deep-sea gigantism

In marine crustaceans, the trend of increasing size with depth has been observed in mysids, euphausiids, decapods, isopods, ostracods and amphipods.{{Cite journal|last1=C.|first1=McClain|last2=M.|first2=Rex|date=2001-10-01|title=The relationship between dissolved oxygen concentration and maximum size in deep-sea turrid gastropods: an application of quantile regression|url=http://link.springer.com/10.1007/s002270100617|journal=Marine Biology|volume=139|issue=4|pages=681–685|doi=10.1007/s002270100617|bibcode=2001MarBi.139..681C |s2cid=83747571|issn=0025-3162}} Non-arthropods in which deep-sea gigantism has been observed are cephalopods, cnidarians, and eels from the order Anguilliformes.{{cite web|author=Hanks, Micah |title=Deep Sea Gigantism: Curious Cases of Mystery Giant Eels |url=https://mysteriousuniverse.org/2011/05/deep-sea-gigantism-curious-cases-of-mystery-giant-eels/ |website=MysteriousUniverse |access-date=5 May 2019}}{{cite book | author=MacDonald, A.G. | year=1975 | title=Physical Aspects of Deep Sea Biology | publisher=Cambridge University Press | pages=[https://archive.org/details/physiologicalasp0000macd/page/17 17–19] | isbn=978-0-521-20397-5 | url-access=registration | url=https://archive.org/details/physiologicalasp0000macd/page/17 }}

{{cquote|Other [animals] attain under them gigantic proportions. It is especially certain crustacea which exhibit this latter peculiarity, but not all crustacea, for the crayfish like forms in the deep sea are of ordinary size. I have already referred to a gigantic Pycnogonid [sea spider] dredged by us. Louis Agassiz dredged a gigantic Isopod {{convert|11|in|cm|abbr=off|disp=sqbr}} in length. We also dredged a gigantic Ostracod. – Henry Nottidge Moseley, 1880{{cite web |author=McClain, Craig |title=Why isn't the Giant Isopod larger? |url=http://www.deepseanews.com/2015/01/why-isnt-the-giant-isopod-larger/ |website=Deep Sea News |date=14 January 2015 |access-date=1 March 2018}}}}

Notable organisms that exhibit deep-sea gigantism include the big red jellyfish,{{cite web|author=Smithsonian Oceans |title=Big Red Jellyfish |url=https://ocean.si.edu/ocean-life/invertebrates/big-red-jellyfish |website=Smithsonian Oceans |access-date=5 May 2019}} Stygiomedusa jellyfish, the giant isopod, giant ostracod, the giant sea spider, the giant amphipod, the Japanese spider crab, the giant oarfish, the deepwater stingray, the seven-arm octopus,{{cite journal|last1= Hoving|first1=H. J. T.|last2= Haddock|first2=S. H. D. |author2-link=Steven Haddock |title= The giant deep-sea octopus Haliphron atlanticus forages on gelatinous fauna|journal= Scientific Reports|volume= 7|date= 2017-03-27|page= 44952|doi= 10.1038/srep44952|pmid=28344325|pmc= 5366804|bibcode=2017NatSR...744952H }} and a number of squid species: the colossal squid (up to 14 m in length),{{cite web |author=Anderton, Jim |date=22 February 2007 |url=http://www.beehive.govt.nz/node/28451 |archive-url=https://web.archive.org/web/20100523152104/http://www.beehive.govt.nz/node/28451 |title=Amazing specimen of world's largest squid in NZ |publisher=New Zealand Government |archive-date=23 May 2010 |url-status=live}} the giant squid (up to 12 m), Megalocranchia fisheri, robust clubhook squid, Dana octopus squid, cockatoo squid, giant warty squid, and the bigfin squids of the genus Magnapinna.

Deep-sea gigantism is not generally observed in the meiofauna (organisms that pass through a {{convert|1|mm|abbr=on}} mesh), which actually exhibit the reverse trend of decreasing size with depth.

