A key to the understanding of the relationship between prey recruitment and abundance and predation intensity on it is to measure these parameters on both small (hundreds of meters) and large (hundreds of kilometers) spatial scales. The combination of large-scale and small-scale studies adds power to, and increases confidence in, inferences about the functional dynamics of ecological communities [24,25]. We therefore tested the relation- ship between predation intensity and prey availability and recruitment using multiple sites in the North and South Islands of New Zealand. We focus our investigation on mussels as prey because (1) they are community dominants on temperate shores in many biogeographic regions, (2) they are important facilitators for other benthic species and (3) they are a major food source in the ecosystem [26]. Our study extends on earlier work that demonstrated the importance of seascape (intertidal reefs with or without nearby subtidal reefs) to predation intensity in the intertidal zone through the presence or absence of subtidal predators (fish and crabs) [27,28]. Those studies showed that at sites where intertidal benches are contiguous with kelp-covered subtidal reefs (reef-to- reef seascapes, hereafter R-R sites) in southeastern New Zealand, the primary predators were highly mobile labrid fishes and crabs that moved from subtidal reefs during high tide and ate low- and to a lesser degree mid-intertidal juvenile mussels [28]. Predation on juvenile mussels was strong at such east-coast R-R sites, but weak on intertidal rocky benches with shallow, sandy, subtidal bathymetry (reef-to-sand seascapes, hereafter, R-S sites). Data collected in a small-scale (2 km shoreline) short-term (2-mo) recruitment-evaluation effort during that study indicated that local recruitment rates of mussels may be much higher at R-S seascapes. This suggested that in this system there may be a disconnection between prey availability (mussel recruitment and abundance) and predation intensity (the abundance and activity of large mobile consumers that prey on mussels). However, that data was too limited, both temporally and spatially, to enable meaningful testing of the relationship between prey recruitment and predation intensity in the seascape context. In the present study, we target this relationship and tested the relative importance of predation and recruitment to intertidal adult mussel populations and the hypothesis that predation intensity and recruitment rates were indeed unrelated. This was done in the context of seascape (intertidal reefs with and without nearby subtidal reefs: R-R and R-S seascapes) and at two spatial scales: small (2– 3 km: area) and large (the North and South Islands). Specifically, we measured the relationships among the following parameters: prey abundance (mussel percent cover), average mussel recruitment rates, predation intensity on juvenile mussels, predator abundance, and finally the relative importance of recruitment and predation intensity on the abundance of mussels. Methods Study sites Eleven intertidal sites were used (Fig. 1). Two areas (each with four sites) enabled us to compare community structure (in the low and mid shore), predation intensity (low shore) and prey recruitment rates (low shore) between R-R or R-S seascapes within small regions. Three additional sites (one in the South Island and two in the North Island) were used to increase sample size for some aspects of this study. Site data and types of data taken in each site are given in Table S1 as well as tide levels. The assumption was that all four sites located within a 2–3 km region (in the North and South Islands) are exposed to the same offshore larval pool [13], and any variability in local larval Intertidal Community Regulation recruitment onshore is the product of differences in very nearshore or onshore processes. In the first area, the northwestern corner of Banks Peninsula on the South Island’s east coast, there were two R-R sites (Moki Point, hereafter MP, and Black Rock, BR) and two R-S sites (Cave Rock, CR, and Taylor’s Mistake, TM). In the second area, Mt. Maunganui in the Bay of Plenty on the North Island, there were two R-R sites (Mt. Maunganui 1, MM1, and Moturiki Island 1, MI1), and two R-S sites (Mt. Maunganui 2, MM2, and Moturiki Island 2, MI2, a rocky bench 200 m east of the Island). In both areas, sites were interspersed to avoid potential confounding effects due to spatial array. Of the three additional sites one was an R-R site on the South Island, Kaikoura Peninsula, where we quantified benthic cover and measured predation intensity at the low and mid shore levels and also measured mussel recruitment rates. The other two sites were in the North Island (Leigh, a R-R site, and Pakiri, a R-S site) where community structure (low, mid zones) and recruitment rates were quantified. All sites were moderately to highly wave-exposed. Benthic cover Percent cover of the main space occupiers (mussels, barnacles, macroalgae) and of ‘free space’ was estimated during spring (North Island) and the end of the Austral summer (South Island) of 2004. Mussels were divided into 3 size classes: small (,5 mm, defined as recruits), medium (5–15 mm, defined as juveniles) and larger mussels (.15 mm, defined as adults). At sites where small mussels covered mature mussel beds, we recorded cover of both size classes, resulting in over 100% cover in some quadrats. Free space was defined as bare rock or rock covered by thin encrusting red algae [see, 29]. We used random-stratified sampling in the middle of the low and mid shore levels to estimate rock cover using twenty 20630 cm quadrats along a 20–50 m transect at each shore level. We avoided deep crevices and rock pools in our sampling. Analysis was done separately on the data from each island because they were sampled in different seasons, which may have affected the cover of small mussel recruits (which were mostly rare in most sites at all dates). An assumption is that our single survey in each site gives a reasonable relative representation of mussel cover at the study sites and at least allows comparison among sites, seascapes and shore heights within a region (island). Predator presence and activity Low tide surveys. Mobile invertebrate macro-predators (sea stars and whelks) were counted in the quadrats described above. We also conducted 10 min. number-per-unit-effort visual surveys in low shore cracks and crevices in the same area where quadrats were laid because these predators can be easily missed or underestimated using only the quadrats. High tide surveys. Sampling the rocky intertidal zone during high tide on wave-swept shores could be done only when seas were relatively calm, recognizing this could also be when subtidal predators were most likely to forage in intertidal areas. At some sites (e.g., Banks Peninsula) we used prior data on the presence and activity of fish [28]. Fish presence and activity in different habitat types at the four North Island Mt. Maunganui sites were assessed during one afternoon high tide on August 2, 2004. Fish were counted by snorkeling using a 15 min. steady swim along and around rocks in the experimental areas. Three 5 min. observations (5 min. intervals between them) were used as replicates to record the number of predatory fish that visited an area (ca. 20 m2) and the number of bites that these fish took off the benthos around experimental plots. Two additional 5 min. snorkeling surveys were done at the four sites on August 30, 2004, at dusk (5:15–6:45 PM), four hours after the initiation of the PLoS ONE | www.plosone.org 2 August 2011 | Volume 6 | Issue 8 | e23958