SW Mediterranean Sea Research Articles

Trawling-Induced Sedimentary Dynamics in Submarine Canyons of the Gulf of Palermo (SW Mediterranean Sea)

Bottom trawling in submarine canyons can affect their sedimentary dynamics, but studies addressing this topic are still scarce. In the Gulf of Palermo (NW Sicily, SW Mediterranean Sea), bottom trawling occurs on the continental slope, but principally concentrates within Oreto Canyon. Hydrographic profiles and time series data of temperature, turbidity, and currents obtained by a CTD probe and by moored instruments, respectively, revealed increased turbidity values and the presence of bottom and intermediate nepheloid layers coinciding with periods of bottom trawling activity. The delay between the onset of trawling activities along the Oreto canyon axis and the increase in water turbidity at the mooring location indicate that trawling resuspended particles are progressively advected down-canyon by hydrodynamic processes. Topographic waves and near-inertial currents seem to contribute to the sediment transport of resuspended particles as bottom and intermediate nepheloid layers. Results presented in this paper highlight the complex relationship between hydrodynamic processes and sediment resuspension by trawling in submarine canyons.

A case study on the function of turf algae as suitable habitat for peracarid crustaceans in disturbed environments from SW Mediterranean Sea

ABSTRACT In the summer of 2014, a field study was carried out in four coastal rocky bottoms from the southeast coast of Spain. In this region, dense canopies of Ericaria mediterranea characterize the undisturbed areas and cover much of the infralittoral stage. Turfs composed of the coralline algae Ellisolandia elongata replace the canopy in places where any anthropogenic disturbance occurs. The main objective of this study was to compare the peracarid fauna inhabiting within the two types of phytal substrate, and to conduct several statistical analyses to detect significant differences between the two assemblages. Contrary to expected, the analyses showed that in E. elongata there was a higher population density of peracarids, as well as higher species richness and values for α-diversity indexes. However, none of these differences was statistically significant, although site-to-site comparison indicated greater differences between locations with the same physical cover. The data pointed out that the assemblage that inhabits the coralline turfs in the area was not an impoverished version of that found in pristine locations, so these algae can act as a suitable habitat for peracarids in case of mild human disturbance.

Impact of lytic phages infecting Salmonella enterica subspecies arizonae on physicochemical and microbiological water quality of the old Port of Bizerte (Tunisia, SW Mediterranean Sea)

Phage therapy is among recent innovative technology to improve wastewater quality. Previous phage studies have focused on the interactions of phages with bacterial host cells or the impact of environmental conditions on phage-host cell dynamics. In this research, we particularly examined the impact of phages on a marine physicochemical and microbiological environmental characteristic. Following three days of incubation, seawaters receiving separately phage fBC-Eco01 (OM272052) and phage PA25, undergone a temperature increase of 1.7 °C and 2.5 °C, respectively. Seawater salinity values saved an increase in conductivity over time that ranged between 51.03 and 53.94 µS and from 51.04 to 53.7 μS for the phage PA25 and the phage fBC-Eco01, respectively. A significant decrease in dissolved oxygen levels of 2,1 mg/L were reported following the addition of both phages PA25 and fBC-Eco01 during three days of incubation, compared to a decrease of 1 mg/L in the control seawaters. The TOC increased from 0.33 ppm to 0.67 ppm in the presence of the PA25 phage and from 0.2 ppm to 1.51 ppm after the addition of the fBC-Eco01 phage, compared to control that saved values decreasing from 0.35 ppm to 0.05 ppm. The absorbance and fluorescence spectrophotometry values were also affected by phages addition. Moreover, phages addition reduced total aerobic mesophilic bacteria (TAMB) and Total aerobic thermophilic bacteria (TATB) abundance, corresponding to a decrease of 2 Ulog and 1 Ulog discharge, respectively following addition of PA25 and 3 Ulog and 2 Ulog discharge, respectively with addition of fBC-Ec01 phage.

