Showing papers in "Scientia Marina in 2004"

Fauna of the Mediterranean Hydrozoa

Abstract: This study provides a systematic account of the hydrozoan species collected up to now in the Mediterranean Sea. All species are described, illustrated and information on morphology and distribution is given for all of them. This work is the most complete fauna of hydrozoans made in the Mediterranean. The fauna includes planktonic hydromedusae, benthic polyps stages and the siphonophores. The Hydrozoa are taken as an example of inconspicuous taxa whose knowledge has greatly progressed in the last decades due to the scientific research of some specialists in the Mediterranean area. The number of species recorded in the Mediterranean almost doubled in the last thirty years and the number of new records is still increasing. The 457 species recorded in this study represents the 12% of the world known species. The fauna is completed with classification keys and a glossary of terms with the main purpose of facilitating the identification of all Meditrranean hydrozoan species

Seasonal patterns in plankton communities in a pluriannual time series at a coastal Mediterranean site (Gulf of Naples): an attempt to discern recurrences and trends

Abstract: SUMMARY: The annual cycle of plankton was studied over 14 years from 1984 to 2000 at a coastal station in the Gulf of Naples, with the aim of assessing seasonal patterns and interannual trends. Phytoplankton biomass started increasing over the water column in February-early March, and generally achieved peak values in the upper layers in late spring. Another peak was often recorded in autumn. Diatoms and phytoflagellates dominated for the largest part of the year. Ciliates showed their main peaks in phase with phytoplankton and were mainly represented by small (< 30 µm) naked choreotrichs. Mesozooplankton increased in March-April, reaching maximum concentrations in summer. Copepods were always the most abundant group, followed by cladocerans in summer. At the interannual scale, a high variability and a decreasing trend were recorded over the sampling period for autotrophic biomass. Mesozooplankton biomass showed a less marked interannual variability. From 1995 onwards, phytoplankton populations increased in cell number but decreased in cell size, with intense blooms of small diatoms and undetermined coccoid species frequently observed in recent years. In spite of those interannual variations, the different phases of the annual cycle and the occurrence of several plankton species were remarkably regular.

The ubiquity and many roles of exopolymers (EPS) in aquatic systems

Abstract: Exopolymers (EPS) are produced by unicellular and multicellular organisms. They consist largely of polysaccharides that hydrate rapidly on contact with water and link to form gels. EPS have many uses: in attachment; in locomotion on substrata; as a protection against predators, pathogens and changes in physico-chemical conditions; as a means of overcoming the threat of desiccation; in preventing abrasion; and in feeding. When free of organisms, some EPS form loosely associated polymer gels that are important in the development of organic matter aggregates. These aggregates, together with mucus-bound faecal pellets, play an essential role in nutrient cycling, and in the metabolism of ecosystems.;

An introduction to Mediterranean deep-sea biology

Abstract: This chapter presents the state of the art concerning the deep-sea Mediterranean environment: geology, hydrology, biology and fisheries These are the fields of study dealt with in the scientific papers of this volume The authors are specialists who have addressed their research to the Mediterranean deep-sea environment during the last years This introduction is an overview but not an exhaustive review

Bioconstruction and biodiversity: their mutual influence*

Abstract: SUMMARY: This paper describes the functional role of main benthic constructor organisms and reviews processes by which bioconstructions increase diversity and abundance of associated biota, and the reverse. Based on the literature, patterns of diversity of carbonate bryozoan bioconstructions, one of the most important groups performing important constructional roles, have been analysed. Diversity of bryozoan bioconstructors seems not to follow the latitudinal gradient, from tropics to increasing distance from tropics, recognised for coral bioconstructors. The only case of a “high diversity bryozoan reef” (Joulters Cays, Bahamas) represents a situation virtually unique in carbonate environments. Dimension and extension of bryozoan bioconstructions show their maximum in temperate environments, where seasonality or variability of environmental parameters could afford advantages for success to bryozoans. With only one exception (the bryozoan-serpulid build-ups from South Australia), diversity of biota associated with bryozoan bioconstructions is high, but comparison is not possible due to the fact that exhaustive faunal studies are rare, sometimes referring only to one taxon, and environments differing in depth range, salinity, hydrodynamics, trophic diversity, etc. are involved.

