Quick Dips

Red Tide

Natural blooms of the protozoan Mesodinium rubrum have caused several red tides around the Auckland region recently.

M. rubrum blooms occur in coastal waters all around New Zealand. They tend to happen in spring, and after rainfalls following long dry spells in summer. They have also been recorded off the coast near coastal upwellings, where they are thought to be associated with movement of nutrients from deep to surface waters.

The blooms can reach densities of 20,000 organisms per millilitre of seawater, and usually last for about a week. Although the die-off of a very dense bloom can cause oxygen depletion in very sheltered waters, they usually cause few problems.