Descriptive Analysis and Classification of Benthic Communities in Some Mediterranean Coastal Lagoons (Central Italy)

Abstract. Benthic samples were taken seasonally at 32 stations in five coastal lagoons of Central Italy (Fogliano, Monaci, Caprolace, Fondi, and Lungo) during a two-year period (1982–1984). Composition and distribution of benthic populations in each lagoon as well as seasonal trends of species richness, density, diversity, and redundancy are presented and discussed.
The faunal differentiation appeared to be mainly due to the different degree of water exchange, both with marine and continental systems.     

Isostasy and paleotemperatures in the Southern Tyrrhenian Basin,Mediterranean Sea

The present-day basement depth of the seafloor in the absence of sediment loading was inferred along a traverse crossing the Southern Tyrrhenian Basin. A correction for sediment loading was proposed on the basis of density, seismic velocity and porosity data from selected deep boreholes. The empirical relation between sediment correction and seismic two-way travel time was extrapolated downward by applying the Nafe–Drake curve and a specific porosity–depth relation. The sediment loading response of the basement calculated for flexural isostasy is on average about one hundred meters lower than results for local isostasy. A pure lithosphere extensional model was then used to predict quantitatively the basement subsidence pattern on the margins of the basin. The basement depth is consistent with uniform extension model predictions only in some parts of the margins. The observed variability in the region of greatest thinning (transition from continental to oceanic crust) is attributable to the weakening effect caused by diffuse igneous intrusions. Subsidence of the volcanic Calabrian–Sicilian margin is partly accounted for by magmatic underplating. The comparison of the calculated subsidence with an oceanic lithosphere cooling model shows that subsidence is variable in some areas, particularly in the Marsili Basin. This argues for a typical back-arc origin for the Tyrrhenian Basin, as a result of subduction processes. By taking into account the geodynamic setting, stratigraphic data from the deepest hole and the terrestrial heat flow, we reconstructed the paleotemperatures of cover sediments. The results suggest that low temperatures generally have prevailed during sediment deposition and that the degree of maturation is expected not to be sufficient for oil generation processes.     

Distribution of soft-bottom polychaetes in two coastal areas of the Tyrrhenian Sea (Italy): Structural analysis

Multidimensional statistical analysis was used to study the polychaete distribution in soft-bottoms of two coastal areas of the Tyrrhenian Sea (Italy), which are influenced by the discharges of the rivers Tiber and Ombrone. In both areas the distributional patterns of these organisms are determined mainly by sediment types and related factors such as hydrodynamics, river input, and sedimentation. The grain-size gradient from the coast to the open sea affects not only species composition, but also species richness, diversity and abundance.In both areas three main communities have been identified: a sandy biocoenosis, a mixed-sediment biocoenosis and a muddy biocoenosis. The sandy coastal community is characterized by only a few species, while the intermediate zone of sandy-mud sediments presents the highest species richness and diversity. At the mouth of the River Tiber the influence of the river is more evident than at the mouth of the River Ombrone. This is due to the Tiber's greater river flow, which determines an environmental uniformity and a ‘cenotic continuum’ from sandy to muddy communities. This does not occur at the mouth of the Ombrone, where the river flow is less important and the polychaete communities are better defined.     

The Amphipod Community as a Bioindicator in Algeciras Bay (Southern Iberian Peninsula) Based on a Spatio-Temporal Distribution

Abstract. The amphipod population associated with Bugula neritina (L.), a verycommon bryozoan species in Algeciras Bay (Strait of Gibraltar), was studied on a spatio-temporal scale, in order to define its role as a bioindicator. Samples were collected in December, March, June and September along a transect running from the external to the internal sampling stations.
Fifty-three species belonging to 22 families were identified; the most abundant species were Jassa marmorata H olmes , Ischyrocerus inexpectatus (R uffo ) and Phtisica marina S labber .
The spatial evolution of the amphipod community reflected the physico-chemical conditions of Algeciras Bay, yielding a clear gradient from the outer to the inner stations. The stations located at the mouth of the bay, characterised by high hydrodynamism and low sedimentation, had a higher diversity and species richness than the inner stations with low water movement and higher sedimentation. Eight species preferred for the outer stations, while another nine species were typical of the inner harbours.
The most notable aspect of the seasonal evolution was the increased dominance of the tube-builder and deposit-suspension feeder Jassa marmorota .
Structural and ordination analyses corroborate the outer-inner gradient in the bay and illustrate the importance of hydrodynamic forces and sedimentation in the amphipod community.     

