MEPS 449:13-25 (2012)  -  DOI: https://doi.org/10.3354/meps09463

ABSTRACT: Models of seabed sediment mobilisation by waves and currents over Australia’s continental shelf environment are used to examine whether disturbance regimes exist in the context of the intermediate disturbance hypothesis (IDH), whereby maximum biodiversity coincides with moderate levels of disturbance. Our study shows that it is feasible to model the frequency and magnitude of seabed disturbance in relation to the dominant energy source (wave-, tide- or cyclone-dominated shelf). Areas are mapped where the recurrence interval of disturbance events is comparable to the rate of ecological succession, which meets criteria defined for a disturbance regime. We focus our attention on high-energy, patch-clearing events defined as exceeding the Shields (bed shear stress) parameter value of 0.25. Using known rates of ecological succession for different substrate types (gravel, sand and mud), predictions are made of the spatial distribution of a dimensionless ecological disturbance (ED) index, given as: ED = FA(ES/RI), where ES is the ecological succession rate for different substrates, RI is the recurrence interval of disturbance events and FA is the fraction of the frame of reference (surface area) disturbed. Maps for the Australian continental shelf show small patches of seafloor where ED indicates the potential existence of disturbance regimes (and inferred greater biodiversity) distributed around the continent, on both the inner and outer shelf. The patterns are different for wave-dominated (patches on the outer shelf trending parallel to the coast), tide-dominated (patches crossing the middle-shelf trending normal to the coast) and cyclone-dominated (large oval-shaped patches crossing all depths) shelf environments. Only a small portion of the shelf (~10%) is characterised by a disturbance regime as defined here.

KEY WORDS: Continental shelf · Physical processes · Ecological succession · Intermediate disturbance hypothesis · Disturbance regime