1,721,263 research outputs found
Percnon gibbesi (H. Milne Edwards, 1853) and Callinectes sapidus (Rathbun, 1896) in the Ligurian Sea: Two additional invasive species detections made in collaboration with local fishermen
No full textThe non-indigenous crabs Percnon gibbesi (H. Milne Edwards, 1853) and Callinectes sapidus (Rathbun, 1896) (Crustacea, Decapoda, Portunidae) are reported from Genoa and La Spezia, respectively, in the Ligurian Sea at the northern rim of the Mediterranean Sea. Both specimens were collected by fishermen who then brought them to the attention of professional scientists. This illustrates the importance of engaging local communities in detecting non-indigenous species and monitoring their spread. © 2017 The Author(s). Journal compilation & 2017 REABIC
Temporal variations of zooplankton biomass in the Ligurian Sea inferred from long time series of ADCP data
No full textThree years of 300 kHz acoustic doppler current profiler data collected in the central Ligurian Sea are analysed to investigate the variability of the zooplankton biomass and the diel vertical migration in the upper thermocline. After a pre-processing phase aimed at avoiding the slant range attenuation, hourly volume backscattering strength time series are obtained. Despite the lack of concurrent net samples collection, different migration patterns are identified and their temporal variability examined by means of time-frequency analysis. The effect of changes in the environmental condition is also investigated. The highest zooplankton biomasses are observed in April-May just after the peak of surface primary production in March-April. The main migration pattern found here points to a "nocturnal" migration, with zooplankton organisms occurring deeper in the water column during the day and shallower at night. Also, twilight migration is highlighted during this study. The largest migrations are recorded in November-December, corresponding to lowest backscattering strength values and they are likely attributable to larger and more active organisms (i.e. euphausiids and mesopelagic fish). The results suggest further applications of the available historical acoustic doppler current profiler time series. © 2014 Author(s)
Trophic webs of deep-sea megafauna on mainland and insular slopes of the NW Mediterranean: A comparison by stable isotope analysis
No full textFood web structure of deep-sea megafauna in the Balearic Basin (NW Mediterranean) was investigated using carbon and nitrogen stable isotopes. A total of 71 species (including 26 fish species and 19 decapod species) were analysed from samples collected with a semi-balloon otter-trawl in 2 contrasting oceanographic settings: The Catalonian Slope (CS), a continental slope area indented by several submarine canyons and an insular slope area north of Mallorca (the Balearic Slope, BS). Three faunally distinct depth zones were sampled in each area in July 2010: 450 to 600 m (upper slope), 1000 to 1300 m (middle slope) and 1400 to 2200 m (lower slope). Different physical- chemical variables and potential food sources were analysed as possible explanatory variables of trophic web variability. A δ15N- δ13C scatterplot indicated a complex food web with fish (i.e. Macrouridae and deep-sea sharks) occupying the highest trophic position. Significant differences occurred in the isotopic composition of species among upper, middle and lower slope assemblages and between the areas (CS vs. BS). Generally, higher δ15N and δ13C values were observed with increasing depth (especially among benthic feeders), and on the CS compared with the BS. Similarly, based on generalized linear models, different environmental-trophic variables ex plained the observed trends. On the BS, δ13C of species was mainly linked to physical variables and to chlorophyll a concentration at 5 m above the bottom as a proxy of marine snow, suggesting assemblages were mainly linked to vertical inputs. Conversely, on the CS, δ13C was related to trophic variables, indicating that species are linked to prey availability and less directly to primary production. The comparison suggests longer food webs over the mainland slope. © Inter-Research 2013
A multi-tissue approach to assess the effects of lipid extraction on the isotopic composition of deep-sea fauna
