The rocky shores of New Zealand (NZ) and Australia provide many interesting comparisons in their intertidal species and structuring processes. Both countries are in the biogeographic realm of temperate Australasia and share many common species and closely related taxa. Here we review similarities and contrasts in communities and structuring processes, especially involving grazing invertebrates and macroalgae. We consider the similarity of the structure of intertidal shores of NZ and south-eastern Australia, a suite of important trophic interactions within and between regions, the utility of local-scale experiments in understanding large-scale processes and how we might better plan for and manage our coasts. The major comparisons are between warm-temperate areas of northern NZ and New South Wales, and the cooler areas of southern NZ and south-eastern Australia. In the quest for ‘ecosystem’-level understanding, which perforce involves large-scale events, there is an increasing tendency to minimise or ignore the hard-won insights gained from well-structured experiments across multiple sites. Because all large-scale effects must be manifested at local sites, it is incumbent on us to determine what scales up or down, and the caveats that make comparisons across biogeographic regions challenging. Here, we discuss these issues using austral shores as models.

Three broad contributions have recently emerged from South African marine biology. First, even strong environmental and biological effects like upwelling are context dependent, nested in biogeography and differ from fine to coarse taxonomic scales. This can lead to small-scale spatial predictability in grazing effects. While top-down control, including fishing, is critical in shallow subtidal systems, the intertidal exhibits stronger bottom-up regulation. Second, phylogeographic patterns can be strong, without coinciding with biogeographic boundaries. This is important because intra-specific genetic lineages can show critical differences in behaviour and physiology, making species responses to environmental change and biological interactions variable at the population level. Third, many non-indigenous species have come to light. Few have become invasive, but they can have dramatic effects, positive and negative. Their simple distributional patterns emerge from complex interactions of many variables, making predicting species distributions under climate change difficult.