Western Mediterranean Sea (western + mediterranean_sea)

Distribution by Scientific Domains

Selected Abstracts

Correlation between sea surface topography and bathymetry in shallow shelf waters in the Western Mediterranean

G. Rodríguez Velasco
Summary In this paper, gravimetric and altimetric data are used to assess an estimation of the sea surface topography in the Western Mediterranean Sea. This is a complex area from different points of view, due to the presence of several islands, coastal lines, shallow waters and a peculiar hydrologic equilibrium due to its proximity to the Atlantic water exchange area. First, a gravimetric geoid was computed using the least-squares collocation (LSC) procedure with the classical remove-restore technique. We also present a local mean sea surface generated from repeat ERS-1 altimeter data fitted to TOPEX. We chose this satellite because it offers a better spatial resolution than the TOPEX data. The time span used in the computations is one year. This is a useful interval for averaging out the regular seasonal variations, which are very large in this area. We present the comparisons between the gravimetric geoidal heights and the adjusted sea surface. This is a way to obtain a rough estimation of the sea surface topography (SST) since we also include the errors in the two surfaces and other oceanic signals. The differences obtained are physically reasonable with a mean of 17 cm and standard deviation (s.d.) of 39 cm. A significant similarity is observed between the features reproduced by these differences and the bathymetry in the area, suggesting some sort of correlation between both magnitudes for the studied region. If we accept such correlation, the SST may be described as a function of depth. This procedure lets us filter out the short wavelength part of the geoid from the first SST estimation. [source]

Feeding habits and trophic levels of bluefin tuna Thunnus thynnus of different size classes in the Mediterranean Sea

G. Sarŕ
Summary Possible changes in diet and trophic levels in relation to size of Mediterranean bluefin tuna, Thunnus thynnus, were investigated using labelled carbon (,13C) and nitrogen (,15N) stable isotopes. Samples were obtained from two locations in the southern Tyrrhenian Sea (Western Mediterranean Sea) in May and October 2004. The ,13C and ,15N analyses revealed at least three significant isotopic groups [small juveniles (0.7,2.2 kg), sub-adults (15,50 kg) and adults (70 to 225 kg)]. ,13C was negatively dependent on weight, while ,15N was positively dependent on weight [TW = 8.2 (±0.16) + 0.03 (± 0.0) *,15N (n = 49; r = 0.91; P < 0.001)]. Different prey contribution to the diet was highlighted for each class. The diet of juveniles comprised zooplankton, small pelagic fish and some coastal fish; sub-adults relied on medium pelagic fish, shrimps and cephalopods, and adults relied mainly on cephalopods and larger fish. The trophic level (TL) of tunas belonging to each size class was closely correlated to weight, starting from ca 3.0 TL for Group I and reaching 4.4,4.8 TL for the giants. Bluefin tuna, from small juveniles to giants, showed a shift in feeding preferences due to different use of habitats and food items as a function of the life stage. [source]

Variability in the structure of epiphytic assemblages of the Mediterranean seagrass Posidonia oceanica in relation to depth

MARINE ECOLOGY, Issue 3 2009
Ugo Nesti
Abstract The aim of the present study was to evaluate whether the variability in the structure of the epiphytic assemblages of leaves and rhizomes of the Mediterranean seagrass Posidonia oceanica differed between depths at a large spatial scale. A hierarchical sampling design was used to compare epiphytic assemblages at two different depths (10 and 20 m) in terms of both species composition and abundance and patterns of spatial variability in the Tuscan Archipelago (North Western Mediterranean Sea, Italy). Results showed significant differences in the structure of assemblages on rhizomes and leaves at different depths. These differences were related to species composition and abundance; differences were not significant for total biomass, total percentage cover and percentage cover of animals and algae. Whereas the higher variability was observed among shoots in all the studied systems, patterns of spatial variability at the other spatial scales investigated differed between the two studied depths. Moreover, in the present study, analogous patterns between depths resulted for both the assemblages of leaves and rhizomes, suggesting that factors that change with depth can be responsible for the spatial variability of both the assemblages (leaves and rhizomes), and operate regardless of the microclimatic conditions and the structure of assemblages. [source]

Length,weight relationships for 22 fish species of the Mar Menor coastal lagoon (western Mediterranean Sea)

