When a whale dies and sinks, it can feed the deep sea for decades.
A whale carcass sinking to the dark seafloor becomes an oasis. Scavengers strip the flesh, worms and snails colonise the bones, and bacteria feed on the fats inside for perhaps 50 to 100 years. These 'whale falls' support whole communities, including species that may live nowhere else.
Most great whales are slightly denser than seawater, so once their lungs deflate their bodies can sink quickly and largely intact, usually to depths beyond 1,000 metres. There, cold and pressure slow decay. The first recorded deep-sea whale skeleton was found by the US Navy submersible Trieste II in 1977. In 1987 a team led by Craig Smith of the University of Hawaiʻi, using the submersible Alvin, found the first full whale-fall ecosystem, at 1,240 metres in the Catalina Basin off California.
Researchers describe a succession of stages. First come mobile scavengers such as hagfish and sleeper sharks, which can eat 40 to 60 kilograms of flesh a day, for months or up to a year and a half. Next, 'enrichment opportunists' colonise the bones and the enriched sediment around them for up to four and a half years. Then comes the longest stage: bacteria break down the fats in the bones without oxygen, releasing hydrogen sulfide. Mats of bacteria that live off these chemicals feed mussels, clams, limpets and snails, possibly for 50 to 100 years. Finally, the bare skeleton may serve as a reef for filter feeders.
Among the strangest residents are Osedax, bone-eating worms that secrete acid to bore into bones and absorb the nutrients inside. Whale falls also host mussels and clams that partner with chemical-eating bacteria, groups otherwise known from hydrothermal vents and sunken wood. One idea is that whale falls act as stepping stones, helping such species spread between the ocean's scattered chemical oases. Researchers estimate that around 690,000 carcasses of the largest whale species are decomposing on the seafloor at any time, about one every 12 kilometres, and as close as 5 kilometres along migration routes.
A typical 40-tonne whale delivers about two tonnes of carbon to the seafloor at once, equal to 100 to 200 years of the normal supply to a hectare of abyssal floor. By removing so many great whales, whaling may have cut deep-sea biomass by more than 30 per cent, by one estimate, and weakened the ocean's ability to lock away carbon.
Source: Wikipedia — Whale fall · Text summarised from Wikipedia (CC BY-SA 4.0)
