Figure 2. Effect of predation on mussel survival rates on R-S and R-R sites. (a) Banks Peninsula (sites: R-S = CR, TM, and R-R = MP, BR), only no-cage treatment and only low-shore level. (b) Kaikoura Peninsula, R-R site, low- and mid-shore levels, full cage control, partial cage and no cage treatments. (c) Mt. Maunganui, four sites (two R-S: MM2, MI2 and two R-R: MM1, MI1), both cage control and no-cage treatment; only low-shore level. Blank symbols = R-S sites, black symbols = R-R sites. Day 0 = day mesh was removed and mussels on tiles placed in the experimental treatments. doi:10.1371/journal.pone.0023958.g002 (and sometimes both) R-S site in each region. At the R-R Kaikoura Peninsula site, only 7 mussels recruited to all collectors over a five month period. Analysis of data for the four months for which we had data for both the North and South Island sites shows that the average recruitment rates at R-S sites was 5.3 times greater than at R-R sites (61.5.8623.4 SE and 11.566.2, per collector, respectively, two-way ANOVA, F1,36 = 7.36, p = 0.01) Intertidal Community Regulation and the seascape effect was consistent between the two island (no island or seascape*island effects). Predation-recruitment-cover relationship Although both recruitment (positively, r = 0.59, p,0.05) and interaction strength (negatively, r = 20.74, p,0.05) strongly correlated with mussel (.15 mm) percent cover, stepwise multiple regression analysis indicated that interaction strength accounted for much more of the variability in mussel cover (beta = 20.59, p = 0.025) compared to recruitment rates (beta = 0.29, p = 0.21). When we run the analysis as an ANCOVA with Seascape as the categorical predictor variable none of the factors was significant as expected (because this relationship is driven by the seascape); however if we run the ANCOVA again with either forward or backward stepwise multiple regression, only interaction strength came up as a significant factor (p = 0.014). Fig. 4a shows that the lowest percent cover of mussels occurred where interaction strength was highest and recruitment was lowest. The relationship between recruitment rates and interaction strength (predation on juvenile mussels) was negative (r = 20.61, p,0.05, Fig 4b), but this relationship was mainly driven by seascape. Overall, R-R sites tended to have high predation intensity and low recruitment rates whereas R-S sites had weaker predation and higher recruitment (Fig. 4b). There were no apparent relationships (correlations) between intertidal predatory invertebrates or subtidal predatory fish and recruitment rates or percent mussel cover (Fig. 5). The lack of significant correlation with fish abundance is mostly due to one outlier site (Moki Point) with high abundance of fish and cover of mussels. This site seems more wave-exposed than the others and perhaps predation activity is reduced there allowing higher survivorship of mussels. Sea stars were found in their highest densities where mussel recruitment was also highest (west coast) but they were also rare or absent in other sites of relatively high mussel recruitment and cover. Discussion The question of the relationship between food supply and predator abundance and predation intensity is fundamental in ecology. Answering this question becomes more difficult in marine systems where supply of young (both prey and predators) can be decoupled from birth (reproduction) rates due to the complex life cycle (pelagic larvae) of most benthic species. Earlier work suggested that prey recruitment and predation intensity might be decoupled by seascape characteristics [27] but there was not enough data to support it. The aim of the present study was to fill that gap. Models that tested those relationships in upwelling systems predicted a strong positive correlation between prey supply rates and the consumption rates on them because most are influenced by the same oceanographic forcing [13]. Current evidence from the last decade suggests a more complex picture. There can indeed be a correlation between prey recruitment and predator abun- dance/predation-rate when both species are similarly affected by oceanographic forcing, for example in coral reef systems [21]. These relationships may not exist however if the species have very long or different pelagic larval duration, as was demonstrate in two large-scale studies on east Pacific coasts in both the north and south hemispheres [20,23,24]. But there can still be a relationship (just not driven by oceanography) if other factors determine predator abundance, such as a direct numerical functional response in non-dispersive predators [23], or the proximity of primary predator habitat determined by seascape that may also PLoS ONE | www.plosone.org 6 August 2011 | Volume 6 | Issue 8 | e23958