Deep-water fish assemblages in the Mediterranean Sea

Abstract: Data collected during the DESEAS survey carried out in three areas of the Mediterranean Sea (Balearic Sea, western and eastern Ionian Sea) were used to describe the structure and spatial distribution of the fish assemblages at depths between 600 and 4000 m. A total of 55 species (8 chondrichthyes and 47 teleost fish) were sampled, 38 of them in the Balearic Sea, 30 in the western Ionian and 37 in the eastern Ionian. Multivariate analysis showed a clear pattern of zonation with depth and geographic area. Three main assemblages were identified across the vertical gradient investigated: on the upper slope around a depth of 600 m, on the middle slope between 800 and 1300 m, and on the lower slope below 1300 m. The geographic characterisation of the ichthyofauna structure was mainly observed on the upper and middle slope. The highest abundance and biomass values were found at depths of 1000-1200 m due to the presence of larger species with high energy requirements, such as Alepocephalusrostratus, Mora moro and Galeus melastomus. On the middle slope, significant differences in the abundance, biomass and mean fish weight were detected between the three areas. Significant differences for these parameters were also shown between the middle and lower slope assemblages. A significant decrease in species richness and diversity was shown with increasing depth, indicating an impoverishment of the megafauna with depth and a higher similarity between the Balearic Sea and the Ionian Sea with regard to the greatest depths. The dominant species on the deepest bottoms were Bathypteroismediterraneus, Chalinura mediterranea and Coryphaenoides guentheri. On the lower slope, the shark Centroscymnuscoelolepis was also found to be relatively abundant off the Balearic Islands, Etmopterusspinax in the eastern Ionian Sea and the teleost fish Cataetyx laticeps throughout the three study areas. The deepest bottoms of the Mediterranean Sea shelter an ichthyofauna dominated by small-medium species living in a food scarce environment in which some large mobile fishes are widespread. The results are discussed in relation to previous studies mostly carried out in the Atlantic and western Mediterranean.

Deep-sea distribution, biological and ecological aspects of Aristeus antennatus ( Risso, 1816) in the western and central Mediterranean Sea

Abstract: The object of the DESEAS Project, funded by the EC, was to gather preliminary data on the abundance and maximum depth distribution of the rose shrimp Aristeusantennatus in the Mediterranean Sea. An exploratory survey was therefore designed with that goal in mind and conducted on the R/V Garcia del Cid, sampling the maximum depths in three specific areas in the central and western Mediterranean, one off Ibiza (Balearic Islands), one off Calabria (western Ionian Sea), and one off the southern Peloponnesian Peninsula (Gulf of Kalamata, eastern Ionian Sea). The depths sampled ranged from 600 to 4000 m, with specimens of A. antennatus being collected down to 3300 m. There were three distinct boundaries marking the abundance of this species: -2 ); 1000-1500 m, relatively moderate abundance (up to 300 ind km -2 ); and > 1500 m, relatively low abundance ( -2 ). The known population structure of this shrimp species, with increasing proportions of males and juveniles with depth, was also recorded in the deep-sea regions in other areas of the Mediterranean. No evidence of any differences in gonad development or in the presence of spermatophores carried by females was found in any of the three sampling areas. Lastly, a tendency for the relative proportion of juveniles to increase with depth was also observed.

Amphipod and sea urchin tests to assess the toxicity of Mediterranean sediments: the case of Portmán Bay*

Abstract: The sediment formed by the tailings of an abandoned mine, which discharged into Portman Bay, Murcia, SE-Spain, was tested to establish a possible gradient of heavy metals. The results were compared with tolerance limits of what was calculated from control sites. Whole sediment toxicity tests were performed on two amphipod species, Gammarus aequicauda and Microdeutopus gryllotalpa, while sediment-water interface and porewater toxicity tests were performed on three sea urchins species, Arbacia lixula, Paracentrotus lividus and Sphaerechinus granularis. The sensitivity of these marine organisms was evaluated by exposure tests using the reference substances: ammonium chloride (NH4Cl), cadmium chloride (CdCl2), potassium dichromate (K2Cr2O7), sodium dodecyl sulfate (C12H25NaO4S) and zinc sulfate (ZnSO4). The concentration of heavy metals decreased along the pollution gradient. Amphipod 10 day acute toxicity tests clearly demonstrated the gradient of toxicity. The sediment-water interface tests conducted with sea urchins also pointed to a pollution gradient and were more sensitive than the tests involving amphipods.

Den ecology of Octopus vulgaris Cuvier, 1797, on soft sediment: availability and types of shelter

Abstract: SUMMARY: To avoid predation, octopuses select and actively modify shelters (also called dens) in the substratum, where they remain most of the time, especially during daylight hours. The main questions that this study deals with are: Is den availability a significant constraint for the distribution of Octopus vulgaris on soft sediment? What kind of dens does O. vulgaris use on soft sediment and what factors affect the selection of one type instead of another? With population density measurements by SCUBA diving and enrichment experiments with artificial dens, we concluded that the availability of solid materials necessary for den construction is a limiting factor for the distribution of O. vulgaris on soft sediment. O. vulgaris used four different types of den on soft sediment: “well” (a vertical hole in the sediment), “rock/stone” (the octopus uses a rock or a large stone to dig a cavity under it), “shell” (an empty shell is used), “human origin” (a solid material of human origin is used). The relative proportion of the four types of den in the areas studied was: 38.7% “human origin”, 29.7% “well”, 21.5% “rock/stone”, 2.9% “shell”. Also, 7.3% of the octopuses were found outside their den. The main types of den were found in different relative proportions in relation to the depth, the distance from shore, the octopus size and the granulometry of the sediment.

