Long-term current prediction in the central Great Barrier Reef

Abstract

Long-term current records in the Great Barrier Reef region are needed to address major ecological problems such as periodic outbreaks of the coral predator, Crown of Thorns Starfish (COTS, Acanthaster sp.). In situ current meter data are sparsely distributed and typically available for deployments shorter than 1 year. A suite of linear systems models has therefore been developed which allow low-frequency along shelf currents to be specified using readily available meteorological and oceanographic forcing data. The models which are essentially statistical, nevertheless reflect our understanding of regional hydrodynamics. Using optimally lagged multilinear regression they allow predictions to be made quickly and economically from input time series and a few specified parameters. Models were calibrated using current meter mooring data obtained from a transect across the central Great Barrier Reef in 1985 and validated using data from similar deployments in 1987 and 1990. The models which are simplest to implement, perform well and are statistically efficient are those based on the geostrophic across-shelf momentum balance. Using as inputs coastal sea levels or, when available, offshore sea level differences, they can precisely predict currents over time spans of up to 25 years. They accurately respond to fluctuations at weather time scales and, when offshore differences are used, at seasonal and inter-annual scales. The predicted currents are being used to drive advective models of COTS larvae dispersal and to set boundary conditions for more complex numerical hydrodynamic current simulation models.