Red Tide Monitoring

Online Phytoplankton Database
Pictures of Non-toxic Phytoplankton
Identification Guide.pdf (large file: 16 MB)
2004 Phytoplankton Data
Article on Shellfish Poisoning
Monitoring on Swans Island and Frenchboro

What Are We Looking For?

MDIWQC monitors the water around MDI for the Maine Shore Stewards program. When we monitor for phytoplankton we are trying to detect 4 toxic types of organisms: Alexandrium, Prorocentrum, Pseudonitzchia, and Dinophysis. These species of phytoplankton are the kind that cause some of our red tides and when they are filtered through shell fish and consumed by humans, they cause paralytic, diuretic, or amnesic shell fish poisoning. Each are serious conditions that people could die from if they could not get immediate help after consumption.

Alexandrium

Alexandrium is an extremely toxic phytoplankton that inhabits Maine's coastal waters. These cells are often irregularly shaped. They are one of the most toxic phytoplankton and frequently treated for in the region. The size ranges from 20-50 microns wide, and 20-45 microns long. Alexandrium is a dinoflagellate. This organism can cause an illness in humans called paralytic shellfish poisoning (PSP).

Prorocentrum Lima

As with many other phytoplanktons, there is more than one species of Prorocentrum, but there is only one, prorocentrum lima, known to be toxic to humans. They are a dinoflagellate, and might be the most common bloom of a dinoflagellate in the state of Maine. The size of these cells range from 10-70 microns in length, and 10-50 microns wide. They are often in the shape of a raindrop and have a small spine attached to the rounded end of the cell. This pine helps them propel through the water. Not all species of Prorocentrum have this spine present. Prorocentrum lima is known to cause diuretic shellfish poisoning (DSP).

Dinophysis

Unlike Prorocentrum and Alexandrium, Dinophysis is a lot easier to identify. Its size ranges from 35-100 microns in length and 20-60 microns in width. Dinophysis has an oval shaped cell, with a "wing" on the side, which is supported by three "ribs". Dinophysis has been known to cause diuretic shellfish poisoning (DSP).

Pseudonitzchia

Pseudonitzchia is a toxic phytoplankton that causes amnesic shellfish poisoning (ASP). They are most commonly found as chain-forming cells. Overlapping of one cell over its neighbor makes the chains. Their sizes range from 70-170 microns in length and 2-8 microns in width. Pseudonitzchia is very easy to identify but can commonly be mistaken for Rhizosolenia, and vice versa. Pseudonitzchia is a diatom.

A Tale of Two Phytoplankters

When our monitors began to sample water in the fall of 1998, we started observing a toxic species of phytoplankton called Pseudonitzchia. This phytoplankton releases domiac acid into a shellfish while it is filter feeding and the acid causes Amnesiac Shellfish Poisoning (ASP) when digested in humans. We thought that it was a very serious issue, but since we had only made a few encounters with this species we felt that we should continue to monitor, watching closely for more Pseudonitzchia, before making any assumptions. We identified this species in many later samples that we observed. Our Lab Biology teacher, Dr. Disney felt that we should call the Department of Marine Resources (DMR) and find out if they were detecting the same Pseudonitzchia as well. The DMR told us that they were seeing no Pseudonitzchia, although they would go to our testing site in Bar Harbor and take their own samples. They reported back to our school that what we had identified as the toxic phytoplankton Pseudonitzchia, was really a non-toxic species called Rhizosolenia.

Our team gathered information on Rhizosolenia and compared our samples to the many pictures that we found. What we had found was really Rhizosolenia and not Pseudonitzchia. These two species are very easy to confuse. Their characteristics are very much the same. They both are found in chain like cells, and range from 70-170 microns in length and 2-8 microns in diameter. They only difference between the two is that Pseudonitzschia has tips that over lap its neighboring cell and Rhizosolenia has points that can either come to a needle like point or remain one cell and not connect with any others. Through these mistaken identities we have learned that we should more closely at the samples that we take and research the data we collect. Also getting information from people and places like the DMR really helps us learn about the species we are identifying.