Editing Whale fall

{{Short description|Whale carcass falling to the ocean floor}}
{{Use dmy dates|date=August 2021}}
{{for|the novel by Daniel Kraus|Whalefall (novel)}}
[[File:Whalefall_hires.jpg|right|thumb|A [[Chemotroph#Chemoautotroph|chemoautotrophic]] whale fall community in the Santa Cruz basin off southern California at a depth of {{cvt|1,674|m}}, including bacteria mats, vesicomyid clams in the sediments, galatheid crabs, polynoids, and a variety of other invertebrates.]]

A '''whale fall''' occurs when the [[Carrion|carcass]] of a [[whale]] has fallen onto the [[ocean floor]], typically at a depth greater than {{convert|1000|m|ft|abbr=on}}, putting them in the [[Bathyal zone|bathyal]] or [[abyssal zone]]s.<ref name=":02">{{Cite journal |last1=Smith |first1=Craig R. |last2=Glover |first2=Adrian G. |last3=Treude |first3=Tina |last4=Higgs |first4=Nicholas D. |last5=Amon |first5=Diva J. |date=2015 |title=Whale-Fall Ecosystems: Recent Insights into Ecology, Paleoecology, and Evolution |journal=Annual Review of Marine Science |volume=7 |issue=1 |pages=571–596 |bibcode=2015ARMS....7..571S |doi=10.1146/annurev-marine-010213-135144 |pmid=25251277 |s2cid=43201905 |doi-access=free}}</ref> On the sea floor, these carcasses can create complex localized [[ecosystem]]s that supply sustenance to deep-sea organisms for decades.<ref name=":02" /> In some circumstances, particularly in cases with lower water temperatures, they can be found at much [[Mesopelagic zone|shallower depths]], with at least one natural instance recorded at 150 m (500 ft) and multiple experimental instances in the range of {{cvt|30-382|m|-2}}.<ref name=":02" /> Whale falls were first observed in the late 1970s with the development of [[Deep-sea exploration|deep-sea robotic exploration]].<ref name=":5">{{Cite book|url=https://www.amazon.com/000-Leagues-Undersea-Submariner-Submergence-ebook/dp/B00VERWICQ |title=30,000 Leagues Undersea: True Tales of a Submariner and Deep Submergence Pilot|last=Vetter|first=Tom|year=2015|publisher=Tom Vetter Books, LLC|isbn=978-1-941160-10-7|language=en}}</ref> Since then, several natural and experimental whale falls have been monitored<ref name=":02" /><ref name=":2">{{Cite journal|last1=Lundsten|first1=Lonny|last2=Schlining|first2=Kyra L.|last3=Frasier|first3=Kaitlin|last4=Johnson|first4=Shannon B.|last5=Kuhnz|first5=Linda A.|last6=Harvey|first6=Julio B. J.|last7=Clague|first7=Gillian|last8=Vrijenhoek|first8=Robert C.|date=2010-12-01|title=Time-series analysis of six whale-fall communities in Monterey Canyon, California, USA|journal=Deep Sea Research Part I: Oceanographic Research Papers|volume=57|issue=12|pages=1573–1584|doi=10.1016/j.dsr.2010.09.003 |bibcode=2010DSRI...57.1573L}}</ref> through the use of observations from submersibles and remotely operated underwater vehicles ([[Remotely operated underwater vehicle|ROVs]]) in order to understand patterns of [[ecological succession]] on the deep seafloor.<ref name=":32">{{Cite journal|last1=Aguzzi|first1=J.|last2=Fanelli|first2=E.|last3=Ciuffardi|first3=T.|last4=Schirone|first4=A.|last5=De Leo|first5=F. C.|last6=Doya|first6=C.|last7=Kawato|first7=M.|last8=Miyazaki|first8=M.|last9=Furushima|first9=Y.|last10=Costa|first10=C.|last11=Fujiwara|first11=Y.|date=2018-07-24|title=Faunal activity rhythms influencing early community succession of an implanted whale carcass offshore Sagami Bay, Japan|journal=Scientific Reports|language=en|volume=8|issue=1|pages=11163|doi=10.1038/s41598-018-29431-5|pmid=30042515|pmc=6057991 |bibcode=2018NatSR...811163A}}</ref>

