale conservation planning initiatives throughout the Mediterranean basin to promote collaboration and reduce redundancy in conservation initiatives. The three focus groups of the workshop build on existing efforts and intend to deliver: (1) a roadmap for setting conservation priorities, (2) a methodological framework for linking threats, actions and costs to improve the prioritization process, and (3) a systematic conservation planning process tailored to complex environments such as the Mediterranean Sea. Joining forces and involving more scientists (especially from the South-eastern part of the region) in following meetings, the participants endeavour to provide guidelines on how to bridge the science-policy gap and hence aid decision-makers to take efficient conservation actions.     

Biodiversity issues for the forthcoming tropical Mediterranean Sea

Present-day Mediterranean marine biodiversity is undergoing rapid alteration. Because of the increased occurrence of warm-water biota, it has been said that the Mediterranean is under a process of ‘tropicalization’. This paper analyses the main patterns of the Mediterranean Sea tropicalization and considers briefly its extent and consequences. As happened during previous interglacial phases of the Quaternary, Atlantic water, entering via the Straits of Gibraltar, carries into the Mediterranean species that are prevalently of (sub)tropical affinity. On the other side of the basin, Red Sea species penetrate through the Suez Canal, a phenomenon called lessepsian migration from the name of F. de Lesseps, the French engineer who promoted the cutting of the Canal. Also the many exotic species introduced by humans voluntarily or involuntarily are nearly always typical of warm waters. Climate change combines with Atlantic influx, lessepsian migration and the introduction of exotic species by humans to the establishment of tropical marine biota in the Mediterranean Sea. Present-day warming ultimately favours the spread of warm-water species through direct and indirect effects, and especially by changing water circulation. It is impossible at present to foresee to what extent the exuberance of warm-water species will affect the trophic web and the functioning of marine ecosystems in the Mediterranean Sea of tomorrow. While Mediterranean Sea communities are modifying their pattern of species composition, they do not seem to be acquiring a more marked tropical physiognomy: Mediterranean coastal marine ecosystems are still dominated by frondose algae (even if the species that are gaining ascendancy are of tropical origin) and not by corals as is normal in tropical seas.     

A new blue-pigmented hasleoid diatom,Haslea provincialis,from the Mediterranean Sea

Haslea provincialis Gastineau, Hansen & Mouget, sp. nov., is a new, morphologically semicryptic blue diatom discovered on the French shores of the Mediterranean Sea. Like H. ostrearia and H. karadagensis, H. provincialis shares the capacity to synthesize a marennine-like blue pigment. Sexual reproduction between clones of H. provincialis has been repeatedly observed and resulted in viable initial cells. There were no sexual interactions with sexually competent clones of H. ostrearia or H. karadagensis, as would be expected for a separate biological species. There are strong similarities between the H. provincialis pigment and the marennine produced by H. ostrearia, evidenced by UV-visible spectrophotometry and Raman spectrometry. However, unlike the marennine from H. ostrearia, no differences were found between the extracellular and the intracellular forms of the pigment in H. provincialis. This indicates that the synthesis pathways and excretion mechanisms among the three ‘blue’ Haslea may be species-specific. Molecular taxonomy and phylogeny (based on rbcL, cox1 and SSU V4 DNA sequences) confirmed the distinct position of this species among the blue Haslea species. Haslea provincialis occurs in environments from which H. ostrearia has already been reported (mostly based on the presence of the blue cell vacuoles). Possible species misidentifications and the impact of the complex geological history of the Mediterranean Sea on blue diatom diversification are also discussed.     

Reevaluating sponge diversity and distribution in the Mediterranean Sea

The aim of this paper was (1) to update sponge diversity and distribution in the Mediterranean and (2) to re-examine faunal relationships among the Mediterranean areas on the basis of their sponge fauna. The Mediterranean demosponge faunal list was updated to 629 species by taking into consideration recent data from previously poorly studied areas. The species lists of 14 Mediterranean areas were compared on the basis of their sponge species richness, species composition, and taxonomic relatedness of species using multivariate analyses and diversity measures, such as PD, Delta+, and Lambda+. The 14 Mediterranean areas examined for their diversity and affinities were assembled into four major zoogeographic groups: the northwestern, northeastern, the central zone, and southeastern areas. Richest in species numbers were the areas belonging to the two northern groups. The species richness comparisons and similarity analyses performed at the generic level showed that it can be safely used as a surrogate for sponge species diversity in the Mediterranean. The results of this study showed that the simple traditional division of the Mediterranean Sea into a western, central, and eastern basin cannot reliably describe the distribution of sponges in the area. Thus, the W to E faunal decline previously presented for several faunal groups shifts to a general NNW-SSE pattern when one examines separately the northern and the southern parts of the traditional basins. This gradient seems to be in agreement with differences in key environmental variables, such as latitude, salinity, temperature, and water circulation, besides the typically examined distance from Gibraltar. Handling editor: T. P. Crowe     

Occurrence of the black yeast Hortaea werneckii in the Mediterranean Sea

Extremophiles - The occurrence of cultivable fungi was investigated along the water column (25–2500 m depth) of four off-shore stations in the Mediterranean basin. An unexpected high...     