Summer larval fish assemblages in the Southern Tyrrhenian Sea (Western Mediterranean Sea)

The purpose of this paper was to study the community structure, in terms of species composition, abundance and spatial distribution, of fish larvae in a wide coastal area of Sicily facing the Southeastern Tyrrhenian Sea, extending for 2300 km² from Cape Cefalù to the west, to Cape Rasocolmo in the east. This study analyses how species are assembled in relation to an inshore–offshore gradient and also how environmental conditions, determined by surface circulation patterns occurring in the Central Mediterranean at the local scale, determine the distribution patterns. Samples from 39 stations were collected using a 60‐cm Bongo net during an ichthyoplanktonic survey carried out in June 2006. In all, 62 taxa, representing 32 families, were identified. Cyclothone braueri (59.6%), Engraulis encrasicolus (9.2%) Lampanyctus crocodilus (4.3%) and Lampanyctus pusillus (4.1%) were the most abundant species. The results showed that the highest abundance value (14830.6 fish larvae per 10 m² sea surface) was observed in the western part of the study area. MDS, SIMPER and CCA analyses revealed well defined groups of stations and assemblages of larvae in accordance with an inshore–offshore gradient. The results of this study could have implications for the management of marine resources because the investigated area has already been identified as a nursery area for many pelagic and coastal fishes and a natural habitat for many species of high commercial interest.     

The operational sex ratio of the sea urchin Paracentrotus lividus populations: the case of the Mediterranean marine protected area of Ustica Island (Tyrrhenian Sea, Italy)

We investigated, with a series of field and laboratory observations, the possible effect of the starfish Marthasteria glacialis predation on the operational sex ratio (OSR), i.e. the number of sexually mature males divided by the total number of sexually mature adults of both sexes at any one time, of the edible sea urchin Paracentrotus lividus . The OSR was estimated three times during the sea urchin summer spawning period (July 2004, June 2005 and July 2006) on barren substrates of Ustica Island Marine Protected Area (Southern Tyrrhenian Sea, Italy). Four sites were selected: two characterized by high M. glacialis density (take zone C) and two controls with low starfish density (no-take zone A). Mature sea urchins were independently collected by SCUBA diving and sexed. The adult sex ratio was skewed towards males at high M. glacialis density sites, whereas it was balanced (1:1) at predator low-density sites. Results of sex-selective feeding experiments in the laboratory showed that females of P. lividus were more vulnerable to M. glacialis predation. These outcomes underline the possible importance of M. glacialis in regulating the OSR of P. lividus populations.     

Composition and geochemistry of clay sediments offshore the northeastern Sicilian coast (Southeastern Tyrrhenian Sea,Italy)

Grain-size, mineralogical and chemical analyses were carried out on fine fraction of sediments collected in the Gulfs of Patti and Milazzo, two borderland basins in the Southern Tyrrhenian extending offshore the northeastern Sicilian coast.     

Fish Larvae Abundance and Distribution in the Coastal Zone off Terminos Lagoon, Campeche (Southern Gulf of Mexico)

Fish larvae abundance and distribution in the coastal zone off Terminos Lagoon and their relation to the environmental features of the Lagoon inlets were analysed (1986–87). The sampling grid consisted of 24 stations extending between 0·5 and 10 km off the Lagoon, including both Terminos Lagoon Inlets; El Carmen and Puerto Real. A total of 23 families and 43 species were identified. Highest larval abundance was registered during the rainy period (July and September) when the fluvial discharges favoured the planktonic development. The lowest larval abundance was recorded in the period of northern cold wind (January–March) when the fluvial discharges decreased. Bray-Curtis index defined two groups of stations, corresponding to each of the lagoon inlets, persisting throughout the year. The first one, ‘ El Carmen ’, was characterized by larvae of Engraulidae and Gobiidae; estuarine-dependent inhabitants. This group could be considered as a functional extension of the Lagoon to the sea. The second group, ‘ Puerto Real ’, was characterized by highest larval abundance of marine dwellers (e.g.Opisthonema oglinumandHarengula jaguana). This situation suggests that the Puerto Real Inlet could be the main entrance of marine fishes into the Lagoon. These results indicate that the coastal zone off Terminos Lagoon constitutes an important nursery area both for species spending part of their life cycle linked to this estuarine system, and for marine species that migrate towards the Lagoon, carried by local currents.     

