Sand hoppers shift 50 kilograms of sand a night for every meter of a California beach

Multiply 50 kilograms per meter of coastline by 25 kilometers and the answer is 1,250 tonnes a night, about four times the 310 tons a day the team reports for the same stretch ^[1]. So the scale-up is not one night of plots times the shoreline. It rests on eight years of earlier hopper counts along that beach ^[9], and running the published total backwards gives an average of roughly 12 kilograms per meter per night, about a quarter of what came off the plots ^[2].

Divide the mound sand by the animals counted underneath it and each hopper moved about 2.3 grams overnight ^[3]. The study reports that as more than ten times body weight, which puts the average hopper at no more than about 0.23 grams ^[7][4]. "I have to admit, I did go back through the numbers multiple times just to double-check my calculations. I was extremely surprised by how much they dug up," Baxter said ^[11].

The record claim is harder to test than the tonnage. Darwin was writing about earthworms remaking English soil more than 150 years ago, and researchers still have no agreed way to compare one animal's work with another's ^[20]. The hoppers' only documented rival, a South African sand prawn, was reported mixing up to 12 kilograms of sand per square meter per day ^[14]. The hoppers were measured per meter of shoreline. The two rates are equal only at one width of occupied beach: about four meters, given 50 kilograms per meter of coast ^[5]. The published account does not give that width. "It's a minefield with the different ways things are reported and measured in this field," said Gemma Harvey, a physical geographer at Queen Mary University of London who was not involved in the work ^[13][12].

Dave Hubbard, an ecologist at the University of California, Santa Barbara, and a co-author, expects the hoppers to win anyway. "If we had measured the sand hoppers' total churn rate, it would have been more than the sand they were putting in mounds on the surface. They would probably win against the sand prawns," he said ^[16][15].

The 310 tons is sand lifted to the surface and still sitting there at dawn. Setting it beside some nearby rivers ^[10] puts a churn rate next to a delivery rate. For hopper work to register in beach shape, those loose grains have to travel, and the study points to wind carrying them up the beach and potentially building dune habitat ^[17]. It describes that as a possibility. Below the surface, the same burrowing draws plankton and oxygen-rich seawater into the sand, feeding other beach dwellers ^[18].

Scraping mounds also only finds animals that build them. Bloodworms and sand crabs, a few feet closer to the water, mix and move sand without leaving piles a researcher can bag and weigh ^[19]. "The impact of animals on beaches is a really understudied area, especially considering how much work they're doing," said Baxter, who led the study and works at the University of Oxford's Pitt Rivers Museum ^[21][4]. The paper is in Journal of Geophysical Research: Earth Surface ^[5].