Invasion Pathway of the Ctenophore Mnemiopsis leidyi in the Mediterranean Sea

Gelatinous zooplankton outbreaks have increased globally owing to a number of human-mediated factors, including food web alterations and species introductions. The invasive ctenophore Mnemiopsis leidyi entered the Black Sea in the early 1980s. The invasion was followed by the Azov, Caspian, Baltic and North Seas, and, most recently, the Mediterranean Sea. Previous studies identified two distinct invasion pathways of M. leidyi from its native range in the western Atlantic Ocean to Eurasia. However, the source of newly established populations in the Mediterranean Sea remains unclear. Here we build upon our previous study and investigate sequence variation in both mitochondrial (Cytochrome c Oxidase subunit I) and nuclear (Internal Transcribed Spacer) markers in M. leidyi, encompassing five native and 11 introduced populations, including four from the Mediterranean Sea. Extant genetic diversity in Mediterranean populations (n = 8, N_a = 10) preclude the occurrence of a severe genetic bottleneck or founder effects in the initial colonizing population. Our mitochondrial and nuclear marker surveys revealed two possible pathways of introduction into Mediterranean Sea. In total, 17 haplotypes and 18 alleles were recovered from all surveyed populations. Haplotype and allelic diversity of Mediterranean populations were comparable to populations from which they were likely drawn. The distribution of genetic diversity and pattern of genetic differentiation suggest initial colonization of the Mediterranean from the Black-Azov Seas (pairwise F_ST = 0.001–0.028). However, some haplotypes and alleles from the Mediterranean Sea were not detected from the well-sampled Black Sea, although they were found in Gulf of Mexico populations that were also genetically similar to those in the Mediterranean Sea (pairwise F_ST = 0.010–0.032), raising the possibility of multiple invasion sources. Multiple introductions from a combination of Black Sea and native region sources could be facilitated by intense local and transcontinental shipping activity, respectively.     

Vertical distribution of the prokaryotic cell size in the Mediterranean Sea

Distributions of prokaryotic cell size and morphology were studied in different areas of the Mediterranean Sea by using image analysis on samples collected from surface down to bathypelagic layers (max depth 4,900?m) in the Southern Tyrrhenian, Southern Adriatic and Eastern Mediterranean Seas. Distribution of cell size of prokaryotes in marine ecosystem is very often not considered, which makes our study first in the context of prokaryotic ecology. In the deep Mediterranean layers, an usually-not-considered form of carbon sequestration through prokaryotic cells has been highlighted, which is consistent with an increase in cell size with the depth of the water column. A wide range in prokaryotic cell volumes was observed (between 0.045 and 0.566?μm³). Increase in cell size with depth was opposed to cell abundance distribution. Our results from microscopic observations were confirmed by the increasing HNA/LNA ratio (HNA, cells with high nucleic acid content; LNA, cells with low nucleic acid content) along the water column. Implications of our results on the increasing cell size with depth are in the fact that the quantitative estimation of prokaryotic biomass changes along the water column and the amount of carbon sequestered in the deep biota is enhanced.     

Biomass seasonality of Caulerpa taxifolia in the Mediterranean Sea

The biomass of the introduced and invasive alga Caulerpa taxifolia was measured monthly over one year at four different sites along the French Mediterranean coast at depths of 5 and 20 m in a sheltered and an exposed area. At the 5 m depth, C. taxifolia mean biomass ranged from 203 to 518 g dry wt. m⁻², while at the 20 m depth, it ranged from 62 to 466 g dry wt. m⁻². The study clearly shows that a major characteristic of C. taxifolia is its perennial life cycle with relatively high biomass values throughout the year, in different biotopes. This could be a factor in the broad ecological impact of C. taxifolia.     

