'End to end' planktonic trophic web and its implications for the mussel farms in the Mar Piccolo of Taranto (Ionian Sea, Italy)

Effects of bivalve aquaculture on plankton and benthic community

Global human population has increased dramatically over the past 50 years. As a result, marine fisheries and finfish aquaculture have become increasingly unsustainable, driving bivalve aquaculture to become an important food industry for the production of marine animal protein to support the growing market demand for animal protein. It is projected that the rate of bivalve aquaculture expansion will be greatly accelerated in the near future as the human population continues to increase. Although it is generally believed that unfed bivalve aquaculture has less impact on the environment than finfish aquaculture, the rapid expansion of bivalve aquaculture has raised concerns about its potential negative impact, especially on plankton and benthic community. Therefore, there is an urgent need to update the potential effects of bivalve aquaculture on plankton and benthic community. This article reviews the present state of knowledge on environmental issues related to bivalve aquaculture, and discusses potential mitigation measures for the environmental impacts induced by expansion of bivalve aquaculture. This review provides guidance for scientists and farm managers to clarify the current state of research and identify priority research needs for future bivalve aquaculture research. Therefore, specific management strategies can be formulated for the sustainable development and expansion of bivalve aquaculture.

Sexual dimorphism in the gonad lipidome of blue mussels (Mytilus sp.): New insights from a global lipidomics approach

Blue mussels (Mytilus sp.) are an economically important species for European aquaculture. Their importance as a food source is expected to increase in the coming net-zero society due to their low environmental footprint; however, their production is affected by anthropogenic stressors and climate change. During reproduction, lipids are key molecules for mussels as they are the main source of energy on which newly hatched embryos depend in the first days of their development. In this work, blue mussels of different origins are analysed, focusing on the differences in lipid composition between the ovary (BMO) and the testis (BMT). The lipidome of blue mussel gonads (BMG) is studied here by combining traditional lipid profiling methods, such as fatty acid and lipid class analysis, with untargeted liquid chromatography-mass spectrometry (LC-MS) lipidomics. The approach used here enabled the identification of 770 lipid molecules from 23 different lipid classes in BMG. BMT, which consists of billions of spermatocytes, had greater amounts of cell membrane and membrane lipid components such as FA18:0, C20 polyunsaturated fatty acids (PUFA), free sterols (ST), ceramide phosphoethanolamines (CerPE), ceramide aminoethylphosphonates (CAEP), cardiolipins (CL), glycerophosphocholines (PC), glycerophosphoethanolamines (PE) and glycerophosphoserines (PS). In BMO, saturated fatty acids (FA14:0 and FA16:0), monounsaturated fatty acids (MUFA) and other storage components such as C18-PUFA accumulated in triradylglycerolipids (TG) and alkyldiacylglycerols (neutral plasmalogens, TG O-), which, together with terpenes, wax esters and cholesterol esters, make up most of oocytes yolk reserves. BMO also had higher levels of ceramides (Cer) and generally alkyl/alkenyl glycerophospholipids (mainly plasmanyl/plasmenyl PC), suggesting a role for these lipids in vitellogenesis. Non-methylene interrupted dienoic fatty acids (NMID FA), typically found in plasmalogens, were the only membrane-forming PUFA predominantly detected in BMO. The results of this study are of great importance for clarifying the lipid composition of BMG and provide an important basis for future studies on the reproductive physiology of these organisms.

Phytoplankton and Bacterial Communities’ Patterns in a Highly Dynamic Ecosystem (Central Mediterranean Sea)

The Straits of Messina (Southern Italy, Mediterranean Sea) are a very complex area: they connect two basins (Tyrrhenian and Ionian) with different hydrographic features and is characterised by upwelling and mixing phenomena. The aim of the study was to evaluate if and how the physical and chemical water conditions and hydrodynamics influenced the phytoplankton and bacterial patterns and the functioning of this ecosystem. During a late winter survey, size-fractionated phytoplankton (from 0.2 to 200 μm) biomass (chlorophyll a), cell densities and species composition as well as total picoplankton abundances, morphotype composition, and activity levels of the enzymes leucine aminopeptidase, β-glucosidase, and alkaline phosphatase were investigated. The obtained results showed a marked diversification among the water masses identified within the Straits area. The analyses of the phytoplankton diversity indices, particularly those based on phylogenetic relationships between species (indices of taxonomic diversity and distinctness), confirmed our findings. In conclusion, the patterns of phytoplankton and bacterial communities provide a suitable approach to evaluate how microbial communities respond to changing environmental scenarios. This tool could be applied to other temperate Mediterranean ecosystems.