D. Verdiell-Cubedo
Summary Length,weight relationships were estimated for 22 species of the Mar Menor coastal lagoon (south-eastern Spain): Lipophrys dalmatinus, Salaria pavo, Callionymus pusillus, Aphanius iberus, Engraulis encrasicolus, Gobius cobitis, G. niger, G. paganellus, Pomatoschistus marmoratus, Symphodus cinereus, Chelon labrosus, Liza aurata, L. ramado, L. saliens, Mugil cephalus, Diplodus puntazzo, D. sargus sargus, Lithognathus mormyrus, Sarpa salpa, Sparus aurata, Hippocampus guttulatus and Syngnathus abaster. The captures were made in shallow areas of the lagoon during 2002,2004. Significant length,weight relationships were found for all species. [source]

Differential correlates of diet and phylogeny on the shape of the premaxilla and anterior tooth in sparid fishes (Perciformes: Sparidae)

M. Linde
Abstract We explore the correlational patterns of diet and phylogeny on the shape of the premaxilla and anterior tooth in sparid fishes (Perciformes: Sparidae) from the western Mediterranean Sea. The premaxilla is less variable, and in spite of the presence of species-specific features, a common structural pattern is easily recognizable in all species (i.e. the ascending and the articular processes are fused in a single branch, as in many percoid fishes). In contrast, tooth shape is more variable, and different structural types can be recognized (e.g. canine-like or incisive). Coupling geometric morphometric and comparative methods we found that the relationship between shape, diet and phylogeny also differs between premaxilla and tooth. Thus, the shape of the premaxilla is significantly correlated with food type, whereas the shape of the teeth is not correlated with diet, and probably reflects the species phylogenetic relationships. Two biological roles, resistance against compressive forces generated in the buccal cavity and the size of the oral gape, would explain the ecomorphological patterns of the premaxilla. The premaxilla and anterior tooth appear to evolve at different rates (mosaic evolution) and represent an example of morphological traits belonging to the same functional unit but following uncoupled evolutionary pathways. [source]

Phylogeography of the common goby, Pomatoschistus microps, with particular emphasis on the colonization of the Mediterranean and the North Sea

E. S. Gysels
Abstract The phylogeographical patterns of a small marine fish, the common goby, Pomatoschistus microps, were assessed at 12 sites along the northeastern Atlantic coasts and the western Mediterranean Sea. A combination of two genetic markers was employed: cellulose acetate allozyme electrophoresis (CAGE) and sequence analysis of a 289 bp fragment of the mitochondrial locus cytochrome b. Both markers were congruent in revealing significant differences between samples (global FST = 0.247 for the allozymes and ,ST = 0.437 for the mitochondrial DNA data) and a pattern of isolation-by-distance. Phylogeographical analyses yielded a shallow branching structure with four groups. Three of those were confined to the Atlantic basin and showed a star-like pattern. The fourth group contained a central haplotype occurring at the edges of the species' distribution, accompanied by a few more rare variants, which were restricted to the Mediterranean Sea. A genetic break was observed around the British Isles, with distinct haplotypes dominating at either side of the English Channel. A significantly negative correlation between the degree of genetic diversity and latitude was recorded both for mitochondrial DNA (mtDNA) and allozymes in the Atlantic basin. Gene flow analysis suggested that recolonization of the North Sea and the coasts of western Scotland and Ireland may have taken place from a glacial refugium in the Southern Bight of the North Sea. These results are discussed in the perspective of possible postglacial migration routes of marine fish along the northeastern Atlantic coasts. [source]

Chorotypes of seaweeds from the western Mediterranean Sea and the Adriatic Sea: An analysis based on the genera Audouinella (Rhodophyta), Cystoseira (Phaeophyceae) and Cladophora (Chlorophyta)

José C. Báez
SUMMARY The aim of the present paper is to identify the possible existence of groups of species in the genera Audouinella (Rhodophyta), Cystoseira (Phaeophyceae) and Cladophora (Chloropyta) with significantly similar distribution patterns (chorotypes), in the western Mediterranean Sea and the Adriatic Sea. Of the 98 species studied, 59 were grouped into 11 chorotypes, whereas 39 species remained ungrouped. Thirty-eight species were included in a generalist chorotype, whereas 6 chorotypes were monospecific. The relationships with the environmental factors that could explain the chorotypes are discussed. [source]