Monitoring of HAB species in the Mediterranean Sea through molecular methods

A qualitative and semi-quantitative polymerase chain reaction(PCR)-based assay was developed for the detection of severalpotentially Harmful Algal Bloom (HAB) species and genera belongingto Dinophyceae, Bacillariophyceae and Raphydophyceae. Oligonucleotideprimers were designed based on Internal Transcribed Spacer (ITS)–5.8Sribosomal DNA (rDNA) sequences available in public databaseor identified in this study. The specificity and sensitivityof the PCR assay were validated using clonal cultures and thennatural seawater samples, as well as the known copy number ofplasmids containing the target ITS–5.8S rDNA regions.A filter system for collecting mixed phytoplankton cells coupledto a target species-specific PCR assay was performed on spatialand temporal series of net and surface seawater samples duringcoastal water monitoring carried out in several localities ofthe Mediterranean Sea. The application of PCR allowed a rapiddetection of various genera and species-specific potential HABtaxa in all examined natural samples. Qualitative and semi-quantitativePCR results obtained from field samples were compared with microscopic[light microscope (LM)] examinations. The two methods gave comparableresults, and the molecular assay was able to detect HAB targetcells at concentrations not detectable by microscopy or thoseof uncertain identity. The highest values of positive detectionof potential HAB taxon presence obtained by PCR assay comparedwith the microscopic examination ranged from 67 to 8.0%.     

Molecular Systematics and Phylogenetics of Gracilariacean Species from the Mediterranean Sea

Mediterranean reports of Gracilariaceae species, in particular those assigned to the G. verrucosa complex, were re-examined with the use of molecular tools, in order to verify their systematic position and better understand their distribution. Within this complex, we recognized four distinct taxa: Gracilariopsis longissima, Gracilaria gracilis, Gracilaria longa and a possible new species. The rbcL gene sequences, together with those of other terete Mediterranean entities, were included in a broad molecular phylogeny of the family. The reproductive characters of the studied taxa do not fit completely with published hypothesis on the generic and intrageneric relationships, suggesting that the anatomy of some subgroups should be better characterized.     

Planktonic dinoflagellates of the northern Levantine Basin, northeastern Mediterranean Sea

In the present study, a checklist of planktonic dinoflagellates was prepared from studies conducted on the northeastern Mediterranean coast of Turkey and by evaluating previously conducted studies. The sampling areas included İskenderun Bay, the coast near Karataş at the west end of the Bay, and Babadıllimanı Bight, situated at the west of Mersin Bay, and its surroundings. The data of the present study derives from over 90 locations visited between 1994 and 2004. A total of 174 taxa were reported. Ceratium (57 taxa) and Protoperidinium (28 taxa) were the most species-rich genera. The most common taxa were Ceratium kofoidii, Ceratium trichoceros, Ceratium tripos var. atlanticum, Protoperidinium divergens, Protoperidinium steinii, Ceratocorys horrida, Goniodoma acuminatum and Gonyaulax polygramma. Toxic species such as Dinophysis caudata, Dinophysis tripos were reported, and Scrippsiella trochoidea and Prorocentrum micans, which are known as red tide species elsewhere, were also common. The number of species is similar to those along other coasts of the Levantine Basin. However, some species were observed that had not previously been reported for the Levantine Basin, which can be attributed to the fact that the number of studies conducted in the region has increased and that new species may have entered the environment.     

Chlorophyll Content Observations of the Near-Surface Scattering Layers in the Mediterranean Sea

Abstract

In several areas of the Mediterranean Sea near-surface sound-reflecting layers have been studied. The amount of total pigment occurring in these layers has been determined. Since these layers occur near the basis of the euphotic zone, the degree of degradation of the pigments has been determined by a fluorimetric method. An increase in total pigment has been noticed in the scattering layer as compared to the over and under-lying water layers. A low degree of decomposition of pigment has been found in the scattering layer compared with that in the immediate over and under-lying layers of the wather column. When a scattering layer is lacking the degradation state of the pigment increases progressively with depth. These results suggest that the plants present in the scattering layers are healthy with regard to photosyntetic pigment.     

Distribution and growth of aerobic anoxygenic phototrophs in the Mediterranean Sea

The distribution of aerobic anoxygenic phototrophs (AAPs) was surveyed in various regions of the Mediterranean Sea in spring and summer. These phototrophic bacteria were present within the euphotic layer at all sampled stations. The AAP abundances increased with increasing trophic status ranging from 2.5 × 10(3) cells per ml in oligotrophic Eastern Mediterranean up to 90 × 10(3) cells per ml in the Bay of Villefranche. Aerobic anoxygenic phototrophs made up on average 1-4% of total prokaryotes in low nutrient areas, whereas in coastal and more productive stations these organisms represented 3-11% of total prokaryotes. Diel bacteriochlorophyll a decay measurements showed that AAP community in the Western Mediterranean grew rapidly, at rates from 1.13 to 1.42 day(-1). The lower AAP abundances registered in the most oligotrophic waters suggest that they are relatively poor competitors under nutrient limiting conditions. Instead, AAPs appear to be metabolically active organisms, which thrive better in more eutrophic environments providing the necessary substrates to maintain high growth rates.