Accurate Estimation of Chlorophyll-a Concentration in the Coastal Areas of the Ebro Delta (NW Mediterranean) Using Sentinel-2 and Its Application in the Selection of Areas for Mussel Aquaculture

Multispectral satellite remote sensing imagery, together with appropriate modeling, have been proven to provide chlorophyll-a maps that are useful to evaluate the suitability of coastal areas for carrying out shellfish aquaculture. However, current approaches used for chlorophyll-a estimation in very shallow coastal areas often fail in their accuracy. To overcome this limitation, an algorithm that provides an accurate estimation of chlorophyll-a concentration in the coastal areas of the Ebro delta (North Western Mediterranean) using atmospherically corrected Sentinel 2 (S2) remote sensing reflectances (Rrs) has been calibrated and validated. The derived chlorophyll-a maps created have been used in a dynamic carrying capacity model that covers areas from very rich waters inside the embayment to the more oligotrophic waters in the open sea. The use of carrying capacity models is recommended to evaluate the potential of marine coastal areas for bivalve mollusk aquaculture. In this context, the depletion of chlorophyll-a is an indicator of negative environmental impact and thus a continuous monitoring of chlorophyll-a is key. The proposed methodology allows estimation of chlorophyll-a concentration from Sentinel-2 with an accuracy higher than 70% in most cases. The carrying capacity and the suitability of the external areas of the Ebro delta have been determined. The results show that these areas can hold a significant mussel production. The methodology presented in this study aims to provide a tool to the shellfish aquaculture industry.info:eu-repo/semantics/publishedVersio

Short-term response of chlorophyll a concentration due to intense wind and freshwater peak episodes in estuaries: The case of fangar Bay (Ebro Delta)

Estuaries and coastal bays are areas of large spatio-temporal variability in physical and biological variables due to environmental factors such as local wind, light availability, freshwater inputs or tides. This study focuses on the effect of strong wind events and freshwater peaks on short-term chlorophyll a (Chl a) concentration distribution in the small-scale and microtidal, Fangar Bay (Ebro Delta, northwestern Mediterranean). The hydrodynamics of this bay are primarily driven by local wind episodes modulated by stratification in the water column. Results based on field-campaign observations and Sentinel-2 images revealed that intense wind episodes from both NW (offshore) and NE-E (onshore) caused an increase in the concentration of surface Chl a. The mechanisms responsible were horizontal mixing and the bottom resuspension (also linked to the breakage of the stratification) that presumably resuspended Chl a containing biomass (i.e., micropyhtobentos) and/or incorporated nutrients into the water column. On the other hand, sea-breeze was not capable of breaking up the stratification, so the chlorophyll a concentration did not change significantly during these episodes. It was concluded that the mixing produced by the strong winds favoured an accumulation of Chl a concentration, while the stratification that causes a positive estuarine circulation reduced this accumulation. However, the spatial-temporal variability of the Chl a concentration in small-scale estuaries and coastal bays is quite complex due to the many factors involved and deserve further intensive field campaigns and additional numerical modelling efforts.Postprint (published version

Short-Term Response of Chlorophyll a Concentration Due to Intense Wind and Freshwater Peak Episodes in Estuaries: The Case of Fangar Bay (Ebro Delta)

Estuaries and coastal bays are areas of large spatio-temporal variability in physical and biological variables due to environmental factors such as local wind, light availability, freshwater inputs or tides. This study focuses on the effect of strong wind events and freshwater peaks on short-term chlorophyll a (Chl a) concentration distribution in the small-scale and microtidal, Fangar Bay (Ebro Delta, northwestern Mediterranean). The hydrodynamics of this bay are primarily driven by local wind episodes modulated by stratification in the water column. Results based on field-campaign observations and Sentinel-2 images revealed that intense wind episodes from both NW (offshore) and NE-E (onshore) caused an increase in the concentration of surface Chl a. The mechanisms responsible were horizontal mixing and the bottom resuspension (also linked to the breakage of the stratification) that presumably resuspended Chl a containing biomass (i.e., micropyhtobentos) and/or incorporated nutrients into the water column. On the other hand, sea-breeze was not capable of breaking up the stratification, so the chlorophyll a concentration did not change significantly during these episodes. It was concluded that the mixing produced by the strong winds favoured an accumulation of Chl a concentration, while the stratification that causes a positive estuarine circulation reduced this accumulation. However, the spatial-temporal variability of the Chl a concentration in small-scale estuaries and coastal bays is quite complex due to the many factors involved and deserve further intensive field campaigns and additional numerical modelling efforts.info:eu-repo/semantics/publishedVersio

