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Habitat mapping in the Kent Group of islands

Jordan, AR, Halley, V, Lawler, MM and Barrett, NS 2002 , Habitat mapping in the Kent Group of islands.

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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)
Authors/Creators:Jordan, AR and Halley, V and Lawler, MM and Barrett, NS
Publisher: Tasmanian Aquaculture and Fisheries Institute
Additional Information:

© 2002 University of Tasmania

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