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

Rhodoliths were collected in Esperance Bay, Western Australia, using a Van Veen grab from a bed that covered an area approximately 2.2 km(2), in depths of 38 +/- 1 m. Rhodolith abundance (biomass per 0.1 m(3)), 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 lump), 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 AD 1050 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.