Tiny, jelly-clad crustaceans known as Holopedium are thriving in some Canadian lakes after years of acid rain, threatening the food chain and “jellifying” the waters, say biologists. Unlike other “water fleas,” Holopedium can survive on very little calcium, making them ideally suited to the calcium-depleted waters of lakes exposed to pollution. But their hard, jelly-protected bodies cause problems for others, clogging up filtration systems, removing nutrients from the food chain and washing up in the form of “goo balls.” A study published in The Proceedings of the Royal Society B says the population of Holopedium in Ontario lakes doubled between the 1980s and mid-2000s.