In crustaceans, it has been proposed that the explanation for the increase in size with depth is similar to that for the increase in size with latitude (Bergmann's rule): both trends involve increasing size with decreasing temperature.{{cite journal | last=Timofeev | first=S. F. | title=Bergmann's Principle and Deep-Water Gigantism in Marine Crustaceans | journal=Biology Bulletin of the Russian Academy of Sciences | volume= 28| issue= 6| pages= 646–650| date=2001 | doi=10.1023/A:1012336823275 | bibcode=2001BioBu..28..646T | s2cid=28016098 }} The trend with latitude has been observed in some of the same groups, both in comparisons of related species, as well as within widely distributed species. Decreasing temperature is thought to result in increased cell size and increased life span (the latter also being associated with delayed sexual maturity), both of which lead to an increase in maximum body size (continued growth throughout life is characteristic of crustaceans). In Arctic and Antarctic seas where there is a reduced vertical temperature gradient, there is also a reduced trend towards increased body size with depth, arguing against hydrostatic pressure being an important parameter.

Temperature does not appear to have a similar role in influencing the size of giant tube worms. Riftia pachyptila, which lives in hydrothermal vent communities at ambient temperatures of 2–30 °C,{{cite book | last=Bright | first=M. | author2=Lallier, F. H. | title=The biology of vestimentiferan tubeworms | volume=48 | pages=213–266 | publisher=Taylor & Francis | year=2010 | url=http://www.sb-roscoff.fr/Ecchis/pdf/10-Bright-OMBAR.pdf | access-date=2013-10-30 | doi=10.1201/ebk1439821169 | archive-url=https://web.archive.org/web/20131031234950/http://www.sb-roscoff.fr/Ecchis/pdf/10-Bright-OMBAR.pdf | archive-date=2013-10-31 | series=Oceanography and Marine Biology - an Annual Review | isbn=978-1-4398-2116-9 }} reaches lengths of 2.7 m, comparable to those of Lamellibrachia luymesi, which lives in cold seeps. The former, however, has rapid growth rates and short life spans of about 2 years,{{Cite journal | last1=Lutz | first1=R. A. | last2=Shank | first2=T. M. | last3=Fornari | first3=D. J. | last4=Haymon | first4=R. M. | last5=Lilley | first5=M. D. | last6=Von Damm | first6=K. L. | last7=Desbruyeres | first7=D. | doi=10.1038/371663a0 | title=Rapid growth at deep-sea vents | journal=Nature | volume=371 | issue=6499 | page=663 | year=1994 | bibcode=1994Natur.371..663L | s2cid=4357672 }} while the latter is slow growing and may live over 250 years.{{cite web |url=http://www.data.boem.gov/PI/PDFImages/ESPIS/2/3071.pdf |access-date=2013-10-30 |title=Stability and Change in Gulf of Mexico Chemosynthetic Communities |last=MacDonald |first=Ian R. |year=2002 |publisher=MMS |archive-date=1 February 2017 |archive-url=https://web.archive.org/web/20170201061412/https://www.data.boem.gov/pi/pdfimages/espis/2/3071.pdf }}

Food scarcity at depths greater than 400 m is also thought to be a factor, since larger body size can improve ability to forage for widely scattered resources.{{cite journal|last1= Gad|first1= G.|title= Giant Higgins-larvae with paedogenetic reproduction from the deep sea of the Angola Basin? Evidence for a new life cycle and for abyssal gigantism in Loricifera?|journal= Organisms Diversity & Evolution|volume= 5|year= 2005|pages= 59–75|doi= 10.1016/j.ode.2004.10.005|bibcode= 2005ODivE...5...59G}} In organisms with planktonic eggs or larvae, another possible advantage is that larger offspring, with greater initial stored food reserves, can drift for greater distances. As an example of adaptations to this situation, giant isopods gorge on food when available, distending their bodies to the point of compromising ability to locomote;{{Cite journal|first1= Patricia |last1= Briones-Fourzán |first2= Enrique |last2= Lozano-Alvarez |year=1991 |title=Aspects of the biology of the giant isopod Bathynomus giganteus A. Milne Edwards, 1879 (Flabellifera: Cirolanidae), off the Yucatan Peninsula |journal=Journal of Crustacean Biology |volume=11 |issue=3 |pages=375–385 |jstor=1548464 |doi=10.2307/1548464|doi-access=free |bibcode= 1991JCBio..11..375B }} they can also survive 5 years without food in captivity.{{cite web|last=Gallagher |first=Jack |url=http://www.japantimes.co.jp/news/2013/02/26/national/tanks-deep-sea-isopod-hasnt-eaten-for-over-four-years |title=Aquarium's deep-sea isopod hasn't eaten for over four years |publisher=The Japan Times |date=2013-02-26 |access-date=2013-05-21}}{{cite web|url=https://www.npr.org/blogs/krulwich/2014/02/22/280249001/i-wont-eat-you-cant-make-me-and-they-couldnt|title=I Won't Eat, You Can't Make Me! (And They Couldn't)|publisher=NPR|date=February 22, 2014|access-date=February 23, 2014}}

