The spatiotemporal variation in taxonomic indices and functional traits of the nematode fauna was investigated along two major environmental (salinity and organic matter enrichment) gradients in the Cabras Lagoon (Sardinia, Italy). We aimed to assess, for the first time in a transitional system of western Mediterranean Sea, how taxonomic and functional components of nematode assemblage respond to such environmental factors. The taxonomic structure was the most sensitive metric to document changes in the nematode assemblage, showing significant differences in relation to all the factors and their interactions. All the taxonomic and functional nematode features, except for the maturity index (MI), proved salinity and organic enrichment to be the primary drivers of nematode distribution. The lack of significant variation in the MI is quite interesting and can be interpreted because of the marked adaptation of nematodes to highly dynamic environmental conditions of brackish and confined habitats. Temperature mainly affected faunal composition, abundance, and diversity, due to its influence on fecundity and biological cycles on almost all species. Integrating the taxonomic and functional components of nematodes as “two-sides of the same coin”, the Shannon diversity index, the percentage of coloniser–persisters and the MI were used together to assess the Ecological Quality Status (EQS) of the study sites, which ranged from poor to bad. Nematodes proved to be good indicators of the environmental variations in the investigated lagoon ecosystem. Importantly, the joint use of taxonomic and functional approaches provided integrative knowledge of nematode response to environmental gradients. We conclude that combining nematode-based taxonomic and functional indicators represent a valuable tool to assess the environmental quality of lagoonal ecosystems and may provide complementary information to macrofauna.

The predator-prey relationship is generally size-specific in the pelagic food webs. Phytoplankton cell size structure can provide information on the successive levels of consumers and therefore on the energy that can flow towards the top consumers. This work focuses on phytoplankton cell size structure in a coastal lagoon (Cabras Lagoon, Italy) considered one of the most important for fishing productivity in the Mediterranean. The inter-annual and seasonal dynamics of picophytoplankton (Pico, cell size <3 μm) and Utermöhl Fraction of Phytoplankton (UFP, cell size >3 μm) were considered during almost three years in relation to the temporal dynamics of selected environmental variables and zooplankton. Small-sized cells with a mean linear cell size <10 μm and a mean cell volume <103 μm3 mainly represented UFP along the entire study period. This size class contributed the most to total phytoplankton biomass (up to 86%) and density (up to 99%) during the first part of the investigation period. A compositional change was detected: smaller species of Chlorophyceae, Bacillariophyceae, filamentous Cyanophyceae, and autotrophic nanoflagellates thrived in the second part of the study, replacing larger Mediophyceae that dominated UFP at the beginning. Picocyanobacteria rich in phycocyanin were the dominant taxa of Pico along the entire investigation period and this size class contributed the most to total phytoplankton biomass (up to 30%) and density (up to 96%) at the end of the study. The observed shift towards different and even smaller UFP and Pico in the second part of the study was most probably due to complex interactions between top-down and bottom-up effects. Indeed, an increased temperature, a decreased salinity and decreased concentrations of nutrients (mainly ammonium and orthophosphate), as well as an increased grazing pressure of rotifers on the larger Mediophyceae were simultaneous with the changes detected in phytoplankton. The obtained results highlight a longer planktonic trophic web in Cabras Lagoon that includes small phytoplankton at the base, ciliates, rotifers, and copepods. This suggests low energy availability for planktivorous fish, with possible future relevant consequences for fishing activities in this coastal lagoon.

Joint use of biological traits, diversity and biotic indices to assess the ecological quality status of a Mediterranean transitional system

Joint analysis of macrofaunal and meiofaunal assemblages improves the assessment of lagoonal environmental heterogeneity

fshr: a fish sex-determining locus shows variable incomplete penetrance across flathead grey mullet populations.

Coastal lagoons are extremely sensitive to increasing temperature, especially in the Mediterranean basin, which has been identified as a hotspot for global warming. The warming effects on the abundance and size structure of a Mediterranean coastal lagoon plankton community were investigated in this study. Water from Cabras Lagoon (Italy) was incubated in laboratory for 16 days in winter, excluding mesozooplankton. Three temperature treatments were applied: (i) the in situ winter mean water temperature; (ii) + 3 °C, as forecasted for the Mediterranean region by the next century; (iii) + 6 °C, as forecasted for the Mediterranean region by the next two centuries. A direct and positive effect of warming on ciliate density was observed in absence of their predators, as well as a taxonomic composition shift from Oligotrichs to Scuticociliatida. In turn, a decrease in heterotrophic nanoflagellate density was detected under warming. Phytoplankton (autotrophic cell size > 2 µm) density increased significantly, while their mean cell size decreased strongly throughout the experiment at the highest temperature. A significant change in phytoplankton class composition, consisting of the increase of smaller Chlorophyceae which replaced larger Bacillariophyceae, was observed under heating. Considering picoplankton (cell size < 2 µm), a decrease in larger autotrophic cell density was contemporary to an increase in smaller heterotrophic cell density, especially at the highest temperature. This work adds novel information to the predictions about plankton community responses on warming considering several trophic levels, which has been little studied in shallow coastal lagoons and in the Mediterranean basin.

