Didymo risk goes beyond green snot in rivers

rock snot warning - is didymo not yet in this river?
CC BY 2.0 rickpilot_2000

BBC news just featured a fascinating report on The green snot taking over the world's rivers.

If you have seen the signs encouraging action to stop the spread of 'rock snot', aka Didymo, you will be interested to read in BBC's report that the Didymo may have been there all along. And everything we thought we knew about them may be wrong.

Didymo is short for or Didymosphenia geminata, the scientific name for one of many alga in the diatom group. Diatoms are well known for their 'bloom and bust' cycles. When nutrient levels rise, the diatom community breeds like crazy, exploding in an algal bloom. In the best case, the death and subsequent decomposition of tons of algal biomass depletes the waters of oxygen, threatening the native ecosystem. In the worst case, the algae release toxins blamed in the deaths of species higher on the food chain.

Teresa Trimm/CC BY-SA 2.0

Didymo sits somewhere in between. While not toxic, it grows masses of 'stalks' which are stringy polymers of sugar and protein which resist degradation. The resulting matted, gooey mess has earned it the descriptive moniker 'rock snot'. The matts prevent access to food sources along the bottoms of streams and rivers, and may goo up the works in human installations such as dams, locks, or boat motors.

Scientists thought the stalks resulted when didymo reproduces, adding one new stalk for each generation of cell division. But it appears this may be wrong. The BBC report likens the stalk generation to cancer, a malignant form of didymo:

"When it creates huge snots, it’s not actually reproducing, scientists have discovered. Instead, it’s morphing, from something benign to something malignant. Each single-celled organism exudes long stringy stalks of mucous that entangle, creating the mats and snots that coat rocks."

And here it gets even more interesting. The didymo turns malignant when there are not enough resources, especially when phosphorous levels get low. So the very programs to reduce run-off of detergents and fertilizers intended to prevent didymo blooms may contribute to the appearance of the persistent snot on river beds.

In another study, scientists have also reported that programs to prevent the spread of didymo are failing not due to people too lazy to prevent the hitchhikers, but because the didymo has been there all along, albeit in its harmless form. One exception may apply: the appearance of the algae in New Zealand may indeed represent invasion by the species, which is now thriving in the naturally low-phosphorous environment there.

While more knowledge is always a good thing, the news on didymo should be used to communicate two major pieces of information to the general public:

  1. Our new understanding of didymo remains the exception in the studies of invasive species. Most invasives have not been there all along. The media must take care not to damage all of the public communication efforts aimed at teaching people to clean and dry equipment between uses, by giving people the idea that these efforts were not useful in this case. We still need to prevent the spread of zebra mussels, asian carp, and many others.
  2. This proves how little we understand about our environment. Our efforts are useful only if we understand the actual impacts of conservation programs. Funding more science to study our environment just makes sense; ignorance is death -- if not for us, for the ecosystem we depend upon, which ultimately might be the same thing.

Tags: Invasive species | Water Conservation


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