was the within-subjects factor. To test the effect of seascape on recruitment we used data from all the sites for which we had information for the same period (September–December 2004). We used sites (6 in the North Island and 4 in the South Island) and sampling months (4 months) as replicates (n = 40) and tested the effect of seascape and island on recruitment (the calculated average recruitment per day for each site/month). Data were square-root transformed to satisfy the ANOVA assumptions. Stepwise multiple- regression analysis evaluated the relative contribution of mussel recruitment and interaction strength to percent cover of large mussels (.15 mm, because we are interested in how related these parameters are to the long-term patterns of the mussel populations). Residuals in probability plots indicated data were normally distributed. We also tested the correlation between mussel recruitment and interaction strength and also between predator abundance (whelks, sea stars, and fish) from our surveys and mussel recruitment rates and percent mussel cover. Ethics All of our work was nondestructive except for the removal of several tens of juvenile mussels at each site for the predation experiment. At the time of this research, no permits or permissions were required for access and use of any of the field sites, or to work with the animals under study (mussels). Approval by the University of Canterbury Animal Ethics Committee was not required for this study. Where mussels were collected from the field, the amount taken was covered under a generic NZ Ministry of Fisheries collection permit, held by the School of Biological Sciences, University of Canterbury. Results Benthic cover The most pronounced difference between R-R and R-S sites at both the North and South Island locations was the low coverage of mussels ,15 mm (,2%) on the low shore at R-R sites and their much greater cover in the R-S sites (.50% in the North Island and .20% in the South Island, Fig. 1). However, there were considerable differences among sites within seascapes, which also varied by shore height. On the North Island, cover of all three mussel size classes varied with sites, seascapes and level on the shore (site(seascape)*shore-height interaction by size class: ,5 mm, F2,152 = 15.6; 5–15 mm, F2,152 = 56.3; .15 mm, F2,152 = 26.4, p,0.0001 for all). On the South Island, a similar pattern occurred for the two smaller size classes (site(seascape)*shore- height interaction by size class: ,5 mm, F2,152 = 6.3 p = 0.002; 5– 15 mm, F2,152 = 4.1, p = 0.017) and seascape had a strong effect on the 5–15 mm size class (F2,2 = 320.2, p = 0.003). Generally, total mussel cover was higher in the R-S sites than at R-R sites in both the low and mid shore, except for the low shore at MP that had high cover of large mussels (Fig. 1). At MI2, mature P. canaliculus beds were covered mostly by P. canaliculus recruits, resulting in .100% cover in many quadrats. Mussel beds were absent from KP, where bare rock, macroalgae (low shore) or barnacles (mid shore) were abundant and individual mussels were found hidden in low zone crevices. Relative abundance and activity of predators At low tide, whelk abundance and species composition varied greatly among sites and Islands with no outstanding differences between seascapes (for details see Table S2 in the online material). In most sites, there were more whelks in the mid than the low shore. In all locations, most individuals were found attached directly to rock during low tide and only a few were observed Intertidal Community Regulation feeding. Small sea stars (Stichaster australis) were seen in crevices only in MM1 (North Island, R-R site). Crabs were rarely seen. At high tide, whelks actively foraged, and sea stars were observed foraging out of cracks in the intertidal zone only in MM1 and at greater numbers after dark than in the daytime (5 and 2 per 5 min. survey, respectively). At the other North Island sites, sea stars were mainly seen in the subtidal zone, even during high tide. Large predatory crabs were rarely seen during daytime at high- tide, but at dusk, swimming crabs (Ovalipes bipustulatus) swarmed low and mid shore levels at the R-S site MI2 (59 were counted during a 5 min. survey) and actively fed on small mussels within and around the mussel bed, including the uncaged experimental mussels (see below). Crabs were not seen on MI1 rocks. Red rock crabs (Plagusia chabrus) occurred in the intertidal zone after sunset at the R-R site MM1 (10 individuals in a 5 min. survey). Predatory fish, Notolabrus fucicola (banded wrasse) and Notolabrus celidotus (spotty), were much more abundant at R-R than R-S sites (34–51 vs. 0–7 fish, respectively, per 15 min. swim), and R-R sites also had higher fish visitation (1.3–5.3 vs. 0–0.3 per 5 min.) and benthic foraging activity rates (0–1.3 vs. 0 bites per 5 min.) during daytime observations (for details see Table S3). Only ‘‘seascape’’ had a strong effect (F1,18 = 34.66, p,0.0001) when fish visitation was compared among islands, seascape and sites. Predation intensity experiments Predation on unprotected juvenile mussels was strong and rapid in all R-R sites throughout the study (Fig. 2). At the Banks Peninsula sites (South Island), the effect of seascape on survival was strong (F1,15 = 132.4, p,0.0001), with far greater survival (70–80%) at R-S sites (CR, TM) than at R-R sites (0–10%) after 45 days. There was also a strong time*seascape interaction (F4,60 = 4.7, p = 0.002) because survival remained high for the duration of the experiment in the R-S sites but was greatly reduced at the R-R sites (MP, BR, Fig. 2A). At the Mt. Maunganui sites in the North Island, there was a strong treatment effect (F1,23 = 118.8, p,0.001) and a weaker seascape*treatment effect (F1,23 = 7.1, p = 0.013) because predation on unprotected mussels (non-caged controls) was high compared to protected mussels (caged) at all sites, but was slower at the R-S (MM2, MI2) compared to the R-R (MM1, MI1) sites (Fig. 2C). A Time effect (F2,46 = 4.4, p = 0.017) and a weak time*treatment effect (F2,46 = 3.2, p,0.04) were also detected. At Kaikoura (R-R site), mortality on unprotected mussels was faster in the low than in the mid shore level (shore-level effect, F1,24 = 12.0, p = 0.002), varied among treatments (caging effect, F2,24 = 150.8, p,0.0001), and there was also a strong time*shore-level*treatment interaction (F12,44 = 5.2, p,0.0001), mainly because mortality in the partial cages was faster in the low than the mid shore level (Fig. 2B). Most mussels disappeared from unprotected tiles within a day at R- R sites. Observations showed that most mussels were eaten during the first high tide after exposure to predation. Fish and crabs were often seen removing mussels within minutes of discovering them on experimental tiles during the first tide after the initiation of an experiment. In several instances, we witnessed that it took only several bites for labrid fishes to remove all the uncaged mussels from tiles in R-R sites in the North Island. Red rock crabs were seen feeding on mussels on the experimental tiles at dusk at R-R sites and swimming crabs were observed feeding on mussel bed and experimental mussels in one R-S site (MI2, North Island). No whelks or sea stars were seen eating the experimental mussels, even though whelks were abundant at most sites (Table S2 in online material). Prey recruitment rates Mussel recruitment varied substantially with time in three regions (Fig. 3). The greatest recruitment was always in at least one PLoS ONE | www.plosone.org 5 August 2011 | Volume 6 | Issue 8 | e23958