Shallow Water Crinoids are on Soft Sediments Too: Evidence from a Video Survey of a Subtropical Estuary
Abstract:Remote underwater videography was used to map and characterize an unusual assemblage of epibenthic invertebrates on soft-sediments in subtropical Moreton Bay, Australia. The assemblage included congregations of the comatulid crinoid Zygometra cf. Zygometra microdiscus (Bell) at densities up to 0.88 individuals m-2, comparable to those found in coral reef habitats. There was no correlation between the distribution of this species and commonly used abiotic surrogates depth (6–18 m), sediment composition, and residual current. The distribution may be related to patterns of tidal currents. There was also no relationship between the distribution of this crinoid species and other macrobenthic taxa, except a negative correlation with the occurrence of the sea pen Virgularia gustaviana. Zygometra is the only crinoid genus occurring commonly on local reefs that can swim, which may assist in locating suitable perches and reducing sediment load. It is not clear whether Z. cf. microdiscus is the same species as Zygometra sp. commonly occurring on local reefs, thus a habitat generalist, or a separate, soft substrate specialist species. This is the first quantitative assessment of crinoid density and distribution in shallow water, soft-sediment environments. The high densities found are significant in terms of the generally accepted picture of shallow-water crinoids as essentially reefal fauna. This highlights the conservation benefits of a more inclusive approach to marine habitat survey and mapping. Assemblages such as the one described, although they may be of scientific and ecological significance, would have been overlooked by common approaches to marine conservation planning, which emphasize highly productive, or aesthetically appealing habitats.
Document Type: Research Article
Publication date: November 1, 2003
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