Co-occurrence of marine and freshwater phycotoxins in oysters, and analysis of possible predictors for management

Cyanotoxins on the move - Freshwater origins with marine consequences: A systematic review of global changes and emerging trends

The increasing occurrence of toxic freshwater cyanobacteria blooms in marine or brackish waters, coupled with elevated cyanotoxin concentrations in marine life, poses an emerging threat to human health. These events are often associated with temperature, salinity and the eutrophication of affected areas, however global changes causing extreme events can cause rapid shifts in their dynamics and subsequent propagation. This systematic review presents reports from 2010 to 2024 where the main objectives were to describe (i) worldwide occurrence of freshwater cyanobacteria toxins in transitional waters; (ii) global changes and shifts in cyanobacteria dynamics and (iii) patterns of the cyanotoxins microcystins, nodularins, saxitoxins, cylindrospermopsin and anatoxins in marine organisms. PRISMA ("Preferred Reporting Items for Systematic Reviews and MetaAnalyses") protocol was used, and literature search was done using two databases (PubMed and Web of Science) to summarise the research outcomes. The higher number of events was reported in the USA (west coast and east coast), followed by the Baltic Sea. Both Mediterranean and Atlantic coasts of Europe had experienced the severe impact of these events in coastal and brackish environments. Locations in South America, Africa and Asia have also been affected. Despite the lack of consensus for cyanotoxin guidelines, the highest values of the most common cyanotoxins accumulated in marine organisms were in bivalves (microcystins) and in fish (nodularins), with values largely exceeding the existing guideline of 51 μg cyanotoxins.kg-1 body weight.

Detection of a late autumn Karenia papilionacea bloom in Virginia, USA, coastal waters

A late autumn Karenia papilionacea bloom was detected within Virginia, USA shellfish harvesting areas in mid-November 2023. Using Imaging FlowCytobot (IFCB) data collected during the Northeast Fisheries Science Center Ecosystem Monitoring October - November 2023 cruise, we were able to document a larger Karenia bloom composed of K. papilionacea, K. brevis-like, K. mikimotoi, and Karenia sp. #3 cells offshore of Virginia three weeks prior to detection inshore. Both K. papilionacea and K. mikimotoi were detected in Virginia state waters (including shellfish harvesting areas) and offshore waters of the Delmarva Peninsula, whereas K. brevis-like and Karenia sp. #3 were only detected offshore. The IFCB data showed that along the cruise track the greatest cell concentrations were east of the Chesapeake Bay mouth on November 1, 2023. However, when conducting a match-up assessment of IFCB in situ data with Sentinel-3 Ocean and Land Colour Instrument (OLCI) satellite imagery using the Red Band Difference (RBD) algorithm, the majority of the bloom was undetected. By comparing in situ match-ups and RBD imagery with NOAA-20 satellite's Visible Infrared Imaging Radiometer Suite (VIIRS) chlorophyll anomaly product we hypothesize that the in situ sampling occurred along the bloom's edge, where cell concentrations were at or below the limit of satellite detection, and/or this particular Karenia bloom was either not fluorescing, expressing relatively low solar-induced chlorophyll fluorescence, or occurring at depths below satellite detection. For this bloom event, the IFCB dataset was also used as a training tool for students learning microscopy-based phytoplankton identification in a virtual environment.

Sublethal exposure of eastern oyster Crassostrea virginica to the goniodomin-producing dinoflagellate Alexandrium monilatum: Fate of toxins, histopathology, and gene expression

OBJECTIVE

The dinoflagellate Alexandrium monilatum forms blooms during summer in tributaries of the lower Chesapeake Bay. Questions persist about the potential for A. monilatum to negatively affect aquatic organisms. Its main toxin, goniodomin A (GDA), a polyketide macrolide, has been shown to have adverse effects on animals, for example through cytotoxicity and interaction with actin.

METHODS

Eastern oysters Crassostrea virginica were exposed for 96 h to sublethal concentrations of A. monilatum (615 ± 47 cells/mL [average ± SD]; containing mainly intracellular GDA [215 ± 7.15 pg/cell] and to a lesser extent goniodomin B, goniodomin C, and GDA seco-acid as quantified by liquid chromatography coupled to tandem mass spectrometry) or to nontoxic phytoplankton or were unexposed. They were subsequently depurated for 96 h by exposure to nontoxic phytoplankton. Clearance rates were estimated, and oysters were sampled daily and tissue (gill, digestive gland, and remaining tissues) excised for analyses by histopathology, gene expression quantified by quantitative PCR, and goniodomin quantification.

RESULT

A positive clearance rate, no mortality, and no tissue pathologies were observed in oysters exposed to A. monilatum. Goniodomin A was detected in gill 6 h after exposure (504 ± 329 μg/kg [average ± SE]) and to a lesser extent in the digestive gland and remaining soft tissues. In the digestive gland, a trend of transformation of GDA to GDA seco-acid was observed. The majority of toxins (≥83%) were depurated after 96 h. Expression of genes involved in oxidative response increased 14-fold after 6 h, and those involved in actin synthesis showed a 27-fold change after 24 h, while expression of apoptosis genes increased 6.9-fold after 96 h compared with the control (eastern oysters exposed to nontoxic phytoplankton).

CONCLUSION

Exposure experiments (nonsublethal or chronic) should be carried out to better assess the threat of this species and toxins for eastern oysters and other marine organisms.

The Occurrence of Karenia species in mid-Atlantic coastal waters: Data from the Delmarva Peninsula, USA

A bloom of Karenia papilionacea that occurred along the Delaware coast in late summer of 2007 was the first Karenia bloom reported on the Delmarva Peninsula (Delaware, Maryland, and Virginia, USA). Limited spatial and temporal monitoring conducted by state agencies and citizen science groups since 2007 have documented that several Karenia species are an annual component of the coastal phytoplankton community along the Delmarva Peninsula, often present at background to low concentrations (100 to 10,000 cells L-1). Blooms of Karenia (> 105 cells L-1) occurred in 2010, 2016, 2018, and 2019 in different areas along the Delmarva Peninsula coast. In late summer and early autumn of 2017, the lower Chesapeake Bay experienced a K. papilionacea bloom, the first recorded in Bay waters. Blooms typically occurred summer into autumn but were not monospecific; rather, they were dominated by either K. mikimotoi or K. papilionacea, with K. selliformis, K. brevis-like cells, and an undescribed Karenia species also present. Cell concentrations during these mid-Atlantic Karenia spp. blooms equalled concentrations reported for other Karenia blooms. However, the negative impacts to environmental and human health often associated with Karenia red tides were not observed. The data compiled here report on the presence of multiple Karenia species in coastal waters of the Delmarva Peninsula detected through routine monitoring and opportunistic sampling conducted between 2007 and 2022, as well as findings from research cruises undertaken in 2018 and 2019. These data should be used as a baseline for future phytoplankton community analyses supporting coastal HAB monitoring programs.