Reconstruction of trophic pathways between plankton and the North Iberian sardine ( Sardina pilchardus ) using stable isotopes

Abstract: SUMMARY: Feeding on phyto- and zooplankton by juvenile (< 1 year old) and adult sardines (Sardina pilchardus) was inferred from analyses of natural abundance of stable carbon and nitrogen isotopes in samples from the northwestern Iberian Peninsula (Spain) collected at the beginning of the upwelling season and peak spawning period of sardine. Plankton samples were fractionated through nets of 20, 200, 500, 1000 and 2000 µm mesh-size and the muscle protein of individual sardines was isolated before isotopic determinations. Up to six planktonic components and two sardine feeding types were identified from the modes in the frequency distributions of isotope abundance values. Also, the most probable pathways for carbon and nitrogen flows between compartments were analysed. The resulting food web revealed a relatively large degree of omnivory, both in plankton and sardine components, which confirms that complex trophic interactions could also occur in pelagic upwelling ecosystems. Young sardines had isotope abundance values clustered around a single mode in the frequency distribution, while adult sardines displayed two main modes. These modes are interpreted as representative of two extreme feeding types: one related to the individual capture of zooplankton prey and the other to unselective filter-feeding. Although both types of feeding could include micro- (20-200 µm) and mesozooplankton (200-2000 µm) prey, phytoplankton appears to be ingested mainly by filter-feeding. However, even adult sardines must be mainly zoophagous to achieve the observed isotopic abundance values, taking into account current assumptions on stable isotope enrichment through trophic levels. From the differences in the resulting pathways using either carbon or nitrogen isotopes, we interpreted that sardines acquire most of the protein nitrogen from zooplankton while a substantial fraction of their carbon would derive from phytoplankton. These interpretations agree with the information available for this species on the gut contents and the anatomy of the filtering apparatus.

Deep-sea decapod crustaceans in the western and central Mediterranean Sea: preliminary aspects of species distribution, biomass and population structure*

Abstract: Three deep-sea areas in the Mediterranean Sea were sampled using a bottom otter trawl during the DESEAS oceanographic survey carried out from early June to early July 2001, covering an area in the western Mediterranean from 600 to 2800 m in depth and two areas in the central Mediterranean, the western and eastern Ionian Sea from 600 to 4000 m in depth. Decapod crustaceans were one of the dominant megafaunal groups, together with fishes, in terms of both biomass and abundance. A total of 2799 decapod specimens belonging to 32 species were collected. Abundance and biomass of the decapod crustaceans decreased with depth. For depths below 1000 m, a decrease in total decapod biomass was recorded from west to east. From the data reported in this study and data from the available literature, decapod crustaceans display differential depth distributions in the different areas. For the most abundant species, size and sex distributions versus depth gradient were examined to compare intraspecific population structures between the sampling areas. Despite differences, among areas, in the species biomass compositions by depth strata and differences in their overall bathymetric ranges of distribution, intraspecific population structures of the most abundant species seem to follow similar trends for size and sex distribution versus depth gradient between the western and central areas. This might be an indication that the individual species structure their populations according to a similar basic pattern regardless of differences in local environmental features. The results have been discussed in the general context of the environmental features encountered by the species in each of the sampling areas.

Chondrichthyes species in deep waters of the Mediterranean Sea

Abstract: Data collected during the DESEAS survey carried out in three areas of the Mediterranean Sea (Balearic Sea, western and eastern Ionian Sea) were used to describe the distribution and abundance of chondrichthyes species at depths between 600 and 4000 m. A total of 8 chondrichthyes species were recorded, 5 of them in the Balearic Sea, 4 in the western Ionian and 6 in the eastern Ionian. A decrease in abundance with depth was observed in each species with the exception of Centroscymnuscoelolepis. The most abundant species were Galeus melastomus and Etmopterusspinax. The depth range of some species was updated. G. melastomus was caught down to 1500 m, exhibiting a smaller-deeper pattern in females, while E.spinax was captured down to 2200 m with a bigger-deeper trend. Mature females of these two sharks were found between 600 and 1500 m. A wide size-range was shown in both species. C.coelolepis was only collected in the Balearic Sea down to 2800 m. The presence of a pregnant female was sampled from a depth of 1500 m. The distribution of the species is discussed in the context of the present knowledge of the Mediterranean ichthyofauna.

