Interaction between temperature and salinity stress on the physiology of Dinophysis spp. and Alexandrium minutum: implications for niche range and blooming patterns

Abstract

Abrupt changes in environmental conditions in estuaries and coastal waters have direct (physiological) and indirect (through changes in water column stability) effects on planktonic microalgae. Understanding and quantifying these effects is important to improve harmful algal bloom predictive models. Dinophysis spp. (D. acuminata, D. acuta and D. caudata) and Alexandrium minutum produce toxins that are transferred through the food web (particulate) by filter feeders and also released in the seawater. These dinoflagellates cause lengthy harvesting bans in European aquaculture sites and affect marine life. The 4 species were exposed to different combinations of temperature (T) and salinity (S) to investigate their short-term response (days) to and their recovery (weeks) from T/S stress. Dinophysis species showed varying capacities to deal with sudden changes in S, from the most resilient D. acuminata, equally affected by T and S stress, to the less tolerant D. acuta, and in particular D. caudata, more affected by S than T stress. The euryhaline A. minutum thrived under all the T/S combinations assayed. Further experiments showed a similar rate of okadaic acid toxin production (pg cell-1 d-1) for the 3 Dinophysis species under different T/S conditions. In contrast, a significant increment of gonyautoxin 4 content per cell was observed in A. minutum with decreasing S without significant effects associated with T. Our results highlight the response to environmental (T/S) stress of 3 species of Dinophysis and A. minutum with specific adaptations to thrive in different sub-habitats of the Galician Rías, an estuarine/coastal upwelling system in NW Spain.