The Cape Rodney-Okakari Point Marine Reserve is New Zealand's oldest no-take marine reserve situated along the Leigh coast (est. 1978; the 'Leigh Marine Reserve' hereafter). Historic information on rocky reef communities in the Leigh Marine Reserve is available from baseline surveys in 1978 (Ayling 1978) and repeated in the 1990s (Babcock et al. 1999). While these provide valuable information on long-term changes in the reserve, they did not include fished reefs outside the reserve that provide a control for the effect of protection. The monitoring program presented here was established in 1999 by N. Shears (University of Auckland) for the New Zealand Department of Conservation and includes four sites inside and four sites outside the Leigh Marine Reserve (Shears and Babcock 2003). At these sites, the reefs are gradually sloping from the intertidal to the reef edge, occurring at ~8–15 m depth. From 1999–2000 the reefs were surveyed in four depth ranges (10 m), but subsequent sampling has focussed on the 4-6 m depth range as this is representative of the depth range where sea urchins (Evechinus chloroticus) are most abundant and can form barren habitat (Shears & Babcock 2003; Shears et al. 2008). This depth range has been sampled sporadically (every 1–3 yr at these sites since 2001; note that only fished sites were surveyed in 2003). The surveys were conducted on SCUBA, and at each site, five 1-m2 quadrats were haphazardly sampled within the 4–6 m depth range. Within each quadrat, the density (the number of individuals per metre square) of sea urchins and all large brown macroalgae were recorded (e.g. Ecklonia radiata, Carpophyllum spp., Cystophora spp. and Sargassum sinclairii). For sea urchins, behaviour was recorded as 'cryptic' (sea urchins found in holes, cracks or crevices) or 'exposed' (sea urchins are out in the open and have a strong impact on macroalgal communities; Spyksma et al. 2017). For all large macroalgae the length of all fronds was measured to the nearest 5 cm using a measuring tape. For E. radiata, measurements were taken for both stipe and total length (i.e. from the top of the holdfast to the meristem and the distal end of the primary lamina, respectively). The percent cover of crustose coralline algae, bare rock, turfing algae (e.g. articulated coralline, red foliose), filamentous algae and sediment was assessed visually in each quadrat. In cases where filamentous algae were recorded as overlaying turf and encrusting algae, such that total cover exceeds 100%, the cover data was standardised to add up to 100%.

All surveys from 1999-2019 were coordinated and carried out by N. Shears with assistance of other trained scientific divers from the University of Auckland. More detailed data including size, percent cover and density of macroalgal species, and mobile and sessile invertebrates, is available on request. Most of the surveys were funded by the New Zealand Department of Conservation with additional funding to NS and OP provided by Auckland Council and the Sustainable Seas National Science Challenge.This project was funded by the Sustainable Seas National Science Challenge, the New Zealand Department of Conservation and the Auckland Council.