Abstract. Heterogeneous patterns of species diversity are rarely linked to the processes that maintain them on spatial scales larger than tens of meters. In this study, subtidal landscapes of a New Zealand fjord were used to study the spatial patterns of epifaunal invertebrate species diversity and to test hypotheses about the mechanisms maintaining the patterns. Patterns of species diversity were quantified along 1000-m 2 sections of vertical rock wall habitat at three sites separated by 3-6 km of horizontal distance during AprilAugust 1993. Species diversity data from random 0.25-m 2 quadrats at four depth strata (3, 5, 10, and 18 m) within a 20 ϫ 50 m area were contoured to reveal spatial patterns at each site. General patterns consisted of localized patches of 300-660 m 2 of high diversity (i.e., HЈ [Shannon-Weiner diversity index] of 2.0-3.2/0.25 m 2 and S [species richness] of 28-32 species/0.25 m 2 ) centered at 10 m depth. High-diversity patches, dominated by bryozoans, sponges, and ascidians, were bounded vertically by low-diversity mussel assemblages and horizontally by low-diversity assemblages dominated by encrusting calcareous algae with areas of bare rock. Vertical patterns of diversity were attributed to physical stress from a low-salinity surface layer impinging on shallow areas (e.g., 0-5 m depth) of the landscapes, while horizontal patterns could be partly attributed to large-scale landslides and severe grazing by sea urchins. The hypothesis that the areas of high diversity could be maintained by larval recruitment was tested by deploying an array of recruitment tiles with predator exclusion treatments. Experiments were conducted on the same spatial scale as the documented patterns of diversity (e.g., at 3, 5, 10, and 18 m depth), with tiles placed in and out of the high-diversity patches. Recruitment densities of calcareous polychaetes, bryozoans, and hydroids showed significant depth and habitat effects (i.e., in vs. out of the high-diversity areas) after 3 mo, but no significant effects of predator exclusion treatment. A positive linear relationship between species diversity and number of recruit species in adjacent areas of wall explained 27-57% of the variance. These data also suggested that the size of the high-diversity patches and location within the fjord are important factors affecting this relationship. We suggest that the localized patches of high diversity over hundreds of meters of continuous habitat can be maintained on temporal scales of months either by spatially limited recruitment of short-lived larvae from the patches or by recruitment near established conspecifics. Additionally, there may be a feedback mechanism involving the interaction of increased biogenic structure provided by the high-diversity patches enhancing recruitment. This feedback would then serve to maintain localized areas of high diversity within the extensive areas of low diversity on scales of hundreds to thousands of meters