Combined flooding and water quality monitoring during short extreme events using Sentinel 2: the case study of Gloria storm in Ebro delta

Short extreme events have significant impact on landscape and ecosystems in low-lying and exposed areas such as deltaic systems. In this context, this paper proposes a combined methodology for the mapping and monitoring of the flooding and water quality dynamics of coastal areas under extreme storms from Sentinel 2 imagery. The proposed methodology has been applied in a coastal bay of the Ebro Delta (Catalonia, NE Spain) to evaluate jointly the impact of Gloria storm (January 2020) in land-flooding and water quality. The experimental results show that the Gloria storm had a strong morphological impact and altered the water quality (chl-a) dynamics. The results show a recovery in terms of water quality after some weeks but in contrast the coastal morphology did not show the same degree of resilience. This paper is the first step of an overall goal that is to set the bases in a long term, for a workflow for rapid response and continuous monitoring of storm effects in coastal areas and/or highly valuable ecosystems such as the Ebro Delta.This research was partially funded by the project New-TechAqua (European Union's Programme H2020, GA 862658). J. Soriano-González held a pre-doctoral grant funded by by Agència de Gestió d’Ajuts Universitaris I de Recerca (2020FI_B2 00148)Peer ReviewedObjectius de Desenvolupament Sostenible::14 - Vida SubmarinaObjectius de Desenvolupament Sostenible::13 - Acció per al ClimaPostprint (published version

Dual quantitative PCR assay for identification and enumeration of Karlodinium veneficum and Karlodinium armiger combined with a simple and rapid DNA extraction method

Karlodinium is a dinoflagellate genus responsible for massive fish mortality events worldwide. It is commonly found in Alfacs Bay (NW Mediterranean Sea), where the presence of two Karlodinium species (K. veneficum and K. armiger) with different toxicities has been reported. Microscopy analysis is not able to differentiate between these two species. Therefore, new and rapid methods that accurately and specifically detect and differentiate these two species are crucial to facilitate routine monitoring, to provide early warnings and to study population dynamics. In this work, a quantitative real-time PCR (qPCR) method to detect and enumerate K. veneficum and K. armiger is presented. The ITS1 region of the ribosomal DNA was used to design species-specific primers. The specificity of the primers together with the melting curve profile provided a reliable qualitative identification and discrimination between the two Karlodinium species. Additionally, a simple and rapid DNA extraction method was used. Standard curves were constructed from 10-fold dilutions of cultured microalgae cells. Finally, the applicability of the assay was tested with field samples collected from Alfacs Bay. Results showed a significant correlation between qPCR determinations and light microscopy counts (y = 2.838 x + 564; R2 = 0.936). Overall, the qPCR method developed herein is specific, rapid, accurate, and promising for the detection of these two Karlodinium species in environmental samples.info:eu-repo/semantics/acceptedVersio

First results of phytoplankton spatial dynamics in two NW-Mediterranean bays from Chlorophyll-a estimates using Sentinel 2: potential implications for aquaculture