New Insights on Phytoplankton Communities as a Tool for the Sustainable Management of the Musselculture in a Mediterranean Coastal Site

A simulation of phytoplankton dynamics in the coastal shellfish farming site of Mar Piccolo in Taranto (Ionian, Mediterranean Sea) is here reported. This simulation is an element of a greater ecological model produced taking into account the System Approach Framework. The model represents a refinement of a previous phytoplankton tool aimed to better understand the complex mosaic of the ecosystem functioning by providing additional information to support mussel farming. In particular, throughout the years the increase of water temperature and intensive musselculture caused a phytoplankton size and biomass reduction. Results of our simulation evidenced that the phytoplankton tool reproduced the size-fractions (micro-, nano- and picophytoplankton) biomass growth and the mussel (Mytilus galloprovincialis) grazing with a good level of performance. This newly calibrated phytoplankton model aims to provide new insights on modelling scenarios for the sustainable production of mussels.

Bioactive Potential of Two Marine Picocyanobacteria Belonging to Cyanobium and Synechococcus Genera

Coccoid cyanobacteria produce a great variety of secondary metabolites, which may have useful properties, such as antibacterial, antiviral, anticoagulant or anticancer activities. These cyanobacterial metabolites have high ecological significance, and they could be considered responsible for the widespread occurrence of these microorganisms. Considering the great benefit derived from the identification of competent cyanobacteria for the extraction of bioactive compounds, two strains of picocyanobacteria (coccoid cyanobacteria < 3 µm) (Cyanobium sp. ITAC108 and Synechococcus sp. ITAC107) isolated from the Mediterranean sponge Petrosia ficiformis were analyzed. The biological effects of organic and aqueous extracts from these picocyanobacteria toward the nauplii of Artemia salina, sea urchin embryos and human cancer lines (HeLa cells) were evaluated. Methanolic and aqueous extracts from the two strains strongly inhibited larval development; on the contrary, in ethyl acetate and hexane extracts, the percentage of anomalous embryos was low. Moreover, all the extracts of the two strains inhibited HeLa cell proliferation, but methanol extracts exerted the highest activity. Gas chromatography–mass spectrometry analysis evidenced for the first time the presence of β-N-methylamino-l-alanine and microcystin in these picocyanobacteria. The strong cytotoxic activity observed for aqueous and methanolic extracts of these two cyanobacteria laid the foundation for the production of bioactive compounds of pharmacological interest.

Linking Microbial Functioning and Trophic Pathways to Ecological Status in a Coastal Mediterranean Ecosystem

Coastal marine ecosystems host complex microbial communities whose composition and metabolism are influenced by continental inputs and mesoscale properties of seawater masses. The identifying traits of the phytoplankton and bacteria such as biomass, size, shape and their metabolism related to organic matter production and degradation, recognized as indicators of the functioning of an ecosystem, were observed in the Gulf of Manfredonia (South Adriatic Sea, Italy) in late spring. This Gulf area is characterized by terrestrial inputs and mesoscale circulation influence such as coastal waters flowing southward from the North Adriatic and offshore waters interested by the Ionian Sea. Water samples were grouped in clusters (Coastal, Intermediate, Offshore and Deep Systems) according to the water column properties. Phytoplankton community biomass and composition, autotrophic and total prokaryotic abundances and microbial metabolism such as enzyme activity rates and prokaryotic heterotrophic production were analyzed to elucidate the trophic pathways with the objective to infer on the ecosystem status. As expected, size-fractionated phytoplankton biomass and production showed greater concentration in coastal waters with prevalence of the largest fractions (micro- and nano-) supported by the diatoms. Conversely, lower biomass and production were measured in all off-shore waters, mainly sustained by smallest fractions (nano-sized phytoflagellates and picophytoplankton). Total and autotrophic prokaryotic abundance decreased from coastal to offshore stations, inversely with respect to cell volume. Prokaryotic heterotrophic production was just below 50% compared to that of phytoplankton in all waters, evidencing an active biomass synthesis. High alkaline phosphatase and leucine aminopeptidase in coastal and offshore waters suggested the quick regeneration of Phosphorus and protein decomposition, respectively. Different levels of phytoplankton-bacteria association might provide a tool to define the ecological status of the studied system in the observed period; an approach to ecosystem assessment exportable to other coastal systems is proposed.

Microbial community and interspecies interaction during grazing of ark shell bivalve (Scapharca subcrenata) in a full-scale bioremediation system of mariculture effluents

