"For ecology in general, the take-home lesson here is that increasing climatic extremes, such as drought stress, can trigger formation of grazer fronts and subsequent waves of habitat die-off in an otherwise stable ecosystem," Silliman said. "For marsh ecology, the message is even clearer: The long-standing paradigm that bottom-up forces rule is officially dead."
Climate change aside, the study also falls in line with other recent studies highlighting the role of predators or other top-down animals. "This study adds to a growing body of evidence showing strong top-down regulation of ecosystems processes, including sharks in the Gulf of Mexico and wolves in Yellowstone Park," Silliman said.
Native and abundant, dime- to quarter-sized periwinkle snails can often be seen hanging on cordgrass above the water line. Contrary to appearances, they don't actually eat the grass, or at least not much of it. Instead, they crunch up the surface to make it easier for colonization by fungi. In a process described as fungal farming, the snails then eat the fungi.
Periwinkle snails normally coexist happily with marsh grasses. But the drought so weakened cordgrass that it began dying off. Snails then moved in, finishing off weakened and dying patches. When these disappeared and exposed mudflats emerged, large numbers of snails moved off the flats and concentrated on the edge of the die off, where healthy grass remained. This migration resulted in the formation of grazer "fronts," which attacked and destroyed more marsh in "waves" of runaway consumption, the authors write.
A team of scientists from UF, the Netherlands Institute of Ecology, Louisiana State University and Brown University reached that conclusion after observations and experiments at 12 randomly selected die-off sites in Louisiana, Georgia and South Caro
Source:University of Florida