Population structure, growth and recruitment of the euryalinid brittle-star Astrobrachion constrictum (Echinodermata: Ophiuroidea) in Doubtful Sound, Fiordland, New Zealand |
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Authors: | B G Stewart P V Mladenov |
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Institution: | (1) Department of Marine Science, University of Otago, P.O. Box 56, Dunedin, New Zealand, NZ |
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Abstract: | The euryalinid brittle-star (snake star) Astrobrachion constrictum (Farquhar) lives coiled around the branches of black coral (Antipathes fiordensis) colonies. Twenty-two vertical transects, 10 m wide by 30 m deep, were swum in Doubtful Sound over a 2.5 yr period from 1993
to 1995. Numbers, disc diameters and colour morphotypes of brittle-stars inhabiting coral colonies were recorded. 36.3% of
the coral colonies >200 mm tall (n = 292) hosted ≥1 Astrobrachion constrictum (range 0 to 12). Overall, the population was patchily distributed on the available coral habitat. The dark red colour morphotype
of A. constrictum was most common (87%, n = 279) followed by the yellow, striped, and then spotted varieties. The population was comprised mainly of large (≥10 mm
disc diam) individuals, and juveniles were rarely encountered, indicating low rates of recruitment or a high mortality of
recruits. Disc-diameter data gathered from this and previous studies indicated that growth in A. constrictum is initially rapid, with individuals reaching a disc diameter of 15 mm in ≃2.5 yr; growth decreases with age, as in other
deep-sea ophiuroids. Growth rate within years, however, was not constant, with faster growth in the spring/summer. Maximum
size for A. constrictum is reached in ≃8 yr at ˜23 mm disc diam. Anecdotal evidence indicates that A. constrictum may not be confined solely to black coral colonies.
Received: 25 September 1996 / Accepted: 16 October 1996 |
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