GIGANTISM

Shown here is a crustacean, the giant Antarctic isopod Glyptonotus antarcticus. Only those Antarctic benthic invertebrates whose growth is not hampered by calcium deficiency seem to reach a large size [1]. Those using little calcium are arenaceous foraminifera, crustaceans, and tubicolous polychaete worms; those not using calcium are hydroids, nudibranchs, ascidians, and many polychaete worms [1].

Why is calcium an issue? It is difficult to precipitate calcium carbonate at low temperatures and as a result, Antarctic calcareous (calcium-using) invertebrates like molluscs, echinoderms, and bryozoans are usually very fragile [1]. Extracting calcium carbonate for shell building and maintenance requires more energy than in warmer waters [8]. Antarctic invertebrate animal groups that are physically small include calcareous foraminifera, prosobranch gastropods (have calcareous shells), bivalves (have calcareous shells), scaphopods, and brachiopods (have calcareous shells) [1]. When an organism in very cold water isn't hampered by a need for calcium, gigantism can be a consequence of a slow rate of development and growth [1]. Biochemical processes relating to growth are influenced by temperature; slower growth occurs in colder water and sexual maturity is somewhat delayed, with a resulting larger adult body size [1,7].


Here is a pile-up of the proboscis worm Parborlasia corrugatus, which grows up to two meters in length; it is chemically defended by an acidic mucus (pH 3.5) which potential predators avoid [2,4].

When an organism in very cold water isn't hampered by a need for calcium, gigantism can be a consequence of low predation pressure --- when predation and competition for food within one's own species are low, organisms grow to a larger size, and to an older age [1,7,8].



This siliceous hexactinellid sponge Scolymastra joubini can be up to two meters high and 1.4 meters in diameter [5].

When an organism in very cold water isn't hampered by a need for calcium, gigantism can be a consequence of a high abundance of available silica --- siliceous organisms like radiolarians, hexactinellid sponges, and diatoms can reach large sizes because the availability of silica is not a limiting factor in Antarctic waters [1].



Here is the inside of the volcano sponge Scolymastra joubini (which, as mentioned above, can be up to two meters high and 1.4 meters in diameter) [5].

As shown here, a cold-water animal can increase its body size by constructing a silica lattice skeleton occupying a large volume; this huge lattice skeleton could not be constructed with calcium carbonate in cold water due to the calcium precipitation problem [3].



Here is the sea spider or pycnogonid Colossendeis australis. This sea spider shows how an animal can increase its body size with little building effort simply by elongating its appendages; it occupies a large amount of space with very little body mass [3].



This serolid isopod illustrates how body size can be increased by flattening to occupy more two-dimensional space; flattening helps an organism minimize sinking into a fine-grained soft bottom on which it may live [3].



This giant arborescent agglutinated foraminiferan Notodendrodes antarctikos stands up to 3.8 centimeters high -- remarkably large for a unicellular organism [6].

Relatively large body size can be gained by using prefabricated building blocks, as in the sediment grains glued together by this foraminiferan Notodendrodes antarctikos [3].

1: Adaptations within Antarctic Ecosystems, Proceedings of the Third SCAR Symposium on Antarctic Biology. GA Llano, ed. Washington DC : Smithsonian Institution, 1977. pp. 135-157; 2: Biology of the Antarctic Seas XIV, Antarctic Research Series 39(4):289-316, 1983; 3: The Environment of the Deep Sea, Rubey Volume II. WG Ernst & JG Morin, eds. Englewood Cliffs, NJ : Prentice-Hall, 1982. pp. 324-356; 4: Journal of Experimental Marine biology and Ecology 153(1):15-25, 1991; 5: Ecological Monographs 44(1):105-128, 1974; 6: Zoological Journal of the Linnean Society 69(3):205-224, 1980; 7: Adaptations within Antarctic Ecosystems : Proceedings of the Third SCAR Symposium on Antarctic Biology. GA Llano, ed. Washington : Smithsonian Institution ; Houston, Tex. : distributed by Gulf Pub. Co., 1977. pp. 327- 334; 8: The Biology of the Southern Ocean. GA Knox. New York : Cambridge University Press, 1994. pp.193-220

Text ©Peter Brueggeman. Photographs ©Norbert Wu, Jim Mastro, Robert Sanders (Sam Bowser/S043 archives), & Canadian Museum of Nature (Kathleen Conlan). Photographs may not be used in any form without the express written permission of Norbert Wu, Jim Mastro, Robert Sanders (Sam Bowser/S043 archives), or Canadian Museum of Nature (Kathleen Conlan). Norbert Wu no longer grants permission for uncompensated use of his photos under any circumstances whatsoever; want more info?