Warmer Oceans Are Changing the Season for Harmful Algal Blooms

There are two particularly toxic types of algae that can cause problems, when harvesting and eating shellfish along the Norwegian coast: 

• Dinophysis acuta - can cause severe stomach issues
• Alexandrium tamarense – can cause paralysis

In a new study published in Nature Communications Earth & Environment, Edson Silva, a researcher at the Nansen Center and the Bjerknes Centre, along with colleagues, investigated how toxic algae are affected by climate change. Climate change leads to both rising ocean temperatures and increased rainfall on land. More rainfall leads to more river runoff, which brings more freshwater to coastal areas.

Both temperature and salinity in coastal waters affect these two types of algae, and the researchers examined how changes in temperature and salinity influence them.
The algae grow rapidly with moderate temperature increases but do not thrive in overly warm water. A climate with 3°C higher air temperature is expected to lead to more algae blooms in spring and autumn, but fewer in summer.

More Stomach issues

While Dinophysis acuta – which causes stomach issues – is not significantly affected by salinity, increased temperatures alone are expected to cause a 50% annual increase in blooms.
 

Less Paralysis 

The algae that cause paralysis, the Alexandrium tamarense, prefer salty water. They are therefore affected by increased freshwater, and their occurrence is expected to decrease by 40% in a world that is 3°C warmer.

When collecting mussels, you should follow Mattilsynets (the Norwegian Food Safety Authority) mussel warnings. Read their advice for safe shellfish harvesting.