Feeding ecology of the gobies Pomatoschistus minutus (Pallas, 1770) and Pomatoschistus microps (Krøyer, 1838) in the upper Tagus estuary, Portugal*

Abstract: The sand goby Pomatoschistus minutus (Pallas, 1770) and the common goby Pomatoschistusmicrops (Kroyer, 1838) are among the most abundant fish species in estuaries, lagoons and along the Atlantic shores of Europe. In the Tagus estuary these species are particularly important in the food web. Fish samples were taken monthly in the upper estuary, and the gut contents of a total of 431 P.minutus and 382 P. microps were analysed in order to study preferences and seasonal changes in their diets and to understand intra- and interspecific relations between these two congeneric gobies. The sand goby had no dominant prey, although mysids were particularly important in the diet of this species. Shrimps and polychaetes were also common prey. P.microps preferentially ingested polychaetes, with isopods, amphipods, bivalves and copepods as secondary prey items. Significant seasonal variations in the ingestion of the main prey groups of both species were obtained, which reflect variations in prey availability. During the reproductive season there were differences in the food consumed by males and females, mainly for P.minutus, reflecting the different activity pattern exhibited by males and females during the breeding season, since parental care is supported by the former. The smallest classes from P.minutus increased their niche widths as they grew. Due to the different length reached by each species, the degree of interspecific overlap decreased with increasing body size.

Mediterranean and Atlantic deep-sea fish assemblages: differences in biomass composition and size-related structure

Abstract: Data obtained over a period of twenty years from 214 bottom trawls, towed on a single warp at depths between 402 and 1993 m in the western Mediterranean (Algerian and Balearic basins) and eastern North Atlantic (Rockall Trough and Porcupine Seabight), allowed a standardised comparison of density, biomass composition and size-related structure for both the whole fish fauna and for the most common species found within the deep-sea fish assemblages All four areas are characterised by distinctly different and well-documented oceanographic conditions, biogeographical affinities and fishing exploitation The results showed clear differences between the Atlantic and the Mediterranean deep-sea fish fauna, not only in density, species richness and composition, but also in the structure of the biomass that constitutes these assemblages These differences are discussed in relation to environmental conditions and fishing pattern, which have determined the adaptive responses of both individual species and the whole ecosystem

The present-day Mediterranean brachiopod fauna: diversity, life habits, biogeography and paleobiogeography

Abstract: The present-day brachiopods from the Mediterranean Sea were thoroughly described by nineteenth-century workers, to the extent that Logan´s revision in 1979 listed the same 11 species as Davidson, almost 100 years earlier. Since then recent discoveries, mainly from cave habitats inaccessible to early workers, have increased the number of species to 14. The validity of additional forms, which are either contentious or based on scanty evidence, is evaluated here. Preferred substrates and approximate bio-depth zones of all species are given and their usefulness for paleoecological reconstruction is discussed. A previous dearth of material from the eastern Mediterranean has now been at least partially remedied by new records from the coasts of Cyprus, Israel, Egypt, and, in particular, Lebanon and the southern Aegean Sea. While 11 species (79 % of the whole fauna) have now been recorded from the eastern basin, Terebratulina retusa, Argyrotheca cistellula, Megathiris detruncata and Platidia spp. appear to be less common than in the western basin. Lacazella mediterranea, I>Tethyrhynchia mediterranea and Gwynia capsula have not yet been recorded from the eastern Mediterranean, but whether this is due to a west-east faunal impoverishment or insufficient collecting is uncertain. L. mediterranea and T. mediterranea may be endemic to the Mediterranean. The Messinian (Late Miocene) salinity crisis caused most species to disappear from the ancestral Mediterranean Sea. T. mediterranea may be a paleoendemic that has survived in marine refuges mostly located on the outer margin of the western basin, while other species either entered or re-entered the Mediterranean from the Atlantic after the Miocene.

Ocean wave mapping from ERS SAR images in the presence of swell and wind-waves

Abstract: We present a method for estimating the significant wave height of ocean waves (SWH) in coastal zones from satellite SAR images and using the value of the width of the spectral azimuthal cutoff. The method deals with the case of an energetic swell propagating over a wind wave system. It requires the preliminary retrieval of swell parameters using the wave-SAR spectral quasi-linear relationship. The method is applied to two ERS-1 SAR images in coastal zones.

