Scubaism

Aaron Wirsing, a researcher in the Department of Biological Sciences at Simon Fraser University, and his colleagues studied how the presence of tiger sharks specifically affected the feedings of dugongs — large aquatic herbivore mammals that somewhat resemble their manatee relatives.

The gentle herbivores prefer to eat segrass in the middle of patches. Growth is lush there and packs more of a nutritional punch due to the presence of extra organic carbon. Escaping from hungry sharks is difficult from these interior areas, however.

Wirsing and his team found that when large tiger sharks were around, dugongs instead chose to feed around seagrass meadow edges. The grass is not as tasty or nutritious at the edges, but the location allows escape to deeper water if predators are near.

By indirectly controlling where dugongs feed, tiger sharks keep the seagrass mowed down at all areas. “Dugong grazing can certainly hold seagrass growth in check,” Wirsing explained.

If left unchecked, however, the herbivores would simply eat all of the seagrass.