July 18, 2018


Kristin Russo, Bureau of Aquaculture

The Department of Agriculture (DoAg)’s Bureau of Aquaculture is responsible for monitoring the levels of phytoplankton in coastal waters.

The phytoplankton DoAg is looking for consists of algae and dinoflagellates, both of which have the potential to produce toxins that can affect shellfish consumption.

Due to their filter feeding nature, shellfish have the ability to concentrate toxigenic dinoflagellates from the water column when the dinoflagellates are present in shellfish growing waters. The toxins produced by the dinoflagellates can cause illness and death in humans.

The danger of these toxins is that they are not typically destroyed by cooking or processing and cannot be detected by taste.

Since the dinoflagellates are naturally occurring, their presence in the water column or traces of their toxin in shellfish meat does not necessarily constitute a health risk.

To protect the consumer, DoAg must evaluate the concentration of the toxin present in the shellfish or the dinoflagellate concentration in the water column against the levels established by the National Shellfish Sanitation Program (NSSP) Model Ordinance to determine what action, if any, should be taken.

There are three types of shellfish poisonings which are specifically addressed in the NSSP Model Ordinance relevant to the waters of Connecticut: paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP) and amnesic shellfish poisoning (ASP), also known as domoic acid poisoning.

All three are dangerous toxins, and PSP and ASP can cause death at sufficiently high concentrations. In addition, ASP can cause long lasting neurological damage. PSP is caused by dinoflagellates of the genus Alexandrium. NSP is caused by brevetoxins produced by the dinoflagellates of the genus Karenia.

Both of these dinoflagellates can produce “red tides”, i.e. discolorations of seawater caused by the blooms of algae. Toxic blooms of these dinoflagellates can occur unexpectedly or follow predictable patterns.

Historically, Alexandrium blooms have occurred between April and October along the Pacific coast from Alaska to California and in the Northeast from the Canadian provinces to Long Island Sound—but these patterns may be changing.

The blooms generally last only a few weeks and most shellfish, with the exception of clams which retain the toxin for longer periods, clear themselves rapidly of the toxin once the bloom dissipates. The suitability of some growing areas for shellfish harvesting is periodically influenced by the presence of PSP, ASP, and NSP, or other marine biotoxins.

The occurrence of these toxins is often unpredictable, and the potential for them to occur exists along most coastlines of the United States and other countries having shellfish sanitation Memoranda of Understanding (MOU) agreements with the United States.

As a result, states or countries with MOUs with the United States need to make contingency plans to address shellfish-borne intoxications.

DoAg staff regularly sample for hazardous algal blooms (HABs) during the months of April to October using three methodologies, the most frequently being phytoplankton net sampling. With regular water sampling phytoplankton samples are collected from 34 sites using a vertical plankton tow.

The samples are then brought back to the lab to be identified and counted. Each phytoplankton net is set up with a rotor to measure the amount of water flowing through the net during a sample.

This information is then used to calculate the number of any identified species in the sample.  Phytoplankton sites are ranked to encourage a heavier focus in areas of historic concern and those that are heavily harvested.

DoAg works with officials in Rhode Island and New York to determine the level of threat of HABs from these surrounding states.  Rhode Island historically has more frequent and severe HABs than occur in Connecticut—so frequent that in 2016 they began to sample for HABs all year round.

Although Connecticut has not seen the HABs that other states within New England have seen, DoAg is prepared to handle more intense and frequent sampling.