Seasonal nitrogen and phosphorus dynamics during benthic clam and suspended mussel cultivation

Spatiotemporal variation of phytoplankton communities and water quality among seaweed, shellfish and cage fish culture systems

Various marine aquaculture systems have different impacts on the environment, but few assessments were focused on the environmental impact by different systems in the same region. To study the effects of various aquaculture systems on phytoplankton community structure and water properties, 5 surveys were carried out in seaweed (Gracilaria lemaneiformis, GL), shellfish (Mytilus coruscus, MC) and cage fish (Larimichthys crocea, LC) mariculture areas in Dongji island, Zhejiang, China from June to September 2020. Significant differences were observed in some environmental parameters and phytoplankton communities among three aquaculture systems. The dissolved oxygen concentrations and Secchi depth in the surface waters in GL area were relatively higher than in the blank and other areas. As for nutrients concentration, LC and MC areas had higher concentrations than blank area, while GL area was the lowest. Though Chlorophyll-a concentration displayed fluctuations, relatively lower concentrations were found in GL area. Shannon diversity index was found to be relatively constant and higher in GL area. The Non-metric multidimensional scaling results revealed that phytoplankton composition had a distinct pattern among sampling times. The correlations and Redundancy analysis showed that total nitrogen, salinity and transparency were primary environmental factors associated with phytoplankton composition. Our study confirmed that different marine aquaculture systems can cause environmental fluctuations. Among the three systems, seaweed cultivation can bring multiple positive effects by improving surrounding water quality and increasing the phytoplankton composition. G. lemaneiformis culture in summer has great positive impact on seawater environment as it can maintain the ecological balance and reduce the risk of harmful algal blooms (HABs), and therefore, it is strongly recommended more G. lemaneiformis cultivation in this region in summer.

A food-web model as a tool for the ecosystem-level management of bivalves in an Atlantic coastal lagoon

The Ria de Aveiro is an important coastal lagoon for wildlife in Portugal, where the production of bivalves reaches approximately 2700 tons annually. However, the illegal overfishing of bivalves is frequent in this lagoon, which causes critical changes in the ecosystem. In this study, using a developed food-web model (Ecopath model), the ecological carrying capacity (ECC) and maximum sustained yield (MSY) of the Manila clam, Ruditapes philippinarum were estimated, and the effects of further increases in clam biomass on other species were investigated. The results showed that 1) the current biomass and legal catch of R. philippinarum do not yet exceed the ECC (172.40 tons km-2) or the MSY (86.20 tons km-2 year-1) in Ria de Aveiro; 2) the harvested Manila clams of the MSY represent removing from the ecosystem ∼ 581 tons carbon (C) and ∼83 tons nitrogen (N) annually, with substantial ecological and economic implications; and 3) a further increase in the biomass levels of this species may cause the ecotrophic efficiency of other groups to become unrealistic, potentially leading to decreases in ecosystem transfer efficiency, biodiversity and health. The results here are expected to guide the sustainable development and management of bivalve aquaculture in Ria de Aveiro and the protection of the local environment.

Mytilus farming drives higher local bacterial diversity and facilitates the accumulation of aerobic anoxygenic photoheterotrophic related genera

Research to assess the impacts of mariculture on the microbiota of the surrounding environment is still inadequate. Here, we examined the effects of Mytilus coruscus farming on the diversity of bacterial community in surrounding seawater using field investigations and indoor simulations, focusing on the variation of members of aerobic anoxygenic photoheterotrophic (AAP) bacteria. In the field, Mytilus farming shaped bacterial community and significantly increased their diversity, including biomass, OTUs, Shannon, relative abundance, number of enriched species, as compared with the non-farming area. Higher abundance of AAP related genera was observed in the Mytilus farming seawater. Under the controlled condition, the presence of M. coruscus significantly shaped the bacterial community composition and caused species composition to become similar after 10 days. Furthermore, the presence of M. coruscus consistently strengthened local diversity in seawater bacterial community, with linkages to the recruitment of AAP members as well. In addition, the tissue-related composition of M. coruscus significantly differed from those in seawater. Our findings highlight a ecological importance of Mytilus farming, as process that shape surrounding water-cultured bacterial community and offer experimental evidence for the accumulation of AAP-related genera in aquaculture systems.

