Title Effects of Predation and Habitat Structure on the Abundance And

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by HKU Scholars Hub Effects of predation and habitat structure on the abundance and Title population structure of the rock shrimp Rhynchocinetes typus (Caridea) on temperate rocky reefs Author(s) Ory, NC; Dudgeon, D; Dumont, CP; Miranda, L; Thiel, M Citation Marine Biology, 2012, v. 159 n. 9, p. 2075-2089 Issued Date 2012 URL http://hdl.handle.net/10722/160588 Rights The original publication is available at www.springerlink.com Mar Biol (2012) 159:2075–2089 DOI 10.1007/s00227-012-1994-6 ORIGINAL PAPER Effects of predation and habitat structure on the abundance and population structure of the rock shrimp Rhynchocinetes typus (Caridea) on temperate rocky reefs Nicolas C. Ory • D. Dudgeon • C. P. Dumont • L. Miranda • M. Thiel Received: 25 February 2012 / Accepted: 21 June 2012 / Published online: 13 July 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com Abstract Human disturbances, such as overfishing, may field and fish stomachs. The presence and the abundance of disrupt predator–prey interactions and modify food webs. R. typus increased with habitat reef complexity and refuge Underwater surveys were carried out at six shallow-water availability. Shrimp abundance was negatively related to reef barrens in temperate waters of northern-central Chile fish abundance in managed areas, but not in open-access from October to December 2010 to describe the effects of areas, where shrimp densities were the highest. Also, pre- predation, habitat complexity (low, medium and high) and dation rates and body-size distribution of shrimps were refuge availability on the abundance and population struc- unrelated, although fish consumed more large shrimps than ture of the rock shrimp Rhynchocinetes typus (Rhynchoci- should be expected from their distribution in the field. netidae), an important mesoconsumer on subtidal hard R. typus occurred most often in shelters with wide openings, substrata. Three sites were within managed (restricted offering limited protection against predators, but providing access) areas for fishermen, and three were unmanaged potential aggregation sites for shrimps. Overall, direct (open-access). Field observations and tethering experiments effects of predation on shrimp densities and population were conducted to examine the relationship between fish structure were weak, but indirect effects on shrimp distri- and shrimp abundances, and the relative predation rates on bution within reefs appear to have been mediated through shrimps. Direct effects of predation on R. typus body-size behavioural responses. Our study highlights the need to distribution were examined from shrimps collected in the assess both numerical and behavioural responses of prey to determine the effects of predator loss on mesoconsumer Communicated by X. Irigoyen. populations. Electronic supplementary material The online version of this article (doi:10.1007/s00227-012-1994-6) contains supplementary Introduction material, which is available to authorized users. N. C. Ory (&) Á C. P. Dumont The loss of marine top predators due to overfishing may The Swire Institute of Marine Science, The University of Hong disturb entire food webs through trophic cascades (Pauly Kong, Pokfulam Rd, Hong Kong, People’s Republic of China et al. 1998; Pace et al. 1999). However, the effects of such e-mail: [email protected] disturbances on intermediate consumers are hard to predict N. C. Ory Á D. Dudgeon Á C. P. Dumont because species of a same trophic level can be affected School of Biological Sciences, The University of Hong Kong, differently by predators (McPeek 1998). An increasing Pokfulam Rd, Hong Kong, People’s Republic of China literature has demonstrated the importance of top-down L. Miranda Á M. Thiel effects on predator–prey interactions, with decreasing Facultad Ciencias del Mar, Universidad Cato´lica del Norte, stocks of large predators releasing prey from predation Larrondo 1281, Coquimbo, Chile pressure (e.g. Myers and Worm 2003; Baum and Worm 2009; Eriksson et al. 2011). M. Thiel Centro de Estudios Avanzados en Zonas A´ ridas (CEAZA), Predation effects on prey may also be mediated by Coquimbo, Chile environmental factors, among the most important of which 123 2076 Mar Biol (2012) 159:2075–2089 is habitat structure (e.g. Almany 2004; Grabowski 2004). (Rhynchocinetidae), which is common at depths of 4–30 m Habitats of high structural complexity may permit prey to on rocky reefs along the coast of Chile (Miranda and Kong maintain higher abundance or species richness by reducing 1970). R. typus plays an important ecological role as prey predation intensity (reviewed by Denno et al. 2005). Prey for many fishes (Caillaux and Stotz 2003; Medina et al. survival is enhanced