Community Regulation: The Relative Importance of Recruitment and Predation Intensity of an Intertidal Community Dominant in a Seascape Context Gil Rilov*¤, David R. Schiel Marine Ecology Research Group, School of Biological Sciences, University of Canterbury, Christchurch, New Zealand Abstract Predicting the strength and context-dependency of species interactions across multiple scales is a core area in ecology. This is especially challenging in the marine environment, where populations of most predators and prey are generally open, because of their pelagic larval phase, and recruitment of both is highly variable. In this study we use a comparative- experimental approach on small and large spatial scales to test the relationship between predation intensity and prey recruitment and their relative importance in shaping populations of a dominant rocky intertidal space occupier, mussels, in the context of seascape (availability of nearby subtidal reef habitat). Predation intensity on transplanted mussels was tested inside and outside cages and recruitment was measured with standard larval settlement collectors. We found that on intertidal rocky benches with contiguous subtidal reefs in New Zealand, mussel larval recruitment is usually low but predation on recruits by subtidal consumers (fish, crabs) is intense during high tide. On nearby intertidal rocky benches with adjacent sandy subtidal habitats, larval recruitment is usually greater but subtidal predators are typically rare and predation is weaker. Multiple regression analysis showed that predation intensity accounts for most of the variability in the abundance of adult mussels compared to recruitment. This seascape-dependent, predation-recruitment relationship could scale up to explain regional community variability. We argue that community ecology models should include seascape context- dependency and its effects on recruitment and species interactions for better predictions of coastal community dynamics and structure. Citation: Rilov G, Schiel DR (2011) Community Regulation: The Relative Importance of Recruitment and Predation Intensity of an Intertidal Community Dominant in a Seascape Context. PLoS ONE 6(8): e23958. doi:10.1371/journal.pone.0023958 Editor: Simon Thrush, National Institute of Water & Atmospheric Research, New Zealand Received April 23, 2011; Accepted August 1, 2011; Published August 26, 2011 Copyright: 2011 Rilov, Schiel. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This research was supported by the Andrew W Mellon Foundation (grant E4710), including a post-doctoral fellowship to G. Rilov, and the New Zealand Foundation for Research, Science and Technology, Coasts and Oceans OBI, contract CO1X0501. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: rilovg@ocean.org.il ¤ Current address: National Institute of Oceanography, Israel Oceanographic and Limnological Research (IOLR), Haifa, Israel Introduction A recent paper [1] identified ‘‘predicting the strength and context-dependence of species interactions across multiple scales’’ as one of three core areas in the ‘‘frontiers of ecology’’. The present study specifically addresses this type of inquiry because it tests species interactions at two context-dependent attributes of the system: the local landscape and its effect on the predator guild, and the recruitment rates of a dominant prey species. In an effort to understand the structure and dynamics of marine communities, the relationships between prey recruitment and abundance, predator abundance, and species interaction strength have been intensely studied in the last few decades. The importance of recruitment rates of dominant prey species to their local abundance [supply-side ecology, sensu 2] has been demonstrated in many studies, and both positive and negative effects of recruitment rate on adult numbers were demonstrated [e.g., 3,4,5]. Predation on dominant organisms is also known to be highly important in shaping community structure in marine communities [e.g., 6,7,8,9,10,11,12]. One important challenge for community ecologists, however, is understanding the context that determines the relative importance of recruitment and predation on the population size of dominant species and therefore of community structure as a whole. Some models of coastal community organization and dynamics and some empirical studies indicate that there is a strong positive relationship between rates of recruitment of basal, benthic, space- occupying species (e.g., barnacles and mussels), and per-capita consumption intensity on their recruits and adults in the context of the regional oceanography [e.g., 3,13,14,15,16]. This ‘‘benthic- pelagic’’ or ‘‘bottom-up/top-down’’ coupling [13,17,18,19,20] can occur because the recruitment of many benthic-dwelling, macro- predators (e.g., sea stars and some whelks) is presumably influenced by the same oceanographic forcing as their prey [indirect causation, 13,see 21 for a coral reef fish example] and probably also because the presence and activity of these predators depend greatly on the local food supply [numerical and functional response, i.e., direct causation, e.g., 14,22]. Data from the Pacific coast of North and South America show that the life history of intertidal predators (i.e., whether or not they have a pelagic larval stage) influences the relationship between prey recruitment and predator abundance, and, in contrast to the other examples, a positive correlation exists only in predators lacking pelagic larvae but not with those with such larvae [23]. PLoS ONE | www.plosone.org 1 August 2011 | Volume 6 | Issue 8 | e23958