Condition of rocky reef communities around Tasmania: a key marine habitat

Research Project

Researchers: Alexander, Timothy, Dr (Principal investigator) ,  Barrett, Neville (Principal investigator) ,  Barrett, Neville (Principal investigator) ,  Barrett, Neville, Dr (Principal investigator) ,  Barrett, Neville, Dr (Principal investigator)
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Brief description The data is quantitative abundance of fish, megafaunal invertebrates and percent algal cover derived from underwater visual census methods involving transect counts at rocky reef sites around Tasmania. This dataset allows examination of changes in Tasmanian shallow reef faunal and floral communities over a decadal scale, with initial surveys conducted in 1992-1995, and again in 2006-2007. There are plans for ongoing surveys. An additional component was added in the latter study - a boat ramp study looking at the proximity of boat ramps and their effects of fishing. We analysed underwater visual census data on fishes and macroinvertebrates (abalone and rock lobsters) at 133 shallow rocky reef sites around Tasmania that ranged from 0.6 - 131 km from the nearest boat ramp. These sites were not all the same as those used for the comparison of 1994 and 2006 reef communities. The subset of 133 sites examined in this component consisted of only those sites that were characterized by the two major algal (kelp) types (laminarian or fucoid dominated). Sites with atypical algal assemblages were omitted from the 196 sites surveyed in 2006. This study aimed to examine reef community data for changes at the community level, changes in species richness and introduced species populations, and changes that may have resulted from ocean warming and fishing. The methods are described in detail in Edgar and Barrett (1997). Primarily the data are derived from transects at 5 m depth and/or 10 m depth at each site surveyed. The underwater visual census (UVC) methodology used to survey rocky reef communities was designed to maximise detection of (i) changes in population numbers and size-structure (ii) cascading ecosystem effects associated with disturbances such as fishing, (iii) long term change and variability in reef assemblages.

Lineage Maintenance and Update Frequency: irregular

Lineage Statement: The underwater visual census (UVC) methodology used to survey rocky reef communities involved quantitative diver-based surveys of fishes, large mobile invertebrates and macroalgae (see below for more detail; also described by Edgar & Barrett, 1997 and Edgar et al., 1997). A total of 136 sites from 8 bioregions around Tasmania were surveyed in both 1992-1995 and 2006-2007. An additional 60 sites were either resurveyed (from sites first surveyed in 1999) or surveyed for the first time in 2006. At each site, 4 x 50m transects were laid at the 5m or 10m depth contour, and fishes, invertebrates (> 2.5 cm) and algae were recorded separately (as described below) by a team of 2 - 3 divers. Details of each site, including the date and GPS location, were recorded and are available at TAFI. FISHES:-The density and estimated size-class of fish species within 5 m either side of the 50 m transect line were recorded by a diver (i.e. 50 m x 10 m). This was done by swimming parallel to the transect line (2.5 m away) and recording fish within a 5 m wide lane, on each side of the transect. Size-classes of total fish length were categorised as 25, 50, 75, 100, 125, 150, 200, 250, 300, 350, 375, 400, 500, 625, 750, 875 and 1000+ mm. Lengths of fish >1000 mm length were individually estimated. MACROINVERTEBRATES:-A diver searched the seabed for a 1 m wide lane along the transect line for cryptic fishes and macroinvertebrates (i.e. 50 m x 1 m). Four 1 m x 50 m transects were surveyed at each site. Algae were swept away from the transect to obtain a clear view of the substratum. Mobile invertebrates (including rock lobsters, abalone, sea urchins, octopus etc) were counted, as were cryptic fishes (also estimated for size). The maximum shell length of abalone and the carapace length of rock lobsters were measured underwater using vernier callipers whenever possible. MACROALGAE:-Macroalgae were surveyed at 10 m intervals along the transect line using a 0.25 m quadrat with a grid of 7 wires crossing perpendicularly. Macroalgal cover was assessed by identifying and counting algae species that occurred directly under the 50 (49 plus one corner) grid positions. Values for each species were converted to percentage of the total values for all algal species. Algae were counted in layers, with percent cover of canopy species recorded first, then pushed aside exposing the understorey species for counting. For the boat ramp component, the UVC methods described above were used to record abundance and size structure of fishes and mobile benthic macroinvertebrates at 133 shallow reef sites around the Tasmanian coastline.

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Natural Resource Management (NRM)

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National Heritage Trust (NHT)

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Stuart-Smith, Rick, Dr

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Frusher, Stewart, Associate Professor

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Schaap, Alex

Notes Purpose
Description of biogeographical patterns on an Australia wide scale, for understanding natural variability over time, detecting changes associated with climate change (range extensions), quantifying impacts of introduced species (e.g. Undaria); understanding and describing ecosystem effects of fishing, and describing the influence of reef based fisheries at the decade scale. The initial survey provided a detailed census of marine life for each site, and by re-examining these sites the aim is to enhance our understanding of how reef species vary over a 12-13 year time scale. These data will allow better management of rocky reef resources from increased knowledge of changes in these systems through natural and human induced events, such as introduced species outbreaks, increased fishing pressure, climate change and disturbance of marine health.

Data time period: 1992 to 31 01 1995

Data time period: 2006-03-01 to 2007-06-26

148.5,-39.5 148.5,-44 144.5,-44 144.5,-39.5 148.5,-39.5

146.5,-41.75

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