Influence of Habitat Heterogeneity on The

Teoh et al. Zoological Studies 2014, 53:67 http://www.zoologicalstudies.com/content/53/1/67 RESEARCH Open Access Influence of habitat heterogeneity on the assemblages and shell use of hermit crabs (Anomura: Diogenidae) Hong Wooi Teoh1,2*, Muhammad Ali Syed Hussein1 and Ving Ching Chong2,3 Abstract Background: Two contrasting intertidal habitats on the western Sabah coast (Malaysia), one is a rocky-sandy-mud flat at Sepangar (N6°02′18.57″; E116°06′40.07″) and the other is a mangrove foreshore at Sulaman (N6°15′33.00″; E116°18′49.80″), are characterized by substrate zonation and homogeneous substrate (mud), respectively. Hermit crabs are one of the most conspicuous benthic macrofauna at both sites. The study examined the influence of habitat heterogeneity on the assemblages and shell use pattern of hermit crabs. Results: The heterogeneous intertidal flat at Sepangar (five species) supported a higher diversity and abundance of hermit crabs compared to Sulaman mangrove foreshore (two species). Hermit crabs at Sepangar used a greater variety of shells (30 species) compared to those at Sulaman (two species). Zonation of hermit crab species occurred at Sepangar where Diogenes klaasi dominated at the high-tide mark and two Clibanarius species (C. striolatus and C. merguiensis) dominated at the low-tide mark. Considerable overlap in habitat use (mid- and lower shore) occurred between D. tumidus and the two Clibanarius species which appeared to influence shell use pattern. Conclusions: This study supports the work of others showing that structurally complex habitats will allow habitat partition among species thus explaining the greater diversity and abundance of hermit crabs. Such a heterogeneous habitat provides a wider choice of shells for the hermit crabs, minimizing interspecific competition for the available shell resources. Keywords: Hermit crabs; Diversity; Habitat heterogeneity; Tropical intertidal Background micro-habitat preferences of hermit crabs including shell Hermit crabs are one of the most conspicuous and eco- use pattern may indicate adaptations to reduce interspe- logically important groups of animals inhabiting inter- cific competition (Leite et al. 1998). Habitat partitioning tidal and subtidal habitats (Schembri 1982). These has been demonstrated since closely related species show animals are unique for their dependency on gastropod variable use of gastropod shells depending on the shell shells as a ‘mobile home’ to protect them from predators size, shape and availability (Teoh and Chong 2014), while (Elwood et al. 1995) and reduce the risk of desiccation a more heterogenous habitat provides more niches and during emersion at low tide (Bertness and Cunnigham ways to exploit the available resources (Bazzaz 1975). 1981). Despite the many world-wide studies on hermit At the intertidal zone, landmark studies on biological crabs, those pertaining to hermit crab-shell interactions zonation are well established (Knox 2001; Harley 2003; are more common than studies investigating habitat par- Veloso et al. 2003; Rodil et al. 2006; Sacrosati and Heaven titioning which are scarce especially in the Indo-Pacific 2007), attributable to the accessibility of sites and the di- region. The available literature on both macro- and versity of species of sessile and slow-moving animals that are readily enumerated (e.g. Connell 1972). There are * Correspondence: [email protected] several important factors influencing intertidal biological 1Borneo Marine Research Institute, Universiti Malaysia Sabah, Sabah, Malaysia zonation which include wave exposure (Stephenson 1961; 2Present address: Institute of Biological Sciences, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia Knox 2001; Harley 2003), temperature (Wethey 1983), sal- Full list of author information is available at the end of the article inity (Druehl 1967) and substrate composition (Rai-mondi © 2014 Teoh et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Teoh et al. Zoological Studies 2014, 53:67 Page 2 of 9 http://www.zoologicalstudies.com/content/53/1/67 1988). Among these factors, sediment texture may invoke a relatively greater influence on distribution and mainten- ance of anomuran populations (Fransozo et al. 2008) as sediment is utilized by these animals as shelter and food source (Abele 1974). The adaptation of intertidal animals towards different environmental settings resulted in the formation of distinct ecological niches along the intertidal zone. This is exemplified by the unique features of rocky shores that exhibit prominent horizontal bands formed by different types of animals and plants (Nybakken 1982). Shells influence