Largest animal bioturbator

Bioturbation is defined as the reworking of sediment or soil by any organism, either animal or plant. Bioturbators are considered "eco engineers" because their activity drastically impacts their environment, affecting not only the structure of their local ecosystem but also the other species that share it. The largest bioturbating animal is the grey whale (Eschrichtius robustus) native to the Pacific Ocean. This migrating species can measure close to 15 metres (49 feet) long and weigh up to 41 tonnes (90,400 pounds). Unlike other filter-feeding baleen whales who gulp down their food in open water, grey whales favour shrimp that dwell on the seafloor. To capture this particular prey, grey whales have developed a technique that involves rolling on to one side and pushing their tongue into the sediment and sucking while swimming along the seabed; the sediment is filtered out in a muddy plume and the shrimp are caught in the baleen. A grey whale "feeding pit" can measure as much as 20 metres (66 feet) long, 2 metres (6 feet 6 inches) wide and 0.8 metres (2 feet 7 inches) deep, with an average volume of 4.6 cubic metres (162.4 cubic feet). This unusual feeding practice has earned them (and a few other animals) the nickname of "benthic bulldozers".

It has been estimated that 3.1–5.7 kg (6 lb 13 oz–12 lb 9 oz) of shrimp are removed per grey whale feeding pit, representing between 55–79% of the shrimp standing stock (Weitkamp et al, 1992).

One study by Johnson et al in 1983 (using side scanning sonar over the seafloor) estimated that 5.7% of the seafloor over 22,000 km2 (8,500 sq mi) of the Bering Sea was worked over by grey whales during the five-month summer feeding season (May-October). At population densities of 10-50 individuals per 1,000 km2 (386 sq mi) in Bering Sea feeding grounds, this translates into 1.55–7.75 million megatonnes of sediment displaced per year per whale!

Setting aside humans, grey whales may also take the record for most soil/sediment annually moved by a single animal species. The Pacific walrus (Odobenus rosmarus) does a lot of benthic "bulldozering" in the same region as the grey whale while digging for bivalves in the seafloor, but although there are more walruses than whales, they are, of course, much smaller in size.