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Habitat mapping in the Kent Group of islands

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Jordan, AR and Halley, V and Lawler, MM and Barrett, NS (2002) Habitat mapping in the Kent Group of islands. Technical Report. Tasmanian Aquaculture and Fisheries Institute, Hobart, Tasmania.

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Abstract

The Kent Group of islands are situated in the middle of eastern Bass Strait and consists of Deal, Dover, Erith, North East and South West Islands, as well as various small rocky islets. The island group is in the Twofold Shelf Bioregion and represents the only location for this bioregion in Tasmanian waters. This report details the spatial distribution of seabed habitat types in the Kent Group of islands out to the 3 nautical mile (Nm) limit. Habitat boundaries were logged in the field using a combination of echosounder and video analysis of the seabed, with the video also used to identify the dominant macroalgae and seagrass present. Habitats were defined at two hierarchical levels, with the higher level categories being rocky reef, unconsolidated vegetated and unconsolidated unvegetated substrate. The Kent Group of islands has a diverse range of habitats reflecting the regions bathymetry, oceanography and geomorphology; including rocky reefs of varying exposure and depth, sheltered coves with seagrass, and extensive areas of sponge and sand habitat. The island group is dominated by hard sand and sparse sponge habitat that combined make up around 87% of the total area. However, the distribution and extent of habitat clearly varies by depth, with shallow waters (0-20 m) dominated by reef (mostly low and medium profile) with lesser amount of sand and seagrass. The mid depth range (20-40 m) still contains significant areas of low and medium profile reef although an increasing proportion of hard sand habitat occurs in the deeper parts of this strata. Over 40 m the habitats are predominantly hard sand and sponge. Reefs on the exposed coasts are typically dominanted by the macroalgae Phyllospora comosa, which extends from the immediate subtidal zone to depths of 10 to 20 m where it is gradually replaced by Ecklonia radiata. However, within the sheltered embayments E. radiata and Cystophora monilifera replaces P. comosa as the dominant algae. Murray Pass is an area of particularly high habitat diversity due to the presence of deep water and strong currents providing a suitable environment for sponge habitat in depths >40 m, rocky reefs with varying depth and exposure and several sheltered coves with seagrass and shallow sand. Seagrass beds consist of single or mixed beds of Halophila australis, Heterozostera tasmanica and Posidonia australis with variations in species composition, patchiness and percentage cover evident within and between coves. Sponge habitat, defined as sparse and dense based on the acoustic reflectance and percentage cover from video analysis, covers around 40% of habitats in depths >40 m. Sparse sponge consisted primarily of sand interspersed with small clumps of low sponge while dense sponge was on a more consolidated substrate with a higher relief and had a high sponge cover of encrusting, erect and branching forms. The ascidian Pyura sp. and many species of octocorals, soft corals, anemones and bryzoans were also present. Sixteen 1:10,000 scale maps of seabed habitat of the Kent Group of islands are presented that can be used, in combination with previous quantitative surveys of flora and fauna, to assist with the planning process for a Marine Protected Area in the region.

Item Type: Report (Technical Report)
Publisher: Tasmanian Aquaculture and Fisheries Institute
Additional Information: © 2002 University of Tasmania
Date Deposited: 17 Aug 2009 23:50
Last Modified: 18 Nov 2014 04:04
URI: http://eprints.utas.edu.au/id/eprint/9086
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