The data is the percent algal cover derived from underwater visual census methods involving transect counts at rocky reef sites around Tasmania. This data forms part of a larger dataset that also surveyed fish and megafaunal invertebrate abundance for the area. The aggregated dataset allows examination of changes in Tasmanian shallow reef floral and faunal communities over a decadal scale - initial surveys were conducted in 1992-1995, and again at the same sites 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.
Maintenance and Update Frequency: irregular
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 by a team of 2 - 3 divers. Details of each site, including the date and GPS location, were recorded and are available at IMAS. The methods below describe the specific survey technique for measuring algal cover:
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.
Natural Resource Management (NRM)
National Heritage Trust (NHT)
Stuart-Smith, Rick, Dr
Frusher, Stewart, Associate Professor
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.