Deep macrobenthic communities from Nazaré Submarine Canyon (NW Portugal)

Abstract: Macrofauna community structure within Nazare Submarine Canyon is analysed and used to assess the potential effects of natural enrichment in this area subjected to accumulation of coastal sediments. A transect including three stations (2894, 3514 and 4141 m) was carried out in the Nazare Submarine Canyon (NW Portugal) during a cruise of OMEX II programme (Ocean Margin Exchange), in the winter season of 1999. Although data was not collected in order to calculate sedimentation rates, sampling station at 2894 m is located in an area characterised by high levels of sedimentation, thus a high amount of organic matter is expected to be available for the local communities. Faunistic data are discussed in the context of the different features of the stations sampled. Multivariate analysis clearly separates the shallowest station from the other ones, which otherwise appear to be very similar. It also revealed a perceptible gradient along sediment depth at all stations, from shallow to deeper layers. Exceptionally depressed species richness and low evenness values were observed at the 2894 m station. The high number of individuals of a single species, Cossura sp. A, and the atypical diversity, dominance and evenness values obtained for this station support the hypothesis of community disturbance due to organic enrichment.

Chemical defenses in Sacoglossan Opisthobranchs: Taxonomic trends and evolutionary implications

Abstract: SUMMARY: Sacoglossan sea slugs (Mollusca: Opisthobranchia) are one of the few groups of specialist herbivores in the marine environment. Sacoglossans feed suctorially on the cell sap of macroalgae, from which they “steal” chloroplasts (kleptoplasty) and deterrent substances (kleptochemistry), retaining intracellularly both host plastids and chemicals. The ingested chloroplasts continue to photosynthesize for periods ranging from a few hours or days up to 3 months in some species. Shelled, more primitive sacoglossans feed only on the siphonalean green algal genus Caulerpa, and they do not have functional kleptoplasty. The diet of Sacoglossans has radiated out from this ancestral food. Among the shell-less Plakobranchidae (=Elysiidae), the more primitive species feed on other siphonales (families Derbesiaceae, Caulerpaceae, Bryopsidaceae and Codiaceae) and fix carbon, while the more “advanced” species within the Plakobranchidae and Limapontioidae have a more broad dietary range. Most of these “advanced” species are unable to fix carbon because the chloroplasts of their food algae are mechanically disrupted during ingestion. Mesoherbivores are likely to be eaten if they live on palatable seaweeds, their cryptic coloration and form not always keeping them safe from predators. Sacoglossans prefer to live on and eat chemically defended seaweeds, and they use ingested algal chemicals as deterrents of potential predators. The most ancestral shelled sacoglossans (Oxynoidae) and some Plakobranchidae such as Elysia translucens, Thuridilla hopei and Bosellia mimetica have developed a diet-derived chemical defense mechanism. Oxynoids and Thuridilla hopei are able to biomodify the algal metabolites. However, the Plakobranchidae Elysia timida and E. viridis, together with Limapontioidea species, are characterized by their ability to de novo synthesize polypropionate metabolites. A whole analysis of kleptoplasty and chemical defenses in Sacoglossans may offer a better understanding of the ecology and evolution of these specialized opisthobranchs. In this paper we summarize some of the latest findings, related mainly to Mediterranean species, and offer a plausible evolutionary scenario based on the biological and chemical trends we can distinguish in them. RESUMEN: DEFENSAS QUIMICAS EN LOS OPISTOBRANQUIOS SACOGLOSOS: TENDENCIAS TAXONOMICAS E IMPLICACIONES EVOLUTIVAS. Los limacos marinos del orden Sacoglosos (Moluscos: Opistobranquios) son uno de los pocos grupos de herbivoros especializados en el ambiente marino. Los Sacoglosos se alimentan suctorialmente del jugo celular de microalgas, de las que “roban” cloroplastos (cleptoplastia) y sustancias disuasorias (cleptoquimia), y conservan intracelularmente tanto los plastidos como las sustancias quimicas del patron. Los cloroplastos ingeridos continuan fotosintetizando por periodos que van desde unas pocas horas o dias hasta 3 meses en algunas especies. Los sacoglosos testaceos, mas primitivos, se alimentan solo de algas del genero de sifonales Caulerpa, y no tienen cleptoplastia funcional. La dieta de los Sacoglosos ha radiado desde este alimento ancestral. Entre los Placobranquidos (=Elisidos), sin concha, las especies mas primitivas se alimentan de otras algas sifonales (familias Derbesiaceas, Caulerpaceas, Briopsidaceas y Codiaceas) y fijan carbono, mientras que las especies mas “avanzadas” pertenecientes a Placobranquidos y Limapontioideos poseen una panoplia alimentaria mas amplia. La mayoria de estas especies “avanzadas” son incapaces de fijar carbono porque los cloroplastos de sus algas alimento se rompen mecanicamente durante la ingestion. Los mesoherbivoros estan expuestos a ser comidos si viven sobre algas marinas comestibles, pues su coloracion y forma cripticas no siempre los mantienen a salvo de los depredadores. Los Sacoglosos prefieren vivir sobre algas defendidas quimicamente y comerlas, y utilizan sustancias quimicas ingeridas como disuasores de depredadores potenciales. Los sacoglosos testaceos mas primitivos (Oxinoidos) y algunos placobranquidos tales como Elysia translucens, Thuridilla hopei y Bosellia mimetica, han desarrollado un mecanismo defensivo derivado de la dieta. Los Oxinoidos y Thuridilla hopei pueden biomodificar los metabolitos algales. Sin embargo, los placobranquidos

