unexplained movements
By Jon Hare
of a moss ball herd
island bioglaciology
My brother sent me an NPR story about a herd of fuzzy green “glacier mice”. The concept is crazy – small rocks, covered in moss, on a glacier, moving in tandem like a herd of miniature muskox. Hotaling et al. (2020) studied moss balls on an Alaskan glacier. They tagged the balls and tracked them for 54 days to understand their movement and then revisited the site over the next three years to understand persistence.
The moss balls moved in unison at approximately 2 cm day-1. Speed of movement was related to rate of ablation of the glacier surface: more ice melting, greater speed of movement. The direction of movement, however, was not related to ablation, nor slope, wind direction, or direction of solar radiation. Further, the moss balls persisted over years with an annual survival rate of 0.86, which equates to a greater than 6 year life span. It is hard to imagine a herd of moss balls surviving six Alaskan winters to move around together in subsequent summers.
These moss balls are also hotspots of biological diversity – they provide an island-like habitat for an array of organisms. How the biodiversity survives the winter is also unknown, as are the rates of colonization and extinction on the moss balls – raising questions of island biogeography on a glacier.
Original research: Hotaling, S, T. C. Bartholomaus and S. L. Gilbert (2020). Rolling stones gather moss: movement and longevity of moss balls on an Alaskan glacier. Polar Biology. https://doi.org/10.1007%2Fs00300-020-02675-6
Dr. Jon Hare is a scientist who works in Woods Hole, Massachusetts. His research background is fisheries oceanography and climate change impacts on marine fisheries. Check out Jon’s other sciku ‘Owls of the Eastern Ice’, ‘Varves’, ‘Signs of Spring’ and ‘Cobwebs to Foodwebs’.