No full textStable isotope analysis (SIA) of carbon and nitrogen is now a common tool to investigate trophic relationships and food-web structure in aquatic ecosystems. However, species-specific and tissue-specific lipid content sometimes hinders the correct interpretation of δ13C and δ15N values because lipids are 13C-depleted with respect to proteins, and thus tissue lipid extraction is generally invoked. We assessed the effects of lipid extraction on δ13C and δ15N compositions and C:N ratios of muscle, liver (or hepatopancreas) and gonads of three common Mediterranean deep-sea species with different locomotory activity, buoyancy mechanisms and feeding modes: the benthic-feeder shrimp Aristeus antennatus, the nektobenthic-feeder shark Galeus melastomus and the pelagic-feeder fish Micromesistius poutassou to evaluate both the effect of lipid extraction on SIA data and the validity of δ13C lipid correction models. Results showed that the effect of lipid extraction is not unique but some common patterns can be identified. Lipid extraction resulted in increased δ15N values in the liver and the muscle and in decreased δ15N values in the gonads, in increased δ13C values in all the tissues of the three species, except in the hepatopancreas of A. antennatus, and in decreased C:N ratios. The magnitude of the changes was species- and tissue-specific. We assessed the validity of δ13Cbulk correction equations for lipid content in muscle and liver tissues available from literature in the species from this study. Such equations provided corrected δ13C values equivalent to those obtained through lipid extraction when applied to a species with similar characteristics (i.e., taxon, behavior, etc.) to those for which the equations were designed. Our results for muscle tissue showed that not one of the equations tested was valid for the deep-sea shark G. melastomus, and we propose a species-specific model with a fairly feasible model efficiency. Besides, tissue-specific equations for liver in G. melastomus provided non-significant differences between δ13Ccorrected and δ13Clipid free values, but all model efficiencies were fairly low. Thus, lipid extraction trials on elasmobranch muscle and liver tissue to determine effects on δ13C and δ15N values on a species-by-species basis are recommended. Our research together with a comprehensive literature review on this topic, highlights that there is no accepted or mandated standard of treatment for lipids when using stable isotope analyses. © 2017 Elsevier B.V
Trophic ecology of Lampanyctus crocodilus on north-west Mediterranean Sea slopes in relation to reproductive cycle and environmental variables
No full textThis study examined the population structure, reproductive cycle and feeding pattern of the lanternfish Lampanyctus crocodilus in the Balearic Basin (north-west Mediterranean Sea) from a depth of 450 to 1800m and at a seasonal scale. Juveniles were mainly located at shallower depths, but also at deepest stations in autumn, while adults mostly inhabited intermediate depths with their centre of population density (CPD) located at 800-1000m of depth. The migration of adults to deeper depths was detected in late summer to autumn, probably linked to the occurrence of nepheloid layers at c. 1200m, which in turn enhances the biomass of the zooplankton prey. The diet was mainly based on euphausiids and mysids, with marked seasonal variations both on the upper (450-800 m) and lower (1000-1800 m), where suprabenthic gammariids and pelagic decapods were also dominant. Stomach fullness increased from winter to autumn on the US, while it had a maximum in spring on the LS, in parallel with high consumption of gelatinous zooplankton, which is probably more available after the phytoplankton bloom in late winter. Reproduction occurred in winter, confirmed by the higher percentage of mature females and high gonadosomatic indices (IG) at both depth ranges. Hepatosomatic indices (IH) showed an inverse trend to IG on the US, except in autumn, and was almost parallel on the LS, probably attributable to the migration of adults, which determined different temporal schemes in energy use and storage for reproduction on the US v. LS. Consistent with the different patterns observed at the two depth ranges, environmental drivers of fullness (i.e. feeding intensity) and IG (as a proxy of reproductive cycle) differed on the US and LS. The biomass of mysids and euphausiids was the greatest explanatory variables of fullness on the US and LS, pointing to the increasing feeding intensity when a resource was more available. IH also explained fullness, suggesting that greater feeding intensity in pre-reproductive periods enabled energy storage in the liver. IG was linked directly (i.e. mysids) or indirectly (i.e. surface primary production recorded 2 months before sampling) to food availability, implying a rapid response to vertical food inputs by deep-sea predators. Also, IG in L. crocodilus was related to population density, which suggests aggregations for reproduction. Estimates of L. crocodilus trophic levels, and of other accompanying mesopelagic fishes, indicated that the species feed through a continuum spanning the third trophic level, confirming the key role of mesopelagic fishes in transferring organic carbon between trophic levels. Trophic niche segregation among mesopelagic species was pronounced and non-overlapping groups could be distinguished because of the different vertical distribution and migratory behaviour. The study highlights the important role of the benthic boundary layer in sustaining benthopelagic communities in the deep Mediterranean Sea and the need to study the biology of a species throughout its whole depth range and not just at exploited depths (i.e. fishing grounds). © 2014 The Fisheries Society of the British Isles
