🌅 The Most Toxic Algal Species Known to Science

SOURCE

Murray et al. (2026)

WHAT TO KNOW

• For the past 15 months, a harmful algal bloom has crept its way across an area of more than 7,700 square miles off the South Australian coast. The bloom has sickened residents and tourists, and killed millions of fish, birds, shellfish, and marine mammals, with no end in sight. Last year, researchers at the University of Technology Sydney tested the bloom and identified the microalgae Karenia cristata as the source of the neurotoxins. Now, the same research team is back with a new paper and deeper analysis of K. cristata, discovering the microalgae is likely the most toxic algal species ever tested.

WHY IT MATTERS

• The researchers found K. cristata is lethal even in extremely low concentrations, killing half of the invertebrates the team studied with as little as five cells per milliliter (or 5,000 cells per liter) of seawater, making it more deadly than any other toxin-producing algae ever tested (for context, the team routinely recorded samples of seawater that contained more than 1 million cells of K. cristata per liter). The lead author of the study described K. cristata as “an order of magnitude more toxic than the next most toxic microalgae that has been studied to date.”

CONNECT THE DOTS

• Hundreds of species of microalgae can be harmful when they accumulate in large numbers, often referred to as an “algal bloom.” Interestingly, scientists don’t fully understand what causes algal blooms, however, research suggests factors like wind, ocean currents, water temperature, extreme weather events, and nutrient runoff from farms and lawns play a role. Until the present study, researchers believed the most toxic algal species were restricted to areas of warm water, like the southeastern U.S. Now, it’s clear that not only is K. cristata likely the world’s most toxic species, it can also proliferate in cooler waters.