Vol. 400: 175–185, 2010 MARINE ECOLOGY PROGRESS SERIES Published February 11 doi: 10.3354/meps08324 Mar Ecol Prog Ser OPENPEN ACCESSCCESS Influence of shelter availability on interactions between Caribbean spiny lobsters and moray eels: implications for artificial lobster enhancement E. Lozano-Álvarez1,*, P. Briones-Fourzán1, L. Álvarez-Filip1, H. M. Weiss2, F. Negrete-Soto1, C. Barradas-Ortiz1 1Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Unidad Académica Puerto Morelos, PO Box 1152, Cancún, Quintana Roo 77500, México 2Project Oceanology, Avery Point, Groton, Connecticut 06355, USA ABSTRACT: The Caribbean spiny lobster Panulirus argus is a valuable fishing resource, but local populations may be limited by availability of crevice shelter on juvenile (seagrass) habitats. This has prompted research into the potential density enhancement of juvenile lobsters with ‘casitas’, large (1.1 m2 surface area) but low-lying (3.8 cm entrance height) artificial shelters that exclude large predators. Moray eels (Muraenidae), however, fit into casitas and could therefore pose a threat to lob- ster enhancement. In a shelter-poor reef lagoon, we examined potential interactions between juve- nile lobsters and the locally dominant morays Gymnothorax vicinus and G. moringa in the absence (four 1 ha control sites) and presence of casitas (five 1 ha ‘casita sites’, each with 10 casitas), before (6 surveys) and after (22 surveys) deployment. Morays and lobsters did not interact as predator–prey, as morays neither consumed nor intimidated co-occurring lobsters. Rather, the 2 taxa appeared to compete for limited shelter on the reef lagoon, as suggested by a significant increase in density and mean size of both taxa on casita sites after deployment. Casitas significantly increased cohabitation of morays and lobsters, yet they tended to co-occur less often than expected by chance, but this result likely reflects behavioral differences between the highly gregarious, more numerous lobsters and the typically solitary, cannibalistic morays. Our study exemplifies the influence of habitat complexity on the nature of interspecific interactions and shows that G. vicinus and G. moringa would not pose a threat to lobster enhancement with casitas. KEY WORDS: Artificial shelters · Casitas · Competition · Environmental context · Interspecific interactions · Predation · Reef lagoon Resale or republication not permitted without written consent of the publisher INTRODUCTION neutral, to positive, depending on the environmental context (Stachowicz 2001, van Baalen & Jansen 2001, Communities are structured by interactions be- Hay et al. 2004). In particular, habitat complexity may tween coexisting species. Interactions are positive have a profound influence on the nature and outcome (e.g. mutualism) when one species improves another of interactions between local species (Forrester & species’ environment, or negative (e.g. predation or Steele 2004, Grabowski 2004, Hixon & Jones 2005) competition) when one species detracts from the because high complexity habitats provide a greater environment of other species or has an impact on its spectrum of resources and more refuges that provide components or fitness, such as survival, growth, or protection from predators than low complexity habi- reproduction. However, interspecific interactions may tats (Sih 1984, Almany 2003, Lozano-Álvarez et al. be conditional, potentially shifting from negative, to 2007). *Email: [email protected] © Inter-Research 2010 · www.int-res.com 176 Mar Ecol Prog Ser 400: 175–185, 2010 Moray eels (Pisces: Anguilliformes: Muraenidae) and ston 1998), thus reducing the time of exposure (the spiny lobsters (Crustacea: Decapoda: Palinuridae) typi- ‘guide effect’ benefit, Childress & Herrnkind 1997). cally coexist in coral reef systems. Morays are general- However, if crevice shelter is limited, resident lobsters ist predators and are certainly able to consume spiny may behave aggressively towards other conspecifics lobsters (Lipcius et al. 1998, Weiss et al. 2006), yet spiny attempting to share their shelter (Childress & Herrn- lobsters are usually not present in stomach contents of kind 1997). Therefore, shelter limitation increases the morays (Hiatt & Strassburg 1960, Randall 1967, Chave risk of predation for those lobsters seeking shelter and & Randall 1971, Young & Winn 2003). If morays switch also for those sheltering alone, potentially resulting in among prey species depending on their relative abun- a local demographic bottleneck (Wahle 2003). dance as most generalist predators do (van Baalen et al. The dire consequences of shelter limitation for juve- 2001, Rudolf 2008), these findings may simply reflect a nile Panulirus argus lobsters have prompted research