Deep sea whale falls are thought to be hotspots of [[adaptive radiation]] for specialized fauna.<ref name=":02" /> Organisms that have been observed at deep-sea whale fall sites include [[Chordate|chordates]], [[Arthropod|arthropods]], [[Cnidaria|cnidarians]], [[Echinoderm|echinoderms]], [[Mollusca|mollusks]], [[Nematode|nematodes]], and [[Annelid|annelids]].<ref name=":02" /><ref name=":3">{{Cite journal |last1=Sumida |first1=Paulo Y. G. |last2=Alfaro-Lucas |first2=Joan M. |last3=Shimabukuro |first3=Mauricio |last4=Kitazato |first4=Hiroshi |last5=Perez |first5=Jose A. A. |last6=Soares-Gomes |first6=Abilio |last7=Toyofuku |first7=Takashi |last8=Lima |first8=Andre O. S. |last9=Ara |first9=Koichi |last10=Fujiwara |first10=Yoshihiro |date=2016-02-24 |title=Deep-sea whale fall fauna from the Atlantic resembles that of the Pacific Ocean |journal=Scientific Reports |language=en |volume=6 |issue=1 |page=22139 |doi=10.1038/srep22139 |pmid=26907101 |pmc=4764926 |bibcode=2016NatSR...622139S }}</ref> New species have been discovered, including some potentially [[Specialist species|specializing]] in whale falls.<ref name=":02" /> 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.<ref name=":02" /> Researchers estimate that 690,000 carcasses/skeletons of the nine largest whale species are in one of the four stages of succession at any one time.<ref name=":0">{{Cite journal|title=Life at the Bottom: The Prolific Afterlife of Whales|journal=Scientific American|year=2010|language=en|doi=10.1038/scientificamerican0210-78|pmid=20128227|last1=Little|first1=C. T.|volume=302|issue=2|pages=78–82, 84}}</ref> This estimate implies an average spacing of {{convert|12|km|mi|abbr=on}} and as little as {{convert|5|km|mi|abbr=on}} along migration routes. They hypothesize that this distance is short enough to allow [[larvae]] to disperse/migrate from one to another.<ref name=":0" />

Whale falls are able to occur in the deep open ocean due to cold temperatures and high hydrostatic pressures. In the coastal ocean, a higher incidence of predators as well as warmer waters hasten the decomposition of whale carcasses.<ref name=":02" /> Carcasses may also float due to decompositional gases, keeping the carcass at the surface.<ref name="allison1991">{{cite journal|last1=Allison|first1=Peter A.|last2=Smith|first2=Craig R.|last3=Kukert|first3=Helmut|last4=Deming|first4=Jody W.|last5=Bennett|first5=Bruce A.|date=1991|title=Deep-water taphonomy of vertebrate carcasses: a whale skeleton in the bathyal Santa Catalina Basin|journal=Paleobiology|volume=17|issue=1|pages=78–89|doi=10.1017/S0094837300010368|jstor=2400991|bibcode=1991Pbio...17...78A |s2cid=129439319 }}</ref> The bodies of most great whales (which includes [[sperm whale]]s and many species of [[baleen whale]]<ref>{{Cite journal|last1=Baldanza|first1=Angela|last2=Bizzarri|first2=Roberto|last3=Famiani|first3=Federico|last4=Garassino|first4=Alessandro|last5=Pasini|first5=Giovanni|last6=Cherin|first6=Marco|last7=Rosatini|first7=Francesco|date=2018|title=The early Pleistocene whale-fall community of Bargiano (Umbria, Central Italy): Paleoecological insights from benthic foraminifera and brachyuran crabs|url=https://palaeo-electronica.org/content/in-press/2148-whale-fall-paleo-community|journal=Palaeontologia Electronica|language=en|volume=21|issue=16|pages=1–27|doi=10.26879/779 |doi-access=free}}</ref>) are slightly denser than the surrounding seawater, and only become positively buoyant when the lungs are filled with air.<ref>{{Cite journal|last1=Reisdorf|first1=Achim G.|last2=Bux|first2=Roman|last3=Wyler|first3=Daniel|last4=Benecke|first4=Mark|last5=Klug|first5=Christian|last6=Maisch|first6=Michael W.|last7=Fornaro|first7=Peter|last8=Wetzel|first8=Andreas|date=2012-03-01|title=Float, explode or sink: postmortem fate of lung-breathing marine vertebrates|journal=Palaeobiodiversity and Palaeoenvironments|language=en|volume=92|issue=1|pages=67–81|doi=10.1007/s12549-011-0067-z|bibcode=2012PdPe...92...67R |s2cid=129712910 |url=http://doc.rero.ch/record/321320/files/12549_2011_Article_67.pdf}}</ref> When the lungs deflate, the whale carcasses can reach the seafloor quickly and relatively intact due to a lack of significant whale fall scavengers in the water column.<ref name=":02" /> Once in the deep-sea, cold temperatures slow [[decomposition]] rates, and high [[Hydrostatics|hydrostatic pressures]] increase gas solubility, allowing whale falls to remain intact and sink to even greater depths.<ref name="allison1991" />

==Contribution to the biological pump==
The amount of [[carbon]] tied up in a typical single whale carcass (about two [[tonne]]s of carbon for a typical 40-tonne carcass) is roughly equivalent to the amount of carbon exported to a hectare of abyssal ocean floor in 100–200 years.<ref name="Smith and Baco 20032">{{Cite book|title=Oceanography and Marine Biology: an Annual Review|last1=Smith|first1=Craig R.|last2=Baco|first2=Amy R.|volume=41|pages=311–354|contribution=Ecology of whale falls at the deep-sea floor|citeseerx=10.1.1.486.8957|contribution-url=https://books.google.com/books?id=64crGFXWn5gC&pg=PA311|name-list-style=amp}}</ref> This amount of organic material reaching the seafloor at one time creates a pulse equivalent to about 2000 years of background [[carbon cycle|carbon flux]] in the 50 square meters of sediment immediately beneath the whale fall.<ref name="Smith and Baco 20032" /> 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.