The spatiotemporal variation in meiofaunal assemblages were investigated for the first time in the Cabras Lagoon, the largest transitional system in the Sardinian Island (W-Mediterranean Sea). Two main environmental (salinity and trophic) gradients highlighted a significant separation of the three study sites across the lagoon, which were consistent through time. The environmental variability and habitat heterogeneity of the Cabras Lagoon influenced the meiofauna. In particular, salinity and dissolved oxygen, primarily, shaped the meiofaunal assemblage structure at the seaward site which was significantly different from both the riverine and the organically enriched sites. On the other hand, the trophic components (e.g., organic matter, Chlorophyll-a, and phaeopigments) and the different degrees of confinement and saprobity among sites were the secondary factors contributing mostly to the separation between the latter two sites. The lack of significant differences in the temporal comparison of the meiofaunal assemblage structure along with the very low contribution of temperature to the meiofaunal ordination indicated that this assemblage was more affected by spatial rather than by temporal variation. This pattern was also supported by significant differences between the three sites in several univariate measures, including total number of individuals, number of taxa, Pielou’s evenness, and the ratio between nematodes and copepods. Thus, the present study corroborates the hypothesis that meiofaunal organisms are good indicators of the spatial heterogeneity in transitional waters (TWs) and could have a greater species richness than that expected. Indeed, the Cabras Lagoon overall showed one of the highest meiofaunal richness values found from both Mediterranean and European TWs.

Dissolved organic matter dynamics in Mediterranean lagoons: The relationship between DOC and CDOM

Trophic levels (TLs) of fish were estimated on three sampling dates (March, May, and August 2006) for different fish sizes in the Cabras Lagoon (Sardinia, Italy). A temporal TL variation for Atherina boyeri, Gobius niger, and Engraulis encrasicolus was observed. In March and May, the TL ranged from 3.3 to 3.4, characterizing these species as secondary consumers, while in August, this range moved to between 3.7 and 3.8, indicating a TL shift towards tertiary consumers. For Liza ramada, TL was consistently lower in small individuals (mean TL 2.5) than in larger individuals (mean TL 3.0). Increased TL of the fish species A. boyeri, G. niger, and E. encrasicolus in August was consistent with the seasonal changes in the macrobenthic assemblage in this system, with a dominance of primary consumers (benthic deposit feeders) in winter–spring and a dominance of secondary consumers (the nereidids Alitta succinea and Hediste diversicolor) in summer. These fish species took advantage of the high availability of nereidids leading to a rise in their TL values. Furthermore, the increase of TL with size of L. ramada, the most economically valuable fish species in the Cabras Lagoon, indicated an ontogenetic diet shift, the juveniles being omnivorous, while the adults being secondary consumers. We conclude that variability in the trophic levels of fish due to species traits, ontogenetic diet shifts, and variation in prey availability should be taken into account to further understand the food web structure of coastal lagoons.

ABSTRACTIn this paper the problem of the optimisation of at-sea campaigns is tackled throughout the implementation of a near real-time decision support system (DSS) for short-term Lagrangian observing platforms. The DSS consisted of two modules: a real-time coastal-ocean forecasting system (CFS), including both hydrodynamic and particle-tracking numerical models, and a module to provide optimised deployment solutions for a set of Lagrangian current-meter buoys. The system was calibrated for a shallow water environment – the Cabras Lagoon in the western Mediterranean Sea. The DSS was then applied to provide in situ optimised measurement strategies during a Lagrangian survey campaign. The different solutions provided by the DSS were verified by real-time measurements and the system was established to be efficient in reducing the cost–benefit ratio and favouring long records and near-synoptic and non-redundant observations.

