Skip to content


Blooming algae off the South West coast

21 August 2020

The last couple of weeks have seen a burst of biological activity off the south coast of the UK. From dolphin sightings to tuna shoals off Plymouth, our local marine environment has been a hub of activity.
Satellite image showing Chlorophyll-a concentrations, which can be used to detect blooms.

Not so noticeable however, was the surge of life in the microscopic world for which often only the impacts are seen. Specifically, PML scientists noticed an increase in the quantity of a potentially harmful algal species, called Karenia mikimotoi, during their weekly sampling of the local waters and found concentrations as high as 24,500 cells per litre.

Karenia mikimotoi  is a photosynthetic dinoflagellate commonly found in the Western English Channel but was first reported in Japan in the 1930s. Often referred to as a ‘red tide’, when this species ‘blooms’ it can have harmful impacts upon the marine environment by reducing in-water oxygen levels and shading out sunlight, potentially causing mortality to marine organisims. It has also been suggested that Karenia mikimotoi produces a weak toxin, which again, can cause mortality in fish and shellfish. About 100 algal species are now considered ‘harmful’ due to the detrimental effects large blooms can have on the marine ecosystem and sometimes, humans too.

Satellite image showing Chlorophyll-a concentrations, which can be used to detect blooms. Produced by NEODAAS from data collected by the VIIRS sensor onboard a the National Oceanic and Atmospheric Administration (NOAA) SUOMI satellite.

From PML’s processed satellite images, generated from National Oceanic and Atmospheric Administration (NOAA, US) satellite data by the NERC Earth Observation Data Acquisition and Analysis Service (NEODAAS), the bloom can actually be seen from space. Then through the pioneering S3 EUROHAB portal, developed at PML, the team can even be fairly certain of the species of these tiny organisms without having to leave their desks.This is achieved by identifying the ‘optical fingerprint’ that is almost unique to each species en masse. Satellite sensors detect the light signature that is being reflected back into space and from this, scientists have classified key algal species and identified those that are harmful.


The S3 EUORHAB portal then uses classification algorithms to establish the likely risk of HAB species being present and provides a traffic light alert system. The S3 EUROHAB portal can also provide a risk indication for other harmful species, such as Pseudo-nitzschia and Phaeocystis, as well and visually display other ocean conditions, such as sea surface temperature, turbidity and phytoplankton biomass.

Using satellites and associated products to identify possible HAB species is far more cost-effective and realistic than in situ sampling, which is expensive and could be likened to looking for a needle in a very large, wet haystack. Having said that, in situ sampling is still an important aspect of monitoring the changes and health of our marine environments as well as providing validation for satellite data. By the two methods working in conjunction with each other, we can have a far better understanding of what is happening in this dynamic environment.

Looking to the future, the PML team will continue to advance this area of science by improving processing techniques, expanding the list of identified classified species and developing artificial intelligence (AI) algorithms to streamline the detection of HABs.

Related information

NERC Earth Observation Data Acquisition and Analysis Service (NEODAAS)

S3 EUORHAB portal