Whale Falls

Whale fall stages lead to stepping-stone 

A group of five or more killer whales has come across a young blue whale and mother. The pod strategizes an attack, where each killer whale takes turns chasing the mother and her calf. The mother tries to push her calf towards the surface to breathe for air, but the killer whales persist on, tiring out the calf and the mother. The calf finally separates from the mother and the killer whales attack preventing the calf from coming up for air. The young blue whale drowns, and the killer whales feast on their prey.

This scenario is one of many that can lead to the production of a whale fall. As the whales’ corpse settles to the bottom of the ocean, three known phases of colonization can occur. These three phases are the mobile scavengers phase, the enrichment – opportunist stage, and the sulfophilic stage (Calkins 2010). Different assemblages of species appear at each stage giving evidences that whale falls may be the stepping-stone between hydrothermal vents and cold seeps. This paper will discuss the formation of each phase, the organisms found at each phase, and the stepping-stone theory between whale falls, hydrothermal vents, and cold seeps.

The first phase is the mobile scavenger phase. This stage lasts only a few months, and is the shortest of the three stages because scavenger organisms like the hagfish, sleeper sharks, rattail fish, amphipods, and crustaceans devour the meat of the whales’ corpse (Calkins 2010). First crustacean plankton colonizes the whale, then sharks, and scavenger fish. There is a high density of species on the whale; however, there is very little diversity between the species. Amphiopods and copepods carve tunnels into the whales’ body as they consume most of the whales flesh. Predators have easier access to the whales’ meat because of this (Bonnemains 2010).

In a study, Craig Smith and his colleagues supported by NURP implanted three whale carcasses off the coast of southern California (Russo 2004). Alvin the Human Operated Vehicle took these scientists to the whale fall sites to observe the mobile scavenger phase in action (Russo 2004). They found that after six weeks of implantation one whale was still largely intact, but had hundreds of hagfish feeding on it (Milius 2005). The hagfish had become forty centimeters long and were feeding on the meat of the carcass (Milius 2005). In order to take a piece of the whales meat for food, the hagfish takes a biting grip in the whale, ties itself in a knot, and then pulls its body out using its force to tear out a piece of the whales meat (Milius 2005). Black hagfish and the white-headed hagfish are the typical hagfish species that aggregate around whale falls (Bonnemains 2010). Hagfish live inside the whales’ skeleton because they are able to survive high levels of carbon gas and methane (Bonnemains 2010). Hagfish are an interesting species because they are the only fish known to keep their blood at the same concentration of salt as the outside environment (Bonnemains 2010). Hagfish are able to live five years and swim to depths of 3000 meters (Bonnemains 2010). They have an extraordinary sense of smell that allows them to smell a whales’ carcass from 0.6 to 0.8 meters away (Bonnemains 2010).

Scientists also found Sleeper Sharks in the midst of the scavenging organisms. This was a new discover because Sleeper Sharks are rarely seen by humans, because they are a deep-water species. Sleeper sharks between 1.5 and 3.5 meters have been seen feeding on grey whale falls by grabbing the whales’ meat and then twisting its body back and forth until a piece is freed (Milius 2005) (Bonnemains 2010). Observations of bite marks on whale falls have led scientist to believe that the sleeper shark, in comparison to other fish species, consumes the bulk of the whales’ meat (Bonnemains 2010).

During this mobile scavenger phase, thirty-eight different species may take part in the consumption of 90 percent of whales’ meat and tissue (Russo 2004).The consumption rate per day is an estimated 40 to 60 kilograms of flesh per day (Bennett 2002). The bulk of the whale meat is gone within eighteen months (Milius 2005). One of the implanted whale carcasses, located off the coast of Santa Cruz, has sustained the mobile scavenger phase for the past nine months, and has the potential to last two years (Russo 2004). The sediment around the whale carcass is full of nutrients from the debris left behind by the scavengers and attracts smaller organisms to start the next phase of colonization (Calkins 2010).

The second phase is the enrichment- opportunist stage. This stage can last 4 months to 5 years (Bonnemains 2010). Snails, little amphipods, and segmented worms aggregate around the whale fall during this stage. Baco-Taylor and other scientists have found that 45,000 individuals are in each square meter of sediment (Milius 2005). These organisms feed off the organic material stored in whalebones and the sediments, up to 3 meters away, which surround the whale skeleton (Bonnemains 2010) (Bennett 2002).

Several polychaetes and clams are exclusive to the enrichment- opportunist stage of whale falls. Smith describes finding a polychaetes worm that sends green root like coils into the bone. These roots then release a rod shaped bacteria that break down organic compounds in order for the worm to digest (Milius 2005). These worms can grow as long as fifty millimeters and resemble centipedes (Russo 2004).

Beggiotoa bacteria also colonize along the bones of the whale skeleton forming a bacterial mat made of long filaments. This bacterium oxidizes hydrogen sulfide as an energy source. Segmented worms called Bathykurile guaymasensis then eat these bacteria and receive their nutrients this way (Milius 2005).

After the worms disappear the Beggiotoa bacteria continues to feed on the fats and oils contained in the whales’ bone (Bennett 2002). This is the start of the third phase, the sulfophilic stage. This phase can last forty to eighty years (Bonnemains 2010). Three key elements characterize this phase. First, bacterial mats cover the surface of the bone (Bonnemains 2010). Then, large populations of clams move in. these clams harbor chemosynthetic bacteria (Bonnemains 2010). Finally, over 30,000 individual bivalves, amphiopods, polychaetes, limpets, gastropods, and crustaceans aggregate (Bonnemains 2010).