Estimates of bed roughness used for predictions of sediment transport are usually derived either from simple scalars of the physical roughness (i.e., ripple height or grain size) or from the hydrodynamic roughness length (Zo) based upon velocity gradient estimates in the benthic boundary layer. Neither parameter accounts for irregular bed features. This study re-evaluates the relation between hydrodynamic roughness and physical bed roughness using high-resolution seabed scanning in the inlet of a shallow lagoon. The statistically-robust relationship, based on a 1D statistical analysis of the seabed elevation at different locations of the Cabras lagoon. Sardinia, has been obtained between Zo and the topographical bed roughness Ks by defining Ks = 2*STD + skin friction, with STD the standard deviation of the seabed elevation variations. This correlation between Ks and Zo demonstrates that the roughness length is directly influenced by irregular bed features, and that the Reynolds number accounts for the total drag of the bed: the data points collapse on the Law of the Wall curves with a fitting factor x = 0.5. Further testing must be done in other locations and in the fully-rough domain in order to test how widely those new parameters can be applied.

Testing the saprobity hypothesis in a Mediterranean lagoon: Effects of confinement and organic enrichment on benthic communities

A comparison study between 10 Mediterranean lagoons has been carried out by means of the 3-D numerical model SHYFEM. The investigated basins are the Venice and Marano-Grado lagoons in the Northern Adriatic Sea, the Lesina and Varano lagoons in the Southern Adriatic Sea, the Taranto basin in the Ionian Sea, the Cabras Lagoon in Sardinia, the Ganzirri and Faro lagoons in Sicily, the Mar Menor in Spain, and the Nador Lagoon in Morocco. This study has been focused on hydrodynamics in terms of exchange rates, transport time scale, and mixing. Water exchange depends mainly on the inlet shape and tidal range, but also on the wind regimes in the case of multi-inlet lagoons. Water renewal time, which is mostly determined by the exchange rate, is a powerful concept that allows lagoons to be characterized with a time scale. In the case of the studied lagoons, the renewal time ranged from few days in the Marano-Grado Lagoon up to 1 year in the case of the Mar Menor. The analysis of the renewal time frequency distribution allows identifying subbasins. The numerical study proved to be a useful tool for the intercomparison and classification of the lagoons. These environments range from a leaky type to a choked type of lagoons and give a representative picture of the lagoons situated around the Mediterranean basin. Mixing efficiency turns out to be a function of the morphological complexity, but also of the forcings acting on the system.

The present study identified and quantified dinoflagellate cysts in surface sediments from three Mediterranean lagoons. Sediment samples were recovered from 11 stations in May 2009 at Cabras Lagoon, eight stations in May 2010 at Corru S'Ittiri Lagoon, and five stations in May 2011 at Santa Giusta Lagoon. Fifty-three dinoflagellate cyst morphotypes were identified. Sixteen species are first reports for the lagoons, and two for the Mediterranean Sea. Moreover, a new Scrippsiella species was discovered in Cabras. Seven harmful algal species were identified, primarily belonging to the potentially toxic genus Alexandrium. Total cyst abundance, number of morphotypes, and assemblages varied among lagoons, and each lagoon showed a distinct morphotype composition. A degree of heterogeneity was also detected within lagoon. Cabras and Santa Giusta cyst assemblages were characterised by morphotypes belonging to the autotrophic genus Scrippsiella, whereas Corru S'Ittiri assemblages showed dominance of heterotrophic morphotypes, including Protoperidinium cf tricingulatum. Differentiation among lagoons was also evident according to environmental conditions. Salinity proved to be a fundamental variable in determining total cyst abundance, morphotype number, and composition. This study was among the first to examine dinoflagellate cyst composition in coastal lagoons, especially from the Mediterranean region, and contributed data that increased our knowledge of cyst-producing dinoflagellates in these environments.

1 - Water quality in four Sardinian lagoons (western Mediterranean Sea) was assessed using the Multimetric Phytoplankton Index (MPI), which is consistent with the EU Water Framework Directive. The index was developed using data on phytoplankton abundances, species structure and chlorophyll a concentrations in Venice Lagoon, Italy. 2 - The aim of this study was to test the MPI on a larger geographical scale and across a range of lagoon types. Therefore, it was applied to assess water quality in the Cabras, S’Ena Arrubia, Santa Giusta and Calich lagoons in Sardinia. These lagoons are all “choked”, but exhibit a range of sizes and morphometric features. They are directly affected by human activity within the lagoons themselves, such as fisheries, aquaculture and the construction of dams and canals, and are indirectly affected by anthropogenic activities in their catchments, including intensive agriculture, industrial activity and urban development. 3 - The data used in the present study were collected monthly over a period of 4 years (Calich, Santa Giusta and S’Ena Arrubia) to 7 years (Cabras). Samples were collected at three stations at each of the Cabras, Santa Giusta and Calich lagoons, and at two stations at the S’Ena Arrubia Lagoon, providing a total of 220 samples. 4 - The water quality in three of the four lagoons investigated (Cabras, S’Ena Arrubia and Calich) was classified as bad using the MPI. Among these three, water in Cabras Lagoon exhibited the worst condition. Water quality in Santa Giusta Lagoon was classified as poor using the MPI. 5 - Although we present preliminary results that require further verification, the index appears to be a useful tool for assessing the ecological status of typical Mediterranean lagoons.

