General Information

Event name: US-20-005
Nature of the harmful event:
Water Discoloration , Seafood toxins
Event directly affected:
Other Terrestrial , Shellfish
Toxicity detected: Yes (Approximate range: 1.5-5.7 ppb microcystin-RR in oysters)
Associated syndrome: OTHER
Unexplained toxicity: No
Species implicated in toxin transmission (transvector):
Report the outcome of a monitoring programme: Yes (Connecticut Department of Agriculture Bureau of Aquaculture (DABA))
Event occurred before in this location: No
Individuals to contact: VAN GULICK, Emily

Location & Date

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Location: Latitude: , Longitude:
General location information: Greenwich Cove, Connecticut
HAB Area code(s): US-07
Additional location information:
Bloom event dates (yyyy/mm/dd): Start: 2020-07-17, End: 2020-12-08
Quarantine levels dates (yyyy/mm/dd):
Additional date-related information:


Causative organism known: Yes
Causative Species/Genus: Microcystis aeruginosa ( cells/L)
<5-10% phytoplankton composition of samples from Greenwich Cove. Microcystis was not present in Binney Pond on 7/17. Dr. Dianne Greenfield, a DABA colleague, confirmed the presence of Microcystis aeruginosa in subsequent samples she collected.
Co-Ocurring Species/Genus:
Chlorophyll concentration, if known: µg/l
Additional bloom information: No cyanobacteria blooms were observed by DABA staff in freshwater or estuarine environments. Phytoplankton samples revealed the presence of "stressed" Microcystis colonies in Greenwich Cove (<5-10% composition of samples). Greenwich Cove was precautionarily closed on 7/16. Oyster samples taken from Greenwich Cove (commercial lots: Mayhew North and Mayhew South) both had low concentrations of microcystin-RR (3.2 and 3.0 ppb, respectively). Microcystin-RR was present in the Mayhew South lot oysters for multiple months (maximum concentration 5.7 ppb on 9/29); however, it was never detected in the adjacent Mayhew North lot again. Testing of Mayhew South was sporadic due to the expense of UPLC-MS/MS testing (~$250/sample), slower turn-around-time than in-house testing performed by the DABA lab, and the knowledge that shellfish can take an extended period of time to depurate cyanotoxins (weeks-months). Given staff limitations, the area was not surveyed again for blooms (and no blooms were reported again), but oyster testing continued until MC-RR was no longer detected. The maximum MC-RR concentration from Mayhew South was detected on 9/29; therefore, subsequent blooms could have occurred and were not reported to DABA, or MC-RR concentrations in oysters increased naturally during the depuration process (which has been noted in multiple shellfish cyanotoxin depuration studies).
Event-related bibliography:

Environmental Conditions

Weather: Turbidity (NTU): Wind direction:
Stratified water: Oxygen content (nL/L): Wind velocity:
Temperature (°C): Oxygen saturation %: Current Direction:
Sechhi disk (m): Salinity: Current Velocity:
Nutrient information:
Temperature Range During Event: Max: °C, Min: °C
Salinity Range During Event:
Bloom location in the water column:
Growth: Advected
Growth Comments Microcystis bloom advected from freshwater ponds to Greenwich Cove
Additional Environmental information:

Toxin Assay Information

Species containing the toxin Toxin type Toxin details Max. concentration Assay type
Eastern oyster Microcystins 5.7 ppb (ng/g) LC
Kit used: Type of kit used:
Additional information: UPLC-MS/MS performed by UCONN Center for Environmental Sciences and Engineering (CESE). Limit of detections reported as: cylindrospermopsin (3.0ppb), anatoxin A (1.7ppb), microcystin-RR (1.5ppb), microcystin-YR (15ppb), microcystin-LR (15ppb), microcystin-LA (7.5ppb). Note that the LOD for microcystin-RR is much lower than the other microcystins, and there are 250+ variants; therefore, it is possible that other MCs were present in oysters, but only MC-RR was detected due to low concentrations and testing limitations. The DABA also screened 2 oyster samples in July for saxitoxins using PSP scotia rapid test kits (FDA approved limited use method), which were negative.
Economic losses: The total commercial economic loss due to closures was estimated at ~$125,000, which compounded additional losses due to COVID-19. There is a recreational (conditionally approved seasonal) area in Greenwich Cove. The reopening was delayed ~1 month.
Management decision: Since cyanotoxins are not yet regulated by the FDA in shellfish, the DABA left the area precautionarily closed until MC-RR was no longer detectable. Mayhew North was reopened in August, while Mayhew South remained closed until December.
Additional harmful effect information: While this was not reported, Binney Pond is surrounded by a park and DABA staff observed many children, families, and dogs at the park on 7/17 during bloom investigation. It is possible that there is a human health impact from exposure to bloom water.
Created at 10:49 on 19 Apr 2021