Correction to: Importance of Copepods in the Diet of Sardina pilchardus and Sardinella aurita : Preliminary Investigation in Bou Ismail Bay (Algerian Basin - SW Mediterranean Sea

Correction to: Importance of Copepods in the Diet of Sardina pilchardus and Sardinella aurita : Preliminary Investigation in Bou Ismail Bay (Algerian Basin - SW Mediterranean Sea

Importance of Copepods in the Diet of Sardina pilchardus and Sardinella aurita: Preliminary Investigation in Bou Ismail Bay (Algerian Basin - SW Mediterranean Sea)

Importance of Copepods in the Diet of Sardina pilchardus and Sardinella aurita: Preliminary Investigation in Bou Ismail Bay (Algerian Basin - SW Mediterranean Sea)

Distribution and species composition of planktonic cnidarians in the Algerian coastal waters (SW Mediterranean Sea)

This study presents an inventory of planktonic cnidarian species collected in Algerian coastal waters (1°10’00” W - 6°52’37” E and 35°37’42” N - 37°01’16” N) from May 2012 to February 2017. The aim was to analyse the qualitative distribution and identify the main components of this gelatinous fauna in different coastal ecosystems in western, central and eastern regions. A total of 60 taxa of planktonic cnidarians were identified, including 57 hydrozoans and three scyphozoans. The class Hydrozoa were represented by 34 hydromedusae, primarily belonging to orders Anthoathecata (15 taxa) and Siphonophorae (23 taxa). Several reported hydrozoan species were recorded for the first time in the southwestern Mediterranean Sea. These new regional records include the hydromedusae Kantiella enigmatica, Leuckartiara octona, Proboscidactylaornata, Cunina globosa, Lovenella cirrata, Cirrholovenia tetranema, Phialella quadrata, Homoeonema platygonon and the siphonophore Forskalia contorta. Seasonal fluctuations were observed in biodiversity, with the highest species richness in spring and summer. The most common species are the calycophorous siphonophores Abylopsis tetragona, Muggiaea atlantica, Lensia subtilis Muggiaea kochii and the holoplanktonic medusae Aglaura hemistoma, Rhopalonema velatum, Solmundella bitentaculata, Liriope tetraphylla and Pelagia noctiluca. The species’ occurrence frequency exhibited seasonal and spatial variability. These distribution patterns were primarily determined by meroplanktonic hydrozoans (Anthoathecata and Leptothecata).

Assessment of short-term spatio-temporal variability in the structure of mesozooplankton communities integrating microscopy and multigene high-throughput sequencing

Variability in composition and structure of the mesozooplankton communities in the Bay of Malaga (SW Mediterranean) were characterized during a 26 h cycle using an integrative taxonomic approach. We combined microscopic identification of organisms, with metabarcoding for the genes of the mitochondrial DNA COI and the V9 hypervariable region of the ribosomal RNA 18S. Richness and diversity obtained by microscopy were higher than those measured with COI, as COI did not detect some phyla. COI however allowed for the identification to species level of several taxa that were left at higher taxonomic rank under the microscope. 18S detected a wider range of taxa than COI and microscopy, although with lower taxonomic resolution. Differences between coastal-night and shelf-day zooplankton communities structure were detected by both microscopy and metabarcoding. The combination of these two approaches increased the known copepod species in the SW Mediterranean Sea by 9%. An integrative approach combining morphology and COI metabarcoding is proposed to further facilitate mesozooplankton biodiversity studies.

Particle fluxes in submarine canyons along a sediment-starved continental margin and in the adjacent open slope and basin in the SW Mediterranean Sea