1 - The work aims to study the feeding habits of Phalacrocorax carbo sinensis wintering in the Cabras and Mistras lagoons and to assess the impact of the cormorants colony on fish stocks. 2 - 438 bird flocks of Great Cormorant (Phalacrocorax carbo sinensis) wintering in the Cabras and Mistras lagoons (central-western Sardinia) (SPA ITB034008 and ITB034006 respectively) were analysed. 3 - Through the morphological analysis of undigested hard body parts, such as otoliths, it was possible to trace to the preyed species and their biomass and, then, to the average daily consumption of cormorants. 4 - The trophic spectrum was dominated almost exclusively by euryhaline, gregarious fish species. Mugilidae, and particularly Liza ramada with a percentage index of relative importance (%IRI) of 75.28 and L. saliens (%IRI = 17.78) were the most important preys, while Dicentrarchus labrax (%IRI = 3.53) was of secondary importance. Other species, as Diplodus vulgaris (%IRI = 0.06), Sparus aurata (%IRI = 0.01), Solea solea (%IRI = 0.04) and Anguilla anguilla (%IRI = 0.01), completed the diet. 5 - The Daily Food Intake (DFI) was estimated in 478.4 ± 18 g/day. The overall amount of biomass preyed by the cormorants during the entire wintering season was calculated in about 422 tons. Considering the Cabras lagoon area, it was possible to estimate an amount of fish taken equal to 189.4 Kg/ha during the same period.

In Mediterranean lagoons, macrophytes often surpass phytoplankton as the most important primary producers. Less frequently, phytoplankton dominates throughout the year, thus knowledge of its dynamics is relatively limited and scattered. In this study, we assessed over two years the dynamics of phytoplankton assemblages, including potential harmful algal species (HAS), in relation to environmental changes in the phytoplankton-dominated Cabras Lagoon (Sardinia, Italy). The lagoon was characterised by uniform spatial conditions, wide temporal variations in salinity (40 PSU) and high nutrient availability. Phosphorus was highest in summer, possibly recycled within the system, while dissolved inorganic nitrogen increased in winter and spring due to watershed discharge. Chlorophyll a, positively correlated with nutrients and rainfall, showed a typical bimodal pattern with summer-winter blooms. Modifications in phytoplankton composition strongly correlated with extreme weather events, such as intense rainfall. This generated an abrupt salinity decrease that, combined with high nutrient availability, favoured the dominance of Cyanophyceae of reduced cell size, such as Cyanobium and Rhabdoderma species. We suggest that the prolonged and intense dominance of Cyanophyceae, added to other HAS, has a negative impact on the primary economic activities of the lagoon, such as fishery, and generally on the whole lagoon functioning.

In Mediterranean lagoons, macrophytes often surpass phytoplankton as the most important primary producers. Less frequently, phytoplankton dominates throughout the year, thus knowledge of its dynamics is relatively limited and scattered. In this study, we assessed over two years the dynamics of phytoplankton assemblages, including potential harmful algal species (HAS), in relation to environmental changes in the phytoplankton-dominated Cabras Lagoon (Sardinia, Italy). The lagoon was characterised by uniform spatial conditions, wide temporal variations in salinity (40 PSU) and high nutrient availability. Phosphorus was highest in summer, possibly recycled within the system, while dissolved inorganic nitrogen increased in winter and spring due to watershed discharge. Chlorophyll a, positively correlated with nutrients and rainfall, showed a typical bimodal pattern with summer-winter blooms. Modifications in phytoplankton composition strongly correlated with extreme weather events, such as intense rainfall. This generated an abrupt salinity decrease that, combined with high nutrient availability, favoured the dominance of Cyanophyceae of reduced cell size, such as Cyanobium and Rhabdoderma species. We suggest that the prolonged and intense dominance of Cyanophyceae, added to other HAS, has a negative impact on the primary economic activities of the lagoon, such as fishery, and generally on the whole lagoon functioning.

Spatial variations in δ13C and δ15N values of primary consumers in a coastal lagoon

A metabolic scope based model of fish response to environmental changes