A novel biological approach using ark shell bivalves as potential species for remediation of effluents was studied to determine the microbial community interspecies interaction and nutrient cycling in a restoration system of mariculture effluents. A field study showed that Scapharca subcrenata was the main driver of the microbial community's interspecies-interaction (PERMANOVA, R = 0.0572, P = 0.005) in the treatment zone (TZ). Analysis of co-occurrence networks based on random matrix theory (RMT) indicated that the network's complexity parameters were enhanced in the TZ and disrupted in the control zone (CZ) due to eutrophic disturbances. Concurrently, the TZ was correlated with more profound network modifications (i.e., higher modularity, total nodes (n), cohesion, and proportion of positive links), suggesting that S. subcrenata influenced microbial interspecies interactions in the system. Similarly, the co-occurring networks of generalists Proteobacteria (OTU2037) at genus Anaerospora and Actinobacteria (OTU9660) at genus Candidatus aquiluna for anaerobic ammonia-oxidation (ANAMMOX) were highly significant in the TZ. The top-down and bottom-up forces of S. subcrenata influenced the removal efficiency of nitrogenous compounds by reducing 81.51% of nitrite (NO₂^--N), 84.61% of total ammonium nitrogen (TAN) and 72.78% of nitrate (NO₃^--N). Generally, the introduction of ark shell bivalve (S. subcrenata) to the system as a biofilter provides a very low-cost bioremediation technology that could be one of the best restorations and remediation tools for mariculture effluents.

Structural and functional response of phytoplankton to reduced river inputs and anomalous physical-chemical conditions in the Gulf of Trieste (northern Adriatic Sea)

We studied the influence of anomalous meteorological and hydrological conditions that occurred in the Gulf of Trieste from March 2006 to February 2007 on phytoplankton structure and function. We computed monthly mean (or median) air temperature, total precipitation, wind speed, river discharge, seawater temperature, salinity, photosynthetic available radiation (PAR), cyanobacteria, nano- and microphytoplankton abundances during the study year and compared them to climatological (1999-2014 for PAR; 1999-2007 for nanophytoplankton; 1998-2015 for the other variables) mean/median data. We then related the cyanobacteria (0.2-2 μm), nano- (2-20 μm) and microphytoplankton (20-200 μm) of the study year to inorganic nutrient concentrations. Median river inputs in October and November were 9- and 15-fold lower, respectively, than the time series medians, with consequent high salinity from May to November (up to +1.26 compared to the climatological data). Monthly mean seawater temperatures were lower than the climatological values (-2.95 °C at the surface) from March to August 2006 and higher (+2.15 °C at the surface) from September to February 2007. Reductions in freshwater input and nutrient depletion were likely responsible for a decrease in microphytoplankton (median annual abundance over 60% lower than the climatologic median) and cyanobacteria (up to 47% lower than the climatology). Significant seasonal differences in cyanobacteria and microphytoplankton abundances (R_ANOSIM = 0.52; p < 0.05), as well as in seawater temperature and salinity (R_ANOSIM = 0.73; p < 0.05) between the study period and the climatology were highlighted. The late spring diatom bloom was not reflected in high photosynthetic rates whereas an unusually high primary production was estimated in November (7.11 ± 1.01 μgC L^-1 h^-1), when a mucilage event occurred due to very stable atmospheric and oceanographic conditions. The typical seasonal succession of pelagic phototrophs (micro-, nanophytoplankton and cyanobacteria) was altered since an exceptional cyanobacteria bloom first developed in April, followed by a delayed diatom bloom in May.

Plankton dynamics across the freshwater, transitional and marine research sites of the LTER-Italy Network. Patterns, fluctuations, drivers

A first synoptic and trans-domain overview of plankton dynamics was conducted across the aquatic sites belonging to the Italian Long-Term Ecological Research Network (LTER-Italy). Based on published studies, checked and complemented with unpublished information, we investigated phytoplankton and zooplankton annual dynamics and long-term changes across domains: from the large subalpine lakes to mountain lakes and artificial lakes, from lagoons to marine coastal ecosystems. This study permitted identifying common and unique environmental drivers and ecological functional processes controlling seasonal and long-term temporal course. The most relevant patterns of plankton seasonal succession were revealed, showing that the driving factors were nutrient availability, stratification regime, and freshwater inflow. Phytoplankton and mesozooplankton displayed a wide interannual variability at most sites. Unidirectional or linear long-term trends were rarely detected but all sites were impacted across the years by at least one, but in many case several major stressor(s): nutrient inputs, meteo-climatic variability at the local and regional scale, and direct human activities at specific sites. Different climatic and anthropic forcings frequently co-occurred, whereby the responses of plankton communities were the result of this environmental complexity. Overall, the LTER investigations are providing an unparalleled framework of knowledge to evaluate changes in the aquatic pelagic systems and management options.

Functional biodiversity of marine soft-sediment polychaetes from two Mediterranean coastal areas in relation to environmental stress

Biological Traits Analysis (BTA) was used to identify functional features of infaunal polychaete assemblages associated with contamination in two Italian coastal areas: the harbour of Trieste (Adriatic Sea) and the Mar Piccolo of Taranto (Ionian Sea). The analysis was performed on 103 taxa, collected at four stations in each area. The two areas differed in species composition. The low diversity and the presence of stress-tolerant species in more polluted sites were not reflected in functional diversity, due to species contributing little to community functions or being functionally redundant. Sand and clay fractions were significant drivers of trait category expressions, however other environmental parameters (depth, total organic carbon and nitrogen, and Hg in sediments) influenced traits composition. Motile was the prevalent trait in environments with coarse sediments, and tube-builder were related to fine-grained ones. Motile, endobenthic and burrower were essential traits for living in contaminated sediments. Epibenthic and sessile polychaetes dominated at stations subjected to high organic loads. BTA offers an integrative approach to detect functional adaptations to contaminated sediments and multiple anthropogenic stressors.

