Whale fall
[2] Since then, several natural and experimental whale falls have been monitored[1][3] through the use of observations from submersibles and remotely operated underwater vehicles (ROVs) in order to understand patterns of ecological succession on the deep seafloor.
[1] Organisms that have been observed at deep-sea whale fall sites include chordates, arthropods, cnidarians, echinoderms, mollusks, nematodes, and annelids.
[1] It has been postulated that whale falls generate biodiversity by providing evolutionary stepping stones for multiple lineages to move and adapt to new environmentally-challenging habitats.
[1] Once in the deep-sea, cold temperatures slow decomposition rates, and high hydrostatic pressures increase gas solubility, allowing whale falls to remain intact and sink to even greater depths.
[10] This amount of organic material reaching the seafloor at one time creates a pulse equivalent to about 2000 years of background carbon flux in the 50 square meters of sediment immediately beneath the whale fall.
[10] This helps to sustain the community structure that develops around a whale fall, but it also has potential implications for the biological pump, or the flux of organic material from the surface ocean to depth.
Based on simple trophic structure, this would mean whales and other large zooplankton feeders can be found at higher abundance around areas of high primary production, potentially making them important exporters of carbon to depth through food falls.
[11] There is growing evidence that the contribution of food falls to the deep ocean carbon flux is larger than originally proposed, especially on the local scale in areas of high primary productivity.
[6] By the 1960s, deep sea trawlers unintentionally recovered other new mollusc species including limpets (named Osteopelta) attached to whale bones.
[17] The DSV Alvin observed the remains using scanning sonar at 1,240 m (4,070 ft) in the Catalina Basin and collected the first photographic images and samples of animals and microbes from this remarkable community.
Mussels and vesicomyid clams belong to groups that harbor chemosynthetic bacteria, which can draw energy from inorganic chemicals, such as sulfur.
[6] Osedax, a genus of deep-sea polychaete worms, acts as an ecosystem engineer by excreting acid to erode whale bones and absorbing the nutrients trapped within.
[20] At whale fall sites it is common to see between three and five trophic levels present, with two main nutritional sources constituting the base of the food web.
[20] Recent studies also show a possible trend of "dual niche partitioning", in which scavengers tend to reach peak densities on the carcass during the day and predators are more present during the night, reducing competition between the two trophic groups.
[1] Though chemosynthetic, and specifically chemolithoautotrophic, microorganisms are significant to the ecology of whale falls, these ecosystems are typically first inhabited by heterotrophic microbes such as actinomycetes, which break down collagen, and sulfate reducers.
[1] Some of these relatively large scavengers that have been recorded include hagfish, sleeper sharks, and various bony fish species such as blob sculpin, Dover sole, and snubnose eelpout.
[1] Two common genera are Ophryotrocha, which displays adaptive radiation on whale falls, and the genus Osedax, which are specialists that burrow into bones.
[22] Smaller cetaceans, such as porpoises and dolphins, do not undergo the same ecological succession stages due to their small size and lower lipid content.
[23] The initial period begins with "mobile scavengers" such as hagfish and sleeper sharks actively consuming soft tissue from the carcass.
As whale bones are rich in lipids, representing 4–6% of its body weight, the final digestion stage can last between 50 and possibly 100 years.
[1] A whale fall enters this stage once the organic compounds have been exhausted and only minerals remain in the bones, which provide a hard substrate for suspension and filter feeders.
Whale falls do however support both sulfur reducing bacteria and methane producing archaea, leading to the conclusion that the area is not electron donor limited or there is minimal or no competition for suitable substrate.
[24] Whale fall fossils from the late Eocene and Oligocene (34–23 MYA) in Washington and from the Pliocene in Italy include clams that also inhabited non-chemosynthetic environments.
[6] As prehistoric whales evolved to live in pelagic waters and dive deeper, structural changes in their anatomy included increased size, reduced bone density and higher lipid content.
[25] The discovery of the limpet Osteopelta in an Eocene New Zealand turtle bone indicates that these animals evolved before whales, including possibly inhabiting Mesozoic (251–66 MYA) reptiles.
Another possibility is that these fossils represent a prior, dead-end evolutionary path, and that today's whale fall animals evolved independently.