Investigating the transfer of particulate matter from the continental shelf to the deep basin is critical to understand the functioning of deep sea ecosystems. In this paper we present novel results on the temporal variability of particle fluxes to the deep in three physiographic domains of a 240 km long margin segment and nearby basin off Murcia and Almeria provinces in the SW Mediterranean Sea, which are submarine canyons forming a rather diverse set (namely Escombreras, Garrucha-Almanzora and Almeria), the adjacent open slope and the deep basin.This margin is located off one of the driest regions in Europe and, therefore, its study may help understanding how mainland aridity translates into the export of particles to deep margin environments. Five mooring lines equipped with currentmeters, turbidity-meters and sediment traps were deployed for one entire annual cycle, from March 2015 to March 2016. We combine oceanographic, hydrological and meteorological data with grain size and bulk elemental data (organic carbon, opal, CaCO3, lithogenic) from the collected sinking particles to understand what drives particle transfers in such an under-studied setting, and to quantify the resulting fluxes and assess their spatio-temporal variability.Weighted total mass fluxes in canyons range from 1.64 g m−2 d−1 in Almeria Canyon to 7.33 g m−2 d−1 in Garrucha-Almanzora Canyon system, which are rather low values compared to other submarine canyons in the Western Mediterranean Sea. This results from the absence of extreme wind-storm events during the investigated time period combined with the reduced sediment input to the inner shelf by river systems in the study area. Our results also show that wind-storms are the main trigger for off-shelf particle transport to the deep margin, both within submarine canyons and over the open slope. The most significant transfer period is associated to a set of north-eastern storms in early spring 2015, when the off-shelf transport likely was promoted by storm-induced downwelling. However, the prevailing oceanographic conditions restricts the advection of water down the canyon heads to a few hundred meters, thus promoting a bottom-detached transport of particles seaward. Overall physiography, canyon head incision into the continental shelf and the distance of the canyon head to the shoreline (e.g. very short in Garrucha Canyon) play a key role in particle trapping capability and, therefore, in easing downslope particle transport. Further, bottom trawling activities around the Garrucha-Almanzora Canyon system, feed a nepheloid layer at depths in excess of 400 m, subsequently enhancing particle fluxes throughout the study period. In contrast, maximum particle fluxes in the deep basin respond to seasonal phytoplankton blooms.Our study shows that particle export from the shallow inner margin to the deep outer margin in sediment-starved settings, even if limited, does occur as dominated by atmosphere and ocean driven short-lived events. However, that export does not reach too far as at several tens of kilometres from the shelf edge advective fluxes are replaced by vertical ones impelled by phytoplankton dynamics.

Isopod assemblages in the Bizerte lagoon (SW Mediterranean Sea): composition, structure and environmental relationships

The spatial and temporal distribution, abundance, and structure of isopod assemblages in Bizerte Lagoon (SW Mediterranean Sea) were studied at 22 stations selected from seagrass and macroalgae sampled during four seasons in 2017. A total of 6808 individuals and 17 species of isopods belonging to 5 suborders, 7 families and 12 genera were identified. Six new species were recorded on Tunisian coasts. In addition, and compared to previous studies, nine isopod species were collected for the first time in this lagoon. Analysis of the trophic structure revealed that most stations are strongly dominated by herbivore-deposit feeders (78.3%), followed by deposit-suspension feeders (13.6%) and carnivores (8.01%). Three isopod assemblages were identified (G1, G2 and G3). The distribution of isopod assemblages is influenced by the nature and structure of the substrates. The seasonal variations in the isopod community patterns at 22 stations showed maximum abundance and diversity during spring, whereas the lowest ones were recorded during winter.

Exceptionally high but still growing predatory reef fish biomass after 23 years of protection in a Marine Protected Area.

Marine Protected Areas (MPAs) help replenish fish assemblages, though different trophic levels may show diverse recovery patterns. Long-term protection is required to achieve total recovery but poaching events may prevent the achievement of full carrying capacity. Here, we have analysed the effect of long-term protection on the entire reef fish community and the different trophic levels in the Cabo de Palos-Islas Hormigas MPA (SE Spain; SW Mediterranean Sea) in order to assess their recovery patterns after 23 years of protection. We compared the values for carrying capacity obtained with the maximum values achieved at regional scale, and we assessed the effect of a reduction in the surveillance over a few years, during which poaching events increased, on the recovery patterns. We found that, overall, biomass of fishes increased with time while density diminished. In particular, piscivorous and macro-invertivore fish increased while the other trophic groups remained constant or declined, suggesting top-down processes. For the entire study period, those trophic groups were approaching carrying capacity; however, when accounting only for the period in which enforcement was high and constant, they grew exponentially, indicating that full carrying capacity may have not been achieved yet. When compared to other Mediterranean MPAs, the Cabo de Palos-Islas Hormigas MPA showed values for biomass that were disproportionately higher, suggesting that local factors, such as habitat structure and associated oceanographic processes, may be responsible for the dynamics found. Our results help to understand the potential trajectories of fish assemblages over a consolidated MPA and highlight empirically how the reduction of surveillance in a period may change the recovery patterns.