Whales and some other large marine animals feed on and follow large aggregations of zooplankton for sustenance. 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.<ref name=":22">{{Cite journal|last1=Higgs|first1=Nicholas D.|last2=Little|first2=Crispin T. S.|last3=Glover|first3=Adrian G.|last4=Dahlgren|first4=Thomas G.|last5=Smith|first5=Craig R.|last6=Dominici|first6=Stefano|date=2012-06-01|title=Evidence of ''Osedax'' worm borings in Pliocene (~3 Ma) whale bone from the Mediterranean|journal=Historical Biology|volume=24|issue=3|pages=269–277|doi=10.1080/08912963.2011.621167|s2cid=85170976 }}</ref> Biological pump models indicate that a large amount of carbon uptake by the deep sea is not supplied by particulate organic carbon (POC) alone, and must come from another source. Lateral [[advection]] of carbon, especially in coastal areas contributes to this deficit in the model, but food falls are also another source of organic carbon for the deep ocean.<ref name=":22" /> Various percentages of the food fall contribution to the total carbon flux to the deep ocean have been hypothesized, ranging from 0.3%<ref>{{Cite journal|last=Smith|first=Craig|date=2005|title=Bigger is better: The role of whales as detritus in marine ecosystems|url=https://www.researchgate.net/publication/228387134|journal=Whales, Whaling, and Ocean Ecosystems|volume=12}}</ref> to 4%.<ref name=":22" />

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. Unfortunately, contributions of food falls to the biological pump are hard to measure and rely on a few serendipitous studies on discovered falls<ref>{{Cite journal|last1=Smith|first1=C. R.|last2=Kukert|first2=H.|last3=Wheatcroft|first3=R. A.|last4=Jumars|first4=P. A.|last5=Deming|first5=J. W.|date=1989|title=Vent fauna on whale remains|journal=Nature|language=en|volume=341|issue=6237|pages=27–28|doi=10.1038/341027a0 |bibcode=1989Natur.341...27S|s2cid=4355561}}</ref><ref name=":22" /> as well as planted carcasses<ref name=":6">{{Cite journal|last1=Kemp|first1=Kirsty|last2=Jamieson|first2=Alan John|last3=Bagley|first3=Philip Michael|last4=Mcgrath|first4=H.|last5=Bailey|first5=David Mark|last6=Collins|first6=M. A.|last7=Priede|first7=Imants George|date=2006|title=Consumption of a large bathyal food fall, a six-month study in the north-east Atlantic|journal=Marine Ecology Progress Series|language=en|volume=310|pages=65–76 |doi=10.3354/meps310065|doi-access=free}}</ref> with much of the deep sea carbon flux studies relying on sediment traps.<ref>{{Cite book|url=https://books.google.com/books?id=PiDT2MbZddkC|title=Biological Oceanography|last1=Miller|first1=Charles B.|last2=Wheeler|first2=Patricia A.|date=2012|publisher=Wiley|isbn=978-1-118-22317-8|language=en}}</ref>

==Discovery==
[[File:Sample_collecting_at_whale_fall.jpg|thumb|The skeleton of a gray whale lies on the [[Monterey Bay|Santa Cruz Basin]] seafloor as a hagfish swims into view of the [[US Navy]]'s [[Deep-submergence vehicle|deep-sea submersible]] [[DSV Alvin|''Alvin'']].<ref name="NOAA2">{{cite web |last=Russo |first=Julie Zeidner |date=24 August 2004 |url=http://www.nurp.noaa.gov/Spotlight/Whales.htm |title=This Whale's (After) Life |website=NOAA's Undersea Research Program |publisher=NOAA |access-date=13 November 2010 |archive-date=3 November 2017 |archive-url=https://web.archive.org/web/20171103151201/http://www.nurp.noaa.gov/Spotlight/Whales.htm |url-status=dead }}</ref>]]
The earliest indication that whale carcasses could host specialized animal communities occurred in 1854 when a new [[mussel]] species was extracted from a piece of floating whale [[blubber]].<ref name=":0" /> By the 1960s, deep sea trawlers unintentionally recovered other new [[mollusc]] species including [[limpet]]s (named ''[[Osteopelta]]'') attached to whale bones.<ref name=":0" />

