seastar Odontaster validus

Odontaster validus is found throughout Antarctica and the Antarctic Peninsula, South Shetland Islands, South Orkney Islands, South Sandwich Islands, South Georgia Island, Shag Rocks, Marion and Prince Edward Islands, and Bouvet Island at depths from 0 to 914 meters [7,10,11,12,14]. O. validus is the most abundant seastar in the shallow shelf waters of Antarctica and is most abundant from 15 to 200 meters [9]. O. validus has a broad disc and short arms tapering to blunt tips [7]. O. validus has been collected at sizes up to seven centimeters in radius from its center to the tip of an arm [7,11]. O. validus varies in color including dark brown, purple, purple-red, orange, red-orange, red, brick red, dark carmine, and pink; it may have light colored arm tips [7,11,14]. O. validus has a characteristic position with its arm tips slightly raised [7].

O. validus is usually bright to dull red on the dorsal (abactinal) surface and yellowish white to pale pink on the ventral (actinal) surface [16]. O. meridionalis is generally pale brown or yellowish white on the dorsal : surface and lighter on the ventral surface [16]. Color in both species can be highly variable and is not always reliable as a field character; the only sure way is to check the number of spines on the actinal plates [16].

Here's a juvenile and adult of Odontaster validus. Size-frequency distribution of O. validus can vary with location and is a reflection of the general level of productivity of a habitat: at McMurdo Station, their size and number decrease with depth; at Cape Evans, they are more numerous and generally smaller; and, at East Cape Armitage, they are less numerous and very small [3]. O. validus is slow growing; well-fed individuals need about nine years to reach thirty grams wet weight which is near the mean size of shallow-water individuals at McMurdo Station [3]. Based on its growth rate, collected sizes, and knowledge from other seastars, O. validus may live beyond one hundred years of age, with very low turnover in a population [17].

Here Odontaster validus is ganging up and eating the sea urchin Sterechinus neumayeri; little red amphipods are stealing food in the process. O. validus appears voracious to the diver, being very numerous in some areas and piled up in feeding groups; one study found that almost 50% of O. validus in the study area were engaged in feeding with their everted stomach [13]. Odontaster validus is omnivorous, capable of filter-feeding and eating a varied diet: detritus, small crustaceans including amphipods and the isopod Glyptonotus antarcticus, seastars, molluscs (scallop Adamussium colbecki, gastropods, bivalves Laternula elliptica and Limatula hodgsoni), hydroids (including Ophiodes arboreus), bryozoans, sponges (Homaxinella balfourensis, Rossella racovitzae, Rossella nuda, Scolymastra joubini, Tetilla leptoderma) , ostracods, sea urchin Sterechinus neumayeri, polychaete worms, carrion (dead Weddell seals), feces (Weddell seals), diatoms, and algae [5,8,9,13,15]. O. validus has been observed feeding on the detrital film on the surface of the sponge Cinachyra antarctica [13].



Odontaster validus is a prey item of the seastar Macroptychaster accrescens [5] and of the anemone Urticinopsis antarcticus (shown at left) [6].

O. validus broadcast-spawns larvae which feed on bacteria and algae and have a low metabolic rate (which predicts long-term larval survival); larvae of a comparable temperate seastar eat only algae and have a higher metabolic rate [1,2].

The seastars Odontaster validus and Acodontaster conspicuus are the two greatest predators on McMurdo sponges [5]. O. validus is a foundation species in the McMurdo sponge-dominated benthic ecosystem and is the keystone to the interaction between the rossellid sponges and one of their primary predators, the large Antarctic seastar Acodontaster conspicuus [4]. A. conspicuus would reach population densities destroying the sponge community if not kept in check by O. validus which preys upon its larvae, young and adults [5]. At left is a gang attack on Acodontaster conspicuus. A single O. validus climbs up onto an A. conspicuus ray, everts its stomach, and digests a hole into it. An attack by a single O. validus isn't fatal but nearby O. validus probably respond to the release of coelomic fluid from A. conspicuus and join the attack [5].



Eventually the larger A. conspicuus seastar's movement is slowed, more O. validus attack, and the large nemertean worm Parborlasia corrugatus (shown in the foreground of the photo above) joins in as well. A. conspicuus seastars can become completely buried under high piles of attacking O. validus seastars and P. corrugatus worms [5].

1: Antarctic Journal of the United States26(5):170-172, 1991; 2: Antarctic Journal of the United States 26(5):163-165, 1991; 3: Marine Biology  99(2):235-246, 1988; 4: Colloquium on Conservation Problems in Antarctica, Sept. 10-12, 1971, Blacksburg, VA, Proceedings. BC Parker, ed. Lawrence, Kansas, Allen Press, 1972. p.81-96; 5: Ecological Monographs 44(1):105-128, 1974; 6: Antarctic Ecology, Volume 1. MW Holdgate, ed. NY: Academic Press, 1970. pp244- 258; 7: The Fauna of the Ross Sea, Part 3, Asteroidea. HES Clark. New Zealand Department of Scientific and Industrial Research Bulletin 151, New Zealand Oceanographic Institute Memoir 21, 1963; 8: Science 245:1484- 1486, 1989; 9: 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.293-326; 10: AM Clark. BANZ Antarctic Research Expedition 1929-1931. Reports, Series B (Zoology and Botany) Volume 9, Asteroidea. Adelaide : BANZAR Expedition Committee, 1962; 11: Discovery Reports 20:69-306 and plates, 1940; 12: South African Journal of Antarctic Research 23(1-2):37-70, 1993; 13: New Zealand Antarctic Record 9(2):34-52, 1989; 14: Equinodermos Antarticos. II. Asteroideos. 5. Asteroideos de la Extremidad Norte de la Peninsula Antartica. I Bernasconi. Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" e Instituto Nacional de Investigacion de las Ciencias Naturales. Zoologia (aka Ciencias Zoologicas) 9(10):211-281 and plates, 1970; 15: Antarctic Science 12(1):64-68, 2000; 16: John Dearborn, personal communication, 2001; 17: Australian Natural History 16(7):234-238, 1969

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