An Assessment of Shallow and Mesophotic Reef Brachyuran Crab Assemblages on the South Shore of O‘Ahu, Hawai‘I
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The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Coral Reefs DOI 10.1007/s00338-015-1382-z REPORT An assessment of shallow and mesophotic reef brachyuran crab assemblages on the south shore of O‘ahu, Hawai‘i 1 1,2,3 4 Kaleonani K. C. Hurley • Molly A. Timmers • L. Scott Godwin • 1 5 1 Joshua M. Copus • Derek J. Skillings • Robert J. Toonen Received: 1 February 2015 / Accepted: 27 November 2015 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract Shallow coral reefs are extensively studied but, communities. A total of 663 brachyuran crabs representing although scleractinian corals have been recorded to 165 m, 69 morphospecies (16 families) were found. Community little is known about other mesophotic coral reef ecosystem composition was not significantly different within depths, (MCE) inhabitants. Brachyuran crabs fill many ecological but was highly stratified by depth. Each depth was distinct, and trophic niches on reefs, making them ideal candidates but the 30 and 60 m depths were least dissimilar from one for evaluating species composition among depths to ask another. We show that deeper reefs host significantly dif- whether MCEs host the same communities as shallower ferent brachyuran communities, and at much lower total reef communities that have been well studied. Here we abundance, than shallow reefs in Hawai‘i, with 4–27 deployed autonomous reef monitoring structures for 2 yr on unique morphospecies per depth and only 3 of 69 mor- the south shore of O‘ahu along a depth gradient (12, 30, 60, phospecies (*4 %) occurring across the entire depth range and 90 m) to sample and assess brachyuran crab sampled. Keywords Biodiversity Depth gradient Cryptic fauna Á Á Á Communicated by Biology Editor Dr. Mark J. A. Vermeij Autonomous reef monitoring structures (ARMS) Electronic supplementary material The online version of this article (doi:10.1007/s00338-015-1382-z) contains supplementary material, which is available to authorized users. Introduction & Kaleonani K. C. Hurley Tropical coral reefs are among the most biodiverse and [email protected] productive ecosystems in the world (Moberg and Folke 1 1999; Roberts et al. 2002; Knowlton et al. 2010). A vast The Hawai‘i Institute of Marine Biology, University of Hawai‘i at Ma¯noa, Coconut Island, P.O. Box 1346, Kaneohe, majority of coral reef studies to date have focused on HI 96744, USA shallow habitats of B40 m due to the physiological 2 Joint Institute for Marine and Atmospheric Research, restrictions placed on divers using SCUBA, but coral reefs University of Hawai‘i at Ma¯noa, 1000 Pope Road, MSB 312, extend well beyond SCUBA depth limits (Maragos and Honolulu, HI 96822, USA Jokiel 1986; Kahng et al. 2010). Mesophotic coral reef 3 Ecosystem Sciences Division, Pacific Islands Fisheries ecosystems (MCEs) occur in the deeper parts of the photic Science Center, National Oceanic and Atmospheric zone (30 to [150 m) and are predominantly characterized Administration, 1845 Wasp Boulevard, Building 176, by light-dependent corals and algae (Hinderstein et al. Honolulu, HI 96818, USA 4 2010). Office of National Marine Sanctuaries, Papaha¯naumokua¯kea Studies to date examining MCEs have primarily focused Marine National Monument, National Oceanic and Atmospheric Administration, 1845 Wasp Boulevard, on fish or the dominant sessile taxa, including sponges, Building 176, Honolulu, HI 96818, USA macroalgae, and scleractinian corals (Lesser et al. 2009; 5 Brooklyn College, 2900 Bedford Avenue, Brooklyn, Bongaerts et al. 2010; Kahng et al. 2010, 2014). A range of NY 11210, USA physical and biological mechanisms results in depth 123 Author's personal copy Coral Reefs zonation of coral reef ecosystems, but such studies are plate, which is affixed to the seafloor (Fig. 2b). Three likewise limited to these same groups (e.g., Wellington ARMS each were deployed at three sites spaced 20 m apart 1982). Despite the overwhelming research focus on these at 12 m in 2009 and retrieved in 2011 (total of 9 units at charismatic taxonomic groups, it is well known that fish 12 m). Six ARMS were deployed at each 30-, 60-, and and reef-building taxa make up only a small portion of the 90-m mesophotic site in 2010 and retrieved in 2012. After total biodiversity; the larger portion of reef organisms is a 2-yr