Metazoan Parasites Infecting Xiphias gladius from the Eastern Coast of Algeria (SW Mediterranean Sea)

Five specimens of Xiphias gladius Linnaeus, 1758 were sampled from the eastern coast of Algeria and examined for their metazoan parasites. Pathological effects of the collected parasites were examined for the whole body of X. gladius. Four metazoan parasites species were collected: two monogeneans (Tristoma coccineum Cuvier, 1817; T. integrum Diesing, 1850), one copepod (Pennella instructa (Wilson, 1917)) and one parasitic nematode (Hysterothylacium aduncum (Rudolphi, 1802)). We report here for the first time a symbiotic species, Conchoderma virgatum Spengler, 1789 (Cirripedia) fixed on P. instructa. Collected monogenean and the copepod species are newly recorded for Algerian coast. Xiphias gladius is a new host for H. aduncum in the studied region. All examined specimens were infected (P = 100 %). The collected copepod parasite, P. instructa (P = 60 %) induces serious pathological effects to its host (necrosis and hemorrhage particularly). Histological sections showed that this copepod causes skin lesions, deteriorations on the dermal and muscle tissue.

Riverine and wet atmospheric nutrient inputs to the Southwestern Mediterranean region of North Africa

This study describes the first simultaneous long-term effort to examine the nutrient inputs to the southern Mediterranean Sea from rivers and wet atmospheric deposition. Extensive daily rainwater sampling (280 samples) from the Annaba region (SW Mediterranean Sea, Algeria) and from river discharges (144 samples) at two river outlets feeding the Annaba Bay, the Seybouse River (SR) and the Mafragh River (MR),were collected and analyzed for dissolved nutrients from 2012 until 2017. During the 6-year study period, the Annaba region experienced contrasted hydrological conditions varying from heavy rainfall events during winter that have triggered large river flooding in 2012 and 2015 to the severe drought of 2016, which have profoundly affected both the atmospheric and riverine freshwater and nutrient inputs. The annual freshwater volume delivered to Annaba Bay averaged approximately 1.7 km3, of which 51% was from MR, 33% from SR, and 16% from precipitation. Precipitation over the Annaba region was associated with unusually high levels of DIP and DSi, resulting in deposition rates (0.54 mmol Si m−2 yr−1and 6.22 mmol P m−2 yr−1, respectively) that are several times higher compared to the average values reported for the Mediterranean region. In contrast, both the DIN and DON deposition rates were relatively low (16.2 and 4.7 mmol N m−2 yr−1, respectively) compared to the values reported for the Mediterranean region. Interestingly, the levels of nitrogen compounds in rainwater were similar to those in the MR waters. For all nutrient species analyzed in this study, SR waters always contained higher nutrient levels compared to those in MR and rainwater. The majority of nutrient loading entering Annaba Bay was delivered through the riverine inputs, averaging 2744, 962 and 92 t yr−1 for DSi, DIN and DIP, respectively. The wet atmospheric deposition contributed only 2.5% of DSi, 10% of DIN and 7% of DIP total annual flux. The riverine stoichiometric N:P and Si:N ratios were imbalanced in most cases, averaging 28 and 0.84, respectively. The N:P and Si:N ratios in rainwater were more balanced, particularly during the dry season when Saharan airflow dominated the region and supplied more DIP and DSi.

Zooplankton abundance and community structure driven by tidal currents in a Mediterranean coastal lagoon (Boughrara, Tunisia, SW Mediterranean Sea)

Lagoons and coastal marine zones are very productive and useful ecosystems, but they are threatened by the effects of global change and anthropogenic pressures. These effects have a negative impact on the zooplankton, weakening its function of phytoplankton consumer, leading to uncontrolled proliferation of microalgae in case of eutrophication. In this study we test the hypothesis that tidal exchanges with the sea can counteract these deleterious effect, by renewing the zooplankton community and by enhancing its top-down control of phytoplankton through selective retention of zooplankton grazers. Our study focused on the southern region of the Gulf of Gabes and the Boughrara lagoon which presents the highest tidal range in the Mediterranean. During two field campaigns (October 2016 and April 2017) we have analyzed zooplankton descriptive (taxonomic composition, abundance; biomass) and functional (ingestion rate, grazing pressure) variables and environmental variables during time series at a fixed station during ebb-flood sequences and at 8 stations along a sea-lagoon transect and during different tidal amplitude periods. Multivariate analyses of both environmental parameters and zooplankton taxa showed the existence of three distinct zones along the sea-lagoon transect, but also the influence of tidal circulation and water mixing on the renewal of the zooplankton community up to the innermost zones of the lagoon. Time series gave clear patterns for the input/output of marine/lagoon species and show a net import for different taxa and for the total zooplankton abundance and biomass (mean flood/ebb ratio = 2.2 for the total abundance and 2.4 for the biomass), leading to differential retention of zooplankton in the lagoon and to an increase in the potential grazing pressure on phytoplankton (mean flood/ebb ratio = 2.8). We also estimated that the grazing pressure in the lagoon was twice higher during the periods of high tidal amplitudes (at or close to spring tide) compared to periods with low amplitude (neap tides), clearly showing that the retention of zooplankton significantly increases the grazing impact on phytoplankton. These results highlight the importance of the tidal forcing for maintaining the good status of the zooplankton structure and function in strongly anthropized coastal and lagoon ecosystems.

