Ecosystems are being transformed as lakes in Ontario, Canada are filling with jellies. The chemistry of the water is not changing, but the microbiological diversity in the lakes is being altered due to environmental conditions. The change of tiny organisms at the base of the food chain may wreak havoc on the entire ecosystem.
A team of scientists published their study, “The Jellification of North Temperate Lake,” on November 19. They found that calcium levels in the lakes across North America and Europe have dropped due to industrial pollution. The lakes have “aquatic osteoporosis.” Organisms with exoskeletons rely on a calcium-rich habitat. The decrease in calcium has made the jellies less healthy and more susceptible to predators.
The biologists collected field data from many sources and concluded that the calcium decrease is “precipitating a dramatic change in Canadian lakes.” The dominant pelagic herbivore in the lakes has been the water flea, or Daphnia. Daphnia are tiny animals (~1mm) that feast on algae and diatoms. They are an essential link for passing the sun’s energy up through the food web. Daphnia are also phosphorus rich organisms. As such, they provide plenty of nutrition for organisms higher up on the food chain and their predators have evolved to crunch through the Daphnia’s exoskeleton. Daphnia require a calcium-rich environment in order to grow, strengthen their exoskeletons and keep their populations stable.
As water calcium levels drop, the Daphnia are being replaced with Holopedium glacialis. These microorganisms are clad with a jelly-like substance rather than an exoskeleton. They thrive in the calcium-poor waters and out-compete the Daphnia for food and resources. Their jelly coating makes them impervious to many predators, so the weakened populations of Daphnia still provide the only food source for larger organisms. The jellies are taking over the lakes and the daphniids are in danger of disappearing.
The study researchers have identified two main negative effects caused by the increase in jellies. First, as the Holopedium replaces other zooplankton, the amount of nutrients available to the food web decreases. Second, “greater absolute abundances may pose long-term problems to water users.” Changing the natural ecosystems of fresh-water lakes could impact the quality of drinking water for communities around the lakes.
The populations of Holopedium have more than doubled in the decades between the mid-1980s and the mid-2000s. If the increase continues, the researchers worry that the organisms will clog filtration systems that provide clean water to residents living in these areas. Currently in Ontario, 20 percent of drinking water comes from calcium-depleted lakes. The jellies could impede extraction of the lake water for residential, agricultural and industrial use. In addition, fish stocks will decline as the nutrient-rich Daphnia are dislodged.
Investigating the history of the lakes, the researchers found that calcium depletion began in the 1850s with the rise of industrialization. It occurred rapidly through the 1900s as acid deposits displaced calcium from the soil. Pollution controls have stopped acid deposition, but calcium levels in the soil may take thousands of years to return to pre-industrial levels. The water flea also has some other human-caused problems. An invasive species from Europe, the spiny water flea preys on the Daphnia and is growing in numbers. Also, climate change is causing oxygen depletion in the lakes. The reduced oxygen levels provide a better habitat for larval midges which are the main predators of Daphnia.
Study co-author Dr. Andrew Tanentzap, from the University of Cambridge, says, “We may have pushed these lakes into an entirely new ecological state.” Human activity began the change in the lakes and now people may be powerless to stop it. Ecosystems are being transformed as lakes in Ontario, Canada are filling with jellies. Residents may have to learn to adapt to changing conditions and find their fish and drinking water elsewhere.
By: Rebecca Savastio