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Sentinel-2 offers great potential for monitoring water quality in inland and coastal waters. However, atmospheric correction in these waters is challenging, and there is no standardized approach yet, but different methods coexist under constant development. The atmospheric correction Case 2 Regional Coast Colour (C2RCC) processor has been recently updated with the C2X-COMPLEX (C2XC). This study is one of the first attempts at exploring its performance, in comparison with C2RCC and C2X, in inland and coastal waters in the east of the Iberian Peninsula, in retrieving water surface reflectance and estimating chlorophyll-a ([Chl-a]), total suspended matter ([TSM]), and Secchi disk depth (ZSD). The relationship between in situ ZSD and Kd_z90max product (i.e., the depth of the water column from which 90% of the water-leaving irradiance is derived) of the C2RCC processors demonstrated the potential of this product for estimating water clarity (r > 0.75). However, [TSM] and [Chl-a] derived from the different processors with default calibration factors were not suitable within the targeted scenarios, requiring recalibration based on optical water types or a shift to dynamic algorithm blending approaches. This would benefit from switching between C2RCC and C2XC, which extends the potential for improving surface reflectance estimates to a wide range of scenarios and suggests a promising future for C2-Nets in operational monitoring of water quality. Jesús Soriano held a pre-doctoral grant funded by Agència de Gestió d’Ajuts Universitaris i de Recerca (2020FI_B2 00148). Esther Patricia Urrego holds a pre-doctoral grant funded by Ministerio de Ciencia, Innovación y Universidades (PRE2019-088232). This research was partially funded by the European Union—ERDF and the Ministry of Science and Innovation and the State Research Agency of Spain under project RTI2018-098651-B-C51 (FLEXL3L4—Advanced Products L3 and L4 for the FLEX-S3 mission).

Ciguatera fish poisoning (CFP) is one of the most relevant seafood-borne diseases worldwide. It is caused by the ingestion of fish containing ciguatoxins (CTXs), lipophilic marine toxins produced by microalgae of the genera Gambierdiscus and Fukuyoa that accumulate into fish flesh and through the food webs. CFP is characterized by severe neurological, gastrointestinal, and cardiovascular disorders and affects approximately between 50,000 and 500,000 consumers annually worldwide. Real incidence of CFP is difficult to ascertain, due to under-reporting and misdiagnosis. Here, the first electrochemical immunosensor for the detection of CTXs is presented. Three different monoclonal antibodies (mAbs), two capture (3G8, 10C9) and a detector (8H4), were merged in a sandwich configuration for the combined detection of two main groups of CTX congeners (CTX1B and CTX3C ). Initially, the applicability of the immunosensor has been demonstrated with the analysis of fish samples coming from La Reunion island, providing results that correlate with mouse bioassay and cell-based assay. Then, fish coming from Mediterranean waters were analysed, giving promising results. Finally, extracts from Gambierdiscus and Fukuyoa were screened, allowing the separate detection of the two groups of CTX congeners, and giving new information regarding the toxin production of the genera. The developed bioanalytical tool is user-friendly, and can help to mitigate ciguatera risk, contributing to the protection of consumers health.

Ciguatera fish poisoning is one of the most relevant seafood-borne illnesses worldwide. It is caused by the ingestion of fish contaminated by ciguatoxins (CTXs). Primary producers of CTXs are dinoflagellates of the genera Gambierdiscus and Fukuyoa. This study is focused on the development of bioanalytical tools for the detection of Gambierdiscus and Fukuyoa. To achieve this objective, Recombinase Polymerase Amplification (RPA), which consists of an isothermal DNA amplification during a short period (30 minutes), was combined with an enzyme-linked oligonucleotide assay (ELONA). To evaluate the specificity of the RPA-ELONA, firstly primers for the genera Gambierdiscus/Fukuyoa were exposed to genomic DNA of different species (G. australes, G. excentricus, G. belizeanus, G. balechi and F. paulensis) and other microalgae used as controls (O. cf. ovata, P. lima and C. monotis). The same genomic DNA pools were also tested with species-specific primers for Gambierdiscus australes and Gambierdiscus excentricus. Finally, DNA was extracted from single cells of the previously mentioned genera and species, and tested with all the primer sets. For both the experiments, detection was achieved only when combining capture probes with their target RPA product, and no significant responses were observed in the presence of non-target DNA. Obtained results demonstrate the ability of the system to discriminate not only the genus Gambierdiscus/Fukuyoa from other microalgae, but also G. australes and G. excentricus species from their congeners. Furthermore, the limit of detection is as low as a single cell. Acknowledgments: The research has received funding from the Ministerio de Ciencia, Innovacion y Universidades through the CIGUASENSING (BIO2017-87946-C2-2-R) project. The authors acknowledge support from CERCA Programme/Generalitat de Catalunya. G. Gaiani acknowledges IRTA-Universitat Rovira i Virgili-Banco Santander for her PhD grant (2018PMF-PIPF-19).

Seafood contamination with marine toxins due to harmful algal blooms (HAB’s) is a global public health issue on the rise. Most Countries have monitoring programs for the detection of toxins in shellfish of toxic phytoplankton in seawater to prevent consumer intoxifications. The use of solid phase adsorbent and toxin tracking (SPATT) technology as toxin detection straight from the aquatic environment could complement the labour-intensive traditional monitoring methods. In this work, several types of cyclodextrins (cyclic oligomers with a conical structure and an internal cavity) have been evaluated as novel materials for SPATT. Cyclodextrins were tested at Masnou harbour (Catalonia, NW Mediterranean) during a Dinophysis sp. bloom. The cyclodextrins and the commercial Diaion (HP-20) were deployed twice for a 1-week period at five different locations of Masnou harbour. At the time of the experiment, Dinophysis sp. reached abundances as high as 91 341 cells /L. Successful accumulations of the lipophilic marine toxins; okadaic acid (OA) and pectenotoxin-2 (PTX2) were quantified by Liquid Chromatography- tandem Mass Spectrometry (LC-MS/MS). Higher levels of PTX2 were found in all cyclodextrins whereas OA and PTX2 contents were similar in the commercial resin. Accumulation of OA was higher in the commercial resin than in cyclodextrins, but these proved best for PTX2 adsorption. A clear correlation between cell abundance and toxin accumulation was observed. The research has received funding from the Ministerio de Ciencia, Innovacion y Universidades (MICINN), the Agencia Estatal de Investigacion (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER) through the CIGUASENSING project (BIO2017-87946-C2-1-R and BIO2017-87946-C2-2-R). The authors acknowledge support from CERCA Programme/Generalitat de Catalunya.

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 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