Zonation patterns of benthic communities in an upwelling area from the western Medierranean (La Herradura, Alboran Sea)

Abstract: Species composition and distribution of marine benthic communities from La Herradura (Alboran Sea, western Mediterranean) are described to characterise its rocky and sedimentary bottoms bionomically. Rocky bottoms were studied by means of several underwater transects and soft bottoms with fixed stations along a bathymetric gradient. The study of the floristic and faunistic composition of the rocky benthic communities highlights depth as the main axis of variation. Factorial Correspondence Analysis segregates deep-water communities below 25 m depth (circalittoral communities) from shallower communities (axis I), and communities thriving between 5 and 25 m depth (lower infralittoral communities) from communities thriving close to the surface (shallow infralittoral communities) (axis II). The study of the sedimentary bottoms also suggests that depth, together with physical sedimentary properties, is the main axis of variation in species distribution. Floristic and faunistic records show the particular composition of La Herradura benthic communities, compared to Mediterranean and Atlantic ones. Mixing of Mediterranean and Atlantic waters, together with deep water upwelling episodes typical of this area, probably determine the peculiar composition of the benthic communities.

Recruitment and post-settlement growth of juvenile Merluccius merluccius on the western Mediterranean shelf

Abstract: Young-of-the-year European hake (Merluccius merluccius) were sampled during four seasonal cruises between November 1998 and September 1999. The greatest numbers and biomass were found in spring 1999. Some 73% of juvenile fish in terms of number, and 81% in terms of biomass, were caught at depths between 60 and 160 m on the outer western Mediterranean shelf, where the water temperature ranged between 13.5 and 14°C. The length composition of samples showed there to be small hake all year around, with modes between 7 and 11 cm total length depending on the season. Otolith analysis was used to establish age at settlement (62.7 days) and to determine seasonal growth. The monthly growth rates ranged from 1.2 cm month-1 for juvenile hake captured on February 1999 to 2.5 cm month-1 for ones captured in June. The growth rates are related to survival, as was shown by the calculated hatch dates and relative abundances of recruits. This work provides information on the first year of life, recruitment and growth processes in an important species of the Mediterranean demersal ecosystem which is heavily exploited by a recruitment fishery.

The limit of the sea: the bathyal fauna of the Levantine Sea*

Abstract: SUMMARY: In the present study, the fish, molluscs, crustaceans and echinoderms collected at depths between 734 and 1558 m during a series of cruises conducted between 1988 and 1999 off the coast of Israel, supplemented by a photographic survey carried out southwest of Cyprus at a depth of 2900 m, were analysed. The main objectives were to determine the faunal composition of the bathybenthic assemblages in the southeastern Levantine Sea, and to compare them with the western Mediterranean assemblages in order to elucidate whether general trends in their bathymetric distribution and population density may be related to environmental/geographic factors. Considering the sampling effort, the diverse gear used and the extended period of sampling, we may assume that the low number of species and specimens recorded actually reflects a lowdiversity, low-density deep water fauna. The faunal scarcity may cause a different parcelling of the populations which is reflected in bathymetric distributions that in many cases extend to greater depths than in the Western Mediterranean. The Levantine bathybenthos is composed of autochthonous, self-sustaining populations of opportunistic, eurybathic species that have settled there following the last sapropelic event.

Deep-sea Mediterranean biology: the case of Aristaeomorpha foliacea (Risso, 1827) (Crustacea: Decapoda: Aristeidae)

Abstract: Data on the distribution, abundance and biological parameters of the giant red shrimp Aristaeomorphafoliacea were collected during a research survey in deep waters (600-4000 m) of the Mediterranean Sea at three locations: the Balearic Sea, the western Ionian and the eastern Ionian in early summer 2001. The shrimp was mainly found in the shallower zone (< 1000 m) of the eastern Ionian Sea. Few specimens were caught in the deeper waters of this region, with 1100 m being the lower limit of its distribution. This is the maximum depth reported for the species in the Mediterranean. At the other two locations, the species was scarcely caught and only in the shallowest zone (< 1000 m). In the area and depth zone of high abundance, 5 modal groups for females and 3 for males were distinguished using the Bhattacharya method. The recruitment seems to take place at the shallowest stations (600 m). More than 50% of adult females were in advanced maturity stages. The striking abundance differences of the species between the western and eastern locations may be explained by the different exploitation level of the deep waters (almost null in the eastern Ionian Sea and extensive more westwards). However, the distribution and biological characteristics of A.foliacea indicate a higher vulnerability to over-fishing comparing to the other commercial co-occurring deep-water shrimp Aristeusantennatus.

