Harmful algal blooms and shellfish aquaculture in changing environment.
Shellfish aquaculture is mainly carried out in sheltered coastal areas that are affected by several anthropogenic stressors, including eutrophication, pollution, biofouling, invasive species, expanding diseases, and harmful algal blooms. In particular, harmful algal blooms (HAB) have been known to cause fish and shellfish kills; contamination of fish, but mainly shellfish, with potent toxins that cause mild to severe poisonings in humans; and in many cases, alteration of ecosystem functions. In shellfish, notably in bivalve molluscs, in addition to mass mortalities, HAB are known to cause acute to chronic physiological and pathological alterations that lead to impediments to aquaculture farms via reduction of bivalve fitness or following closure of production due to long-term contamination with toxins detrimental to human health. The frequency, magnitude, duration, and in several cases, the geographic distribution of HAB have been increasing, putting shellfish aquaculture farms under further stress. Several factors have been attributed to such increase in HAB, including climate change. Range expansions of some cosmopolitan HAB species associated with warming ocean temperature have been reported across the North Atlantic and North Pacific. In addition, range expansions of some other cosmopolitan HAB species have been projected across the North Western European Shelf-Baltic Sea system and North East and South East Asia, associated with increased nutrient loads under projected climate change scenario A1B of the IPCC, IPSL-CM4. Warming water temperature driven by climate change is also expected to induce thermodynamic changes in physiological functions of shellfish, with potential shifts in their thermal sensitivity and performance, and it is also expected to alter the responses of bivalves to HAB. In this mini-review, the effects of HAB and ocean warming - and other climate driven stressors like ocean acidification - on these important cultured shellfish species will be discussed in light of the findings of relevant studies reported in the literature.