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Brown tides vs. Red tides. What’s the difference?

Familiarizing Yourself with Long Island’s Harmful Algal Blooms 

Another year has come and passed and another record breaking harmful algal bloom plagued the shores of Long Island. In fact, it is estimated that every major waterbody on Long Island - 15 lakes and 20 beaches – was affected by these blooms. While these products of nitrogen pollution and comprised water quality are unfortunately becoming all too common across the island, confusion still exists over the exact definitions for terms like “brown tides” and “red tides”. Since the consequences of both tides differ, knowledge of the distinct characteristics behind each is an essential step in joining the fight to save Long Island’s water quality.

Perhaps the most well-known of the two, “brown tide” algal blooms have most affected the area of the Great South Bay, where the hard clam population has particularly been decimated. Caused by the alga known as Aureococcus, brown tides have the ability to kill off entire shellfish populations and degrade eelgrass ecosystems, which in turn translates into a loss of millions of dollars annually. For instance, in the 1990s, brown tides completely eradicated the $2 million dollar per year Peconic Bay scallop industry, which is only now returning through restoration and seeding efforts. In 2017 alone, one of the worst brown tides on record developed a month earlier than predicted and killed off numerous shellfish and eelgrass populations. While extremely harmful to marine life and local economies, brown tides caused by auerococcus have no known impacts on human health. 

“Red Tides”, frequently caused by the organism known as Alexandrium, on the other hand, often times pose a threat to the health of the public. Most prominent among these threats is the dangers of “Paralytic Shellfish Poisoning”. When ingesting shellfish that has been contaminated with Alexandrium-produced Saxitoxins, humans can begin to feel numbness in their face and extremities, which can lead to a loss of coordination. In severe cases, paralytic shellfish poisoning can lead to respiratory failure and can even be fatal. On Long Island, the existence of saxitoxin-induced paralytic shellfish poisoning in the region’s waterbodies unfortunately led to a mass die-off of dozens of turtles in Peconic Bay back in 2015.

While posing different types of threats to Long Island, the consequences of both Brown Tides and Red Tides cannot be underestimated. Through ongoing and planned nitrogen reducing efforts, it is the Long Island Clean Water Partnership’s hope that the frequency of harmful algal blooms in Long Island’s waters will begin to decline. The goal of ending the dual threats of Brown and Red Tides must play a major role in all future water quality efforts for the island in order to preserve the region’s water, wildlife and industry

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