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Detailed measurements of three-dimensional beach cusp morphology were made on a steep gradient, low energy, microtidal beach in Perth, Western Australia. During the field campaign a variety of wave conditions and tidal ranges were experienced, and these differing hydrodynamic conditions were reflected in a consistent pattern of morphological changes to the beach cusp system. A useful parameter to delineate between trends of cusp destruction and re-formation appeared to be the surf similarity parameter ξ = tan β⁄√H o ⁄L o , where H o is offshore wave height, L o is deep water wave length and tan β is beach gradient. For ξ<1·2 the beach cusps were planed off, whereas cusp morphology was enhanced when ξ>1·2.A small storm was experienced at the start of the field campaign period and resulted in considerable erosion of the beach face. The cusp morphology across the lower beachface was destroyed, but a subtle remnant of the pre-storm cusp morphology was preserved on the upper beachface. When cusps reformed after the storm, under the influence of declining wave conditions, they appeared at the same location and with the same dimensions as the pre-storm cusp morphology. Hence, it is considered that the cusp re-formation was controlled more by the antecedent morphology than the hydrodynamic conditions. This indicates that positive feedback between swash hydrodynamics and beachface morphology, necessary to form beach cusps, does not require a large variation in relief.

Many indices are available for assessment of spatial patterns in landscape ecology, yet there is presently no consensus about which ones effectively quantify habitat fragmentation. Research that has been carried out to date has evaluated indices primarily using computer-simulated models of terrestrial environments, but how they perform when applied to real landscapes, particularly in the marine environment, has received little attention. Eleven indices that are commonly used for quantifying habitat fragmentation were assessed for their abilities to measure different levels of fragmentation in 16-ha landscape windows of mapped seagrass. The landscape windows were grouped into five categories, from highly fragmented to continuous seagrass landscapes. Nested within the fragmentation categories were high and low levels of seagrass cover. Hierarchical analysis of variance techniques were used to differentiate between the different fragmentation categories and levels of seagrass cover within the fragmentation categories. Principal component analysis was also employed to determine strong correlations between the indices. The results suggest that (1) landscape division and (2) area-weighted mean perimeter to area ratio were the most appropriate indices for differentiating between independent levels of seagrass fragmentation. The splitting index may also be useful when the detection of small differences in cover is important.