Harmful algal blooms

Harmful Algal Blooms (HABs) present a major problem, often made worse by pollution and temperature changes, they can cause massive mortality of marine and freshwater life through eutrophication and toxins.

In Chile, blooms were initially restricted to the Magallanes region, but in recent years they have spread northward to the Aysén and Los Lagos regions and have become more frequent, more intense, widespread and catastrophic. For example, in early 2016 extensive blooms of Alexandrium catenella strongly impacted aquaculture in southern Chile. An increasing number of toxic algal species have also been causing events (eg Clement et al., 2016), but A. catenella remains the dominant species of concern.

The term “red tide”, although it is widely used, has been substituted in the technical scientific literature by the term Harmful Algal Blooms (HAB), since in most cases these phenomena do not produce a red coloration or reddish from the water.

Global products for red tide detection

These blooms usually give a distinct coloration visible in the images, such as red tide, although the coloration varies depending on the type of bloom.

Given the importance of knowing how these blooms affect aquatic life, remote sensing techniques have been developed using a variety of available images.

World map showing Sentinel-3 OLCI Level-2 Algal Pigment Concentration.  Map: EUMETSAT, 2017.