Morphometry, growth and reproduction of an Atlantic population of the razor clam Ensis macha (Molina, 1782)

Abstract: Fil: Baron, Pedro Jose Consejo Nacional de Investigaciones Cientificas y Tecnicas Centro Nacional Patagonico; Argentina Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina

Abundance of Octopus vulgaris on soft sediment

Abstract: SUMMARY: Until now the distribution and abundance of Octopus vulgaris had been investigated in the main fishing areas of the species only by fishing surveys. The catching efficiency of fishing gear is variable and depends on several aspects of the animal’s behaviour and life history as well as on the type of the gear and the environmental characteristics of the area surveyed. A good alternative for studying the abundance of octopus is by visual census. The population density of O. vulgaris was measured by visual census with scuba diving. The survey was conducted in coastal areas of Greece and on soft sediment. O. vulgaris density ranged from 0 to 6.88 individuals/1000m 2 and the mean density values of this study were much higher than those mentioned in other papers. Octopus density was significantly associated with season. Densities of octopuses lower than 500 g were higher in coarse sediments than in finer ones. The density of large octopuses (> 500 g) increased with depth. Octopuses larger than 200 g tended to dwell deeper during the period of intense thermocline than during the nothermocline period.

Mechanisms regulating amphipod population density within macroalgal communities with low predator impact

Abstract: In eight mesocosms (land based basins) macroalgae communities with associated fauna were transplanted from the sea and established during two years. Then, different doses of nutrients (N and P) were added to the basins throughout the following three years. During the period of nutrient addition, macroinvertebrate grazers showed seasonal fluctuations with densities usually between 500,000 and 1 million individuals per mesocosm during summer and to a level of about 100,000 during winter. The macroinvertebrate grazers mainly consisted of about 10 species of amphipods and isopods, among which the amphipod Gammarus locusta dominated strongly by biomass. Although the number of predators was very low, the grazer populations never reached a density where considerable grazing impact could be found on the macroalgae. No increase in grazer density was found in the basins with improved nutrient conditions. Thus food quality may be insufficient for further population growth, or density dependant regulation mechanisms may have prevented the grazers from flourishing and overgrazing the system. In aquarium experiments we showed that G. locusta could grow and reproduce on Fucus serratus, Ulva lactuca, periphyton and detritus, and that cannibalism by adult G. locusta on juveniles may have great impact on the population growth. The basins were run with a water flow through system. Nets were placed in front of the inflow and outflow tubes to measure immigration and emigration. Only few individuals (and no Gammarus sp.) were recorded in the inflowing water, while high numbers of both amphipods and isopods were found in the outflowing water. Emigration reached peak values during night-time, and it was then two to three times as high as during day-time. Emigration of mobile grazers from the basins amounted to 1-2% of the standing stock daily. These mechanisms that regulate grazers do contribute to maintenance of the seaweed dominance and thus the stability of the seaweed community.

Temporal patterns of larval fish distribution and abundance in a coastal area of northern Greece

Abstract: Species composition, abundance and diversity of fish larvae were assessed in the Strymonikos and Ierissos Gulfs (northern Aegean Sea, Greece) Both gulfs are affected by the freshwater input of the Rivers Strymon and Rihios; water depth does not exceed 80 m Samples were collected using a bongo net sampler (250 µm mesh size) over a grid of 35 stations in six cruises between June 1997 and May 1998 A total of 48 taxa of fish larvae (36 species, 5 genera and 7 families) were identified The majority of identified fish larvae taxa consisted of demersal species that included larvae of Bothidae, Gobiidae, Callionymidae, Sparidae and Serranidae The highest number of species occurred in the warm season (May, June, July, September) and this was attributed to the summer spawners that start their reproduction period during spring/early summer The European anchovy (Engraulis encrasicolus) was the dominant species between July and September, and the European sardine (Sardina pilchardus) between November and March Two distinct seasons (warm and cold) were identified by multivariate analysis, highlighting the importance of seasonality in shaping the community structure The absence of well-defined larval fish associations revealed the importance of depth in the identification of different spatial patterns in an area

Estimation of photosynthesis and calcification rates of Corallina elongata Ellis and Solander, 1786, by measurements of dissolved oxygen, pH and total alkalinity*