Environmental drivers of megafaunal assemblage composition and biomass distribution over mainland and insular slopes of the Balearic Basin (Western Mediterranean)
No full textThe influence of mesoscale physical and trophic variables on deep-sea megafauna, a scale of variation often neglected in deep-sea studies, is crucial for understanding their role in the ecosystem. Drivers of megafaunal assemblage composition and biomass distribution have been investigated in two contrasting areas of the Balearic basin in the NW Mediterranean: on the mainland slope (Catalonian coasts) and on the insular slope (North of Mallorca, Balearic Islands). An experimental bottom trawl survey was carried out during summer 2010, at stations in both sub-areas located between 450 and 2200m water depth. Environmental data were collected simultaneously: near-bottom physical parameters, and the elemental and isotopic composition of sediments. Initially, data were analysed along the whole depth gradient, and then assemblages from the two areas were compared. Analysis of the trawls showed the existence of one group associated with the upper slope (US=450-690m), another with the middle slope (MS=1000-1300m) and a third with the lower slope (LS=1400-2200m). Also, significant differences in the assemblage composition were found between mainland and insular slopes at MS. Dominance by different species was evident when the two areas were compared by SIMPER analysis. The greatest fish biomass was recorded in both areas at 1000-1300m, a zone linked to minimum temperature and maximum O2 concentration on the bottom. Near the mainland, fish assemblages were best explained (43% of total variance, DISTLM analysis) by prey availability (gelatinous zooplankton biomass). On the insular slope, trophic webs seemed less complex and were based on vertical input of surface primary production. Decapods, which reached their highest biomass values on the upper slope, were correlated with salinity and temperature in both the areas. However, while hydrographic conditions (temperature and salinity) seemed to be the most important variables over the insular slope, resource availability (gelatinous zooplankton and Calocaris macandreae) predominated and explained 59% of decapod assemblage variation over the mainland slope. Both fish and decapods were linked to net primary production recorded over the mainland 3 months before sampling, while the delay between the input of food from the surface and fish abundance was only 1 month on the insular slope. Our results suggest that trophic relationships over insular slopes probably involve a shorter food chain than over mainland slopes and one that is likely more efficient in terms of energy transfer. © 2013 Elsevier Ltd
Depicting the novel Eastern Mediterranean food web: a stable isotopes study following Lessepsian fish invasion
No full textThe introduction of Red Sea species through the Suez Canal has caused dramatic alteration of Eastern Mediterranean marine communities, however changes at the level of trophic interactions remain poorly understood. Capitalizing on this spectacular bioinvasion, we used stable isotope analysis to depict the novel fish food web occurring in the Eastern Mediterranean, off the Lebanese coast. Multivariate analyses were performed on six trophic groups contrasting the δ15N–δ13C ratios of native (MED) versus non-indigenous (Lessepsian-LES) species. Community-wide aspects of trophic structure were explored by means of recently developed quantitative metrics, such as the average distance to centroid and the standard ellipse area. Although the trophic positions of Lessepsian and native species were comparable, native fishes generally showed a greater trophic diversity than Lessepsians, the latter being mainly located in the central region of the available trophic space. We argue that the original trophic niche of native species has widened out due to the shift they have made towards less preferred food items, whilst highly competitive invaders are exploiting more energetic resources. In the absence of historical data, our observations agree with the idea of a rapid change of the Eastern Mediterranean food web, driven by niche displacements through trophic competition. © 2015, Springer International Publishing Switzerland
Abundance patterns at the invasion front: The case of Siganus luridus in Linosa (Strait of Sicily, Central Mediterranean Sea)