Shifts in the protist community associated with an anticyclonic gyre in the Alboran Sea (Mediterranean Sea).

The diversity of protists was researched in the Alboran Sea (SW Mediterranean Sea) by means of high-throughput sequencing technologies based on the amplification of the V9 region of 18S rRNA. Samples were collected at different depths in seven stations following an environmental gradient from a coastal upwelling zone to the core of an oligotrophic anticyclonic gyre (AG). Sampling was performed during summer, when the water column was stratified. The superphyla Alveolata, Stramenopila and Rhizaria accounted for 84% of the total operational taxonomic units (OTUs). The most diverse groups were Dinophyceae (21% of OTUs), Marine Alveolates-II (MALV-II; 20%), Ciliophora (9%) and MALV-I (6%). In terms of read abundance, the predominant groups were Dinophyceae (29%), Bacillariophyta (14%), MALV-II (11%) and Ciliophora (11%). Samples were clustered into three groups according to the sampling depth and position. The shallow community in coastal stations presented distinguishable patterns of diatoms and ciliates compared with AG stations. These results indicate that there was a strong horizontal coupling between phytoplankton and ciliate communities. Abundance of Radiolaria and Syndiniales increased with depth. Our analyses demonstrate that the stratification disruption produced by the AG caused shifts in the trophic ecology of the plankton assemblages inducing a transition from bottom-up to top-down control.

Density-driven habitat use differences across fishing zones by predator fishes (Serranidae) in south-western Mediterranean rocky reefs

The characterization of habitat use by predator species is crucial to understand its effect over fish distribution. We tested the hypothesis that fish density affects habitat use as well as influence on the relationships between top predators (groupers) and meso-predators (combers) by evaluating their distribution in and outside a marine reserve (MR) in SW Mediterranean Sea. All groupers showed significant higher densities inside MR. All species but Epinephelus costae (grouper) displayed a distinct microhabitat use between high- and low-density locations. When density is reduced, groupers occupied previously rejected microhabitats (shallow habitats) at MR, indicating the density-related distribution. Combers were negatively correlated and showed an opposite microhabitat-depth use demonstrating niche segregation. Groupers overlapped their spatial niche and were positively correlated probably due to food partitioning. We suggest the existence of cascading top-down effects on Serranus scriba (comber) population, at MR, reinforcing the importance of the protected areas for the recovery of top-predator populations and their key role on healthy ecosystem.

Inventory and new records of benthic amphipods from macrophytes and fine sand communities of the Bizerte lagoon (Tunisia, SW Mediterranean Sea)

Shallow water benthic communities from the Bizerte lagoon (northern Tunisia) were investigated at 33 stations sampled in April and July of 2016 and 2017. A total of 18 amphipod species were recorded among which two new species were recorded: one for Tunisian coasts (Jassa marmorata) and a second one for the Mediterranean Sea (Serejohyale spinidactylus). In addition, and compared to previous studies, nine amphipod species were collected for the first time in this lagoon. Amphipod assemblages were numerically dominated by the families Melitidae (28%), Caprellidae (14.5%) and Ampithoidae (11.7%). Three species: Cymadusa filosa, Dexamine spinosa and Elasmopus rapax were numerically dominant. According to their biogeography, most of the recorded amphipod species (11–18) showed an Atlantic–Mediterranean distribution, whereas four were cosmopolitan and three lessepsian Indo-Pacific migrants, but no species were Mediterranean endemic. Specimens of both Jassa marmorata and Serejohyale spinidactylus are illustrated and described.

