bush sponge Homaxinella balfourensis

Homaxinella balfourensis is found throughout Antarctica and the Antarctic Peninsula, South Shetland Islands, South Georgia Island, and Kerguelen Island from 0 to 550 meters depth [1,3,6,7,9,10,13]. The body of H. balfourensis can be clavate (gradually thickening near the distal end - shaped like a club) or ramified and arborescent (split into branches) [6]. The body of H. balfourensis is up to fifty centimeters long, and attached to the bottom by a root system or creeping stolons [10,12,16]. Lower branches are densely structured and cylindrical; upper branches are broadened with a loose consistency [6,8]. A branch can be ten centimeters long and 0.8 centimeter in diameter [7,16]. H. balfourensis has a smooth surface and its color is white, yellowish gray, yellow, orange, brown, or light gray [6,7,8,10,12,16].

Anchor ice (shown here) impacts the population of H. balfourensis significantly, being capable of almost entirely eliminating it in an area [4,5]. Anchor ice damage discolors H. balfourensis whereas predation leaves a spongin skeleton; 87% of tagged H. balfourensis was lost or damaged by anchor ice in a two year period [4].


Homaxinella balfourensis is seen in the second benthic zone of Cape Armitage from 15 - 33 meters [5].

A dramatic population explosion of H. balfourensis was studied at 15 - 30 meters depth at Hut Point and Cape Armitage [4,5]. It was rare at this depth previously and within 6 - 7 years, H. balfourensis was almost 80% of the surface cover at Hut Point and less dense but impressive at Cape Armitage [4,5].

H. balfourensis may host diatoms within its food-capturing cells that line the passages through which the sponge circulates water; these endobiont diatoms live by consuming carbohydrates produced by the sponge and also by photosynthesis [15]. This symbiotic adaptation by the diatoms enhances their survival in the low light levels found down deep under the ice (as well as the dark months of winter) [15].


The important predators of Homaxinella balfourensis are the seastars Odontaster meridionalis, Odontaster validus (at least two in photo at left), and young Perknaster fuscus antarcticus (at least one in photo at left) [4].

H. balfourensis almost always has arcturid isopods perched on it [11].

An extract from Homaxinella balfourensis has antibacterial, antifungal, and antiyeast activity [2].



The Antarctic scallop Adamussium colbecki may have Homaxinella balfourensis attached [12,14].

H. balfourensis is found on scallops larger than seven centimeters, with the sponge up to fourteen centimeters in height [14]. The usual position of H. balfourensis on the scallops is near the shell's peripheral margin, suggesting that the sponge is seeking the water flow over the scallop shell in order to facilitate its own filter feeding [14].

Taxonomic Note: H. balfourensis is very close to H. flagelliformis; balfourensis branches are flattened and flagelliformis branches are tapered [8].

1: B.A.N.Z. Antarctic Research Expedition, 1929-1931, under the command of Sir Douglas Mawson, Kt., O.B.E., B.E., D.Sc., F.R.S., Reports -- Series B (Zoology and Botany). Volume 9, part 4. Porifera -- Part 1: Antarctic Sponges. VM Koltun. Adelaide : Mawson Institute for Antarctic Research, University of Adelaide, 1976; 2: Antarctic Science 4(2):179-183, 1992; 3: Hooper, JNA & Wiedenmayer, F. Porifera. IN: Zoological Catalogue of Australia. Volume 12. Wells, A, ed. Melbourne : CSIRO Australia, 1994; 4: Science 245:1484-1486, 1989; 5: Biologie des Spongiaires, Sponge Biology. C Levi and N Boury-Esnault, eds. Colloques Internationaux du Centre National de la Recherche Scientifique Number 291. Paris : Centre National de la Recherche Scientifique, 1979. pp.271-282; 6: Sponges of the Antarctic. I. Tetraxonida and Cornacuspongida. VM Koltun. IN: Biological reports of the Soviet Antarctic Expedition, 1955-1958 (Rezultaty biologicheskikh issledovanii Sovetskoi antarkticheskoi ekspeditsii, 1955-1958). Volume 2. EP Pavlovskii, ed. Jerusalem : Israel Program for Scientific Translations. 1966. pp.6-131; Appendix, Index of Latin Names on pp. 443-448; 7: Instituto Antartico Chileno. Serie Cientifica 39:97-158, 1989; 8: Ross Sea Expeditions 1987-1988 and 1989-1990, Straits of Magellan Expedition 1991, Data Report Part 3, Physical, Chemical and Biological Oceanography. F Faranda and L Guglielmo, eds. Genova : Repubblica Italiana, Ministry of the University and Scientific and Technological Research, National Scientific Commision for Antarctica, 1994. pp.67-100; 9: Polar Biology 12:559-585, 1992; 10: Les Demosponges du Plateau Continental de Kerguelen-Heard. N Boury-Esnault & M Van Beveren. CNFRA Number 52, 1982. Paris : Comite National Francais pour les Recherches Antarctiques; 11: Rob Robbins, personal communication, 1999; 12: Tethys Supplement 4:9-24, 1972; 13: US National Museum Polar Invertebrate Catalog at http://www.nmnh.si.edu/iz/usap/usapdb.html; 14: Ecology of the Circumpolar Antarctic Scallop, Adamussium colbecki (Smith, 1902). Paul Arthur Berkman. Ph. D. Dissertation, University of Rhode Island, 1988; 15: Biological Bulletin 198:29-33, 2000; 16: Systema Porifera. JNA Hooper and RWM Van Soest. New York: Kluwer, 2002

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