the growth and reproduction of hermit crabs (Fotheringham 1976; Bertness 1981a; Elwood et al. 1995), and thus, the selection of a shell of optimum size and shape is essential for their survival. Hermit crab populations are limited by the availability, size and qual- ity of their shells (Vance 1972). Since they rely on empty shells and rarely predate on gastropods or remove the flesh from dead gastropods, hermit crabs compete intra- or interspecifically for the shell resource (Bach et al. 1976). Although the availability of empty shells may be subjected to advective forces such as tides and waves as well as the hermit crabs themselves, the co-occurring as- semblage of living gastropods typically reflects the availability of shells in intertidal mud habitats (Teoh and Chong 2014). In the western coast of Sabah, Malaysia, the heterogeneous environment of Sepangar intertidal flat (Figure 1) is characterized by distinct substrate zonation ranging from a mixture of sand-mud, gravels, rocks, coral rubbles to large rocky boulders. On the other hand, Sula- man mangrove fringe, which is located about 30 km northeast from Sepangar, is characterized by homogenous environment dominated by sand-mud substrate. Hermit crabs are one of the most conspicuous benthic macrofauna at both sites. However, the contrasting habitat set- Figure 1 Schematic diagrams of sampling design at (a) Sepangar and (b) Sulaman shores. tings appear to evoke different adaptations among the hermit crab species, possibly influencing their diversity, abundance and shell use pattern. In this study, spatial 49.80″) at Sulaman, both sites located in the State of distribution and shell use of the hermit crab commu- Sabah, Malaysia. A vast part of the intertidal rocky shore nity in Sepangar and Sulaman shores were quantified to at Sepangar is uncovered during spring low tide to ap- answer the following research questions: 1) Does a proximately 200 m from the highest tide mark. The structurally heterogeneous habitat host greater diversity Sulaman's mangrove area however has a lower, bare and and abundance of hermit crabs than homogeneous muddy zone of about 50 m from the mangrove fringe to habitat?2)Areshellsusedbyhermitcrabsmoredi- the sea which is completely exposed during spring low verse in a heterogenous habitat than homogeneous tide. Samplings were performed at both sites, each on habitat? 3) How are hermit crab species ecologically three separate occasions in December 2007 and January partitioned (distribution and shell use pattern) in rela- 2008 during spring low tide. tion to substrate zonation in the heterogenous habitat? At Sepangar shore, three 100-m transect lines were laid perpendicular to the shoreline 50 m apart between Methods transects. Along each transect line, five stations were Field work designated at intervals of 25 m. These stations were Field samplings were carried out in an intertidal rocky marked as 0, 25, 50, 75 and 100 m from the high-tide flat (N6°02′18.57″; E116°06′40.07″) at Sepangar Bay mark (Figure 1a). The 0 m marked the highest tide and fringing mangrove forest (N6°15′33.00″; E116°18′ mark. At each station, 1 × 1 m quadrate sampling in Teoh et al. Zoological Studies 2014, 53:67 Page 3 of 9 http://www.zoologicalstudies.com/content/53/1/67 triplicates were performed within a 5-m radius from Table 1 Substrate characteristics of each station along a each station point, taking care that unsampled quadrates transect line at Sepangar shore were not disturbed while sampling. All hermit crabs that Station (m) Substrate characteristics were found within each quadrate were collected starting 0 Narrow sandy strip bordered by sand-mud with from the sides of the quadrate to minimize escapement sparse gravels, rocks and coral rubbles of hermit crabs. A similar sampling method was 25 Sand-mud with sparse gravels, rocks and coral rubbles employed for Sulaman's bare mangrove zone, but given 50 Sand-mud overlain by dense gravels, rocks and its narrow shore width (maximum 50 m), 30-m transect coral rubbles lines were laid with three designated stations set 15 m 75 Gravels, rocks and coral rubbles apart (Figure 1b). The 0-m mark however marked the 100 Large boulders and coral rubbles lowest fringe of the mangrove forest. Substrates at the intertidal flat at Sepangar Bay were visually characterized based on the distinctive mixture of substrates present This analysis was performed using SPSS software version (Table 1) whereas the sediment at Sulaman's bare man- 12.0. Chi-square test at 5% significance level was per- grove zone was characterized as homogenously domi- formed to determine whether the distribution

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