What are red tides?

Red tide, algae, bloom

A red tide is the rapid accumulation of a mass of aquatic algae made up of mobile single-celled micro-organisms called dinoflagellates – which means ‘whirling whip’ due to the nature of the tail-like projections that propel them through the water. The algae grows, or blooms, more rapidly than usual in order to consume nutrients that have suddenly risen up from the colder depths of the ocean below. The red hue is down to the presence of a certain species of dinoflagellate, or phytoplankton.
Together with the more abundant diatom algae, dinoflagellates make up the majority of ocean plankton. Despite the rather startling appearance of a sea turned red, many algal blooms are actually harmless. However, you shouldn’t consume seafood following a red tide as certain phytoplankton can release harmful substances into the water. Some dinoflagellates can produce toxins when eaten by other creatures and the harmful substances then concentrate inside the creatures that feed on them, and subsequently any humans who go on to dine on the contaminated seafood.
The billions of microscopic dinoflagellates in a red tide can also cause spectacular bioluminescence at night. One species in particular – the lingulodinium polyedrum – can create its own light from within. When the organism is jostled or collides with something in the ocean, a chemical reaction occurs when an enzyme called luciferase and a substrate called luciferin, both contained within the organism, combine. This is the catalyst for a chemical reaction that releases a flash of blue light. When this occurs millions of times simultaneously, the effect is quite remarkable for onlookers.