Humans may be trying to save the whales, but two newly discovered worm species can't wait for the giant mammals to die. The worms, which lack mouths and digestive systems, use rootlike appendages packed with bacteria to feed on the bones of dead whales on the ocean floor. Researchers say the worms' feeding strategy is unlike anything seen before and highlights the extraordinary diversity of deep-sea creatures.
The deep ocean floor was once thought to be a biological wasteland, bereft of the light and nutrients needed to sustain life. But deep-sea exploration, culminating in the 1977 discovery of tube worms and other creatures living in total darkness near sulfur-spewing hydrothermal vents, indicated that life could thrive in the most unlikely places. Living on the bottom can be rough, however, and scientists are still trying to understand the many ways deep-sea animals adapt to their environment.
The bone worms, which researchers discovered living on a whale skeleton nearly two miles (3.2 kilometers) below the Pacific Ocean, have adapted by forming a symbiotic relationship with bacteria. The bacteria convert the oils and fats inside whale bones to sugars the worms can use, researchers report in the 30 July issue of Science. This partnership with bacteria plus DNA analysis place the bone worms close to hydrothermal vent worms on the evolutionary tree. However, whereas vent worms harbor bacteria that break down inorganic chemicals (such as sulfur) within a specialized organ, the bone worms are host to bacteria that break down organic compounds within green rootlike appendages that dig through bone. These differences prompted the researchers to give the bone worms their own genus, Osedax, Latin for "bone devouring." The ability of Osedax worms to feed on whale skeletons shows that "a dead whale can provide a big energy source for nutrient-poor regions of the ocean," says Robert Vrijenhoek, an evolutionary biologist at the Monterey Bay Aquarium Research Institute in Moss Landing, California, and a co-author on the study.
The adaptations of the Osedax worms are "extreme" and "bizarre," says Craig Smith, a biological oceanographer at the University of Hawaii in Honolulu. He adds that the study provides a "link between whales in the upper ocean and biodiversity at the deep-sea floor." For that reason, Smith believes that whale hunting may be disrupting an important deep-sea ecosystem, robbing the worms of having their whales and eating them too.