Crude oil spills can cause the initiation of harmful algal blooms (“red tides”)

Tuesday 01 May 18


Rodrigo Almeda
Senior Researcher
DTU Aqua

After oil spills and dispersant applications, the formation of red tides or harmful algal blooms (HABs) has been observed, but the link between both phenomena was unknown until now.

In a new study we demonstrate a connection between oil spills and HABs. We determined the effects of crude oil and dispersants on the structure of natural plankton assemblages in the Northern Gulf of Mexico. Large tintinnids and oligotrich ciliates, major grazers of phytoplankton, were negatively affected by the exposure to oil and dispersant, whereas bloom-forming dinoflagellates notably increased their concentration.  The removal of key grazers due to oil spills disrupts the predator-prey controls (“top-down controls”) that normally function in plankton food webs. This disruption of grazing pressure opens a “loophole” that allows certain dinoflagellates with higher tolerance to oil and dispersants than their grazers to grow and form blooms when there are no growth limiting factors (e.g. nutrients). Therefore, oil spills and dispersants can act as disrupters of predator-prey controls in plankton food webs and as indirect inducers of potentially harmful dinoflagellate blooms.

Disruption of microzooplankton grazing control in plankton food webs as a result of petroleum pollution or other toxicants should be considered as an additional factor to understand the causes of increasing occurrence of harmful dinoflagellate blooms in coastal waters with intense anthropogenic pressure. 

The paper can be read here:

Almeda R.*, Cosgrove S., Buskey E. J. (2018) Oil Spills and Dispersants Can Cause the Initiation of Potentially Harmful Dinoflagellate Blooms (“Red Tides”). Environmental Science & Technology, 10.1021/acs.est.8b00335
12 JULY 2020