The first recorded abyssal whale fall was discovered by US Navy [[bathyscaphe]] pilots LT Ken Hanson, Master Chief George Ellis and LT Tom Vetter diving in bathyscaphe ''[[Trieste II]]'' (DSV-1) on 19 February 1977.<ref name=":5" /> The skeleton of the carcass, which was completely devoid of organic tissue, remained intact and collapsed flat on the seafloor. The submersible recovered a [[jawbone]] and [[phalanges]]. The whale was considered to be a [[gray whale]] based on the size of the bones and the skeleton, the lack of teeth and its location west of Santa Catalina.<ref name=":0" />

The first whale fall ecosystem, which included a [[Chemotroph#Chemoautotroph|chemoautotrophic]] assemblage living on the anaerobic breakdown of organic material in whale bones, was discovered by a team of scientists led by [[University of Hawaiʻi]] [[Oceanography|oceanographer]] Craig Smith in 1987.<ref>{{cite journal|last1=Smith|first1=C. R.|last2=Kukert|first2=H.|last3=Wheatcroft|first3=R. A.|last4=Jumars|first4=P. A.|last5=Deming|first5=J. W.|year=1989|title=Vent fauna on whale remains|journal=Nature|volume=341|issue=6237|pages=27–28|doi=10.1038/341027a0|bibcode=1989Natur.341...27S|s2cid=4355561}}</ref> The [[DSV Alvin | DSV ''Alvin'']] observed the remains using scanning [[sonar]] at {{convert|1240|m|ft|abbr=on}} in the [[Santa Catalina, California|Catalina]] Basin and collected the first photographic images and samples of animals and microbes from this remarkable community.<ref name=":0" />

[[File:Distribution of known whale falls.jpg|thumb|Distribution of currently known whale falls in the world. (May 2022)]]
Many other whale falls have since been found by more researchers and deep-sea explorers, as well as by naval [[submarine]]s. The increase in detection is largely due to the use of cutting-edge [[side-scan sonar]] which can minutely examine the ocean floor for large aggregations of matter. A 2022 study identified 45 known natural whale falls, 38 implanted ones, and 78 fossil ones, mostly in the Pacific, but a significant number, particularly of fossil ones, in the Atlantic.<ref>{{cite journal |last1=Li |first1=Qihui |last2=Liu |first2=Yaping |last3=Li |first3=Guo |last4=Wang |first4=Zhikai |last5=Zheng |first5=Zheng |last6=Sun |first6=Yuyang |last7=Lei |first7=Ningfei |last8=Li |first8=Qi |last9=Zhang |first9=Weizhen |date=May 18, 2022 |title=Review of the Impact of Whale Fall on Biodiversity in Deep-Sea Ecosystems |journal=Frontiers in Ecology and Evolution |volume=10 |doi=10.3389/fevo.2022.885572|doi-access=free }}</ref>

==Ecology==
[[File:Whale_fall_Whale_bone_recovery.jpg|thumb|A [[whale bone]] being recovered from the Santa Catalina Basin floor five years after experimental emplacement. The bone surface contains patches of white bacterial mats and a [[squat lobster]]. [[Hydroids]] have sprouted on the loop of yellow line attached to the bone.<ref name="NOAA2" />]]
Whale falls are distributed heterogeneously throughout space and time, with a concentration along migration routes.<ref name="allison1991" /> There is much faunal overlap in these whale falls across oceans. Mussels and [[Vesicomyidae|vesicomyid clams]] belong to groups that harbor [[chemosynthetic]] bacteria, which can draw energy from [[inorganic chemicals]], such as sulfur. Before their presence was discovered at whale falls, the only known habitats of these groups were sunken wood and [[hydrothermal vent]]s. Similarly, [[Lucinidae|lucinid clams]] were previously only known to inhabit carbon seeps and [[Hypoxia (environmental)|anoxic]] [[seafloor sediments]].<ref name=":0" /> ''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.<ref name=":02" /> This enhances biodiversity in the deep sea by increasing the water diffusion into the matrix of bones and facilitating colonization of the bone matrix by rarer species.<ref>{{Cite journal|last1=Alfaro-Lucas|first1=Joan M.|last2=Shimabukuro|first2=Maurício|last3=Ferreira|first3=Giulia D.|last4=Kitazato|first4=Hiroshi|last5=Fujiwara|first5=Yoshihiro|last6=Sumida|first6=Paulo Y. G.|date=2017-12-01|title=Bone-eating ''Osedax'' worms (Annelida: Siboglinidae) regulate biodiversity of deep-sea whale-fall communities|journal=Deep Sea Research Part II: Topical Studies in Oceanography|series=Geo and bio-diversity in the South West Atlantic deep sea: the Iatá-piúna expedition with the manned submersible Shinkai 6500|volume=146|pages=4–12|doi=10.1016/j.dsr2.2017.04.011 |bibcode=2017DSRII.146....4A}}</ref> Members of ''Osedax'' have more dramatic effects in juvenile skeletons, which are not as well-calcified as adult skeletons.<ref name=":42">{{Cite journal|last1=Alfaro-Lucas|first1=Joan M.|last2=Shimabukuro|first2=Maurício|last3=Ogata|first3=Isabella V.|last4=Fujiwara|first4=Yoshihiro|last5=Sumida|first5=Paulo Y. G.|date=2018-05-28|title=Trophic structure and chemosynthesis contributions to heterotrophic fauna inhabiting an abyssal whale carcass|journal=Marine Ecology Progress Series|language=en|volume=596|pages=1–12|doi=10.3354/meps12617 |bibcode=2018MEPS..596....1A|doi-access=free}}</ref>