Biodeposition of oysters in an urbanized bay area alleviates the black-malodorous compounds in sediments by altering microbial sulfur and iron metabolism

The occurrence of the 'black-malodorous phenomenon' in a waterbody is a clear sign of a highly eutrophic bay, the formation of which is associated with microbial sulfur and iron metabolism in the sediments. Oyster farming restoration has been widely studied as an important method for treating eutrophication and related ecological problems. However, few studies focus on the ecosystem-level consequences of oyster farming concerning microbial sulfur and iron cycles in the sediment. Here, we compared the physicochemical features and microbial functions of oyster farms with those of reference areas using the Geochip5.0 technique. Our results showed a significant reduction of acid volatile sulfide (AVS) content associated with oyster farming, thus alleviating the black-malodorous status of Shenzhen Bay in China. Oyster farming created loose and porous sedimentary structures and stimulated the oxidation of black-odorous compounds. Moreover, we observed that the introduction of oysters changed microbial biodiversity significantly based on gyrB gene structure, with typical sulfur- and iron-cycling microbes being enriched. We also demonstrated that microbial abilities involved in sulfur and iron metabolism were greatly increased in oyster farming areas compared with reference areas. Under such circumstances, some cascading processes (AVS uptake and rates of organic matter turnover) were improved, which eventually contributed to black odor reduction. From the microecological perspective, we conclude that the biodeposition of oysters was the key factor for water retention and improvement of microbial metabolism. This study suggests that biodeposition shapes the microbial functional communities in adjacent territories and presumably alleviates the black-malodorous compounds in sediments.

Ecosystem Service Assessments within the EU Water Framework Directive: Marine Mussel Cultivation as a Controversial Measure

To combat the persistent eutrophication in coastal waters, sustainable sea-based measures are recommended. Yet, they are the subject of controversial stakeholder discussion, which hampers the implementation and planning process. The aim of this study is to evaluate if a participatory mapping (PM) approach and ecosystem service assessments (ESA) can be suitable tools within Water Framework Directive (WFD) implementation to support the communication with different target groups to improve and accelerate the planning and realization of new sea-based mitigation measures. We conducted three stakeholder-based PMs to visualize the perception of sea-based mitigation measures in coastal waters and seven different ESAs to investigate the perceptions of different mussel cultivation scenarios as mitigation measures. The PMs showed that ecological measures were preferred. The ESA approach showed that, while experts rated mussel cultivation scenarios positively overall, non-expert stakeholders still seemed skeptical and preferred alternative measures like floating wetlands. The methodological results indicate that PM can be a cost-effective tool to visualize stakeholders’ perceptions, but it needs to be applied with an ESA to be beneficial for the WFD implementation process. A web-based ESA improves the discussion with stakeholders and can reveal potential misperceptions and concerns faster and lead to a more focused discussion.

Spatial and Temporal Distribution of the Multi-element Signatures of the Estuarine Non-indigenous Bivalve Ruditapes philippinarum

Filter-feeder bivalves such as non-indigenous Ruditapes philippinarum absorb and accumulate metals, resulting in multi-element profiles. The goal of this study was to analyse spatial and temporal distributions of the multi-element signatures in R. philippinarum populations of the Tagus and Sado estuaries (SW coast, Portugal). The clam and sediment samples were collected at three sampling sites in each estuary, on three sampling occasions, and the analysis were done by ICP-MS (inductively coupled plasma mass spectrometry). The chemical elements were categorized according to estuarine geomorphology sources (Se, Co, Ni and Cu), elements with function in metabolic processes of the clams (Mn, Fe, Zn and Cr) and elements derived from the anthropogenic inputs (As, Pb and Cd). Zinc, Co, Ni and Pb were the main contributors for the chemical signatures of Tagus estuary populations, whilst for the Sado estuary populations were Cu, Fe, Cr, As and Cd. They were representative of all elemental categories and proved to be spatial and temporal habitat discriminators of bivalves' estuarine populations. The multi-element signatures of R. philippinarum as a natural tag derived from the physical and chemical conditions of its habitat is a potential rapid tool to use in ecological monitoring and habitat assessment.

