When a dead whale sinks to the ocean floor, it becomes home to a thriving marine ecosystem. Researchers using a pair of remotely-operated vehicles (ROVs) have captured the extent of this growing community under the waters of the North Pacific.
When mapping a nutrient-poor region of the deep seafloor off the California coast, scientists on board Hercules’s research vessel were surprised to spot a whale skeleton near the bottom. The team returned to the ship to examine the skeleton, which they determined was likely a blue or fin whale, a species that can reach lengths of 40 meters or more.
The skeleton created a mini ecosystem at the bottom of the ocean, also known as the benthic zone, that resembles a small ecosystem on land. The decomposing body is a new habitat for animals that would otherwise not be there, providing food and shelter. The discovery offers new insights into how these remains allow ecosystems to thrive.
As with all such communities, a whale carcass creates complex ecological events. The first phase is the mobile-scavenger stage, during which scavengers like scarves and hagfish move through the soft tissue. Once the soft tissue is gone, bacteria slowly break down the fatty acids trapped in the bones. This releases hydrogen sulfide, which can poison animals, but certain specialized chemosynthetic bacteria can oxidize the gas for energy.
These bacterial communities, in turn, attract other organisms to the area. The resulting mix of grazers and predators includes octopuses, eelpout fish, crabs, grenadier fish, bristle worms, and a giant squat lobster. The octopuses gathered around the skeleton are particularly interesting because octopuses typically hunt live prey, not dead ones.
This is not the first time scientists have observed a thriving community of animals surrounding a whale carcass, but it has been one of the most detailed studies yet. The phenomenon was first described in 1854 when a new mussel species lived inside pieces of floating whale blubber. Only in industrial deep-sea trawling began in the 1960s did scientists discover more examples of these unique ecosystems.
A single whale carcass can host communities that span five different trophic levels or food chains. This is more than a thousand times the average density of life on the deep seafloor, where creatures usually rely on smaller decomposing plants and animals to survive. Scientists are now using cameras and submersibles to study the evolution of these communities. Sometimes, they have set up a time-lapse camera to take pictures of the changing communities. They have also started to collect water and sediment samples around the whale falls to analyze environmental DNA. The data could help them understand the role these communities play in ocean carbon cycling and how they are affected by environmental changes.
