Algal blooms become a problem for two main reasons, One, they can be filled with toxic species, and two, large growth of algae leads to large die-off of algae, which, in turn, suck the oxygen from the water and cause large die-offs of other organisms.
In Maine, the toxic species of note are dinoflagellates in the genus Alexandrium, usually A. catenella. In Florida, which has large blooms every year, the dinoflagellate Karenia brevis is the species of most concern.
Dinoflagellates are microscopic single-celled photosynthesizing plankton (phytoplankton). They have two flagella; one wraps the cell and causes a spinning movement. This is where the name dinoflagellate comes from; the dino root means whirling. Dinoflagellates are common all over the planet in marine and fresh waters, only a few species are toxic.
The common name for a toxic algal bloom is Red Tide, a misnomer for two reasons. First, toxic levels can occur far below when the water appears a different color, and second, often, the algae pigment does not cause a red color of the water, but some other color change. The current bloom is brown.
This bloom in the Gulf of Maine does not appear to house many toxic dinoflagellates. Instead, the bloom consists of the dinoflagellate Tripos muelleri (pictured above). The forecast issued by NOAA for toxic plankton blooms in the Gulf of Maine predicted toxic bloom chances to be low this year (2023).
As I mentioned above, toxins are only one issue with massive algal blooms. Another problem is that when mass blooms occur, die-offs follow. The organisms (primarily bacteria) break down the dead cells and use oxygen. Thus, large masses of decaying cells use up large amounts of oxygen.
This is why mass fish kills occur along ocean shorelines and lakes after algal blooms. These “fish” die-offs do not just kill the fish; the fish are usually the most visible and recognizable organisms.
One short-term consequence of large algal blooms is a rise in pH. As algae use up carbon dioxide, free hydrogens in the water are shifted into molecules. Fewer free hydrogen ions equals a rise in pH. This is the opposite of what is happening worldwide as carbon dioxide increases in the atmosphere and more and more dissolves into the world’s waters, causing lower pH (more acidic conditions). The change is temporary as consumers eat the algae and expel more CO2. Then the short-lived algae begin to die—the bacteria feast, using the oxygen (causing die-offs as mentioned above) and expel more CO2. An interesting note: The change in CO2 and pH is one thing that alerted researchers to the massive bloom in the first place.
What is the cause of this massive algal bloom in the Gulf of Maine? So far, the question remains unanswered. However, researchers are looking; perhaps I’ll update you in another post when the reasons are evident.
Sources and Further Readings:
Anderson, D.M. 1997. Bloom dynamics of toxic Alexandrium species in the northeastern U.S. Limnology and Oceanography 42(1009-1022).
Brosnahan, M. L., Fischer, A. D., Lopez, C. B., Moore, S. K., & Anderson, D. M. 2020. Cyst-forming dinoflagellates in a warming climate. Harmful Algae 91.
Dolan John: Photo of Tripos muelleri.
McGillicuddy Jr. DJ, Brosnahan ML, Couture DA, He R, Keafer BA, Manning JP, Martin JL, C.H. Pilskaln, Townsend DW, and Anderson DM. 2014. A red tide of Alexandrium fundyense in the Gulf of Maine. Deep Sea Res Part 2 Top Stud Oceanogr. 2014 May 1; 103: 174–184. doi:10.1016/j.dsr2.2013.05.011
NOAA. NCCOS, Gulf of Maine Alexandrium catenella Predictive Models. https://coastalscience.noaa.gov/science-areas/habs/hab-forecasts/gulf-of-maine-alexandrium-catenella-predictive-models/
WoRMS taxa: https://www.marinespecies.org/aphia.php?p=taxdetails&id=495363
Ceratium tripos (O.F.Müller) Nitzsch, 1817 accepted as Tripos muelleri Bory de Saint-Vincent, 1826.