In situ characterization of benthic fluxes and denitrification efficiency in a newly re-established mussel farm

Mussel farming has been proposed as a mechanism to mitigate eutrophication in coastal waters. However, localizing the intensive filtration of organic matter by mussels can cause a concomitant enrichment of organic matter in sediments below farms, which may influence biogeochemical processes and fates of nutrients in the system. In the context of mitigating eutrophication, it is important to quantify sedimentary changes induced at early life stages of mussel farms. Accordingly, this study investigated how a newly re-established mussel farm affected sedimentation rates, sediment characteristics, sediment-water solute fluxes and nitrate (NO₃^-) reduction rates (measured in situ) during the first year of production. Sedimentation rates were enhanced at the farm relative to a reference station, and both organic and inorganic carbon accumulated in the sediment with time. Increased organic matter input likely drove the slightly elevated sedimentary effluxes of ammonium (NH₄⁺) and dissolved inorganic phosphorus (DIP) in the farm. Denitrification was the main NO₃^- reduction process, however, there was a relative increase in the remobilization of bioavailable nitrogen underneath the farm as dissimilatory nitrate reduction to ammonium (DNRA) rates were enhanced by >200% and the denitrification efficiency was 49% lower compared to the reference station. The sedimentary methane (CH₄) release tended to be higher at the farm, but fluxes were not significantly different from reference conditions. Low sedimentary pigment concentrations indicated a reduced presence of benthic microalgae at the farm, which likely influenced sediment-water solute fluxes. Over the production cycle, the release of dissolved inorganic nitrogen (DIN) and DIP underneath the farm were respectively 426% and 510% relative to reference conditions. Impacts of the mussel farm were thus measurable already during the first year of establishment. These immediate changes to the sediment biogeochemistry, as well as long-term effects, should be considered when estimating the environmental impact of mussel aquaculture.

Functions of constructed wetland animals in water environment protection - A critical review

Constructed wetlands (CWLs) are widely used for water environment protection. In some cases, CWL animals can help improve CWL treatment efficiency and contribute to CWL maintenance and management. However, while plants, microorganisms, and substrates in CWLs have received much attention, animals have been largely ignored. Therefore, the aims of this review are to determine the roles wetland animals play in the water environmental protection of CWLs. This study introduced species of wetland animals and the main factors that can affect their survival. The way in which CWL animals affect pollutants was discussed in detail from four perspectives: adsorption and bioaccumulation, bioturbation, and the influence of CWL animals on plants and microorganisms. The characteristics of CWL animals that can be used for biological monitoring are summarized, and the use of CWLs for the protection of wetland biodiversity is also discussed. Finally, some prospects are proposed for future research. This study will help researchers better understand the role of CWL animals in CWLs and encourage researchers to focus on studies of wetland animals.

Contrasting Effects of Bioturbation Studied in Intact and Reconstructed Estuarine Sediments

Macrofauna can produce contrasting biogeochemical effects in intact and reconstructed sediments. We measured benthic fluxes of oxygen, inorganic carbon, and nitrogen and denitrification rates in intact sediments dominated by a filter and a deposit feeder and in reconstructed sediments added with increasing densities of the same organisms. Measurements in reconstructed sediments were carried out 5 days after macrofauna addition. The degree of stimulation of the measured fluxes in the intact and reconstructed sediments was then compared. Results confirmed that high densities of bioturbating macrofauna produce profound effects on sediment biogeochemistry, enhancing benthic respiration and ammonium recycling by up to a factor of ~3 and ~9, respectively, as compared to control sediments. The deposit feeder also increased total denitrification by a factor of ~2, whereas the filter feeder activity did not stimulate nitrogen removal. Moreover, the effects of deposit feeders on benthic fluxes were significantly higher (e.g., on respiration and ammonium recycling) or different (e.g., on denitrification) when measured in intact and reconstructed sediments. In intact sediments, deposit feeders enhanced the denitrification coupled to nitrification and had no effects on the denitrification of water column nitrate, whereas in reconstructed sediments, the opposite was true. This may reflect active burrowing in reconstructed sediments and the long time needed for slow growing nitrifiers to develop within burrows. Results suggest that, in bioturbation studies, oversimplified experimental approaches and insufficient preincubation time might lead to wrong interpretation of the role of macrofauna in sediment biogeochemistry, far from that occurring in nature.