Shellfish aquaculture has a major socioeconomic impact on coastal areas, thus it is necessary to develop support tools for its management. In this sense, phytoplankton monitoring is crucial, as it is the main source of food for shellfish farming. The aim of this study was to assess the applicability of Sentinel 2 multispectral imagery (MSI) to monitor the phytoplankton biomass at Ebro Delta bays and to assess its potential as a tool for shellfish management. In situ chlorophyll-a data from Ebro Delta bays (NE Spain) were coupled with several band combination and band ratio spectral indices derived from Sentinel 2A levels 1C and 2A for time-series mapping. The best results (AIC = 72.17, APD < 10%, and MAE < 0.7 mg/m3) were obtained with a simple blue-to-green ratio applied over Rayleigh corrected images. Sentinel 2–derived maps provided coverage of the farm sites at both bays allowing relating the spatiotemporal distribution of phytoplankton with the environmental forcing under different states of the bays. The applied methodology will be further improved but the results show the potential of using Sentinel 2 MSI imagery as a tool for assessing phytoplankton spatiotemporal dynamics and to encourage better future practices in the management of the aquaculture in Ebro Delta bays.info:eu-repo/semantics/publishedVersio

Seasonal patterns of settlement and growth of introduced and native ascidians in bivalve cultures in the Ebro Delta (NE Iberian Peninsula)

Ascidians are important both as invasive species and as a fouling group in artificial marine habitats, causing negative impacts in aquaculture settings and the surrounding environment. The Ebro Delta is one of the major centres of bivalve production in the Mediterranean and is affected by proliferation of ascidian species (mostly introduced forms). Knowledge of the patterns of settlement and growth of the fouling species is mandatory to attempt mitigation measures. Settlement PVC plates were deployed from May to September 2015 at different depths (0.2, 1 and 2 m) in the Ebro Delta oyster aquaculture facilities. The occurrences of all species and the area cover of a selected subset of 6 species were monitored on a monthly basis from June 2015 to December 2016. Fifteen species were found, of which 10 are introduced. There were some differences between the deployed plates and the oyster ropes in species abundance and composition, likely due to differences in substrate complexity. For instance, Didemnum vexillum and Clavelina oblonga occurred in few plates in contrast to their abundance on oysters. The most abundant species were Styela plicata and Clavelina lepadiformis, which together with Ecteinascidia turbinata showed a preference to grow on plates deployed in May and June. Most of the species grew more at 0.2 m depth than at deeper plates. Thus, to minimise fouling on bivalves, spat immersion during fall and below 1 m depth is recommended. The number of occurrences and cover of the species was found to be similarly informative; suggesting that a periodic monitoring of species occurrence on replicate plates is sufficient for detecting new introduced species as soon as possible and will provide information useful for management.postprin

Seasonal patterns of settlement and growth of introduced and native ascidians in bivalve cultures in the Ebro Delta (NE Iberian Peninsula)

Ascidians are important both as invasive species and as a fouling group in artificial marine habitats, causing negative impacts in aquaculture settings and the surrounding environment. The Ebro Delta is one of the major centres of bivalve production in the Mediterranean and is affected by proliferation of ascidian species (mostly introduced forms). Knowledge of the patterns of settlement and growth of the fouling species is mandatory to attempt mitigation measures. Settlement PVC plates were deployed from May to September 2015 at different depths (0.2, 1 and 2 m) in the Ebro Delta oyster aquaculture facilities. The occurrences of all species and the area cover of a selected subset of 6 species were monitored on a monthly basis from June 2015 to December 2016. Fifteen species were found, of which 10 are introduced. There were some differences between the deployed plates and the oyster ropes in species abundance and composition, likely due to differences in substrate complexity. For instance, Didemnum vexillum and Clavelina oblonga occurred in few plates in contrast to their abundance on oysters. The most abundant species were Styela plicata and Clavelina lepadiformis, which together with Ecteinascidia turbinata showed a preference to grow on plates deployed in May and June. Most of the species grew more at 0.2 m depth than at deeper plates. Thus, to minimise fouling on bivalves, spat immersion during fall and below 1 m depth is recommended. The number of occurrences and cover of the species was found to be similarly informative; suggesting that a periodic monitoring of species occurrence on replicate plates is sufficient for detecting new introduced species as soon as possible and will provide information useful for management.info:eu-repo/semantics/acceptedVersio

Marine biotoxins in the Catalan littoral: could biosensors be integrated into monitoring programmes?

