|The Question: I saw these bright green jelly like blobs in Easdale Tarn, in Cumbria, England. The blobs ranged in size from about 1.5 cm (1/2 inch) to 4 cm (1 ½ inches) cm. There were quite a few of them, some floating in the water and a couple attached to rocks. What are they? Are they some sort of egg?
Submitted by: Alison, Cumbria, England
The Short Answer: These blobs are made by a colonial microscopic single-celled protozoan called Ophrydium versatile. They can be found all over the world in fresh water. The individual cells line up side by side in the “blob” and attach themselves to a jelly-like substance they secrete. They are symbiotic with microscopic Chlorella algae which live inside the Ophrydium cells and give the blob its green color. This page shows a number of pictures of the blobs in the water:
This brief youtube video clearly shows the hundreds of green Chlorella cells living inside the Ophrydium cell:
This one shows the cilia that Ophrydium uses to gather particles including bacteria, other organisms and detritus from the water:
More Information: Ophrydium cells reproduce by dividing. As the number of Ophrydium cells increase, they remain on the outside of the growing blob, and the interior, which is now empty of Ophrydium cells, becomes a watery gel. This soupy interior gel can become home to all kinds of microorganisms such as mastigotes, euglenids, chlorophytes, heliozoans, diatoms, bacteria, rotifers, nematode worms, other ciliates, and even tiny crustacean copepods, leading some to compare Ophrydium blobs to a floating zoo of tiny creatures.
Ophrydium is always found with its algal symbionts. The Ophrydium structure probably helps the algae gather light efficiently. The Ophrydium also shares nutrients like nitrogen it gains from the bacteria and other particulate material it sweeps from the water with its cilia. In return, the algae supplies Ophrydium with sugars it makes through photosynthesis. During the summer, the majority of the carbon assimilated into the colony comes from photosynthesis. In the winter, the colonies remain active, but most of the carbon assimilated comes from the organisms Ophrydium gathers from the water column.
Other Common Blobs: One of the most common questions to AskaNaturalist.com is “What is this blob I found in the water?” I’ve written about Bryozoan blobs and amphibian egg masses. Other possibilities for fresh water blobs include snail egg masses, fish egg masses and freshwater jellyfish. Keep those blob questions coming!
Thanks to Ophrydium expert and University of Saint Joseph professor Mark Johnson for his help identifying these blobs and for the information in his dissertation Seasonal Changes in Distribution and Tropic Mode of the Mixotrophic Ciliate, Ophrydium versatile, in a Freshwater Pond Ecosystem.
Sand-Jensen, K, Pedersen, O, & Geertz-Hansen, O. (1997). Regulation and role of photosynthesis in the colonial symbiotic ciliate ophrydium versatile. Limnology and oceanography, 42(5), 866-873.
Duval, B, Margulis, L. (1995). The microbial community of ophrydium versatile colonies: endosymbionts, residents and tenants. Symbiosis, 18:181-210.