in complex habitats because detection 2004), but also as a mesoconsumer that controls benthic is more difficult and many refuges of different sizes are assemblages by selective consumption of prey (Dumont available (Eggleston et al. 1990; Canion and Heck 2009). et al. 2009, Dumont et al. 2011a, b). During ontogeny, The protective value of complex habitats, however, is also R. typus males go through several developmental stages: influenced by the identity and behaviour of prey and pre- typus (female-like), intermedius and robustus, the dominant dators (Main 1987; Primavera 1997). An important task for terminal-moult stage (Correa et al. 2000). Robustus and ecologists is to estimate biotic (direct and indirect preda- intermedius individuals are usually larger than typus males tion) and environmental (habitat structure) effects on and possess hypertrophied chelipeds and third maxillipeds, predator–prey interactions (Denno et al. 2005) in order to possibly making them more susceptible to fish predators. better predict the consequences of predator loss on meso- More specifically, we investigated the relationship consumer prey. between R. typus and predatory fishes by testing the Benthic prey without morphological defences against hypothesis that shrimp abundance increased with the predators (e.g. juvenile crustaceans, many shrimp species) complexity of the habitat, in particular the availability of is usually associated to complex habitats with small refuges small refuges. We also tested whether reduced predation that are inaccessible to most large predators. Tethering pressure led to enhanced shrimp abundance by comparing experiments in the field have confirmed that the survival of sites where fishing activity was restricted with open-access such prey increases with refuge availability (Eggleston unmanaged sites where, it was assumed, fish would be less et al. 1990; Mintz et al. 1994). However, this dependence numerous. These comparisons were supplemented by on protective habitats tends to be reduced as the prey direct measurements of predation rates on shrimps tethered organisms grow and develop morphological defences in the field. Finally, we used data from stomach content (Wahle and Steneck 1992). In habitats of low complexity, analyses of predatory fish to test for a relationship between or where suitable refuges are limited, vulnerable prey may preferred prey size and shrimp population structure, based aggregate in large groups that reduce the risks posed by upon the assumption that prey of the preferred body size predators (O’Brien and Ritz 1988; Childress and Herrnkind would be relatively more depleted at sites with the highest 2001a) or environmental stress (Thiel 2011). For example, predation rates and fish abundance. the rockpool prawn Palaemon elegans (Palaemonidae), which inhabits areas of hard substratum where burying is impossible, has a greater tendency to aggregate than the Materials and methods brown shrimp Crangon crangon (Crangonidae), which is associated with soft substratum and can hide by burying Study sites itself (Evans et al. 2007). The largest individuals of smaller and vulnerable prey This study was conducted in northern-central Chile, from may be exposed to higher predation risk because (1) suitable October to December 2010 at 6 sites, separated by 1 to refuges for their body size are limited, (2) they are more *120 km (Fig. 1). Since we were interested in studying detectable (Greene 1986), or (3) they are preferentially areas with differential predation pressure, we a priori selected by predators (e.g. Main 1985). Variations in pre- selected sites that were assumed to have high abundances of dation risk in relation to body size and ontogeny have been fish predators and sites with suppressed numbers of preda- intensively examined using lobsters as model animals (e.g. tory fishes. Three managed areas (MA1—MA3) were Herrnkind and Butler 1986; Wahle and Steneck 1992; chosen because they are ‘management and exploitation Childress and Herrnkind 2001b), but have been less studied areas’ (Castilla 1994), where access is limited to local in shrimps. This is despite the fact that shrimps are the fishermen only. Managed areas may have higher fish dominant prey of many predatory fishes in temperate coastal abundance compared to open-access sites, as shown for waters (e.g. Albers and Anderson 1985; Garrison and Link sites elsewhere along the Chilean coast (Gelcich et al. 2008) 2000) and an important link between primary producers and or in other parts of the world (McClanahan et al. 2006). higher trophic levels (Edgar and Shaw 1995a). MA1 is about 15 km away from the major city Coquimbo, The aim of this study was to examine predator–prey while the two other sites were located close to small

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