Current distribution and potential expansion of the harmful benthic dinoflagellateOstreopsiscf.siamensistowards the warming waters of the Bay of Biscay,North‐EastAtlantic

Abstract

In a future scenario of increasing temperatures in North-Atlantic waters, the risk associated with the expansion of the harmful, benthic dinoflagellate Ostreopsis cf. siamensis has to be evaluated and monitored. Microscopy observations and spatiotemporal surveys of environmental DNA (eDNA) were associated with Lagrangian particle dispersal simulations to: (i) establish the current colonization of the species in the Bay of Biscay, (ii) assess the spatial connectivity among sampling zones that explain this distribution, and (iii) identify the sentinel zones to monitor future expansion. Throughout a sampling campaign carried out in August to September 2018, microscope analysis showed that the species develops in the south-east of the bay where optimal temperatures foster blooms. Quantitative PCR analyses revealed its presence across almost the whole bay to the western English Channel. An eDNA timeseries collected on plastic samplers showed that the species occurs in the bay from April to September. Due to the water circulation, colonization of the whole bay from the southern blooming zones is explained by inter-site connectivity. Key areas in the middle of the bay permit continuous dispersal connectivity towards the north. These key areas are proposed as sentinel zones to monitor O. cf. siamensis invasions towards the presumably warming water of the North-East Atlantic.

First Characterization of Ostreopsis cf. ovata (Dinophyceae) and Detection of Ovatoxins during a Multispecific and Toxic Ostreopsis Bloom on French Atlantic Coast

“…Hence, the presence of cells of this ribotype in the 2021 bloom sample is not surprising, since it has been reported in the area for several years [ 66 , 67 , 70 ]. In a more recent study, a real-time polymerase chain reaction (RT-PCR) approach on many sampling sites confirmed previous observations, and this species was found in several sites between Comillas (Spain) and Biarritz (France) [ 71 ]. Furthermore, although no cells could be observed to the north of Biarritz, results from RT-PCR showed that eDNA of Ostreopsis sp.…”

“…Interestingly, O. cf. ovata was not previously detected in this area despite a sampling in 2018 at a large geographical scale on the French Atlantic coast and the use of sensitive molecular methods in a previous study in 2018 [ 71 ]. Hence, the hypothesis of a recent introduction cannot be excluded, and the presence of this invasive dinoflagellate might cause new problems in the future, in relation to global warming.…”

“…Furthermore, although no cells could be observed to the north of Biarritz, results from RT-PCR showed that eDNA of Ostreopsis sp. 9 has a wider distribution area in the Bay of Biscay, since it could be detected in other sites in the median part of the Bay (Aquitaine) and up to Brittany [ 71 ]. Interestingly, no other Ostreopsis species have been detected in a previous study in north Spain and Basque coasts, and Ostreopsis sp.…”

“…In a recent study based on eDNA and RT-PCR methods, where numerous samples collected in summer 2018 on the Spanish and French Basque coast were analyzed, no positive result was obtained for O. cf. ovata [ 71 ]. Given the sensitivity of the method, this indicates that, if present, this species was below the detection limit, and it is probably rare.…”

“…ovata was later found in samples from Portugal [ 67 , 68 , 69 ], it has never been detected in northern places such as the Cantabrian and Basque coasts, where only O. cf. siamensis was shown to be present and considered to be the unique Ostreopsis species present in this area to date [ 70 , 71 ].…”