Recent evolution of the physical-chemical characteristics of a Site of National Interest-the Mar Piccolo of Taranto (Ionian Sea)-and changes over the last 20 years

The Mar Piccolo of Taranto, classified as a 'Site of National Interest' (SIN), is a semi-enclosed basin divided into two inlets with lagoon features and sea influences, seriously affected by anthropic activities. In the framework of the RITMARE project, a study has been carried out to evaluate the functionality of this ecosystem. As part of this work, measurements of the water abiotic parameters were performed in order to assess the physical-chemical features of this area after the activation, in the last decade, of treatment plants for various urban and industrial dumping. Seawater intrusions and continental inputs, as well as several submarine freshwater springs, clearly affect physical-chemical characteristics of the water column in the two inlets. This finding suggests that small-scale patterns in water circulation have the potential to influence the chemical properties of the seawater. The comparison with a 20-year dataset reveals a drastic decrease in nutrient concentrations after the year 2000, validating the functionality of the treatment plants. The reduction of nutrient inputs into the basin (up to -90 % in the first inlet characterized by lower hydraulic residence time) has changed the biogeochemical characteristics of the Mar Piccolo from being relatively eutrophic to moderately oligotrophic.

Mobilization of trace metals and PCBs from contaminated marine sediments of the Mar Piccolo in Taranto during simulated resuspension experiment

The effects of sediment resuspension on the fate of metals and polychlorinated biphenyls (PCBs) were studied by using a short-term small reactor. Sediments and water were collected nearby the most contaminated site of the Mar Piccolo of Taranto. Contaminant partitioning was calculated between the solid and water phases and, in the latter, between the dissolved and particulate phases and related to physical-chemical variables. Before and after resuspension, metal concentrations in sediments did not vary remarkably. Except for Cd, all the analyzed metals exceeded by many folds both threshold effect level (TEL) and probable effect level (PEL) SQGs. Igeo index values for Hg designated the sediment quality as extremely polluted for Pb, Cu and moderately polluted for Zn. In the dissolved phase, Mn increased of about 70 times, Fe of about 7 times and Hg and Zn of 4 and 3 times, respectively. PCBs in sediments before and after resuspension did not vary for more than 15 %. PCB concentrations exceeded for more than ten times PEL values. After resuspension, PCBs increased from 0.82 to 4.82 ng L(-1) in the dissolved phase and from 0.22 to 202.21 ng L(-1) in the particulate one. The dissolved phase was initially enriched in light- to mid-weight compounds. After resuspension, the particulate phase was enriched in heavier congeners. In particular, hexachlorobiphenyl-153, 149 and 138 together with heptachlorobiphenyl-180 and 187 accounted for 57 % of total PCBs. The dissolved organic carbon (DOC) that increased from 1.31 to 8.55 mg L(-1) likely influenced the fate of metals and PCBs in the dissolved and particulate phases. Despite that the residence time of the contaminated resuspended sediments in the water column is limited, they are still highly toxic for the pelagic trophic web.

Microbenthic community structure and trophic status of sediments in the Mar Piccolo of Taranto (Mediterranean, Ionian Sea)

This study aimed to assess the benthic ecosystem trophic status in a heavily polluted marine area and the response of the microbenthic community to multiple and diffuse anthropogenic impacts, integrating information coming from the active and resting (plankton's cysts) components of microbenthos. Two sampling campaigns were carried out in the period 2013-2014 and four sampling sites at different levels of industrial contamination were chosen within the first and second inlet of the Mar Piccolo of Taranto. The chemical contamination affected to a higher extent the active microbenthos than the resting one. In the central part of the first inlet, characterised by more marine features, thrives a very rich and biodiverse microbenthic community. In contrast, at the polluted site near the military navy arsenal, extremely low densities (9576 ± 1732 cells cm(-3)) were observed for active microbenthos, but not for the resting community. Here, the high level of contamination selected for tychopelagic diatom species, i.e., thriving just above the surface sediments, while the other life forms died or moved away. Following the adoption of a 10 μm mesh, for the first time, resting spores produced by small diatoms of the genus Chaetoceros were found. Our results further indicate that although the Mar Piccolo is very shallow, the benthic system is scarcely productive, likely as a consequence of the accumulated contaminants in the surface sediments that probably interfere with the proper functioning of the benthic ecosystem.