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. Adult whale carcasses can house up to five trophic levels, whereas juveniles more typically have three.<ref name=":42" />

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.<ref name=":32" /> There is also a possible trend in tidal patterns and species occurrence, indicating that tides play a role in niche partitioning as well.<ref name=":32" />

Similar ecosystems exist when other large volumes of nutrient-rich material fall to the sea floor. Sunken beds of [[kelp]] create kelp falls, and large trees can sink to create wood falls. In more recent years, [[shipwrecks]] have also provided bases for deepwater communities. In ecosystems formed following a whale fall event, there are four stages of ecological succession.<ref name=":02" />

===Biodiversity===
Many different taxa are known to interact with and inhabit whale falls, including multiple newly discovered species.<ref name=":02" /> At the base of these ecosystems is the microbial community.<ref name=":02" /> Sulfur-oxidizing, sulfate-reducing, and methanogenic microbes are the most prevalent types found on whale falls.<ref name=":02" /> Among the sulfate-reducing bacteria, [[Desulfobacteraceae]] and [[Desulfobulbaceae]] are the most common, while [[Methanomicrobiales]] and [[Methanosarcinales]] are the most common among the methanogenic archaea.<ref name=":02" /> Though chemosynthetic, and specifically [[chemolithoautotrophic]], microorganisms are significant to the ecology of whale falls, these ecosystems are typically first inhabited by [[Heterotroph|heterotrophic]] microbes such as [[Actinomycetales|actinomycetes]], which break down collagen, and sulfate reducers.<ref name=":02" /> The presence of such heterotrophic microbes paves the way for the chemosynthetic organisms, which then form [[bacterial mats]] that provide for larger organisms, such as certain annelid species.<ref name=":02" />

Chordate scavengers are also early inhabitants of whale falls.<ref name=":02" /> Some of these relatively large scavengers that have been recorded include [[hagfish]], [[sleeper sharks]], and various [[Osteichthyes|bony fish]] species such as [[blob sculpin]], Dover sole, and [[snubnose eelpout]].<ref name=":2" /> Many crustacean species can also be found on whale falls, including [[Tanner crab|tanner]] and [[Galatheoidea|galatheid crabs]].<ref name=":2" /> Another common crustacean inhabitant of whale falls is [[Amphipoda|amphipods]], which often show up in relatively high concentrations.<ref name=":2" />

Whale falls also house cnidarians, echinoderms, and mollusks.<ref name=":3" /> [[Sea anemone|Sea anemones]], [[Brittle star|brittle stars]], and [[Sea urchin|sea urchins]] in particular have been recorded at whale fall sites.<ref name=":3" /> Additionally, there are many species of [[Bivalvia|bivalve]], including members of [[Mytilidae]] and [[Vesicomyidae]], and of marine [[Gastropoda|gastropods]], including members of the bone-eating genus ''[[Rubyspira]]''.<ref name=":02" /> Marine nematodes in the genera ''Halomonyhystera'', ''Anticoma'', and ''Theristus'' have also been recorded, though research on them is less extensive than other whale fall taxa.<ref>{{Cite journal |last1=Avila |first1=Ana K. F. |last2=Shimabukuro |first2=Maurício |last3=Couto |first3=Daniel M. |last4=Alfaro-Lucas |first4=Joan M. |last5=Sumida |first5=Paulo Y. G. |last6=Gallucci |first6=Fabiane |date=2023-05-02 |title=Whale falls as chemosynthetic refugia: a perspective from free-living deep-sea nematodes |journal=Frontiers in Marine Science |language=English |volume=10 |page=1111249 |doi=10.3389/fmars.2023.1111249 |doi-access=free }}</ref>

Of all taxa observed at whale falls, annelids have received the most research focus. Though marine leeches have been observed at whale falls,<ref name=":2" /> polychaetas tend to be the focus of much of the annelid research on whale falls. This is in part due to the number of new polychaeta species discovered in these ecosystems.<ref name=":02" /> Two common genera are ''[[Ophryotrocha]]'', which displays adaptive radiation on whale falls, and the genus ''Osedax'', which are specialists that burrow into bones.<ref name=":02" /> Members of ''Osedax'' can be found on whale falls across the globe,<ref name=":02" /> though different species have been discovered on Atlantic whale falls than on Pacific whale falls.<ref name=":3" />