According to Kleiber's law,{{cite journal|last1= Kleiber|first1= M.|title= Body Size and Metabolic Rate|journal= Physiological Reviews|volume= 27|issue= 4|year= 1947|pages= 511–541|doi= 10.1152/physrev.1947.27.4.511|pmid= 20267758}} the larger an animal gets, the more efficient its metabolism becomes; i.e., an animal's basal metabolic rate scales to roughly the ¾ power of its mass. Under conditions of limited food supply, this may provide additional benefit to large size.

An additional possible influence is reduced predation pressure in deeper waters.{{cite journal|author1-link=Elizabeth Harper (biologist)|last1= Harper|first1=E. M.|last2= Peck|first2=L. S.|title= Latitudinal and depth gradients in marine predation pressure|journal= Global Ecology and Biogeography|volume= 25|issue= 6|year= 2016|pages= 670–678|doi= 10.1111/geb.12444|doi-access= free|bibcode= 2016GloEB..25..670H}} A study of brachiopods found that predation was nearly an order of magnitude less frequent at the greatest depths than in shallow waters.

Dissolved oxygen levels are also thought to play a role in deep-sea gigantism. A 1999 study of benthic amphipod crustaceans found that maximum potential organism size directly correlates with the increased levels of dissolved oxygen levels in deeper waters.{{Cite journal |last1=Chapelle |first1=Gauthier |last2=Peck |first2=Lloyd S. |date=1999 |title=Polar gigantism dictated by oxygen availability |url=http://www.nature.com/articles/20099 |journal=Nature |language=en |volume=399 |issue=6732 |pages=114–115 |bibcode=1999Natur.399..114C |doi=10.1038/20099 |issn=0028-0836 |s2cid=4308425}} The solubility of dissolved oxygen in the oceans is known to lower in oxygen-poor intermediary depths (ranging 200-1000 meters) until the increasing pressure, decreasing salinity levels, and colder temperatures of deeper water can contribute increasing solubility once more.

However, solubility does not necessarily equate to access as many areas of colder waters have exhibited lower levels of available oxygen. The proposed theory behind this trend is that deep-sea gigantism could be an adaptive trait to combat asphyxiation in frigid, dense ocean waters.{{Cite journal |last1=Verberk |first1=Wilco C. E. P. |last2=Atkinson |first2=David |date=2013 |title=Why polar gigantism and Palaeozoic gigantism are not equivalent: effects of oxygen and temperature on the body size of ectotherms |journal=Functional Ecology |volume=27 |issue=6 |pages=1275–1285 |bibcode=2013FuEco..27.1275V |doi=10.1111/1365-2435.12152 |issn=0269-8463 |jstor=24033996 |s2cid=5636563 |hdl-access=free |hdl=2066/123399}} Larger organisms are able to intake more dissolved oxygen within the ocean, allowing for sufficient respiration. However, this increased absorption of oxygen runs the risk of toxicity poisoning where an organism can have oxygen levels that are so high that they become harmful and poisonous.{{Cite journal |last1=Verberk |first1=Wilco C. E. P. |last2=Atkinson |first2=David |date=2013 |title=Why polar gigantism and Palaeozoic gigantism are not equivalent: effects of oxygen and temperature on the body size of ectotherms |journal=Functional Ecology |volume=27 |issue=6 |pages=1275–1285 |bibcode=2013FuEco..27.1275V |doi=10.1111/1365-2435.12152 |issn=0269-8463 |jstor=24033996 |s2cid=5636563 |hdl-access=free |hdl=2066/123399}}

