Robustness of size measurement in soft corals
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Accurate colony size measurement in soft-bodied sessile aquatic invertebrates is more difficult than in hard corals because of the variable state of the hydroskeleton in the former. The present study examined variation in colony height, oral disc diameter and basal circumference in three species of soft coral of different morphological types (Sarcophyton elegans, Sinularia flexibilis and Dendronephthya sp.) over a 24-h period. Individual colonies changed considerably in size over this period. Coefficients of variation for height measurements and oral disc were 0.09–0.36 and 0.08–0.28, respectively, but were only 0.02–0.09 for basal circumference, in all three species. Measurements of basal circumference in the field showed the highest correlation with colony biomass (volume after water displacement in formalin) confirming basal circumference to be a sound measure of colony size in repeated measurement studies.
KeywordsSoft coral Soft-bodied sessile invertebrate Morphology Size variation
We thank four anonymous reviewers for helpful comments on an earlier draft of the manuscript, and the staff at Lizard island Research Station. P. Alderslade (Northern Territory Museum, Darwin) confirmed identification of the species. M Egerrup, A McCoy and S Uthicke assisted in the field. J Eklöf commented on the statistical analysis. J Näslund, J Spens and B Jaeschke assisted with the figures. The study was supported by the Australian European Awards Programme, E & G Ehrnrooth Foundation, Finnish Academy, Oskar Öflund Foundation and Swedish Cultural Foundation in Finland. The samples were collected with a permit from the Great Barrier Reef Marine Park Authority.
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