Life Cycle Assessment (LCA) Proves that Manila Clam Farming (Ruditapes Philippinarum) is a Fully Sustainable Aquaculture Practice and a Carbon Sink

Manila clam (Ruditapes philippinarum, Adams and Reeve, 1850) farming is a quantitatively important and valuable form of aquaculture production worldwide but, to our best knowledge, no life cycle assessments (LCA) have been undertaken on it. However, being a filter feeder and producing a thick shell during the growing cycle, the capacity of Manila clam to remove nutrients, carbon, nitrogen and phosphorous from the marine environment potentially has some positive effects on the environment. This study was performed in the Sacca di Goro lagoon, located in the southernmost part of the Po River Delta, in the northwestern Adriatic Sea. The LCA of clam farming from a cradle-to-gate perspective have been carried out, including the production stages as seed procuring, sowing, harvesting, depuration and packaging to obtain 1 ton of fresh ready-to-sell clams. The results show that area preparation, fuel combustion and plastic bags were the main contributors to the environmental impacts. The potential capability as a carbon sink of 1 ton of clams has been calculated and the effects on eutrophication reduction by fixing nitrogen and phosphorous in shells, with a net sequestration of 444.55 kg of CO2, 1.54 kg of N and 0.31 kg of P per year.

Effects of the Bioturbating Marine Yabby Trypaea australiensis on Sediment Properties in Sandy Sediments Receiving Mangrove Leaf Litter

Laboratory mesocosm incubations were undertaken to investigate the influence of burrowing shrimp Trypaea australiensis (marine yabby) on sediment reworking, physical and chemical sediment characteristics and nutrients in sandy sediments receiving mangrove (Avicennia marina) leaf litter. Mesocosms of sieved, natural T. australiensis inhabited sands, were continually flushed with fresh seawater and pre-incubated for 17 days prior to triplicates being assigned to one of four treatments; sandy sediment (S), sediment + yabbies (S+Y), sediment + leaf litter (organic matter; S+OM) and sediment + yabbies + leaf litter (S+Y+OM) and maintained for 55 days. Mangrove leaf litter was added daily to treatments S+OM and S+Y+OM. Luminophores were added to mesocosms to quantify sediment reworking. Sediment samples were collected after the pre-incubation period from a set of triplicate mesocosms to establish initial conditions prior to the imposition of the treatments and from the treatment mesocosms at the conclusion of the 55-day incubation period. Yabbies demonstrated a clear effect on sediment topography and leaf litter burial through burrow creation and maintenance, creating mounds on the sediment surface ranging in diameter from 3.4 to 12 cm. Within S+Y+OM sediments leaf litter was consistently removed from the surface to sub-surface layers with only 7.5% ± 3.6% of the total mass of leaf detritus added to the mesocosms remaining at the surface at the end of the 55-day incubation period. Yabbies significantly decreased sediment wet-bulk density and increased porosity. Additionally, T. australiensis significantly reduced sediment bio-available ammonium (NH4+bio) concentrations and altered the shape of the concentration depth profile in comparison to the non-bioturbated mesocosms, indicating influences on nutrient cycling and sediment-water fluxes. No significant changes for mean apparent biodiffusion coefficients (Db) and mean biotransport coefficients (r), were found between the bioturbated S+Y and S+Y+OM mesocosms. The findings of this study provide further evidence that T. australiensis is a key-species in shallow intertidal systems playing an important role as an ‘ecosystem engineer’ in soft-bottom habitats by significantly altering physical and chemical structures and biogeochemical function.

