On the sea bottom, specialists such as the blind zombie worm help clear away whole whale carcases, writes Dick Ahlstrom
The hidden lives of whales are being revealed as never before with the use of advanced genetic technology and deep-dive submarines. Underwater listening posts are teaching us the power of whale-song and chemical analysis of whale tissues shows just how polluted our seas have become. A collection of scientists outlined their research efforts on whales at the American Association for the Advancement of Science annual meeting which ended last week in Washington.
One of the most startling sessions described the "undertakers in the deep sea" the "specialist" organisms such as "blind zombie worms" and carpet worms that slowly dismantle whales when they die and sink to the bottom.
Prof Craig Smith of the University of Hawaii studies whales that die at sea, referred to as "whale falls". Their decomposing bodies and skeletons provide an energy source for whole communities of animals for as much as a full century.
Prof Smith and colleagues happened upon a whale skeleton in 1987 while involved in a deep sea survey using the submersible Alvin. They were surprised to count hundreds of species encrusting the bones, some of them similar to the sulphur-loving animals that are found around hydrothermal vents near undersea rifts.
He now believes that vent worms and clams may have originated from much shallower species that used plentiful whale falls as stepping stones, food archipelagos, along the way to their eventual home near deep sea vents.
"Whale bone worms have been around for 30 to 40 million years," says Prof Smith. "It is conceivable that the whale worms first appeared on whales and later adapted to deep-sea hydrothermal vents."
The worms and other species are specialists indeed. Discovered only months ago on a whale fall off California, the blind zombie worms use an internal "bacterial garden" to break down the whale bone, allowing them to feed on the fats and proteins inside. "They are an example of extreme evolutionary novelty," says Prof Smith.
Many of these species are under threat now however given the sharp decline in world whale populations. Whale abundance in the northeast Pacific is sufficient to allow whale falls to dot the seafloor at about five to 10km apart, close enough to support animal dispersal from carcass to carcass, says Prof Smith.
This is not so in the north Atlantic however where whale populations are perhaps no more than 10 per cent of their past highs. "Some of the oddest animals ever discovered occur on whale falls," Prof Smith states. "If we want to understand the nature of life, what evolution can do, we must understand these habitats before extinctions occur."
Just how far whale numbers have fallen has been revealed by work done by marine biologist Steve Palumbi. He used whale DNA to build a family tree for these spectacular creatures as a way to assess genetic diversity, information that also reveals population density. He didn't have to plumb the ocean depths to get his samples. Unfortunately all the samples he needed were available in Japanese food markets. Japan takes more than 300 Antarctic minke whales for "scientific research" every year, animals that find their way into the shops as food.
His initial work showed that these same food shops offered minke but also meat from humpbacks and other protected species. That work started 10 years ago and caused huge controversy. Since then, Palumbi and graduate student Joe Roman have published studies on humpback, fin and minke whale populations based on DNA analysis.
Their results make depressing reading. Estimates for the world population of humpbacks stand at about 20,000 but the two showed they might have numbered as high as 1.5 million before the 1800s. Their estimate is more than 10 times higher than the widely accepted historical estimate of 100,000.
Their work is based on using maternally inherited mitochondrial DNA samples from hundreds of humpbacks. "Our study shows that humpback whales today actually have about 10 times more genetic variation than would be expected from previous estimates of their populations," says Palumbi.
The power of whale song was discussed at the meeting by Cornell University bioacoustics expert Christopher Clark. He has spent the last nine years studying whale song using underwater microphones placed by the US navy to track Soviet submarines.
He and former navy acoustics specialists Chuck Gagnon and Paula Loveday have learned to track singing blue, fin, humpback and minke whales from across the Atlantic using the navy's Sound Surveillance System (Sosus).
Prof Clark has obtained thousands of acoustical tracks of singing whales for different species throughout the year. "We now have the ability to fully evaluate where they are and how long they sing for," he says. "We now have evidence that they are communicating with each other over thousands of miles of ocean. Singing is part of their social system and community."
The whales can hear one another from thousands of miles away, right across the Atantic ocean basin, he says. The sound system allows him to listen in as they travel, with "cohorts of humpback singers moving coherently" from one underwater feature to the next. "They may have acoustic memories analogous to our visual memories," Prof Clark says.
Roer Payne and Scott McVay were the first to discover that humpback whales sing. Now Payne, of the Ocean Alliance, is pioneering a new frontier in whale research, creating a map of global ocean pollution based on skin samples from whales. "Our goal is to determine how badly contaminated oceanic fish are with persistent organic pollutants," he says. Ocean pollution is a serious world problem given that 70 per cent of the world's population, up to 4.2 billion people, depend on seafood as a primary source of animal protein.
"What we are working on may be the worst public health crisis that humanity has ever faced," says Payne. His five-year study has recovered skin samples from 1,100 sperm whales from remote oceans around the globe. "The oceans act as a conveyer belt carrying contaminants across the globe and depositing them in the fats of seafood," he says.
Ocean Alliance is now testing these samples for 30 different pollutants, information that will give us a snapshot of how polluted our seas actually are.