===Ecosystem stages===
There are four stages of decomposition associated with a whale fall.<ref name=":02" /> These stages vary in duration and overlap with one other with the size of the carcass, water depth, and other environmental variables, such as tidal flow.<ref name="allison1991" /> Large, intact whale falls appear to pass through the four decomposition stages, while the stages on smaller or partial carcasses may be truncated.<ref name=":12">{{Cite journal|last1=Hilario|first1=Ana|last2=Cunha|first2=Marina R.|last3=Génio|first3=Luciana|last4=Marçal|first4=Ana Raquel|last5=Ravara|first5=Ascensão|last6=Rodrigues|first6=Clara F.|last7=Wiklund|first7=Helena|date=2015|title=First clues on the ecology of whale falls in the deep Atlantic Ocean: results from an experiment using cow carcasses|journal=Marine Ecology|language=en|volume=36|issue=S1|pages=82–90|doi=10.1111/maec.12246 |bibcode=2015MarEc..36...82H|doi-access=free}}</ref> Smaller cetaceans, such as porpoises and dolphins, do not undergo the same ecological succession stages due to their small size and lower lipid content.<ref name=":12" /> Researchers believe the presence of ''Osedax'' worms may also be a contributing factor in the observed successional differences.<ref name="pap2">{{cite web|url=http://www.livescience.com/5744-worm-species-discovered-dead-whales.html|title=New Worm Species Discovered on Dead Whales|last=Bryner|first=Jeanna|date=21 September 2009|website=Live Science}}</ref>

====Stage 1====
The initial period begins with "mobile scavengers" such as [[hagfish]] and [[sleeper shark]]s actively consuming soft tissue from the carcass. Consumption can be at a rate of {{convert|40|-|60|kg|lb}} per day.<ref name=":0" /> This stage typically lasts months up to 1.5 years.<ref name=":32" />

====Stage 2====
The second stage introduces the "enrichment opportunists". These are animals which colonize the bones and surrounding sediments that have been contaminated with organic matter from the carcass and any other tissue left by the scavengers.<ref name=":0" /> This stage can last months up to 4.5 years.<ref name=":32" />

====Stage 3====
In the third stage, [[Chemotroph|sulfophilic bacteria]] anaerobically break down the [[lipid]]s embedded in the bones. Instead of [[oxygen]], they reduce dissolved sulfate ({{chem|SO|4|2-}}) and excrete [[hydrogen sulfide]]. Due to the toxicity of {{chem|H|2|S}}, only resistant chemosynthetic bacteria survive. The [[bacterial mat]]s provide nourishment for mussels, clams, limpets and sea snails. 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.<ref name=":0" />

====Stage 4====
Some scientists postulate a fourth stage of ecological succession at whale fall sites, called the "reef stage".<ref name=":02" /> 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.<ref name=":12" />

===Methanogenesis===
A process called [[methanogenesis]] can also occur around whale falls. Archaea that produce methane can be abundant in anoxic sediment, but are typically not found in co-occurrence with the sulfur reducing bacteria found at whale falls. 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.<ref name=":7">{{cite journal|last1=Treude|first1=Tina|last2=Smith|first2=Craig R.|last3=Wenzhöfer|first3=Frank|last4=Carney|first4=Erin|last5=Bernardino|first5=Angelo F.|last6=Hannides|first6=Angelos K.|last7=Krüger|first7=Martin|last8=Boetius|first8=Antje|date=2009|title=Biogeochemistry of a deep-sea whale fall: sulfate reduction, sulfide efflux and methanogenesis|journal=Marine Ecology Progress Series|volume=382|pages=1–21|bibcode=2009MEPS..382....1T|doi=10.3354/meps07972|jstor=24873149|doi-access=free|hdl=21.11116/0000-0001-CC9B-B|hdl-access=free}}</ref> Concentration gradients of both sulfide and methane can be found around whale falls, with the highest concentration coming within one meter of the carcass, which is several orders of magnitude higher than the surrounding sediment concentrations. Methanogenesis appears to only occur in sediments as opposed to sulfur reduction, which occurs both in sediments and on the bones of the carcass.<ref name=":7" /> The addition of sulfur reduction in both sediments and high lipid whale bones is a key factor for why whale falls are able to sustain deep-sea communities for extended periods of time.<ref name=":7" />