Changes in infaunal assemblage structure influence nutrient fluxes in sediment enriched by mussel biodeposition

Although many studies have described the influence of bivalve aquaculture on the benthic environment, effects on benthic functional diversity are poorly known, as are links with ecosystem processes. We investigated the response of a benthic ecosystem in terms of taxonomic and functional diversity (infauna >500 μm), biogeochemical indicators (organic matter content, redox potential, sulfides level, bacteria) and metabolism (nutrient fluxes), subjected to various levels of mussel biodeposition as a general model of organic enrichment. Results show that local benthic conditions may recover fairly quickly depending on environmental conditions whereas modifications of the benthic community structure persist over a longer time scale with an impact on benthic ecosystem functioning. Fauna-mediated oxidation of the sediment likely increased nitrogen recycling through nitrification whereas binding and release of phosphorus to the water column seems to be driven by more complex processes. Results highlight the importance of species identity (ecological traits) on biogeochemical cycling and solute exchange across the sediment-water interface, with implications for the ecological functioning of exploited areas.

Environmentally applications of invasive bivalves for water and wastewater decontamination

The environmental and economic impact of invasive bivalve species implies the development of suitable pest management strategies. Chemical control is the most usual approach. However, the production of toxic intermediates as well as the unavoidable impact over non target biota is of special concern. Another approach consists on the physical removal of the animals from the invaded sites. The high biofiltration and bioaccumulation capacity of such animals make them interesting for the removal of contaminants from water and wastewater. In this context, environmental applications can be given for these pests encompassing nutrients removal for the recovery of eutrophic sites, water disinfection, organic and metal contaminants abatement. These approaches may be integrated with pest management where the physical removed animals from the invaded spots could be used for assembling biofilter for water and wastewater decontamination. However, some drawbacks must be addressed before proposing such alternative. In fact, the further spreading of the bivalves into non-invaded sites must be avoided. Moreover, some operational questions must be addressed such as the fate of contaminated animals after biofiltration. Bearing in mind the interesting results already available in this subject, this paper aims to critically overview literature regarding the environmental applications of invasive bivalves.

Estimating the carrying capacity of green mussel cultivation by using net nutrient removal model

This study aims to evaluate the nutrient removal potential and carrying capacity of green mussel cultivation by using the mass balance model. The developed model takes into consideration the green mussel growth rate, density and chlorophyll a concentration. The data employed in this study were based on culture conditions at Sriracha Fisheries Research Station, Thailand. Results show that net nutrient removal by green mussel is 3302, 380, and 124mg/year/indv for carbon, nitrogen, and phosphorus respectively. The carrying capacity of green mussel cultivation was found to be 300indv/m² based on chlorophyll a concentration which will not release phosphorus in the water environment beyond the standard (45μg-PO₄^-3-P/L). Higher chlorophyll a concentration results in lowered green mussel carrying capacity. This model can assist farm operators with possible management strategies for a sustainable mussel cultivation and protection of the marine environment.

Uptake, release, and absorption of nutrients into the marine environment by the green mussel (Perna viridis)

The nutrient uptake and release by the mussels in relation with amount of food consumption are emphasised in this research. Results of the study demonstrate that about 16% of the total mass dry weight food consumed by the mussels was released as faeces. The depositions of particulate carbon, nitrogen, and phosphorus in mussel faeces were found to be 26.3, 5.7, and 0.6mg/day/indv respectively. Soluble inorganic nutrients such as NH4(+)-N (2.5mg/day/indv), and PO4(3-)-P (0.6mg/day/indv) were also released as mussel excretion. The nutrient absorption efficiency for the green mussel body was found to be 65.1% for carbon, 62.1% for nitrogen, and 79.2% for phosphorus. Subsequently, green mussels can remove particulate carbon, nitrogen and phosphorus at 108.1, 13.5, and 4.6mg/day/indv from aquatic systems. Finally, the results can help in estimating the carrying capacity of mussel cultivation without deteriorating the water quality in marine ecosystems.