Abstract: Experiments were conducted on the calcareous red alga, Corallina elongata, a species representative of shallow water vegetal cover in Mediterranean areas with biomass ranging from 820 to 2544 gDW.m-2, in order to estimate its productivity and calcification rates. Carbonate and oxygen budgets were estimated on samples incubated in situ under natural light cycles, by measuring initial and final dissolved oxygen, pH and alkalinity levels. In light conditions, oxygen concentrations and pH values increased as a consequence of oxygen production and carbon dioxide consumption due to the productivity process, and were a direct function of sample biomass. Strictly-reverse dynamics were recorded in dark conditions. A comparison of photosynthetic performances was conducted on a non-calcareous green alga, Ulva rigida, which showed higher rates of oxygen production and pH modification than C. elongata, but no significant change in total alkalinity. For C. elongata, a significant decrease in total alkalinity with incubation time was observed under light conditions, which was directly related to the algal sample biomass (R2 = 0.95; n=16). Light to dark calcification ratio (L/D) was about 3.6. In these experiments, the photosynthetic quotient of C. elongata was 0.89, its net carbon productivity was 2.5 g C.m-2.d-1, gross production to daily respiration (Pg/R) was about 4.9 and its calcification rate was estimated at 13.8 g CaCO3.m-2.d-1.

Body fish size tendencies within and among species in the deep-sea of the western Mediterranean

Abstract: Data collected south-west of the Balearic Islands (Western Mediterranean) on two cruises, Quimera-I (October, 1996) and Quimera-II (May, 1998), were used to establish general ecological patterns in deep-sea fish assemblages. A total of 39 trawls were taken at depths between 400 and 1714 m. Fish assemblages were analysed in terms of species composition, ecological parameters and biomass spectra. Differences in species composition between cruises and depth (Upper slope: 400-800 m, Middle slope: 801-1400 m and Lower slope: 1401-1714 m depth) were evaluated using multivariariate analysis. The most important feature was the existence of a biomass peak at intermediate depths. Moreover, the analysis of the biomass spectra indicated the absence of large individuals at the shallower depth interval considered. To determine the causes of the biomass peak on the middle slope four hypothesis were explored: (1) species richness is higher on the middle slope; (2) the fish assemblage from the middle slope can be characterised by the highest abundance (number of fish/area); (3) species found on the middle slope are larger (the species assemblage is built up by larger species); and (4) there is a trend for the specimens of several species to be larger at the middle slope. The data gathered support that the biomass peak is better explained by the existence of abundance peaks of medium and large-sized species, and by the presence of some of the largest individuals of other large-sized species, in both cases related to specific depth size trends which do not always follow a bigger-deeper trend.

Composition and distribution of benthic molluscs on intertidal flats of Paranaguá Bay (Paraná, Brazil)*

Abstract: Mollusc species composition, abundance and spatial distribution were analysed from April 1996 to October 1997 on two tidal flats in Paranagua Bay (SE Brazil) at the entrance (St. I) (Lat. 25o3´S) and in the intermediate sector (St. II) (Lat. 25o3´S) of the estuary. At St. I, with the highest and least variable salinity, species richness (R = 40) and diversity ( H´= 1; D S = 0.85) were higher than at St. II ( R = 22 and H´ = 0.54; D S = 0.57 ). The tropical clam Anomalocardia brasiliana was the most conspicuous mollusc of the two assemblages, followed by Cerithium atratum, Neritina virginea and Crassostrea sp. at St. I and by Macoma constricta and N. virginea at St. II. On the two flats, the decrease in species richness and abundance towards the upper tidal levels suggests a strong relationship between relative tolerance to physiological stress in the organisms and the degree of immersion/submersion.

Preservation of juvenile hake ( Merluccius merluccius L) in the western Mediterranean demersal trawl fishery by using sorting grids

Abstract: The Mediterranean fishery has experienced a decline in catches over the past 20 years due to an excessive increase in effort caused by both increased trawler engine power and rapid technological advances in fishing technology and fish location. This has led to overexploitation, in which immature individuals support an increasing portion of the catches. The present study was undertaken to test a sorting grid and square-mesh-panel as juvenile exclusion systems. Our experience was a pilot study of such a system in the western Mediterranean. The purpose of these exclusion systems was to help juvenile hake escape from the net. The results demonstrate that the use of sorting grids for small fish in trawl gears in the Mediterranean is an efficient and practical means of avoiding the capture and discarding of unwanted individuals, with escape rates of over 50% (ranging between 50 and 90%). The grids were efficient and useful for excluding hake ( Merluccius merluccius ) on bottoms located at depths between 50 and 300 m, where hake are found all year round. A bar spacing of 20 mm yielded escape rates of L 50 at 18.8 cm TL (L 25 = 16.8 cm and L 75 = 20.9 cm). Panels made of square meshes achieved poorer results than the grids. The grid system was effective for most of the species caught in the study area.