sea urchin Sterechinus neumayeri

Sterechinus neumayeri is found in Antarctica and the Antarctic Peninsula, South Shetland Islands, South Orkney Islands, South Sandwich Islands, South Georgia Island, South Patagonia Island, Prince Edward Island, Marion Island, Crozet Island, and Kerguelen Island at depths from 5 to 640 meters [8,9,10]. S. neumayeri is abundant in shallow waters of McMurdo Sound at depths less than fifteen meters and plays a major role in McMurdo's benthic ecosystem. Color of the test (shell) and spines of Sterechinus neumayeri is variable, from greenish- olive to dark purplish/violet or whitish; the test is more generally greenish- olive or green-gray [8,9,10]. It is slow growing, reaching a maximum diameter of seven centimeters at forty years of age [1]. The bare test (shell) of the genus Sterechinus is distinguised by a large periproct within its ring of apical plates, distinctly darker lines formed by tube feet in the pore zones, and denser distribution of tubercules on the oral side than the aboral side [19]

Largely herbivorous, half of the diet of Sterechinus neumayeri is algae; it also eats diatoms, foraminiferans, sponges, bryozoans, hydrozoans, polychaetes including Spirorbis sp., and amphipods [4,18]. At left, S. neumayeri and the seastar Odontaster validus cruise the shallow bottom foraging for food around the crystalline anchor ice. Weddell seal feces are a food item for S. neumayeri in shallow water; S. neumayeri can be observed piled up on feces along with the seastar Odontaster validus. The gut content of S. neumayeri is filled with seal feces at locations where this occurs [5]. S. neumayeri has been observed feeding on the detrital film on the surface of the sponge Cinachyra antarctica [13].

Like many other urchins, Sterechinus neumayeri attaches bits of shell and debris to itself. The shells and debris often have stinging hydroids on them (see the whitish polyps on top of the urchin). If an anemone like Urticinopsis antarcticus touches the urchin's hydroids, it releases the urchin. If the urchin is aware of the anemone's tentacles, the urchin releases its protective camouflage and escapes the anemone's grasp. If this camouflage isn't present on the urchin, the anemone captures and eats the urchin [3].

Other predators are the anemone Isotealia antarctica, the octopus Pareledone sp., the fish Trematomus bernacchii, the seastars Macroptychaster accrescens and Odontaster validus, and the brittle star Ophiosparte gigas [6,7,11,12,14,16].

Sterechinus neumayeri attaches pieces of algae like Phyllophora antarctica (shown here) and Iridaea cordata to itself as protection against the anemone Isotealia antarctica [14]. Both algae manufacture unpalatable defensive chemicals to avoid getting eaten by S. neumayeri, yet the urchin attaches algal pieces to itself as a detachable shield to shed when the anemone's tentacles grab onto the attached algae [14,15].

The Antarctic scallop Adamussium colbecki may be colonized on either shell by small (two millimeters high) hydroids Hydractinia angusta [17]. H. angusta hydroids eat tube feet and pedicellariae of sea urchins including Sterechinus neumayeri, which grazes on the algal film growing on the surface of the scallop's shell, but is not a predator of the scallop [17]. A. colbecki shells are very thin and such urchin grazing may damage the shell; thus the hydroids act in defense of the scallop [17].

At some sites where these algae occur with Sterechinus neumayeri, 96.5% of the urchins were using Phyllophora antarctica for 90% or more of their cover [14]. This is a mutually beneficial relationship between S. neumayeri and the algae [14]. The urchins move fertile drift algae throughout sunlit waters, thereby keeping drift algae in the reproductive area with other attached and drift algae; the urchins also extend the vertical and horizontal range of the algae and facilitate recolonization after ice scouring of the bottom or when conditions allow growth of attached plants at greater depths [14].

Sterechinus neumayeri spawning is timed so that its feeding larvae are in the plankton during the short summer peak of phytoplankton abundance [2].

1: Marine Biology 124(2):279-292, 1995; 2: Biological Bulletin 173(1):126-135, 1987; 3: Antarctic Ecology, Volume 1. MW Holdgate, ed. NY: Academic Press, 1970. pp.244-258; 4: Antarctic Journal of the United States 11(1):24-26, 1976; 5: Biological Bulletin 130(3):387-401, 1966; 6: Polar Biology 13(5):347-354, 1993; 7: Ecological Monographs 44(1):105-128, 1974; 8: A Monograph of the Echinoidea. Volume 3, Part 3. Camarodonta 2. Echinidae, Strongylocentrotidae, Parasaleniidae, Echinometridae. T Mortensen. Copenhagen : CA Reitzel, 1943. pp106-108; 9: Bulletin du Museum National d'Histoire Naturelle, Section A, Zoologie, Biologie, et Ecologie Animales 14(2):405-441, 1992; 10: Equinodermos Antarticos. I. Equinoideos. 1. Equinoideos de Shetland del Sur y Archipielago Melchior. I Bernasconi. Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia" e Instituto Nacional de Investigacion de las Ciencias Naturales. Zoologia 9(9):197-210 and plates, 1969; 11: Bulletin de l'Institut Oceanographique 66(1368), 1966; 12: Adaptations within Antarctic Ecosystems : Proceedings of the Third SCAR Symposium on Antarctic Biology. GA Llano, ed. Washington : Smithsonian Institution ; Houston, TX : distributed by Gulf Pub. Co., 1977. pp.293-326; 13: New Zealand Antarctic Record 9(2):34-52, 1989; 14: Marine Ecology Progress Series 183:105-114, 1999; 15: Journal of Phycology 34(1):53-59, 1998; 16: Polar Biology 16(5):309-320, 1996; 17: Polar Biology 23(7):488-494, 2000; 18: Polar Biology 26(2):99-104, 2003; 19: Sea Urchins, a Guide to Worldwide Shallow Water Species. H Schultz. Hemdingen, Germany: Heinke & Peter Schultz Partner Scientific Publications, 2006

Text ©Peter Brueggeman. Photographs ©Peter Brueggeman & Norbert Wu. Photographs may not be used in any form without the express written permission of Peter Brueggeman or Norbert Wu. Norbert Wu no longer grants permission for uncompensated use of his photos under any circumstances whatsoever; want more info?