Whale fall

Whale fall is the process that occurs after a whale dies and its remains settle to the ocean floor. It is a multi-step process that results in a rich ecosystem that feeds and supports dozens of types of deep-sea life, including scavengers, invertebrates, and microbes. This results in a unique and important ecosystem that sustains countless deep-water ocean dwellers for as long as a century after the whale dies.

Background

Whales belong to a class of animals called cetaceans, from the Greek ketos, which means “sea monster,” along with the suffix acea, which means “in the nature of.” The cetacean class includes about ninety different species of whales, porpoises, and dolphins. Whales are the largest animal species on earth with an estimated population of 1.5 million worldwide.

The largest whales are from the fifteen species classified as baleen whales. These species include right whales, bowheads, gray whales, humpbacks, and the largest species, blue whales. Baleen whales are so named because they eat by filtering prey through plates of baleen in their mouths. Baleen plates are flexible strips made of material similar to human fingernails. Baleen whales are also known as great whales, and create the largest whale-fall ecosystems after their death. The natural life span for whales can be as little as ten years or as long as ninety, depending on the species.

The first human discovery of a whale fall occurred in 1854. A century later, deep-sea trawling ships pulled more evidence of whale falls out of the ocean. During the 1970s, the development of robotic underwater devices first allowed scientists to explore whale fall ecosystems where they happened. In 1977, the US Navy discovered the first deep ocean whale fall found at what scientists call abyssal depths, or about 10,000 to 20,000 feet (3,000 to 6,000 meters) below the water’s surface. Whale carcasses that land in shallower water generally decompose and disappear more quickly; they are generally referred to as whale falls when the animal’s remains reach abyssal depths.

Overview

When a whale dies, its body usually remains near the surface for a few days, held afloat by gases built up inside. Eventually, the movement of the ocean’s currents and waves pulls the carcass under the water’s surface and it sinks to the bottom and becomes a whale fall. This often occurs in deep water along the paths used by the migratory species of whales.

Whales are large animals with a large amount of body fat, or blubber. This, combined with the higher pressure and extremely cold temperatures of deep water means that their bodies take a very long time to decompose on the ocean floor. The slow process allows a wide variety of sea life to feed on and benefit from the dead whale. Some scientists have said a whale fall is the equivalent of a sea creature banquet that lasts for decades.

Whale Fall Stages

The first to arrive at the whale fall are scavengers that move around easily and freely in the ocean depths. These include some types of sharks, hagfish, rattails, and crustaceans such as lobsters. These creatures eat the whale’s flesh and soft tissue, clearing most of it in a time span that ranges from a few months to about a year and a half. This is referred to as the mobile scavenger stage because the animals come from greater distances to feed.

Next to arrive are smaller crustaceans, worms, and other organisms of a similar size that live mostly in the sediment around the whale fall. These animals feed on the decaying flesh that falls into the sediment. This is known as the enrichment-opportunist stage because the organisms are benefitting from a very fortunate opportunity. This stage generally lasts up to two years.

The third stage is the longest, sometimes taking decades to complete. Called the self-fulfilling stage or sometimes the sulfophilic stage, this is the part of the process where the smallest creatures take over. Bacteria moves in to begin breaking down the fat inside the whale’s bones, releasing hydrogen sulfide. Other bacteria feeds on this, creating a thick living mat that covers the remains. These bacteria come in various colors and can even make the bacteria mat have a glowing appearance.

This hydrogen sulfide-rich bacterial mat attracts other types of sea life, which includes some types of worms and a kind of clam called a Vesicomyid, as well as mussels and snails. The animal life that comes to feed during this stage of the whale fall ecosystem is the largest and most diverse of all the stages. They form a community that is larger than any other along the bottom of the ocean. This stage can last between fifty and one hundred years. As a result, it is the hardest for scientists to study.

For many years, scientists thought there were only these three stages to a whale fall. As the use of robotic underwater exploring devices has made more detailed study possible, a fourth stage has been identified. Called the reef stage, it begins when the whale’s bones have been completely depleted of all fat. At this point, deep sea suspension feeders move in and feed on the fat-stripped bones until there is nothing left of the whale.

Benefits

Whale falls are a boon to the deep-sea life in an area that is often otherwise bare of food sources. While the field of whale fall study is relatively new, experts have estimated that a whale fall at the bottom of the North Pacific Ocean can feed almost 12,500 different organisms from more than forty species, and will do so over the course of up to a century. They do so in an area that usually survives on what scientists call marine snow, a collection of smaller dead animal parts and fecal matter that slowly drifts to the bottom of the sea. This marine snow is mostly made up of forms of carbon-based plant and animal life on which the deep-sea creatures feed. Experts say one forty-ton whale fall represents the equivalent of two thousand years of marine snow falling on a fifty square meter area, providing a bounty of food for thousands of creatures.

Bibliography

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