Lead Agency: Institute of Marine and Antarctic Studies (IMAS)
End Date: 31 December 2021
Status: In Progress
Aims and Objectives:
The principle aim of this project is to map the fine-scale spatial distribution of key abalone and urchin reef habitats in < 25 m water depth using multibeam acoustic imagery. Detailed substrate type (boulder, flat rock, cobble) and kelp coverage maps will be produced with a focus on key abalone blocks and Centrostephanus impacted areas. Large urchin barrens will be mapped, and the level as to which small incipient barrens can be detected will be quantified. The initial focus on key abalone and Centrostephanus areas will facilitate strategic decision making for urchin control and abalone management.
Barrens are the physical representation of impact and again, understanding their distribution and dynamics is fundamental to strategic decision making. Prior to the formation of barrens, kelp forests show marked changes in the density and the size of individual plants. Being able to detect incipient barrens as early as possible would allow for timely interventions.
The project has the following key objectives:
- To map the overlapping abalone and urchin habitat and substrate complexity via new water column acoustic methods.
- Establish a 2020 baseline of kelp abundance at depths where urchin impact on blacklip abalone habitat is greatest (10 – 20m).
- Determine acoustic threshold limits where incipient barrens can be detected.
- Identify areas of urchin barren, and areas susceptible to extensive barren formation
- Determine the suitability and cost effectiveness of acoustic sonar water column methods for state wide reef monitoring.
Since this project began in October 2020 exceptional progress has been made on the fieldwork elements. We ran a preliminary pilot study in Wineglass Bay and outside of Maria Island to ensure that the multi-beam acoustic system could collect the data at the resolution required for the full surveys from the contractor’s vessel. In April 2021 the full survey from Sloop Rock (Block 30) to Tasman Island (Block 22) was completed. We collected close to 600 Km of survey lines across the depth range of 10-25 m.
The data from the project thus far makes it possible to identify the extent of the larger centrostephanus barrens.
The next stage of the project is to continue working on the analysis of both the acoustic data and also analysing the video data.
The data will be used to provide an estimate of the change in algal cover over 20 years for key abalone blocks, quantify temporal changes in patch size and density, explore the key environmental drivers of patch size and density, and examine the significance of kelp patch dynamics in the formation of urchin barrens.
Featured image: Scott Ling, Institute of Marine and Antarctic Studies