The Prolific Afterlife of Whales

o u g a lv es On a routine expedition in 1987, oceanographers in the submersible Alvin were mapping the typically barren, nutrient-poor seafloor in the Santa Catalina Basin, off the shore of southern California. On the final dive of the trip, the scanning sonar detected a large object on the seafloor. Piercing through the abyssal darkness down at 1,240 meters, Alvin’s headlights revealed a 20-meter-long whale skeleton partly buried in sediment. On reviewing the dive video tapes, expedition leader Craig Smith and his team saw that the skeleton was probably either a blue or a fin whale. The creature appeared to have been dead for years, but the bones and their surroundings teemed with life—wriggling worms, centimeter-size clams, little snails and limpets, and patches of white microbial mats. The skeleton was a thriving oasis in a vast, desertlike expanse. Almost a year later Smith, an oceanographer at the University of Hawaii at Manoa, returned for a proper study of the skeleton site. His team described several species previously unknown to science, plus some that had been observed only in unusual environments, such as at deep-sea hydrothermal vents. Since then, investigators have documented dozens of communities that are supported by sunken whale carcasses and have described more than 400 species that are living in and around them, of which at least 30 have not been seen anywhere else. The research has begun to sketch out a picture of how these surprising whale-fall communities work and how they have evolved. The first hint that dead whales could host specialized animal communities came as early as 1854, when a zoologist described a new species of centimeter-size mussel extracted from burrows in floating whale blubber collected off the Cape of Good Hope in South Africa. When industrial deep-sea trawling began in the 20th century, researchers learned that such dependence on dead whales was not a freak occurrence. From the 1960s onward an increasing number of whale skulls and other bones with attached specimens of new mollusk species were recovered from nets around Scotland, Ireland, Iceland and particularly the Chatham Rise to the east of New Zealand. One bone specimen trawled off the South African coast in 1964 was covered with the same small mussel first seen in 1854 in roughly the same area. Mussels were not the only new animals found in recovered whale bones: a tiny, previously unknown species of limpet—limpets are snail-like mollusks with conical rather than spiral shells— was described in 1985, soon followed by others. The limpets were named Osteopelta because of their association with bones. But not until Smith’s fortuitous discovery in 1987 did the full extent of the ecological novelty of sunken dead whales become clear. The mollusk species his team found were especially interesting. The clams and mussels belonged to groups known to harbor chemosynthetic bacteria. Such bacteria can draw energy from inorganic chemiOn the deep seafloor, the carcasses of the largest mammals give life to unique ecosystems ● By Crispin T. S. Little The Prolific Afterlife of life science