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Southeast Tasmania Temperate Reef Survey Post-Survey Report

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Barrett, NS and Nichol, SD (2009) Southeast Tasmania Temperate Reef Survey Post-Survey Report. Technical Report. Geosciences Australia, Canberra.

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Abstract

This report provides a description of the CERF Marine Biodiversity Hub survey of southeast
Tasmanian temperate reefs, aboard RV Challenger, as part of the Hub’s Surrogates Program. The
survey was undertaken as a collaboration between the Tasmania Aquaculture and Fisheries Institute
(TAFI, University of Tasmania) and Geoscience Australia (GA), and was completed in two stages
during 2008 and 2009. The purpose of field surveys in the Surrogates Program is to collect highresolution,
accurately co-located physical and biological data to enable the robust testing of a range of
physical parameters as surrogates of patterns of benthic biodiversity at relatively fine spatial scales. The
objective is to test these relationships in strategically selected areas that are representative of much
more extensive benthic environments, and where the bio-physical data collected complement existing
data for these areas.
This report describes the methods employed in the mapping and video characterisation of shallow-shelf
temperate reef habitats across seven survey sites in southeast Tasmania: Freycinet Peninsula; Maria
Island; Tasman Peninsula (Fortescue area); Port Arthur; Huon Estuary/D’Entrecasteaux Channel; The
Friars; and Tinderbox (D’Entrecasteaux Channel). Preliminary results are provided of the analysis of
multibeam sonar and underwater video data. Examples of the types of biota encountered in the towed
video and stills images, and initial interpretations of the benthic communities are also provided. In
addition, initial results are presented from the deployment of an Autonomous Underwater Vehicle
(AUV) to collect high resolution photographs of reefs and associated biota.
For the seven sites surveyed, the geomorphology of the nearshore and shelf is characterised by a mix of
hard and soft seabed features that provide a range of potential habitat types. The most extensive reefs
are formed where outcrops of bedrock extend offshore from headlands and nearshore islands, with
small areas of reef occurring as isolated patch reefs on the shelf. Away from the reefs, the seabed is
typically sediment covered and flat. The morphology of the mapped reefs ranges from high relief reefs,
which rise several tens of metres above the surrounding seafloor (e.g. The Hippolyte Rocks), to low
relief reefs that are only a few metres high and often partially covered in sediment (e.g. Freycinet
Peninsula, outer shelf). In detail, reef morphology displays strong geological control, as shown by the
highly fractured dolerite reef surface at The Friars and the stepped morphology of some inshore
sandstone reefs along the Tasman Peninsula. Reefs in the more sheltered areas of Port Arthur and the
Huon River / D’Entrecasteaux Channel are less extensive than along the open coast, occurring as
narrow zones of hard-ground along shorelines and surrounding small islands. Otherwise, the mapping
in these areas mostly reveals relict landforms such as incised river channels, drowned terraces and other
soft sediment features (e.g. pockmarks).
In this survey, large linear areas of seafloor were video-taped and the video footage used to characterise
the benthic habitats evident in five of the seven survey areas. A range of benthic habitats was identified
including high-relief bedrock reef at The Hippolyte Rocks, low-lying and partially sediment-covered
bedrock in the Freycinet Marine Protected Area (MPA), transitional patch reef adjacent to sandy seabed
at the margin of bedrock exposures, and extensive sand flats. A variety of sand wave and rippled
habitats was often recorded in and around the reefs themselves. Biological habitats were also diverse
with several distributional patterns recorded. The most dominant pattern was a strong depth zonation,
with a kelp forest zone (dominated by Ecklonia radiata) in water depths < 45 m, which quickly
transitioned into a sponge-dominated deep reef zone (reef depths > 45 m). Beyond the reefs, the shelf
sediments were often carpeted with screw shells and where present in high densities provided hard
substrata for a range of suspension-feeding invertebrates. Although this depth pattern was very
consistent between locations, some differences were observed. For example, differences in the level of
exposure to wave energy between locations appeared to influence the density and structure of these
zones. Kelp morphologies were thinner and longer in more exposed sites (e.g. The Friars), while
sponges here were less dense and smaller in size. Screw shells, which occurred extensively on shelf
sediments and within the sheltered inlets and channels of the Huon Estuary and Port Arthur, varied in
their density between locations. The densest shell beds were recorded north of the Nuggets, while sparse screw shells were recorded in areas of higher wave energy (e.g. around The Friars) and where
the substratum was muddy (e.g. Huon Estuary).
In future work, the morphological characteristics of reefs in the study area will be quantified by a range
of metrics, including slope, relief, rugosity and surface curvature. These parameters will be used to test
for co-variance with spatial and bathymetric patterns in reef biological assemblages, as defined by the
video characterisations. This analysis for co-variance will also consider variations in reef biological
communities that may be a function of differences in wave energy regime between the study sites.
The aim of this work is to improve our understanding of the degree of influence of physical
characteristics on the spatial distribution of biological communities that exist on temperate reefs.
Significantly, this assessment will incorporate a statistical measure of the degree to which derived
physical parameters can be used as surrogates to map and model patterns of marine biodiversity. In
turn, these outputs can be used to better inform the management of similar shallow marine systems
elsewhere in Australia.

Item Type: Report (Technical Report)
Publisher: Geosciences Australia
Identification Number - DOI: ISSN 1448-2177
Date Deposited: 08 Dec 2010 22:46
Last Modified: 27 Oct 2011 22:40
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