Red Tide

What is 'Red Tide'?

A red tide is also known as a harmful algae bloom (HAB). The algae often turns the water red, hence 'red tide'. Some species:

Alexandrium fundyense 

Alexandrium catenella

Karenia brevis

How Does This Affect Animals?


This bloom is caused by microscopic toxic algae that can kill fish, shellfish, mammals, and birds, and may cause illness in people. HABs also include non-toxic species that have harmful effects. For example, when algae decompose, it can  cause the water to become so unoxygenated that animals either leave or die. A red tide in 1996 killed 10% of Florida manatees and 162 dolphins in Mexico. A red tide bloom in 2005 resulted in a widespread hypoxic  zone off the coast of Southwest Florida.  Significant amounts of bottom-dwellers died.


What Causes HABs to Bloom?


Major factors inducing red tide include warm ocean surface temperatures, low salinity (amount of salt water), high nutrient content, calm seas, and rain followed by sunny days during the summer. Red tide can spread or be carried long distances by winds, currents, storms, or ships.

How Does Climate Change Affect This?

 As climate change worsens, sea level rises and water increases in temperature. Algae, including red tide, thrive in unusually warm waters. Therefore, climate change will fuel 'red tide'.

How Does 'Red Tide' Move/Reproduce?


Like other dinoflagellates these tiny, single-celled organisms photosynthesize using chlorophyll like a plant, yet they are mobile with the use of two flagella that propel them through the water. Their dominant role of reproduction is asexual cell division –cells divide/split in half. 

Where Can You FInd 'Red Tide'?


Red tide can be found along the Atlantic coast from the Canadian Maritimes to southern New England or along the Pacific coast from California to Alaska. Karenia brevis, the biggest and most troublesome species of red tide, is found in the Gulf of Mexico along the west coast of Florida.