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What lies beyond the death of a whale?

Have you ever wondered what happens after the death of a whale? When a whale’s life ends, its body turn into a new ecosystem for many life forms. Do you want to learn more about whale falls? Which are the stages of a whale fall? Do you want to discover some incredible new species? 

INTRODUCTION

Whales are amazing animals and they play a significant role in the marine ecosystems, as well as other cetacean species. Take the humpback whale for instance. This species feeds using a unique system called the net bubble method, in which seabirds can take advantage of it due to the fact that whales drive prey to the surface. Another key role they play is the transport of nutrients. Finally, another example is the one that we are going to explain in this post: the whale falls.

WHAT IS A WHALE FALL?

Whale corpses are known to serve as a host for animals that live in the bottom of the oceans. When the whale carcasses fall to the bottom of the sea, concretely in the bathyal or abyssal zone (at depths of 2,000 m or more), they are called whale falls. These animals take benefit from the dead whales since they serve as a source of food for them.

Whale fall (Picture: Ocean Networks).
Whale falls are ecosystems by themselves (Picture: Ocean Networks).

It is believed that whale falls may have provided a stepping stone for deep-sea species to colonise the sea floor. In addition, the more research, the more new species described and the more potential commercial applications.

STAGES OF COLONIZATION

A dead whale creates by itself a new and rich ecosystem because produces intense organic enrichment in a very small area. After this, successive stages of colonization take place. Species found in these areas are similar to those in hydrothermal vents. According to researchers, whale falls pass through three stages:

  1. Mobile scavengers stage
  2. The enrichment-opportunist stage
  3. Sulfophilic stage
Decomposition of a whale carcass in Monterey Canyon over 7 years (Picture: MBARI).
Decomposition of a whale carcass in Monterey Canyon over a 7-year period (Picture: MBARI).

It is thought that tens of thousands of organisms from about 400 animals species depend on a single whale fall. Astonishingly, scientists estimate that one whale corpse provides with the nutritional equivalent of 2,000-years worth of normal biological detritus sinking to the seafloor.

1. MOBILE SCAVENGERS STAGE

The first stage is dominated by mobile scavenger species. In this stage, the dead whale is covered by a dense aggregaton of hagfishes, small numbers of lithodid crabs, rattail fish, large sleeper sharks and millions of amphipods.

These animals are responsible of the disappearance of the soft tissue. They can eat 40-60 kg per day. In a 5-ton carcass, it lasted for 4 months, while in 35-tone carcasses for 9 months to 2 years.

Grey whale decomposition, 2 month after deposition (Picture: Hermanus Online).
Grey whale decomposition, 2 and 18 month after deposition (Picture: Hermanus Online).

2. THE ENRICHMENT-OPPORTUNIST STAGE

During the second stage, the animal’s skeleton is surrounded by dense aggregations of polychaete worms, cumaceans (crustaceans) and molluscs such as snails. There have been described some whale fall specialist species, previously unknown. These animals feed on the rest of the body, including the sediment surrounding because it is full of decomposing tissue.

Se (Picture: Hermanus Online).
During the enrichment-opportunist stage, the skeleton is surrounded by many species of animals (Picture: Hermanus Online).

3. SULFOPHILIC STAGE

This is by far the longest stage in whale falls: it might last from 10 to 50 years, or more. The so-called sulfophilic stage owes its name to the sulfide produced by bones due to the action of chemosynthetic bacteria, who use sulfate to break down the lipids inside the bones and produce sulfide. The sulfide allow the presence of dense bacterial mats, mussels and tube worms, among others. It have been found more than 30,000 organisms in a single skeleton.

Sulfide stage (Picture: Hermanus Online).
Sulfophilic stage (Picture: Hermanus Online).

NEW SPECIES DISCOVERED

As it has been mentioned above, new species have been described in whale falls. In this section, we are going to present only some of them.

The anemone Anthosactis pearsea is a small, white and cube-shaped species. Its importance lies on the fact that it is the first anemone found on a whale fall.

df (Picture: MBARI).
Anthosactis pearseae (white animals) (Picture: MBARI).

Species included in the genus Osedax have also been discovered. Their common name, bone-eating zombie worms, reflects exactly their task: to eat bones. These animals have neither eyes nor mouth, but they present reddish plumes that act as gills and some kind of green roots, where symbiotic bacteria break down proteins and lipids inside the bone, which supply nutrients for the worms. The macroscopic form of the animals is always a female, who contains dozens of microscopic males inside its body

Osedax frankpressi (Picture: Greg Rouse).
A female Osedax frankpressi (Picture: Greg Rouse).

Another strikingly awesome worm is the bristleworm, Ophryotrocha craigsmithi. In spite of lacking any particular adaptation, it is thought that they are exclusive at whale falls or similar ecosystems.

Ophryotrocha craigsmithi (Picture: Live Science)
Bristleworm, Ophryotrocha craigsmithi (Picture: Live Science)

A final example to take into consideration is the gastropod Rubyspira, whale-fall specialists molluscs which are 3-4 cm in length.

Rubyspira snails on whale bones (Picture: MBARI). Lat= 36.61337280 Lon= -122.43557739 Depth= 2895.4 m Temp= 1.683 C Sal= 34.618 PSU Oxy= 2.31 ml/l Xmiss= 84.1% Source= digitalImages/Tiburon/2006/tibr991/DSCN8049.JPG Epoch seconds= 1148489479 Beta timecode= 07:21:57:03
Rubyspira snails on whale bones (Picture: MBARI).

I encourage you to watch these videos about whale falls. In the first one, you can see a diving on the Rosebud whale fall carried out by the team of E/V Nautilus, searching for the life it supports. In the second one, you can see a feast in the deep in a whale fall in Monterey Canyon, recorded by the Monterey Bay Aquarium Research Institute (MBARI).

REFERENCES

Difusió-anglès

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