Characteristics of a Dinophysis cf acuminata Population from a Tidewater Glacier Lagoon in a Temperate Latitude: Applications to Dinophysis Studies

<i>Dinophysis acuminata</i>, the main agent of diarrhetic shellfish poisoning (DSP) worldwide, shows a high variability in morphology and toxin content between strains from contrasting habitats. Most frequent uncertainties in morphological discrimination are within the "<i>D. acuminata</i> complex", but confusion with other species (e.g., <i>D. norvegica</i>, <i>D. fortii</i>) also occurs. Here we describe a unique PTX2-containing population of <i>Dinophysis</i> cf <i>acuminata</i> observed during opportunistic samplings in San Rafael Lagoon (Chilean Patagonia), the only tidewater glacier lagoon remaining in the glacier with the world's lowest latitude. <i>Dinophysis acuminata</i> was the only <i>Dinophysis</i> species observed during three seasonal surveys in the well-mixed cold (4-7° C) and brackish (salinity 14-15) waters of the lagoon. Cell densities ranged from 500 cells L^-1 (winter) to 2800 cells L^-1 (summer). Partial sequences of their ITS rDNA aligned them with <i>D. acuminata</i> strains from Europe and North America, and sequences of their stolen plastids 23S rDNA confirmed ciliates of the <i>Mesodinium rubrum</i> + <i>major</i> complex as their prey and plastid source. All these reasons make this lagoon a highly sensitive area and natural laboratory for climate change-related topics and <i>Dinophysis</i> issues related to (i) the effect of long-term exposure of marine fauna to pectenotoxins and (ii) the adaptations of <i>D.</i> cf <i>acuminata</i> to persist in a unique ecosystem with austral water characteristics located in a warm temperate latitude light regime. Results here add knowledge to the biogeography and habitat ranges of <i>D. acuminata</i> and the problems faced to monitor and provide early warning of its distribution.