Phytoplankton and Algal Blooms Identification


Our Phytoplankton monitoring programme is essential to monitor both harmful species and also to study trends in water quality. 

Phytoplankton are possibly the most important group of organisms on the planet as they generate most of the oxygen that we breath. Also, as they convert inorganic nutrients and sunlight into vegetative matter, most marine food chains depend on their presence as a primary food source. A small proportion of species produce highly potent toxins and the monitoring of these are very important to ensure food safety.

Photo of redtide credit: Irish Air CorpsNoctiluca Scintillans

Some interesting facts about this group:

  • They generally photosynthesise to survive – although some eat other species.
  • They can exist in solitary form but some form chains or spherical shaped colonies.
  • They generate most of the planet's oxygen.
  • They are of enormous importance in the aquatic food chain.
  • They have been responsible for producing the reserves of hydrocarbon fuels beneath the sea.

Algal Blooms

Photo of offshore redtide south east Ireland.Most individual phytoplankton are too small to be seen with the naked eye. When present in high numbers however, their presence may appear as dramatic discoloration of the water

such as the aerial photos taken by the Irish Air Corps in the Southeast Irish Sea shown on this page. This population growth can be rapid, and typically occur when temperature and nutrient levels rise, usually in late Spring and Autumn. It is commonly known as an “algal bloom”. The colour of a bloom can vary from a green to a dark red colour depending on the phytoplankton present.

While blooms can provide more food to organisms higher up the food chain, too much phytoplankton can also do harm. Dissolved oxygen becomes rapidly depleted as the phytoplankton die, sink to the bottom and decompose. This can result in the death of other organisms including shellfish, crabs and fish.


Ceratium TriposThe main groups of Phytoplankton include Diatoms, Dinoflagelates, Coccolithophorids and Micro-Flagellates. Each of these groups has distinguishing features that allow specialists to identify them to species level.

Download an identification sheet (PDF, 177KB) for the most important problematic species.

For further information contact: Rafael Salas