About sixty percent of the whales’ weight is made of lipid, which bacteria break down in order to produce sulfide (Calkins 2010). Bacteria then use chemosynthesis to oxidize sulfide to make organic matter that supports other organisms like the Vestimentiferan tubeworm.

Bacteria form the basis of the food web, because without chemosynthesis life would no longer occur. Light is unable to penetrate the depths at which the whale skeleton has sunk, and there is no longer and meat left on the bones. The only way to survive is to harvest bacteria that use the process of chemosynthesis for energy.

Mollusks aggregate around the whale fall during the last stage. Vesicomyid clams carry a sulfide- metabolizing bacteria and get their energy directly from the sulfide. The Idas washingtonia mussel has been seem to colonize in the 10,000’s on a single whale (Milius 2005).

Scientists have found 190 different bottom dwelling species on a single whale carcass (Calkins 2010). These organisms use the whale fall as a food source and a substrate. Carnivorous gastropods feed on the bivalves, the bivalves feed off their bacteria, and the bacteria gain their energy through chemosynthesis. In fact, the sulfophilic stage can have at least three different levels on the food web at any given time (Bonnemains 2010).

In the late stages of the sulfophilic stage, the whale fall community begins to resemble the communities found at hydrothermal vents and cold seeps. Hydrothermal vents and cold seeps also have bacteria as the basis of their food webs and are host to ten to twenty percent of the 200-sulpholic species found at whale falls (Bennett 2002). Just as the bacteria found at whale falls the bacteria at hydrothermal vents and cold seeps also oxidize sulfide in order to make organic matter.

In addition, DNA analysis allowed Smith and other scientists to compare the genetic makeup of Idas washingtonia found on whale falls to a mussel found on deep- sea wood. Scientists found that these two mussels share the same sub family, Bathymodilinae, with mussels found on hydrothermal vents and cold seeps (Russo 2004). In fact, these molecular studies show that whale falls may actually serve as a stepping-stone between cold seeps and hydrothermal vents (Smith 2003). Smith theorizes that the ancestors of these mussels may have moved deeper into the ocean following the whale falls organic food source. The mussels then moved from the organic richness of the whale fall to the sulfide rich hydrothermal vents and cold seeps. This theory could be true for other organisms. For example, California whale falls share ten species with vents, nine with seeps, four with anoxic sediment, and one with wood falls (Russo 2004).

Whale falls are an important bridge between hydrothermal vents and cold seeps. Hydrothermal vent are commonly found along the mid-ocean ridge, such as the east pacific rise and the mid Atlantic ridge. Some cold seeps include the Florida Escarpment and the Laurentian Fan. Hydrothermal vents and cold seeps are not located near each other therefore organisms are unable to travel to these locations without the help of whale falls. Whale falls are more widespread than hydrothermal vents and seeps (Smith 2003). Researchers estimate that roughly every five to sixteen kilometers along the sea floor is a whale fall (Bennett 2002). This would make the journey of organisms from hydrothermal vents, close seeps, and whale falls, easier because locations would be closer together.

Each phase of the whale falls brings a diverse assemblage of species. The first stage, mobile scavenger phase, features organisms that feed on the meat. The second stage, enrichment – opportunist phase, features organisms that feed on the bones. The third stage, sulfophilic phase, features organisms that use chemosynthesis for energy. Each stage processes new life on the whale fall. The whale fall may even give passageway for organisms to move to hydrothermal vent and cold seeps, proving the stepping- stone theory correct.

Work Cited:
Bennett, Kim. "Whale Falls—islands of Abundance and Diversity in the Deep Sea." Monterey Bay Aquarium Research Institute. Dec. 2002. Web. 22 Nov. 2010. <http://www.mbari.org/news/news_releases/2002/dec20_whalefall.html>. Bonnemains, Jacky. "Of Whales and Their Usefulnessy." Robin Des Bois. Apr. 2010. Web. 22 Nov. 2010. 
<http://www.robindesbois.org/english/Of_whales_and_their_Usefulness.pdf>. 
Calkins, Mandy. "Whale Falls." Science and the Sea. The University of Texas Marine Science Institute, 08 Mar. 2010. Web. 22 Nov. 2010. 
<http://www.scienceandthesea.org/index.php?option=com_content&task=view&id=276&Itemid=6>. 
Milius, Susan. "Decades of Dinner Underwater Community Begins with the Remains of a 
Whale." Science News Online. 07 May 2005. Web. 22 Nov. 2010. <http://www.phschool.com/science/science_news/articles/decades_of_dinner.html>. 
Russo, Julie Z. "This Whale's (After) Life." NURP. NOAA's Undersea Research Program, 21 Aug. 2004. Web. 22 Nov. 2010. <http://www.nurp.noaa.gov/Spotlight/Whales.htm>. 
Smith, Craig R. and Baco, Amy R. (2003): Ecology of whale falls at the deep-sea floor. In R.N. 
Gibson and R.J.A. Atkinson, eds., Oceanography and Marine Biology: an Annual 
Review, vol. 41, pp. 311-354.