==Paleontology==
Whale fall fossils from the late [[Eocene]] and [[Oligocene]] (34–23 [[Mya (unit)|MYA]]) in [[Washington (state)|Washington]] and from the [[Pliocene]] in Italy include clams that also inhabited non-chemosynthetic environments. Chemosynthetic-only animals do not appear until the [[Miocene]] (23–5 MYA) in California and Japan.<ref name=":1" /> This may be because the lipid content of early whale bones was too low.<ref name=":0" /> 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.<ref name="allison1991" /> It is this increased lipid content that led to the establishment of chemosynthetic communities in the deep sea.<ref name=":1">{{Cite journal|last=Kiel|first=Steffen|date=2008-10-01|title=Fossil evidence for micro- and macrofaunal utilization of large nekton-falls: Examples from early Cenozoic deep-water sediments in Washington State, USA|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=267|issue=3|pages=161–174|doi=10.1016/j.palaeo.2008.06.016 |bibcode=2008PPP...267..161K}}</ref>

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.<ref>{{Cite journal|last1=Kaim|first1=Andrzej|last2=Kobayashi|first2=Yoshitsugu|last3=Echizenya|first3=Hiroki|last4=Jenkins|first4=Robert G.|last5=Tanabe|first5=Kazushige|date=2008|title=Chemosynthesis-Based Associations on Cretaceous Plesiosaurid Carcasses|journal=Acta Palaeontologica Polonica|volume=53|issue=1|pages=97–104|doi=10.4202/app.2008.0106 |doi-access=free}}</ref> They may have survived in seeps, wood-falls and vents while waiting out the 20 million year gap between the reptiles' extinction and whales' emergence. Another possibility is that these fossils represent a prior, dead-end evolutionary path, and that today's whale fall animals evolved independently.<ref name=":0" />

==Anthropogenic effects==
[[File:Cheynes_whale.jpg|thumb|Whalers stand with a whale that they have recently caught.]]
It has been suggested that the [[whaling]] industry has had an effect on the biological pump through the elimination of many large whales, reducing the amount of whale falls. The effects of this on [[Benthic zone|benthic]] whale fall community assemblages is not well understood.<ref name=":8">{{Cite journal|last1=Pershing|first1=Andrew J.|last2=Christensen|first2=Line B.|last3=Record|first3=Nicholas R.|last4=Sherwood|first4=Graham D.|last5=Stetson|first5=Peter B.|date=2010-08-26|title=The impact of whaling on the ocean carbon cycle: why bigger was better |journal=PLOS ONE|language=en|volume=5|issue=8|page=e12444 |doi=10.1371/journal.pone.0012444 |pmc=2928761|pmid=20865156|bibcode=2010PLoSO...512444P|doi-access=free}}</ref> However, it is suggested that the removal of large whales might have reduced the total [[Biomass (ecology)|biomass]] of the deep sea by more than 30%.<ref name=":8" /> Whales stored massive amounts of carbon that were exported to the deep sea during whale fall events. Whaling has thus also reduced the ability of the deep sea to [[Carbon sequestration|sequester carbon.]]<ref name=":8" /> Carbon can be sequestered for hundreds to thousands of years in the deep sea, supporting benthic communities.<ref name=":8" /> It is estimated that, in terms of carbon sequestration, each whale is equivalent to thousands of trees.<ref>{{Cite web|url=https://www.imf.org/external/pubs/ft/fandd/2019/12/natures-solution-to-climate-change-chami.htm|title=Nature's Solution to Climate Change – IMF F&D|website=www.imf.org|access-date=2019-12-08}}</ref>

==Contrast with other large food-falls==
There have also been studies based on the carcasses of other, non-mammalian marine vertebrates that have fallen to the deep sea. In particular, the chance discovery of a [[whale shark]] carcass and three [[mobulid]] ray carcasses led to observations on the communities that form surrounding large [[Elasmobranchii|elasmobranch]] falls as opposed to whale falls.<ref name="higgs2">{{cite journal|last1=Higgs|first1=Nicholas D.|last2=Gates|first2=Andrew R.|last3=Jones|first3=Daniel O. B.|last4=Valentine|first4=John F.|date=2014|title=Fish Food in the Deep Sea: Revisiting the Role of Large Food-Falls|journal=PLOS ONE|volume=9|issue=5|pages=e96016|bibcode=2014PLoSO...996016H|doi=10.1371/journal.pone.0096016|pmc=4013046|pmid=24804731|doi-access=free}}</ref> Whale sharks inhabit waters of roughly 1,000 meters depth regularly, which suggests it could be a regular form of food fall in areas where it is abundant.<ref>{{cite journal|last1=Weir|first1=Caroline R.|date=2010|title=Sightings of whale sharks (''Rhincodon typus'') off Angola and Nigeria|journal=Marine Biodiversity Records|volume=3|page=e50|doi=10.1017/S1755267209990741|doi-broken-date=1 November 2024 |bibcode=2010MBdR....3E..50W }}</ref> Many [[eelpout]]s (Zoarcidae) were found surrounding the whale shark with some evidence of direct feeding as boreholes were observed on the carcass. Another theory suggests that the eelpouts were waiting for their main prey, [[amphipods]] and other small benthic animals. The three rays found were at different stages of decomposition, leading to varying assemblages found surrounding the individuals.<ref name="higgs2" /> A higher abundance of scavengers was found surrounding the more intact individuals, including scavengers typical of whale falls like hagfish. Around the least intact individual a [[bacterial mat]] was observed in the zone of enrichment, but no clams or mussels typical of whale falls were seen.<ref name="higgs2" />