Aquest article descriu els sensors enzimàtics i immunosensors electroquímics que s'han desenvolupat als nostres grups per a la detecció de la biotoxina marina àcid okadaic (OA), i discuteix la possibilitat d'integrar-los en programes de seguiment. Els sensors enzimàtics per a OA que es presenten es basen en la inhibició de la proteïna fosfatasa (PP2A) per aquesta toxina i la mesura electroquímica de l'activitat enzimàtica mitjançant l'ús de substrats enzimàtics apropiats, electroquímicament actius després de la seva desfosforació per l'enzim. Els immunosensors electroquímics descrits en aquest article es basen en un enzimoimmunoassaig sobre fase sòlida competitiu indirecte (ciELISA), amb fosfatasa alcalina (ALP) o peroxidasa (HRP) com a marcatges, i un sistema de reciclatge enzimàtic amb diaforasa (DI). Els biosensors presentats aquí s'han aplicat a l'anàlisi de dinoflagel·lats, musclos i ostres. Les validacions preliminars amb assaigs colorimètrics i LC-MS/MS han demostrat la possibilitat d'utilitzar les bioeines desenvolupades per al cribratge preliminar de biotoxines marines en mostres de camp o de cultiu, que ofereixen informació complementària a la cromatografia. En conclusió, tot i que encara cal optimitzar alguns paràmetres experimentals, la integració dels biosensors a programes de seguiment és viable i podria proporcionar avantatges respecte a altres tècniques analítiques pel que fa al temps d'anàlisi, la simplicitat, la selectivitat, la sensibilitat, el fet de poder ser d'un sol ús i l'efectivitat de cost.This article describes the electrochemical enzyme sensors and immunosensors that have been developed by our groups for the detection of marine biotoxin okadaic acid (OA), and discusses the possibility of integrating them into monitoring programmes. The enzyme sensors for OA reported herein are based on the inhibition of immobilised protein phosphatase 2A (PP2A) by this toxin and the electrochemical measurement of the enzyme activity through the use of appropriate enzyme substrates, which are electrochemically active after dephosphorylation by the enzyme. The electrochemical immunosensors described in this article are based on a competitive indirect Enzyme- Linked ImmunoSorbent Assay (ciELISA), using alkaline phosphatase (ALP) or horseradish peroxidase (HRP) as labels, and an enzymatic recycling system with diaphorase (DI). The biosensors presented herein have been applied to the analysis of dinoflagellates, mussels and oysters. Preliminary validations with colorimetric assays and LC-MS/MS have demonstrated the possibility of using the developed biotools for the preliminary screening of marine biotoxins in field or cultured samples, offering complementary information to chromatography. In conclusion, although optimisation of some experimental parameters is still required, the integration of biosensors into monitoring programmes is viable and may provide advantages over other analytical techniques in terms of analysis time, simplicity, selectivity, sensitivity, disposability of electrodes and cost effectiveness

First report of Gambierdiscus in the Western Mediterranean Sea (Balearic Islands)

Gambierdiscus (Dinophyceae) species are benthic dinoflagellates living in marine littoral zones of circumtropical areas and have recently been described in temperate waters [1]. Some species are producers of potent neurotoxins: ciguatoxins (CTXs) and maitotoxins (MTXs). Ciguatoxins are linked to Ciguatera Fish Poisoning (CFP). Ciguatera used to be restricted to tropical and subtropical areas, but since the last decade, it appears to be expanding to more temperate latitudes. For example, outbreaks of ciguatera have been reported in the Canary Islands and Madeira (eastern Atlantic Ocean), where several species of the genus Gambierdiscus have been identified.info:eu-repo/semantics/publishedVersio