Whale Falls


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Whale Falls

By Jeremy Geist
USGS Volunteer for Science
Oct. / Nov. 2010

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Above: Whale fall "Grady" (species unknown), recently found at 586-m depth in Monterey Bay. Photograph courtesy of Monterey Bay Aquarium Research Institute. [larger version]

When a whale dies, it drifts to the seafloor. Its carcass, known as a "whale fall," provides massive amounts of nutrients to the normally food-deprived inhabitants of the deep sea, resulting in a wholly unique ecosystem. In addition to some of the more common scavengers, such as hagfish and crabs, microscopic organisms known as foraminifera (commonly abbreviated as "forams") live at whale falls, providing valuable fossil records for the future.

One whale fall in particular, located in Monterey Bay on the central California coast, has undergone a massive increase in the population of a certain species of foram, providing fascinating insights to these environments. To Mary McGann of the U.S. Geological Survey (USGS) and her colleagues at the Monterey Bay Aquarium Research Institute, this carcass is known as "Puppy." "Puppy wasn't found on the seafloor but was towed out to sea and dropped after it had washed up onto the beach," said McGann. Unfortunately, the whale fall was accidentally placed in a strong current, leading to rapid scatter of the bones. Some interesting results could still be gained, however, from studying the earlier phases of carcass decomposition, most notably the dramatic increase in the abundance of a specific foram species.

Above: Five whale falls (one in British Columbia, Canada, and four in Monterey Bay, California) where USGS scientist Mary McGann has studied foraminiferal distributions. [larger version]

Puppy is one of five whale-fall sites off California and Canada where McGann has studied foraminiferal distributions. Forams are present in many marine environments, in many different varieties. Their shells are commonly left behind as fossils, providing a biological record for scientists to use to determine what conditions were like in the ocean millions of years ago. In addition, foram assemblages can be used as indicators of environmental degradation and repair.

Above left: Carcass of a gray whale, "Puppy," sunk in 381 m of water in Monterey Bay. Puppy is in the first stage of decomposition (the mobile-scavenger stage), with eel-shaped hagfish and small white amphipods feeding on the carcass. Photograph courtesy of Monterey Bay Aquarium Research Institute. [larger version]

Above right: In a later photograph, little flesh remains on Puppy’s bones, which have been jumbled by currents. Photograph courtesy of Monterey Bay Aquarium Research Institute. [larger version]

"In Santa Monica Bay near Los Angeles, various sewage outfalls have been in use since the 1920s. In the 1960s, they added a very large one that polluted the area because they were dumping untreated sewage offshore. When the distribution of forams was studied, two species of one genus had been very negatively impacted. They both used to be in great abundance in Santa Monica Bay, but their numbers declined dramatically after the new outfall came on line. Both of these species have not returned to their former abundance, even though new remediation techniques have been employed that, supposedly, stopped the pollution. Instead, a third species is more abundant than it used to be before the 1960s," said McGann.

Like human-caused pollution, whale falls introduce new components—such as unusually large amounts of nutrients—to the seafloor environment. Scientists investigating whale falls are particularly interested in how this new input affects seafloor ecosystems. To study Puppy's effect on foraminifera, samples of the sediment underneath the whale fall were taken with push cores, plastic tubes inserted into the sediment by a remotely operated vehicle (ROV) from the Monterey Bay Aquarium Research Institute. The sediment was then analyzed centimeter by centimeter for the presence of forams. This analysis uncovered a spike in the abundance of one foram species, Epistominella pacifica, at the top of the core.

Above left: Gray whale "Pebbles," sunk to 632 m in Monterey Bay. Photograph courtesy of Monterey Bay Aquarium Research Institute. [larger version]

Above right: Remotely operated vehicle (ROV) from the Monterey Bay Aquarium Research Institute inserts a push core into sediment near Pebbles. Photograph courtesy of Monterey Bay Aquarium Research Institute. [larger version]

This population explosion contributes to a current theory concerning whale falls: that foraminifera, which reproduce both sexually and asexually, multiply in large numbers when there is a ready supply of nutrition. Unlike some other organisms, such as worms and clams, no forams are endemic to whale falls, and the foram species that drastically multiplies during decomposition depends on the water depth at which the whale lands.

Above: Skeleton of a fin or blue whale, "Shannon," observed off Vancouver Island, British Columbia, Canada, at 1,288-m depth. Photograph courtesy of Monterey Bay Aquarium Research Institute. larger version]

Although Puppy is a particularly short-lived site to study forams, the evidence gathered there will contribute to further research into the prevalence of certain foram species over others and the factors that contribute to this phenomenon.

About the author: USGS volunteer Jeremy Geist is a freshman at Santa Clara University, with a double major in English and Theater.