Invertebrate Biology 132(2): 133–144. © 2013, The American Microscopical Society, Inc. DOI: 10.1111/ivb.12021 Demography and feeding behavior of the kelp crab Taliepus marginatus in subtidal habitats dominated by the kelps Macrocystis pyrifera or Lessonia trabeculata David Jofre Madariaga,1,2 Marco Ortiz,2 and Martin Thiel1,3,a 1 Facultad de Ciencias del Mar, Universidad Catolica del Norte, Coquimbo, Chile 2 Instituto Antofagasta de Recursos Naturales Renovables (IARnR), Instituto de Investigaciones Oceanologicas, Facultad de Recursos del Mar, Universidad de Antofagasta, Antofagasta, Chile 3 Centro de Estudios Avanzados en Zonas Aridas, Coquimbo, Chile Abstract. We studied the population and feeding ecology of the kelp crab Taliepus margina- tus in subtidal kelp forests dominated by either of two morphologically different kelp spe- cies (Macrocystis pyrifera or Lessonia trabeculata) in northern Chile. The sizes and abundances of T. marginatus differed between the two kelp habitats. Kelp crabs were more abundant in the M. pyrifera forest than in the L. trabeculata forest. Size-frequency distribu- tions showed that juvenile and immature crabs were more common in the M. pyrifera forest than in the L. trabeculata forest, where reproductive adults predominated. The smaller crabs in the M. pyrifera habitat also consumed a higher proportion of kelp tissues than the larger crabs in the L. trabeculata habitat, which had a higher proportion of animal food in their diet. In both kelp forests, individuals of T. marginatus showed a similar pattern of noctur- nal feeding over a 24-h period, consuming more food at night than during the day. The more complex and dense forests of M. pyrifera appear to present better nursery habitats for juvenile kelp crabs than the more open and less dense forests dominated by L. trabeculata. These results suggest that the role of the two kelp habitats for T. marginatus varies during the life cycle of the kelp crabs, with M. pyrifera tending to have nursery function and L. trabeculata being more suitable as a reproductive habitat. Additional key words: habitat use, nursery habitat, reproductive habitat, diet Habitats differ in their availability of food items, prey, and thus represent an important trophic link predation pressure, and physical disturbance (e.g., hab- (Hines 1982). As consumers, they obtain most of itat-specific environmental factors), resulting in specific their nutrition from algal material (Hines 1982; costs and benefits for individuals (Amaral et al. 2008). Kilar & Lou 1986; Daly & Konar 2010). The nutri- For example, habitats with higher structural complex- tional value and abundance of this algal material ity offer more shelter and resources, thereby support- are factors that determine its consumption (Wolcott ing high densities of individuals. On the other hand, &O′Connor 1992), and multiple structural and high densities may result in interference competition chemical adaptations have evolved that might for resources and space, leading to emigration and reduce the palatability of seaweeds (Duffy & Hay occupation of less favorable habitats by some individu- 1990). Despite this, some herbivores from temperate als, allowing for more feeding time, albeit possibly on kelp beds consume large amounts of algal biomass less preferred food items (Amaral et al. 2008). (Leighton 1966; Vasquez & Buschmann 1997). Kelp beds are highly productive benthic ecosys- Some algal consumers, primarily the smaller, less tems (Vasquez 1992; Steneck et al. 2002; Ortiz mobile ones, commonly specialize in one type of 2008), which provide shelter for a wide variety of food (e.g., the habitat-forming macroalgae) and live species (e.g., fishes, seastars, crabs, and snails) with directly on it, using it as both food and shelter different feeding behaviors (Smith et al. 1996). Maj- (Hines 1982; Woods 1993; Stachowicz & Hay 1999; id crabs living on kelps act as both consumers and Gutow et al. 2012). In contrast, larger individuals that roam farther also incorporate other food items aAuthor for correspondence. in their diet. This may lead to spatial segregation E-mail: [email protected] between different ontogenetic groups. 134 Jofre, Ortiz, & Thiel In many habitats, crab consumers have special Methods feeding rhythms to avoid interspecific competition for food and predation risk (Jesse 2001; Kronfeld- Study area Schor & Dayan 2003). For example, members of many brachyuran species feed mainly during the This study was carried out in austral fall during night, with no or low foraging activity during the the months of April 2006 and April 2007 near Isla day (Aris et al. 1982; Jesse 2001; Novak 2004; Santa Marıa at the southern tip of the Mejillones Almeida et al. 2008). By limiting their activity per- Peninsula (SE Pacific coast, Antofagasta, Chile: iod to times of low predation pressure, these crabs 23°27′S–70°36′W). The study area is close to an reduce the amount of time available for foraging important upwelling center that supplies