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  • Writer's picturemariagross

FACT: What we thought was Ophrydium earlier might not have been.

Updated: May 5, 2021

A few weeks ago (August 26) I posted about Ophrydium found in So Cove (zone 10), stuck in clusters onto a water Marigold. Via email Amy helped us identify it as Ophrydium, a colonial animal species. From that moment on I started looking to find any more, anywhere. Early September Don and I did collect some similarly shaped organisms attached to pondweeds and floating free in shallow water. These were found on the same day in a small cove within Doloff (grid 3404) and in So Cove, zone 11, bottom of grid 31. These organisms appeared to presented themselves in various shapes from quite globular to a “jelly fish” shape, some felt firm to the touch and others much less so. See photos below.

After sending these images to Amy Smagula at DES, she suggested we send the samples to Amanda McQuaide of DES Cynobacteria Lab in Concord, stating: With algae-like globs like this we cannot be 100% sure unless we see them under the microscope.  This could be Ophyridium, which is a colonial animal that has green algae in the matrix with it, or it could be an algae of concern.

FACT: There is Cynobacteria in every waterbody.

Cyanobacteria are microscopic organisms found naturally in all types of water. These single-celled organisms live in fresh, brackish (combined salt and fresh water), and marine water. These organisms use sunlight to make their own food. (

Though often referred to as a blue-green algae cyanobacteria are not algae at all, but types of photosynthetic bacteria. They are normally present in bodies of water. This type of bacteria thrives in warm, nutrient-rich water. When conditions are right, the cyanobacteria can grow quickly forming “blooms.” Certain varieties of can produce toxins that are linked to illness in humans and animals. (

Freshwater localities with diverse trophic states are the prominent habitats for cyanobacteria. Numerous species characteristically inhabit, and can occasionally dominate, both near-surface epilimnic and deep, euphotic, hypolimnic waters of lakes (Whitton, 1973). Others colonize surfaces by attaching to rocks or sediments, sometimes forming mats that may tear loose and float to the surface.

Below are images of specimens that were found in a small cove within Doloff Cove, called Heron Cove, in early September 2020 - grid 3404

Images below were taken late August in So Cove, zone 10 between grids 424 and 464. These various globe-like forms were clustered on a native Marigold and were tentatively identified with the naked eye as Ophrydium. That was never verified by microscope. Note there are some striking similarities between the images above and those below. That said the ones above were identified as Rivularia, a cynobacteria.

FOLLOW UP by the Cynobacteria lab at DES:

Note from Amanda McQuaide read:

I do not know how to really tell the difference other than by microscope. The colonies first looked like Ophrydium and I might have totally dismissed it. I had not seen Rivularia before and surprised just how similar they look. I looked at quite a few colonies (in the sample you sent) and they all were Rivularia. I have since read that they do produce microcystins (toxins). These types don’t really bloom like other cyanobacteria. They can be found in clusters as you have discovered.

I would not be too worried about these. You would have to consume them for them to be toxic. They can also cause rashes though.

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