Parts of the Freycinet Commonwealth Marine Reserve (CMR) east of Tasmania were opportunistically mapped by the Marine Biodiversity Hub during transit voyages between Hobart and the Flinders CMR, a focus of Hub research. The transit mapping, plus additional, targeted transects, revealed relict coastline reefs in 80─100 m depths extending north of Bicheno. The reefs appear relatively continuous in the CMR, and provide important habitat for Stripey Trumpeter, an important species for commercial and recreational fishers.

Further mapping detected reef features inshore of the relict coastline: complex granite reef systems supporting more substantial fish and invertebrate assemblages. Most notable was a 200 m long granite reef 7 km south-east of Bicheno that rose sharply from 80 m to 60 m. Benthic habitats and biodiversity have been photographed in repeated surveys with an autonomous underwater vehicle (AUV).

(AUV surveys were begun at Freycinet CMR during the Commonwealth Environment Research Facility Marine Biodiversity Hub; later surveys have been supported by the Integrated Marine Observing System, the Institute for Marine and Antarctic Studies and the Department of the Environment.)

Ship deck with equipment being launched.

IMAGE: The AUV Sirius being deployed in the Flinders CMR from the Australian Maritime College Vessel Bluefin, on charter to the NERP Marine Biodiversity Hub. Image: IMAS

Diagram of swathe of granite reef near Bicheno, Tas.

IMAGE: An isolated granite reef mapped 7 km to the south-east of Bicheno at the Freycinet CMR. Tracks show the location of AUV surveys undertaken in 2011 and 2014 to provide an understanding of the biota and its temporal variability in high-profile deep reef systems of the CMR network. Image: GA/IMAS.

Preliminary examination of the AUV imagery indicates that the relict reef systems are generally very low profile and partially sand-inundated, with a sparse coverage of sponges and similar invertebrates, few benthic fish, and with distinct brittlestar aggregations at the reef to sand interface. In stark contrast, the granite reef has an extensive and complex sponge, bryozoan and ascidian fauna and an abundant fish assemblage, dominated by Butterfly Perch.

Further work on the AUV imagery would provide a greater understanding of bioregional patterns, and year-to-year variability in biological indicators of change. The acquired imagery and metadata is available on the Australian Ocean Data Network.

Seafloor relict reef.

IMAGE: An AUV-derived image of the benthos at the interface between sediments and relict reef systems on the shelf in the Freycinet CMR. Features include bare sand to the right, an interface marked by brittlestars, sponges, ascidians and drift algae, and the sand inundated invertebrate turf matrix typical of the relict reef itself. Image: IMOS/IMAS.

Granite reef at Freycinet.

IMAGE: An AUV-derived image from the granite bommie survey shows large sponges (massive and finger morphotypes), sea fans, and butterfly perch. Image: IMOS/IMAS


Neville Barrett
(03) 6227 7210