lower local abundance of spiny lobsters relative to other into their potential enhancement (increase in density types of prey. Alternatively, morays may affect lobsters and biomass) with artificial shelters (review in Briones- indirectly (by intimidation) rather than by consumption Fourzán et al. 2007). Although artificial shelters may (Preisser et al. 2005). However, morays and lobsters of- also attract local predators, potentially increasing mor- ten share crevices without showing any obvious inter- tality of resident lobsters (Butler & Herrnkind 1997, actions (Berry 1971, Abrams et al. 1983, Lozano- Sosa-Cordero et al. 1998, Behringer & Butler 2006), it Álvarez & Spanier 1997, Young & Winn 2003, Weiss has been found that ‘casitas’ (large but low-lying artifi- et al. 2006). Berry (1971) considered this occurrence as cial shelters) tend to increase survival and density of a potential mutualism, wherein the lobster would be juvenile lobsters by excluding large predators while protected from other predators (e.g. octopuses) by the offering lobsters the potential for gregariousness moray, and the moray would profit from consuming (Eggleston et al. 1990, Eggleston & Lipcius 1992, other predators attracted by the lobster. Briones-Fourzán et al. 2007). But casitas do not exclude However, because morays (Hixon & Beets 1989, morays, which fit into narrow crevices given their 1993, Gilbert et al. 2005) and spiny lobsters (e.g. Butler snake-like bodies (Hixon & Beets 1989, 1993). Thus, & Herrnkind 1997, Briones-Fourzán et al. 2007) morays have been considered as potential predators strongly depend on crevice shelter for protection for lobsters in casitas (Eggleston et al. 1990, Sosa- against their predators, the 2 taxa might compete for Cordero et al. 1998). limited shelter. For example, on soft-bottom seagrass However, in a controlled experiment conducted in habitats across the Puerto Morelos reef lagoon (Mexi- the Puerto Morelos reef lagoon, casitas significantly can Caribbean), crevice shelters (e.g. solution holes, enhanced juvenile lobsters despite being also readily small coral heads, and the bases of sponges and octo- colonized by morays (Briones-Fourzán et al. 2007). corals) are scarce and generally small (Briones- This experiment thus provided an arena to test several Fourzán & Lozano-Álvarez 2001). In this and other hypotheses concerning potential interactions between Caribbean reef lagoons, juvenile Caribbean spiny lob- morays and lobsters on shelter-poor (without casitas) sters Panulirus argus (Latreille, 1804) coexist with pur- and shelter-enhanced (with casitas) sites. If morays plemouth Gymnothorax vicinus (Castelnau, 1855) and tend to consume co-occurring lobsters, this would be spotted morays G. moringa (Cuvier, 1829) (Young & reflected in a meaningful contribution of lobsters to the Winn 2003, Briones-Fourzán et al. 2007). diet of morays and in a negative relationship between Panulirus argus is one of the most important fishery the average numbers of morays and lobsters per casita. resources in the Caribbean region (Phillips & Melville- If morays affect lobsters indirectly (by intimidation), Smith 2006), but local populations of juvenile lobsters, their presence would be expected to affect the distrib- which are more vulnerable to predation than adults, ution of lobsters among shelters, be they natural may be limited by availability of crevice shelters. crevices (hereafter referred to as ‘crevices’) or casitas. These lobsters, however, are gregarious and their per If morays and lobsters potentially compete for limited, capita survival tends to increase in large shelters that small shelters but can share large shelters, then allow for cohabitation of multiple lobsters across a morays — like lobsters — should undergo a significant broad size range (Dolan & Butler 2006) because the enhancement with casitas, and both taxa would tend to larger lobsters collectively defend the shelter from cohabit more in casitas than in crevices. If cohabitation approaching predators (the ‘group defense’ benefit, is beneficial to both taxa, then they should tend to co- Childress & Herrnkind 1997) while the smaller lobsters occur in individual shelters more often than expected may profit from a ‘dilution effect’ (Eggleston & Lipcius by chance. However, because social behavior may dic- 1992, Briones-Fourzán & Lozano-Álvarez 2008). Also, tate the pattern of shelter occupancy, we compared the lobsters seeking shelter home in on chemical cues tendency of individuals of each taxon to dwell alone or released by sheltered conspecifics (Ratchford & Eggle- aggregated. Lozano-Álvarez et al.: Interactions between spiny lobsters and moray eels 177 MATERIALS AND METHODS sisted of 6 surveys because prior to these surveys no