No abstract

Marine heatwaves (MHWs) have doubled in frequency since the 1980s and are projected to be exacerbated during this century. MHWs have been shown to trigger harmful algal blooms (HABs), with severe consequences to marine life and human populations. Gymnodinium catenatum, a paralytic shellfish toxin (PST) producer inhabits temperate and tropical coastal waters. This study aims to understand, for the first time, how MHWs impact several parameters relating to cell growth and toxin production of this species. For that, two MHW were simulated - category I (i.e., peak: 19.9°C) and category IV (i.e., peak: 24.1°C) - relative to baseline in Cascais, Portugal (18.5°C). Based on several physiological parameters – e.g., no changes in abundance, size, photosynthetic efficiency and toxin production -G. catenatum showed to have high tolerance to MHWs. However, MHWs may have elicited sublethal effects since chain-formation was significantly reduced under category IV MHW, suggesting these conditions may be sub-optimal growth conditions for this population. Regarding the toxin profile, a significant decrease in several compounds with increased severity of the MHW was observed. Our study suggests the increase in frequency, intensity and duration of MHWs may lead to reduced severity of G. catenatum toxic blooms.

Marine heatwaves (MHWs) have doubled in frequency since the 1980s and are projected to be exacerbated during this century. MHWs have been shown to trigger harmful algal blooms (HABs), with severe consequences to marine life and human populations. Within this context, this study aims to understand, for the first time, how MHWs impact key biological and toxicological parameters of the paralytic shellfish toxin (PST) producer Gymnodinium catenatum, a dinoflagellate inhabiting temperate and tropical coastal waters. Two MHW were simulated—category I (i.e., peak: 19.9 °C) and category IV (i.e., peak: 24.1 °C)—relative to the estimated baseline in the western coast of Portugal (18.5 °C). No significant changes in abundance, size, and photosynthetic efficiency were observed among treatments. On the other hand, chain-formation was significantly reduced under category IV MHW, as was PSP toxicity and production of some PST compounds. Overall, this suggests that G. catenatum may have a high tolerance to MHWs. Nevertheless, some sublethal effects may have occurred since chain-formation was affected, suggesting that these growth conditions may be sub-optimal for this population. Our study suggests that the increase in frequency, intensity, and duration of MHWs may lead to reduced severity of G. catenatum blooms.