Warmer global temperatures may have an effect on the deep sea as much as the shallower surface waters of the ocean, as evidence suggests that deep-sea ecosystems can be sensitive to shifts within the climate.{{Cite journal |last=Rogers |first=Alex David |date=2015 |title=Environmental Change in the Deep Ocean |journal=Annual Review of Environment and Resources |language=en |volume=40 |pages=1–38 |doi=10.1146/annurev-environ-102014-021415 |doi-access=free |issn=1543-5938}} Despite appearing relatively unchanging, the dependence of life in the depths on food supply to drift down in the form of marine snow and water currents traveling throughout all depths of the ocean calls into concern the manner in which global climate change may affect these organisms and the biomes they live in.

Following trends from the Paleocene-Eocene thermal maximum and related timescales, research suggests that current predictions of continuous greenhouse gas emissions and climate change will lead to higher ocean temperatures and a significant reduction in levels of dissolved oxygen in the deep sea.{{Cite book |last=Yang |first=Jianing |chapter=A Prediction upon Deep-Sea Gigantism Characteristics of Crustaceans in Respond to Future Global Climate |series=Applied Economics and Policy Studies |date=2023 |editor-last=Li |editor-first=Xiaolong |editor2-last=Yuan |editor2-first=Chunhui |editor3-last=Kent |editor3-first=John |title=Proceedings of the 6th International Conference on Economic Management and Green Development |chapter-url=https://link.springer.com/chapter/10.1007/978-981-19-7826-5_14 |language=en |location=Singapore |publisher=Springer Nature |pages=147–159 |doi=10.1007/978-981-19-7826-5_14 |isbn=978-981-19-7826-5}} Should global warming lead to a warmer ocean state, thermohaline circulation would no longer be able to maintain an oxygen-rich deep sea, which would eventually lead to deep water becoming higher in both temperature and salinity.

Based upon current theories regarding the existence of deep-sea gigantism, we would expect to see the phenomenon diminish in response to these changes in the environment, as it may become unfavorable or even impossible for these organisms to sustain a larger body form.

File:Giant isopod.jpg|A giant isopod (Bathynomus giganteus) may reach up to {{convert|0.76|m|ftin|abbr=on}} in length.

File:Japanese spider crab.jpg|A Japanese spider crab whose outstretched legs measured {{convert|12|ft|m|abbr=on|order=flip}} across

File:Moroteuthis robusta bronco.jpg|A robust clubhook squid, whose mantle reaches {{convert|2|m|ftin|abbr=on}} in length, caught off Alaska

File:Giant Oarfish.jpg|A {{convert|7|m|ft|abbr=on}} king of herrings oarfish, washed up on the beach of a Navy SEAL training base in California

File:Colossendeis colossea Smithsonian Natural History Museum.jpg|A Colossendeis colossea sea spider, displayed at the Smithsonian

File:Stygiomedusa Gigantea ov.jpg| A Stygiomedusa jellyfish, which can grow up to {{cvt|10|m|ft}} in length

File:Plesiobatis daviesi cochin.jpg|A deepwater stingray, which can reach up to {{convert|2.7|x|1.5|m|ftin|abbr=on}} in size

• Cephalopod size
• Dwarfing
• Island gigantism
• Insular dwarfism
• Largest organisms
• Megafauna

{{reflist}}

• [https://www.sciencedaily.com/releases/2006/07/060710164527.htm Science Daily: Midgets and giants in the deep sea]

{{Biological rules}}

{{DEFAULTSORT:Deep-Sea Gigantism}}

Category:Animal size

Category:Evolutionary biology concepts

Category:Marine organisms

Category:Ecogeographic rules