Ecological disturbance index

Brief description

This data represents a dimensionless ecological disturbance index, as the ratio of ecological succession and disturbance recurrence interval times the fraction of the area disturbed in any event. Small values of the ecological disturbance index represent decreasing proportions of time when disturbed/recovering habitats are present.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Geoscience Australia's GEOMACS (Geological and Oceanographic Model of Australia's Continental Shelf) model was utilised to produce hindcast hourly time series of continental shelf (~20 - 300 m depth) bed shear stress on a 0.1 degree grid covering the period March 1997 to February 2008 (inclusive). The hindcast data represents the combined contribution to the bed shear stress by waves, tides, wind and density-driven circulation. The ecological disturbance index is calculated using the following equation: ED=FA*ES/RI Where ED is the ecological disturbance index, FA is the spatial fraction multiplier, ES is the ecological succession (in days), and RI is the recurrence interval (in days). In this study, FA was assigned 1.0. ES equals 1 year (365 days) for mud, 3 years (1095 days) for sand and 5 years (1825 days) for gravel. While, RI is the average time between events when the Shields parameter exceeding 0.25 (the geomacs_ri layer).The seabed sediment was classified into gravel, sand or mud using a simple classification scheme (Folk, 1974). Grid cells were assigned to the gravel class if percent gravel was >30, and if the percent gravel was <30 they were assigned to either the sand or mud class depending on which ever had the largest percentage. The sediment grain size data used for this exercise were from the predicted layers of Li et al. (2011). Please refer to Hughes et al. (2010) for further details. Hughes, M.G., Harris, P.T., Brooke, B.P., 2010. Seabed exposure and ecological disturbance on Australia's continental shelf: Potential surrogates for marine biodiversity. Geoscience Australia Record 2010/43, 77pp. Li, J., Heap, A.D., Potter, A., Huang, Z., 2011. Seabed gravel content across the Australian continental EEZ 2011, http://www.ga.gov.au/meta/ANZCW0703014835.html Li, J., Heap, A.D., Potter, A., Huang, Z., 2011. Seabed sand content across the Australian continental EEZ 2011, http://www.ga.gov.au/meta/ANZCW0703014867.html