POPULATION-STRUCTURE, GROWTH AND RECRUITMENT OF THE EURYALINID BRITTLE-STAR ASTROBRACHION-CONSTRICTUM (ECHINODERMATA, OPHIUROIDEA) IN DOUBTFUL SOUND, FJORDLAND, NEW-ZEALAND

The euryalinid brittle-star (snake star) Astrobrachion constrictum (Fa rquhar) lives coiled around the branches of black coral (Antipathes fi ordensis) colonies. Twenty-two vertical transects, 10 m wide by 30 m d eep, were swum in Doubtful Sound over a 2.5 yr period from 1993 to 199 5. Numbers, disc diameters and colour morphotypes of brittle-stars inh abiting coral colonies were recorded. 36.3% of the coral colonies >200 mm tall (n = 292) hosted greater than or equal to 1 Astrobrachion con strictum (range 0 to 12). Overall, the population was patchily distrib uted 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 mai nly of large (greater than or equal to 10 mm disc diam) individuals, a nd juveniles were rarely encounter-ed, indicating low rates of recruit ment 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 similar or equal to 2.5 yr; growth decreases with age, as in other de ep-sea ophiuroids. Growth rate within years, however, was not constant , with faster growth in the spring/summer. Maximum size for A. constri ctum is reached in similar or equal to 8 yr at similar to 23 mm disc d iam. Anecdotal evidence indicates that A, constrictum may not be confi ned solely to black coral colonies.