SYMBIOSIS

Sterechinus neumayeri urchins attach algae to themselves as a detachable shield to shed when a potential predator (including anemones, seastars) grabs onto the attached algae [1,2]. The algae manufactures unpalatable defensive chemicals to avoid getting eaten by the urchin [1,2]. The urchins pick up loose algae drifting on the seafloor and move fertile drift algae throughout sunlit waters, thereby keeping the fertile algae in the reproductive area with other attached and drift algae [1]. 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 [1].


Commensalism is a relationship between two species in which one species obtains food, shelter, support, locomotion, or another benefit from the other, without harming or benefiting it.

The free-swimming Antarctic scallop Adamussium colbecki may have the bush sponge Homaxinella balfourensis attached [3,4]. The usual position of the sponge 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 [3].



Another commensal relationship

The crinoid Promachocrinus kerguelensis can be seen perched on large volcano sponges Anoxycalyx (Scolymastra) joubini, using the sponge for support to feed higher up in the water column, where they feed off particles and organisms drifting in the current [9].

Parasitism is a relationship between two species in which one benefits at the expense of the other, without killing it.

Parasitic copepods like this one on the Antarctic cod Dissostichus mawsoni are free-swimming as juveniles [5,6]. Females find a host, attach, and are stationary for life, diverting their energy to reproduction; males move or swim around to find females to reproduce [5,6]. This female parasitic copepod is burrowed into the skin, sucking blood and fluids or grinding away at flesh [5,7]. The female stores the male's sperm and fertilizes its eggs as it expels them into chitinous sausage-like ovisacs [7,8]. The ovisacs gradually lengthen as eggs are expelled [8].

1: Marine Ecology Progress Series 183:105-114, 1999; 2: Journal of Phycology 34(1):53-59, 1998; 3: Ecology of the Circumpolar Antarctic Scallop, Adamussium colbecki (Smith, 1902). Paul Arthur Berkman. Ph. D. Dissertation, University of Rhode Island, 1988; 4: Tethys Supplement 4:9-24, 1972; 5: Copepod Parasites of Marine Fishes. NK Pillai. Calcutta : Zoological Survey of India, 1985; 6: Parasitic Copepoda of British Fishes. Z Kabata. London : Ray Society, 1979; 7: Parasitic Copepodes on the Fishes of the USSR = Paraziticheskie Veslonogie Ryb SSSR. AP Markewitch. New Delhi : Published for the Smithsonian Institution and the National Science Foundation by the Indian National Scientific Documentation Centre ; Springfield, VA : available from the National Technical Information Service, 1976; 8: British Parasitic Copepoda. T Scott & A Scott. London : Ray Society, 1913; 9: Antarctic Science 10(4):398-405, 1998

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