In Narragansett Bay, the arrival of warm weather can lead to algal blooms that can form large rusty red or green mats on the water surface, which can create low-oxygen environments and contaminate shellfish – a potential harm to the state’s $14 million oyster and clam wild and farmed harvests.
This rapid growth of phytoplankton is caused by temperate coastal waters mixing with sub-polar currents deep below the surface, along with longer days, warmer water temperatures, and greater availability of light in the water column, that lead to an abundance of available nutrients, such as nitrogen, which fuel temporary surges in various phytoplankton populations.
While some blooming phytoplankton species have no environmental impact, others can produce harmful impacts on wildlife and humans by depleting dissolved oxygen and releasing biotoxins that can accumulate in fish and shellfish. One of the largest toxic algal bloom events to ever occur on the West Coast of the U.S. happened earlier this summer, disrupting recreational and commercial activity from central California to British Columbia.
Understanding the population parameters and behaviors of potentially harmful phytoplankton in New England waters has long remained a high priority for marine biologists in the region.
The fluidity of the coastal environment often leads to the dispersal or migration of large blooms, making the management and observation of these events extremely difficult. Some species are known to double, or triple, their population size in a matter of days once exposed to optimal conditions. Salinity, wind-turbulence, and run-off sources on land can also cause variances in the strength of these events.
Once a population depletes the nutrients within its environment, the bloom collapses and the species must recalibrate. While blooms may only last several days or weeks, their impacts can be severe. In large numbers, some species of phytoplankton can deplete dissolved oxygen within the water and release natural toxins, resulting in the deaths of numerous marine species.
Toxic “red tides” have been a common natural occurrence along the east coast of the U.S. for centuries. Coastal activity such as fishing and aquaculture is often disrupted during spring blooms because of the potential danger for humans linked to exposure.
For nine years, David Borkman, a planktologist from the URI Graduate School of Oceanography, has been observing the presence of the toxic dinoflagellates in Narragansett Bay, specifically, Alexandrium tamarense, Alexandrium peruvianum, and Alexandrium fundyense.
His recently published research in the journal Harmful Algae has shed new light on the expansion of these species in Rhode Island waters. His observation in Narragansett Bay of the Alexandrium peruvianum species – of concern due to its neurological impacts if consumed – is only the third sighting on the East Coast and the first in New England. Other sightings reported in Europe and Malaysia suggest this particular species is an emerging one globally.
Through extensive sampling of surface water and subsequent laboratory analysis, Borkman has verified that an indigenous population of Alexandrium exists in the Wickford Cove area of Narragansett Bay. While some occurrences of Alexandrium in Narragansett Bay can be linked to larger regional blooms, these results indicate the first-known re-occurring population in the coastal estuarine waters of Rhode Island.
The extent to which Alexandrium has established itself in Wickford Cove raises several questions regarding its presence in this area:
Has Alexandrium been introduced to Narragansett Bay inadvertently?
Is it an emerging species that will continue to grow and expand?
What impact could Alexandrium have on human activity in the Bay?
According to Borkman’s research, little is known about the extent to which Alexandrium exists in Narragansett Bay outside of Wickford Cove.
“It’s not a question of if it exists in other parts of the bay, it’s a matter of where and how much is there,” said Borkman, explaining that there are between 18 and 30 other species of potentially problematic algae existing in Narragansett Bay.
“Improved monitoring of Narragansett Bay is required to quantify the spatial extent of Alexandrium,” he said in his report. “This is particularly needed because of the burgeoning development of shellfish aquaculture in Narragansett Bay.”
While Borkman’s research has observed the presence of these species, there have been no cases of contaminated shellfish in open areas and there currently isn’t a large enough population for consumers to be concerned.
While there is potential future harm tied to these toxic dinoflagellates, more research is needed to understand how these populations have established themselves in Rhode Island waters, and whether or not their presence will continue to increase and/or pose a threat to shellfishing, wildlife, and humans.
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Evan Ridley | Sea Grant Science Communications Intern and Marine Affairs Graduate student at the University of Rhode Island