Harmful Algal Blooms
Bay's Small Algae Can Cause Big Trouble
(Published by The Quoddy Tides, June 28, 2002)
Some of the most dangerous organisms in Cobscook Bay come in tiny packages. The bay is home to a variety of very small algae, called phytoplankton. Individuals of these algae can only be seen through the lens of a microscope, and serve as food for marine animals of all types and sizes. However, four species of phytoplankton here are known to cause very serious illness in humans, and can have a big impact on the local economy.
Every year, toxic red tides lead to the closure of clam flats up and down the coast of Maine. Red tides are the bloom of a phytoplankton called Alexandrium, which generally occur during the warm weather months. When the number of Alexandrium in the water reach high numbers, it can turn the water a reddish color. As clams filter the water during a bloom, the Alexandrium concentrates in the clam stomach.
"While Alexandrium does not harm the clam, the toxins it contains cause Paralytic Shellfish Poisoning, or PSP, in humans. If people eat clams during a red tide, the PSP toxins can shut down their respiratory system and can cause death," explains Heidi Leighton of the Cobscook Bay Resource Center (CBRC) in Eastport. The state Department of Marine Resources relies on CBRC to give early warnings about the presence of harmful phytoplankton in Cobscook Bay.
The other phytoplankton species of concern monitored by CBRC and the state include Dinophysis, Prorocentrum lima (called P. lima for short), and Pseudonitzschia.
Stephanie Allard, who teaches the marine resources class at Shead High School, has introduced these microscopic plants to her students for the past five years. This past spring, you may have seen Allard and her students down at the breakwater collecting water samples.
"After collecting samples, the students go back to the lab and identify the different organisms under microscopes," says Allard. "This year we started really early when the water was cold. At first, we didn't see much diversity, only three species of phytoplankton. By the last [sampling] tow, we saw up to 12 different species."
"The students create a field guide by drawing what they see and identifying it," Allard explains. "They also research the illnesses caused by some phytoplankton and do a Powerpoint presentation for the class."
"It is really amazing to watch the phytoplankton moving around under the microscope and to know some of them can cause such sickness. The phytoplankton are very pretty. I am amazed at how interested the students are in looking at them under a microscope," Allard says.
In past years, the students have contributed data to a statewide effort to monitor coastal waters for phytoplankton that pose public health risks. This year, they did not send in data, but did spend some time with Leighton to learn about scientific sampling techniques.
Allard adds, "It's good for the kids to meet Heidi and see her doing this work, because she graduated from Shead High School and came back to work here. She's a good role model for students."
CBRC monitors five sites from the municipal piers of Lubec to Robbinston all year round, but more frequently in the summer (twice a week).
"Phytoplankton nets are used to take tows," explains Leighton. "We use a 3 foot long piece of mesh attached to a sample jar, with a wider end at the top of the net and a narrow end, or cod-end, at the bottom. We tow it up and down in the water column for three minutes, called swimming the net. The net acts as a filter, with all the water going out of the net and the bigger phytoplankton falling down to the bottom."
This technique is used to sample for Alexandrium and also Dinophysis, a toxic phytoplankton which causes diarrhetic shellfish poisoning (DSP) in humans.
P. lima, which also causes DSP, requires a different sampling method. P. lima is usually found attached to brown filamentous macroalgae; here it is found in association with a species called Pilayella.
"We take a sample of brown hairy seaweed off a dock or pier and shake it in a bag of seawater for at least a minute. After filtering the water through a series of sieves we look at the remaining sample under a microscope," says Leighton. "P. lima wasn't thought to occur in northern U.S. coastal waters, but 3 to 4 years ago it was found in southern Maine. We haven't found it yet in Washington County."
Pseudonitzchia is of concern in Cobscook Bay and nearby Canadian waters because it produces domoic acid, and concentrates in oysters, clams and quahogs during blooms. Domoic acid can cause amnesiac shellfish poisoning (ASP), which leads to irreversible memory loss and even death if consumed in large doses. Shellfish harvesting bans have been in place off and on since April on many inland and tidal waters of the Maritime Provinces due to the presence of this toxin.
Frequent monitoring by CBRC provides DMR with information about what phytoplankton species are in the water. DMR also samples shellfish meat to analyze them for the toxins found in Alexandrium.
Jay McGowan, marine resource scientist for DMR at the Lamoine lab, says, "Once a week we go down to stations in the Cobscook Bay area in coves or on a point of land, and collect shellfish samples from clams or mussels. At the lab, we do what is called a mouse bioassay of shellfish tissues."
During this process, liquid is extracted from the shellfish. The liquid is stabilized in acid and cooked for five minutes, then injected into the stomach lining of a mouse. If the toxin is there, it will kill the mouse. The amount of time it takes the mouse to react to the toxin tells them how much of the toxin is there.
"If we have a strong enough concentration of toxins, we will close the area to clam digging. We do this from April to October," McGowan says.
Keeping a careful watch over the many different types of phytoplankton carried by the tides of Cobscook Bay is important to public safety and to the economic health of the region. Working with CBRC and other partners along the coast allows DMR to better focus its resources to make the smallest and most accurate public health closures for the shortest amount of time.
This column was prepared by Cheryl Daigle. Cobscook Bay
Soundings was a monthly column produced by the Maine Chapter
of The Nature Conservancy.
Return to Cobscook Bay Resource Center homepage.