Factors driving the seasonal dynamics of Pseudo-nitzschia species and domoic acid at mussel farming in the SW Mediterranean Sea

ABSTRACTThe seasonal variations in Pseudo-nitzschia species and domoic acid (DA) concentration were investigated, at three shellfish farms in SW coastal Mediterranean. In parallel, the toxicity of mussels was tested. Two distinct groups of species were enumerated according to morphology and size (Pseudo-nizschia delicatissima and P. seriata groups). DA was detected over a nine-week period from July to October 2012 in the Lagoon, with a maximum concentration recorded in July (12.71 ng DA L−1). DA was positively correlated with the presence of P. seriata-group and P. delicatissima-group and was mostly occurred during P limitation period in seawater. No DA was found in mussels that were collected during the period of DA absence in seawater. Our results suggest that temperature, salinity, inorganic and organic nutrients were significant for the seasonal dynamics of P. seriata and P. delicatissima groups, but that the P limitation was the most driving factor for DA production in these areas. The relative influence of environmental factors should be further studied to better understand the recent surfacing of massive blooms of toxigenic Pseudo-nitzschia in SW Mediterranean coast.

Harmful Fouling Communities on Fish Farms in the SW Mediterranean Sea: Composition, Growth and Reproductive Periods

Biological fouling organisms on fish cages represent a major issue and costly factor in marine finfish aquaculture. Cnidarians have been identified as one of the most problematical groups, contributing significantly to the occlusion and structural stress of the cage nets, but also dramatically affecting farmed species health in aquaculture facilities worldwide. Recently, significant relationships were established in different Spanish aquaculture facilities between hydrozoans and juvenile fish affected by gill injuries and mortality episodes. Community composition, growth rate and reproductive potential of biofouling were monitored on fish cages over two seasonal periods of fry cages farming, located in southern Spain (SW Alboran Sea), with a special focus on cnidarians. Biomass and community composition of biofouling changed with time and between studied periods, with a marked seasonality in colonization periods and taxonomic composition, particularly for the colonial hydrozoans. The hydroids Ectopleura larynx and Pennaria disticha were found at the highest densities. P. disticha was responsible for major biomass contribution to total hydroid biomass with the fastest growth rates. In addition, actinulae larvae of E. larynx were identified in zooplankton samples at high densities especially during periods of fry introduction in sea cages (when fish are highly vulnerable). These results corroborate evidence of the detrimental influence of fouling cnidarians in Mediterranean finfish aquaculture due to a direct harmful impact on fish health. Investigations on population dynamics, reproductive biology and envenomation potential of fouling hydrozoans should be regarded as key component of best monitoring practices to ensure good farmed fish welfare, maximization of aquaculture production and overall marine spatial planning.

Molecular identification of the diet of Sardina pilchardus larvae in the SW Mediterranean Sea

Molecular identification of the diet of Sardina pilchardus larvae in the SW Mediterranean Sea

Species composition and distribution of Medusae (Cnidaria: medusozoa) in the Algerian coast between 2°e and 7°e (SW Mediterranean Sea)

The composition and abundance distribution of the Medusae community of the Algerian coast (between 2°E to 7°E) were investigated during autumn 2014. Zooplankton sampling was performed in the upper layer (0-100 m) at 14 stations. Fourteen species related to Hydromedusae and Scyphomedusae were identified. The Hydromedusae populations were represented by Leptomedusae (5 species), Narcomedusae (3 species), Trachymedusae (3 species) and Anthomedusae (2 species). Some species such as Cirrholovenia tetranema and Cunina globosa were newly recorded at the sampling areas. The total abundance of Medusae was under 10 individuals.m-3. Maxima of concentrations (> 4 ind.m-3) were localized at the central coast between Bou Ismail (2.6° E) and Algiers (3.2° E) Bays. Here, the populations of Aglaura hemistoma and Liriope tetraphylla were dominant (≈ 40%). A quantitative variability was showed between two populations groups (Liriope tetraphylla) and (Pelagia noctiluca and Rhopalonema velatum) characterized respectively the central region and the eastern region. Their distributions were analyzed in relation to environmental parameters (temperature, salinity, and chlorophyll-a) and the interaction with Copepods prey.