Population Ecology of the Amphipod caprella equilibra Say in a Lagoon Estuary (Northern Adriatic Sea, Italy)

Abstract. The population ecology and dynamics of Cuprella equilibra were studied in a lagoon estuary of the Northern Adriatic Sea during 1985 to 1986. The breeding activity showed peaks in April and September and a decrease in summer due both to high temperatures and a dystrophic crisis; breeding stops in winter. Females produced more than one brood per year.     

Bionomy of the Amphipods in the Evros Delta (North Aegean Sea)

Abstract. The composition and distribution of the amphipod fauna in the area of Evros Delta (North Aegean Sea) have been investigated by means of quantitative sampling. On the basis of similarity in distribution among stations, 3 groups of species have been distinguished. The dependence of the distribution of these 3 groups, as well as of each species separately, on certain environmental factors is discussed.     

Disturbance and Community Pattern of Polychaetes Inhabiting Valle Magnavacca (Valli di Comacchio,Northern Adriatic Sea,Italy)

Abstract. Polychaete community structure in Valle Magnavacca, the largest basin of the Valli di Comacchio (Northern Adriatic Sea) lagoonal ecosystem, was analyzed in a three‐year study. Three shallow‐water stations were sampled at about 3‐month intervals. Univariate and multivariate analyses were utilized to investigate community structure changes in relation to natural and man‐induced disturbance. The polychaete community at station 3, in the central area of the lagoon, was the most disturbed, while that of station 2 was the most well structured. We hypothesize that polychaete community structure results from regular seasonal disturbances which lead to almost predictable fluctuations in species abundance. Superimposed on these regular cycles are acute disturbance events that further reduce species abundance or exclude species from the habitat.     

秦皇岛绿潮暴发区微观繁殖体的时空分布特征及影响因素

2015年至今,秦皇岛近岸海域连年发生绿潮灾害,造成严重社会影响和经济损失.微观繁殖体作为绿潮藻的种源,在绿潮的发生过程中起着十分重要的作用.为此,于2020年5月至9月对秦皇岛绿潮暴发较为严重的金梦海湾海域(119°32 ′54″～119°33′00″E,39°52′45″～39°53 ′30″N)进行采样调查,分析...     

Benthic mucilaginous aggregates in the Mediterranean Sea: Origin, chemical composition and polysaccharide characterization

Benthic mucilaginous aggregates are frequently formed in various parts of the Mediterranean basin, as in the Tyrrhenian and Adriatic Seas. Notwithstanding their wide spatial distribution, the role played by these aggregates in the biogeochemical cycling of organic matter is still largely unknown.The characteristics of the benthic aggregates examined in the present study showed that they are different from other mucilaginous aggregates, such as the “pelagic” ones that can form in the same areas in the water column and subsequently sediment to the seafloor. The aggregates are usually formed of structures of the filamentous macroalgae Acinetospora crinita, Chrysonephos lewisii and Nematochrysopsis marina. The elemental composition of the aggregates showed a marine macrophyte origin on the basis of the bulk organic matter content of the aggregates. Carbohydrates and proteins account for 26.6 to 55.9% of the organic carbon in the mucilage, respectively. Monosaccharide composition of exopolysaccharides in the mucilage aggregates revealed a characteristic pattern, with galactose, xylose or mannose and fucose as the major components. The relatively high content of deoxysugars is another distinctive feature. The abundant sulphate and uronic groups present in the polysaccharides in addition to their macromolecular dimensions and elongation contribute to inter-chain aggregation. Electron microscopic observations suggest that the polysaccharide fraction is the main macromolecular component in the formation of the persistent gel network in the aggregates.     