nutrients to (Aris et al. 1982). the coastal ecosystem (Escribano et al. 2004). These Taliepus marginatus (BELL 1835) (Superfamily nutrient-rich coastal areas are dominated by subtidal Majoidea) is a decapod crab widely distributed kelp forests of Macrocystis pyrifera and Lessonia along the Chilean coast, but little is known about trabeculata, which develop in different environmen- its life cycle. Recently settled juveniles of its conge- tal conditions (Ortiz 2008). Macrocystis pyrifera ner T. dentatus (MILNE EDWARDS 1834) are com- forms extensive and complex patches in coastal monly found in shallow subtidal habitats, often areas mostly protected from direct wave exposure, dominated by turf algae, and while the habitats of where they often grow on boulders extending over growing juveniles and subadults are not known, the depths of 2–10 m (Vega et al. 2005; Villegas et al. reproductive adults generally occur in subtidal kelp 2008). Blades of M. pyrifera grow along the entire forests (Pardo et al. 2007; Palma et al. 2011). Talie- stipe, forming a dense mesh of algal canopy from pus marginatus has been reported from deeper sub- the bottom to the sea surface (Villegas et al. 2008). tidal waters (Antezana et al. 1965) in subtidal kelp In contrast, L. trabeculata grows mostly on more systems dominated by either Macrocystis pyrifera exposed coasts on bedrock ranging in depth from 8 (LINNAEUS)C.AGARDH 1820 or by Lessonia trabecu- to 14 m (Vega et al. 2005; Villegas et al. 2008). The lata VILLOUTA &SANTELICES 1986 (Villegas et al. blades of older kelp stands usually originate from 2008). These two kelp species show important dif- the stipes at some distance above the bottom, but ferences; they develop in different environmental the individual kelp plants rarely exceed 1.5 m in conditions, have contrasting morphological struc- height and thus do not reach the sea surface. Given tures (Ortiz 2008; Villegas et al. 2008), and likely their different bathymetric distribution, at the study differ substantially in their tissue consistency and site the kelp forests composed of M. pyrifera are attractivity for grazers (for differences between M. closer to the shore, growing over a gentle slope pyrifera and Lessonia spp. see for example Pansch down to ~6 m depth, while stands of L. trabeculata et al. 2008). Based on these ecological differences, start at the seaward edge of the M. pyrifera patches, we expected that the natural diet, density, size dis- extending in depth from ~5 m down to ~12 m tribution, and foraging activity of T. marginatus (Fig. 1). might differ between these two kelp habitats. Specif- Both kelp forests have a high standing biomass, ically, we hypothesized that smaller crabs would be but system throughput (a measure of ecosystem more common in the shallow and dense kelp beds metabolism) in M. pyrifera kelp beds is higher than of M. pyrifera, while larger crabs would dominate in L. trabeculata (Ortiz 2008, 2010). A wide diversity in the deeper and more open beds of L. trabeculata. of different invertebrates is found in the kelp forests We also expected to find differences in the feeding around Isla Santa Marıa; among these, sea urchins ecology of crabs between the two kelp systems. and their seastar predators dominate in biomass This study thus aims to contribute to knowledge (Vasquez et al. 2006; Gaymer et al. 2010). Fish pre- of the demography and feeding ecology of T. mar- dators are also important in these kelp forests (Ortiz ginatus in two subtidal kelp habitats. The objectives 2008), which offer more refuge and food than sur- were to compare the (i) size structure, (ii) density, rounding barren grounds (e.g., Vasquez et al. 2006; (iii) natural diet, and (iv) daily feeding cycle of T. Villegas et al. 2008; Perez-Matus et al. 2012). marginatus inhabiting beds dominated by either M. In these kelp systems, Taliepus marginatus is one pyrifera or L. trabeculata. This work is part of an of the most abundant brachyuran crabs. Settlement extensive study examining the properties of the kelp occurs primarily during austral spring (personal forest ecosystems formed by M. pyrifera and L. tra- observations), and growing juveniles and subadults beculata (Ortiz 2008, 2010). were expected to be most abundant during late Invertebrate Biology vol. 132, no. 2, June 2013 Demography and feeding behavior of a kelp crab 135 Fig. 1. Location of the study area on the Mejillones Peninsula close to Santa Marıa Island, SE Pacific coast (northern Chile), showing Macrocystis pyrifera (dark shading) and Lessonia trabeculata (light shading) kelp forests. Sampling plots in each kelp habitat are shown. summer and fall, as had also been reported for systems. The scuba divers collected crabs on the other kelp inhabitants (Gaymer et al. 2010) and for bottom and in the kelp canopy by carefully survey- kelp crabs in California (Hines 1982). Consequently, ing the entire fronds (e.g., searching on both sides sampling of crabs was conducted during early aus- of the blades).