No full textThe dusky spinefoot (Siganus luridus) has spread through much of the eastern Mediterranean since its introduction in 1920. In the present study, we monitored the abundance of this invader around the island of Linosa (Strait of Sicily), where the species was first recorded in 2003. Data were periodically collected along two temporal windows, 2005-06 and 2012-15, by both underwater visual census and surface snorkelling. Local ecological knowledge was investigated to gain complementary information. Both approaches highlighted significant proliferation of this tropical invader, with an average abundance of 0.36 individuals per 250m2 across the 0-30-m depth range. Dense aggregations of more than 100 adult individuals were observed in September 2015, and a coherent spatial structure at the small scale (<1km) was demonstrated. Considering the biogeographical relevance of this population, located at the western edge of its exotic distribution, these findings can be taken as a valuable case study for understanding invasion processes in the marine environment. © CSIRO 2017
Spatial variability in the trophic ecology and biology of the deep-sea shrimp Aristaeomorpha foliacea in the Mediterranean Sea
No full textThe trophic ecology, energy and reproductive states of the deep-water shrimp Aristaeomorpha foliacea, widely distributed along the slopes of the Mediterranean Sea Basins, were analysed in eight areas spread along ca. 3000km in order to identify patterns in the habitat conditions supporting the species. From W to E the areas were situated between the north side of Eivissa (39°12'N, 1°20'E, in the Balearic Basin) and off Mersin, Turkey (36°15'N, 34°19'E, in the Levantine Sea). Trends identified mainly as a function of longitude from west to east were: (i) higher δ15N, parallel to δ15N shifts in the top 200m of the water column for particulate organic N (Pantoja et al., 2002). The δ15N trend indicates that the deep trophic web, i.e. A. foliacea at 400-600m, reflects the δ15N signal of the photic zone; (ii) a similar significant trend of δ13C, related with exploitation of pelagic versus benthic resources by A. foliacea in each area (i.e. by local variability of terrigenous inputs via submarine canyons). More depleted δ13C was found at mid-longitudes (Tyrrhenian Sea and Sicily Channel) linked to higher consumption of macroplankton prey (Pasiphaea spp., euphausiids and mesopelagic fishes). The feeding intensity (gut fullness, F) and prey diversity (J) of A. foliacea were related, according to generalized linear models, with the temperature and salinity of intermediate waters, variables in turn associated with latitude and longitude. Both F and J were higher in areas with greater shrimp density. The optimal ecological habitat of A. foliacea appears to be located in the Tyrrhenian Sea and the Sicily Channel, where we found the highest F, the greatest trophic diversity and A. foliacea in the best biological condition (i.e. with higher hepato-somatic index, HSI). These are also the areas with the highest densities of A. foliacea. In contrast, in the western Mediterranean Sea (Balearic Basin and the southern Balearic Islands), where A. foliacea has low densities, the shrimp showed generally lower values of trophic indicators and biological condition. © 2014 Elsevier Ltd
Biological condition and trophic ecology of the deep-water shrimp Aristaeomorpha foliacea in the Levantine Sea (SW Turkey)
No full textThe trophic ecology (diets, stable isotope composition) and life cycle (gonado-somatic, GSI, and hepato-somatic, HSI, indices) of Aristaeomorpha foliacea were analysed seasonally (in May, June, and November 2012 and January 2013) off southeast Turkey (Levantine Basin), over the slope at 442-600 m depth. Aristaeomorpha foliacea females were mature in June, suggesting gonad maturity was somewhat delayed off southeast Turkey compared to other areas in the Eastern Mediterranean. The HSI of A. foliacea was highest in May and June (8.2% of body weight) for males and both immature and mature females, sharply lower in November (3.5%) and then increasing again in winter (7.1%). Stomach fullness (F) showed a tendency similar to HSI in both females and males, increasing from May to June. Aristaeomorpha foliacea had rather low δ15N (6.68‰ to 8.26‰) off southeast Turkey, with females having higher δ15N with increasing size. The δ13C signal (-14.85 to -14.68‰) indicated that diet was mainly though not exclusively based on zooplankton (pelagic shrimps and small myctophids of 1.3-4.5 mm TL, cnidarians, hyperiids and pteropods). The increase of A. foliacea remains in A. foliacea guts and of some benthic prey (polychaetes, bivalves, gastropods) after the reproductive period would explain the moderate depletion of δ13C in spring-summer. The greatest changes in the diet occurred between periods of water mass stratification (June and November) and periods of water mass homogeneity (May and January), with greater consumption of zooplankton in the latter season. Aristaeomorpha foliacea seems to have lower reproductive capacity (GSI 5.6%) than other deep-water species of penaeidae living in shallower (Parapenaues longirostris) and deeper waters (Aristeus antennatus). The species has a more specialized zooplankton diet, exploiting short, more efficient trophic chains, which could be an advantage explaining its dominance in oligotrophic areas of the Central-Eastern Mediterranean, including the Turkish slope
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