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Harmful Algal Blooms and Marine Biotoxins

What is it?

The ocean is full of phytoplankton, small plant-like organisms (algae) that are invisible to the human eye and form the basis of the aquatic food chain. Most are harmless and are important for their role as food for certain marine species. Yet, there are some species that, if given the right conditions, can grow rapidly, creating a widespread "bloom" that overwhelms marine habitats and wreaks havoc on the ecosystem. Scientists refer to these "blooms" as harmful algal blooms (HABs). Additionally, of the various species that may cause these HABs, there are a handful that can produce dangerous toxins (marine biotoxins) that are harmful to the health of marine organisms and humans.

Harmful algal blooms may color the water red or brown, and are often referred to as "red tide" or "brown tide". The discoloration of the water is caused by the millions of microscopic phytoplankton that bloom. However, some algal blooms that color the water may have no harmful impacts.

Algal Blooms and Marine Biotoxins in New York

Harmful algal blooms (HABs) and marine biotoxins are a part of the marine ecological community in New York State marine waters. Within the past twenty-five years, HABs, such as the brown tide bloom in the 1980s and 1990s, have devastated areas of New York coastal waters, threatening important habitat, disrupting food chains for many marine species, and impacting economically viable fisheries.

Alexandrium spp. Courtesy of NYS DEC Shellfish Lab
Alexandrium spp
Courtesy of NYS DEC Shellfish Lab

Toxic Marine Algal Blooms

One species of phytoplankton has made a strong appearance in Long Island waters, Alexandrium spp. Alexandrium spp. has been present in Long Island waters since the 1970s and made its first harmful bloom on Long Island in 2006, causing large shellfishing closures in Northport and Huntington Harbors in the Town of Huntington (Northwest Suffolk County).

How Is It Harmful to Humans?
The algae, Alexandrium spp. produces saxitoxin, a dangerous neurotoxin that can destroy, damage, or impair the functioning of nerve tissue. Molluscan shellfish like scallops, mussels and clams, that filter particulates out of the water for food can filter in these toxic Alexandrium cells from the water. Saxitoxin can then be concentrated in the body tissues of these shellfish and make them very dangerous for human consumption.

Symptoms from Consuming Toxic Shellfish: Saxitoxin causes Paralytic Shellfish Poisoning (PSP), which includes numbness and tingling in the face and extremities, followed by headache, dizziness, nausea and a loss of coordination. According to the Center for Disease Control, when people consume saxitoxin in sufficient quantities, the onset of symptoms can be rapid, anywhere from between 15 minutes to 10 hours after eating the contaminated shellfish. In mild cases, the individual might recover in a few days; however, in more severe paralysis, respiratory failure and death can occur within two to 25 hours. Unfortunately, saxitoxin cannot be removed through cooking as it accumulates in the tissues of molluscan shellfish.

Map of Long Island monitoring sites
Long Island biotoxin monitoring sites.

Marine Biotoxin Monitoring Program

The Division of Marine Resources Shellfisheries Bureau conducts marine biotoxin monitoring of local waters to identify where these toxic HABs may be occurring in order to protect human health.

Searching for Biotoxins in Long Island Waters

Every year, beginning in the spring and continuing through the fall, the Shellfisheries Bureau conducts an extensive Marine Biotoxin Monitoring program across Long Island. We search for the presence of Alexandrium cells in the water column as well as the presence of saxitoxin in molluscan shellfish. Alexandrium is a microscopic, photosynthetic dinoflagellate. It is widely distributed along the coast and lives in the upper layer of the ocean. This dinoflagellate produces saxitoxin, the neuromuscular toxin that causes Paralytic Shellfish Poisoning (PSP). The toxin accumulates in the tissues of any animals that eat the dinoflagellate and may be present in high concentrations in shellfish. Eating shellfish that may have consumed Alexandrium may pose a health threat for animals and humans.

A staff deploying a biotoxin Monitoring bouy into the sea
Shellfisheries staff deploying a biotoxin monitoring

Monitoring Technique

We have deployed mesh bags of blue mussels that are suspended in the water at sites around Long Island. The map above shows the location of our monitoring sites. Mussels are collected from the bags weekly and are examined for the presence of saxitoxin. In addition, samples of locally harvested clams and oysters and samples of shellfish from wholesale markets are examined for the presence of saxitoxin. When mussels from a site test positive, the surrounding area is immediately closed to the harvest of molluscan shellfish and won't reopen for harvest until three consecutive tests over a two week period come back negative for the toxin. Closures resulting from the presence of toxins are reported on the Temporary Shellfish Closures page.

We use blue mussels as our test organism because they concentrate the toxin faster than other species of shellfish. When we collect mussels at each site, we also collect a plankton sample from the water and look for the presence of Alexandrium at the site.

Non-Toxic Marine Algal Blooms

Long Island residents are likely familiar with the term "brown tide". The term is generic, which can refer to several different phytoplankton species that color the water brown at high concentrations. The species most common in Long Island waters is Aureococcus anophagefferens. Unlike Alexandrium spp., as described above, this organism produces a non-toxic bloom and is harmless to humans. Aureococcus has been found in both Great South Bay and Peconic Bays.

How Are Non-Toxic Algal Blooms Harmful?
At high concentrations Aureococcus can significantly decrease the amount of sunlight that penetrates through the water, thereby reducing the ability of other plants and algae to produce the energy they need to survive. This shading effect results in the mortality of important habitats like eelgrass beds and can also inhibit the ability of shellfish to eat, grow and reproduce. Additionally, Aureococcus can deplete oxygen levels in the water causing much marine life to move out of the impacted area.

Freshwater Harmful Algal Blooms

Different algae species, particularly blue-green algae, can also form harmful blooms in freshwater. These freshwater harmful algal blooms occur in lakes and ponds across New York State.