Effects of warming on the toxinology and toxicity of Harmful Algal Blooms (HAB)

Harmful algal blooms (HAB) are an ancient and natural phenomenon that reflects the outgrowth of microscopic phytoplankton in aquatic environments. Events of HAB are associated with human intoxication via the consumption of contaminated seafood with their potent toxins, and to mass mortalities and ecosystematic impacts affecting biodiversity and several economic sectors and related services. Several complex climatic, environmental and anthropogenic factors contribute to the development of HAB, including climate change. Warming water temperature has been suggested and, in some cases, linked to the range expansion of some HAB species. However, the effects of temperature on the toxinology and toxicity of HAB is still being studied. In the present research, the effects of warming temperature on the toxin production of two cosmopolitan HAB species causative of the human poisoning Diarretic Shellfish Poisoning (DSP) and a HAB species responsible for mass mortalities of shellfish were investigated. The DSP-causative species Dinophysis acuminata and D. caudata were cultured under a wide range of temperature, 5–32 °C. Their specific growth was assessed and their toxin productions were quantified using LC-MS/MS, following solid phase extraction (SPE). The toxicity of the shellfish-killer, Heterocapsa circulariquama, was assessed following exposure of Mediterranean mussels, Mytilus galloprovincialis, and Manila clams, Ruditapes philippinarum, over a warming temperature from 15 to 25 °C. Physiological parameters, histological indexes and enzymatic activities were assessed in the shellfish. The results of these studies show that for Dinophysis spp. temperature enhances toxin production via an enhancement of growth, and that H. circularisquama toxicity is enhanced by increased temperature. Ocean warming is expected to enhance the toxinology and toxicity of some HAB species, at least the species used in the present experiments.