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Age estimates and description of rhodoliths from Esperance Bay, Western Australia

Published online by Cambridge University Press:  15 December 2006

Nisse Goldberg
Affiliation:
University of Western Australia, School of Plant Biology, Crawley, 6009, Australia. E-mail: lumilumi@yahoo.com
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Abstract

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Rhodoliths were collected in Esperance Bay,Western Australia, using a Van Veen grab from a bed that covered an area approximately 2.2 km2, in depths of 38 ±1 m. Rhodolith abundance (biomass per 0.1 m3), mean size (maximum diameter), and morphotypes were compared among the inshore margin, offshore margin, and middle area of the bed. Accelerator Mass Spectrometry was used to estimate ages of five free-living rhodoliths. Rhodolith taxa included Hydrolithon munitum, Lithothamnion sp., an unidentified Melobesiodeae (a Mesophyllum or Synarthrophyton) and possibly a species of Sporolithon, with lumpy, warty, and fruticose morphologies. The middle area of the bed had significantly greater abundance of rhodoliths than either margin. Biomass of warty rhodoliths was greater in the middle area of the bed whereas fruticose and lumpy rhodoliths had similar biomass across the bed. The <20 mm size-class was the most abundant and these rhodoliths may originate from fragmentation of larger individuals. Radiocarbon age estimates ranged between calibrated ages of AD1050 and modern, indicating that a proportion of living rhodoliths consisted of fossil rhodoliths that had been recolonized. The combination of coastal morphology, gently-sloping sea-floor, hydrodynamics, and rhodolith morphology was representative of rhodolith beds found elsewhere in the world.

Type
Research Article
Copyright
2006 Marine Biological Association of the United Kingdom