Overall, the four carcasses observed showed no evidence of progression past the scavenger stage. The size limitations, as well as physiological differences between large elasmobranchs and whales more than likely causes the changes observed in the communities surrounding their respective carcasses.<ref name="higgs2" /> [[Osedax]] worms have the ability to extract collagen from bones as well as lipids, enabling them to sustain themselves on bones other than the lipid-rich remains of whales.<ref>{{cite journal|last1=Jones|first1=William J.|last2=Johnson|first2=Shannon B.|last3=Rouse|first3=Greg W.|last4=Vrijenhoek|first4=Robert C.|date=2008|title=Marine worms (genus ''Osedax'') colonize cow bones|journal=Proceedings of the Royal Society B: Biological Sciences|volume=275|issue=1633|pages=387–391|doi=10.1098/rspb.2007.1437|pmc=2596828|pmid=18077256}}</ref> Although no ''Osedax'' were found on the non-mammalian remains in this study, their absence may have been due to the timing of observation, and the ''Osedax'' had not yet colonized the carcasses.<ref name="higgs2" /> Various studies on smaller cetaceans and other marine vertebrate food falls come to similar conclusions that these falls bring a large amount of new organic material to depth, but support mostly a scavenger community, as opposed to the diverse assemblage seen at whale falls. This conclusion can be drawn based on the knowledge that large whales have much higher [[lipid]] content in their bulk composition and bone marrow, which supports the diverse communities present in succession at whale falls.<ref name=":6" /><ref name=":22" />

Researchers have compared [[Sauropoda|sauropod]] carcasses to modern whale fall events. The largest carcasses would have been energy rich reservoirs, and it has been argued that they may have been the primary resources of many terrestrial carnivorous dinosaurs, which were argued to have been obligate scavengers. A single dead sauropod would have had enough calories to sustain multiple big theropods for weeks or months, and since they were terrestrial, sauropod carcasses didn't float over long distances or sink into the depths so they were more available to local carnivores than modern whale falls.<ref>{{Cite journal|last1=Pahl|first1=Cameron C.|last2=Ruedas|first2=Luis A.|date=October 2021|title=Carnosaurs as Apex Scavengers: Agent-based simulations reveal possible vulture analogues in late Jurassic Dinosaurs|url=https://linkinghub.elsevier.com/retrieve/pii/S0304380021002611|journal=Ecological Modelling|language=en|volume=458|page=109706 |doi=10.1016/j.ecolmodel.2021.109706|bibcode=2021EcMod.45809706P |url-access=subscription}}</ref><ref>{{Cite journal |last1=Pahl |first1=Cameron C. |last2=Ruedas |first2=Luis A. |date=2023-11-01 |title=Big boned: How fat storage and other adaptations influenced large theropod foraging ecology |journal=PLOS ONE |language=en |volume=18 |issue=11 |page=e0290459 |doi=10.1371/journal.pone.0290459 |pmc=10619836 |pmid=37910492 |doi-access=free|bibcode=2023PLoSO..1890459P }}</ref>

==See also==
*[[Cetacean stranding]]
*[[Deep-sea community]]
*[[Marine snow]]
*[[Detritivore]]
*[[Jelly-falls]]
*[[Whaling]]
*''[[Osedax]]''
*[[Carbon sequestration]]
*[[Deep-sea wood]]

==References==
{{reflist}}

==External links==
*[https://web.archive.org/web/20050516161602/http://www.westnurc.uaf.edu/dwnlds/Smithecologywhalefalls.pdf Smith and Baco 2003 paper on whale fall ecology (University of Hawaiʻi)]
*[http://www.nurp.noaa.gov/Spotlight/Whales.htm Article from NOAA's Undersea Research program (NURP)] {{Webarchive|url=https://web.archive.org/web/20171103151201/http://www.nurp.noaa.gov/Spotlight/Whales.htm |date=3 November 2017 }}
*[https://web.archive.org/web/20051026205431/http://nationalzoo.si.edu/Publications/ZooGoer/2005/2/whaleworms.cfm Robin Meadows, "A Whale of a Tale"]
*[https://www.sciencedaily.com/releases/2007/09/070913165159.htm (Science Daily), University of California, Berkeley, "Fossil Whale Puts Limit On Origin of Oily, Buoyant Bones In Whales"] 14 September 2007

{{Aquatic ecosystem topics|expanded=marine}}

{{DEFAULTSORT:Whale Fall}}
[[Category:Animal death]]
[[Category:Aquatic ecology]]
[[Category:Whales]]