Relict sand dredging for beach nourishment in the central Tyrrhenian Sea (Italy): effects on benthic assemblages

The aim of this study is to analyse the effects in space and time of relict sand-dredging activities on macrobenthic assemblages, in an area situated offshore Montalto di Castro (central Tyrrhenian Sea, Italy), and to analyse the recolonisation processes of macrobenthos in the dredged areas. The area in question is characterised by relict sand deposits (Holocenic paleo-beaches), used for beach nourishment along the Latium coast. The effects of sand extraction on benthic assemblages were investigated before, during and after three dredging operations. The sites analysed are located within the dredged areas (inside stations) and in neighbouring, not dredged, areas (outside stations). The results showed that the impact of sand extraction was confined to the dredged stations and to the areas in proximity to the dredged areas. During dredging activities, the structure of benthic assemblages within the impacted stations was characterised by low species richness and diversity. Both the direct removal of sediment and the re-suspension and consequent deposition of fine sediment affected benthic assemblages of the impacted stations. A few months after the dredgings, a recolonisation process was still observed at all the impacted stations. A gradual recolonisation process was observed at those stations affected by only one dredging, whereas a different recolonisation was observed at those stations affected by two dredgings over time. This study suggests that differences of re-colonisation processes of benthic assemblages are related to the intensity of dredging operations in terms of dredging frequency.     

Temporal Variations of Nutrients, ­Chlorophyll a and Particulate Matter in Three Coastal Lagoons of Amvrakikos Gulf (Ionian Sea, Greece)

Abstract. The temporal variations of nutrients, chlorophyll a (chl a ), suspended particulate matter (SPM) and particulate organic carbon (POC) were measured over 12 months in three shallow coastal brackish water lagoons of the Amvrakikos Gulf, Ionian Sea. Two of the lagoons, Tsoukalio and Rodia, are interconnected but separated from Logarou by a narrow strip of land. Logarou has a better water exchange with the sea as indicated by the higher salinity and dissolved oxygen concentrations and the smaller variation of the above-mentioned parameters. Nitrate concentrations were largely the same in the three lagoons and higher than in the Amvrakikos Gulf. Phosphate concentrations in Logarou exceeded by far those of Tsoukalio/Rodia; the increased phosphate levels recorded in January caused an extended phytoplankton bloom with chl a concentrations higher than in the other two lagoons. Chl a in Tsoukalio was positively correlated with nitrate whereas in the most shallow lagoon, Logarou, it showed a positive correlation with light winds (force 4 and lower), probably caused by resuspension from the sediment. Increased phytoplankton biomass in Logarou coupled with the better water exchange may be related to the higher fish production in this lagoon.     

Temperature Effects on Photosynthesis and Depth Distribution of the Seagrass Cymodocea nodosa (ucria) Ascherson in a Mediterranean Coastal Lagoon: the Mar Menor (SE Spain)

Abstract. Seasonal variation of temperature effects on photosynthesis and respiration of Cymodorea nodosa (Ucria) Ascherson was investigated in a 1 m depth meadow in the Mar Menor lagoon (SE Spain). Light-saturated net photosynthesis (P_max)and dark respiration (R) rates were linearly correlated with water temperature between 10 and 30°C. and 10 and 35°C, respectively, during the year. Water temperature had a similar effect on R rates in August, November, and February, but increased P_max rates in August vs. those in February, thus promoting a shift of the maximum P_max/R ratio values from 15°C in February to 30°C in August. P-I curves had higher P_max values in May and August than in November or February, while Ic values remained relatively constant throughout the year. Whole-plant carbon balances suggested that C. nodosa might not be able to survive in the central basin of the lagoon and that the spatial distribution of this seagrass in the Mar Menor might be controlled by light availability.     

Ecological Differences in the Distribution of two Tethya (Porifera, Demospongiae) Species Coexisting in a Mediterranean Coastal Lagoon

Abstract. In the Sicilian lagoon Stagnone di Marsala, Tethya aurantium and T. citrina show different ecological distributions, although some overlapping occurs. The first species reaches its highest density where linear currents are maximal, and in this habitat it is particularly frequent on Posidonia oceanica rhizomes. The second species is more abundant in still water locations and is equally common on Posidonia rhizomes and on calcareous concretions. Such distributions can be related to water movement, Posidonia shoot density, and associated factors such as sedimentation and food availability. These observations are consistent with an adaptive interpretation of the morphofunctional features distinguishing the two species.