soak period, ARMS were removed from the benthos comprised of cryptic reef dwellers (Small et al. 1998; by encapsulating the unit within a 100-lm mesh-lined crate Fautin et al. 2010; Knowlton et al. 2010). Because so few that prevented motile organisms from escaping (Fig. 2c). studies target cryptic reef fauna, however, it remains Once at the surface, ARMS were transported to shore and unknown how the ecology and diversity of these species placed into a container full of seawater where the mesh- change across reefs, across latitude, or with increasing lined crate was removed and the unit was systematically depth (Fautin et al. 2010; Leray and Knowlton 2015). disassembled plate-by-plate. Seawater from the disassem- The shallow coral reefs of Hawai‘i have been exten- bly container was filtered using 2-mm, 500-lm, and sively studied (reviewed by Jokiel 1987; Kay 1994; Ziegler 100-lm geologic sieves (see Leray and Knowlton 2015 for 2002; Bahr et al. 2015), and although scleractinian corals ARMS processing details), and organisms obtained were have been recorded in mesophotic zones to 150 m (south of preserved in 95 % ethanol for future studies. Adult Hawai‘i Island; Kahng and Maragos 2006), little is known brachyurans (C5 mm) were photographed, identified, about cryptic reef inhabitants that make up the vast assigned a sample number, and preserved in 95 % ethanol majority of marine biodiversity, including dominant taxa (Fig. 2d) and were sent to the Bernice Pauahi Bishop such as brachyuran crabs (Bickford et al. 2007; Fautin et al. Museum for curation (Honolulu, HI, USA). 2010). Brachyurans are ubiquitous members of reef com- munities that fill many trophic niches (Plaisance et al. Data analysis 2011) and are among the most species-rich inhabitants of the benthic community. Because of their abundance and Brachyuran species lists and counts were collated for each ecological importance on tropical coral reefs (Costello ARMS unit and summary statistics on abundance and et al. 2010; Fautin et al. 2010; Knowlton et al. 2010), family distributions were obtained in R v3.1.3 (R Core brachyurans make ideal candidates for the investigation of Team 2015). Although megalopae were present in some cryptic reef infaunal biodiversity. The objective of this ARMS units, they were not included in analyses. Species study was to characterize the abundance and diversity of variability among ARMS at a single depth and among brachyuran crab assemblages across a depth gradient. We depths at a single site was assessed using canonical anal- test the hypothesis that brachyuran crab assemblages are ysis of principal coordinates (CAP), permutational analysis comparable across the depth gradient from 12 to 90 m. of variance (PERMANOVA), and permutational analysis of dispersion (PERMDISP) on Bray–Curtis similarity of square-root-transformed ARMS species abundance data in Materials and methods PRIMER v6 PERMANOVA software (Clarke and Gorley 2006; Anderson et al. 2008). Although this program allows Sample collection for accurate analyses of unbalanced designs, we addition- ally conducted CAP, PERMANOVA, and PERMDISP Standardized collecting and marine biodiversity measuring tests on the abundance data across depths randomly tools called autonomous reef monitoring structures removing three of nine ARMS from 12-m sites to compare (ARMS) were deployed by divers in shallow and meso- with tests on all data from all ARMS (6 units per depth). photic coral reef sites along a depth gradient on the south CAP constrains ordination that is based on distance or shore of the island of O‘ahu, Hawai‘i (Fig. 1). ARMS are dissimilarity measures (Anderson and Robinson 2003; long-term collecting devices designed to mimic the struc- Willis and Anderson 2003). CAP using Bray–Curtis dis- tural complexity of a coral reef and attract colonizing tance and 9999 permutations was used to visualize differ- motile and sedentary marine taxa (Brainard et al. 2009; ences between crab assemblages at each depth. To identify Knowlton et al. 2010; Plaisance et al. 2011; Leray and which crabs characterize differences among groups, vec- Knowlton 2015). They are composed of 10 gray, type 1 tors were imposed based on Spearman rank correlations of PVC plates (23 cm 9 23 cm) stacked in an alternating individual species. PERMANOVA and PERMDISP were series of open and semi-enclosed layers with the topmost also based on Bray–Curtis similarity and 9999 permuta- layer composed of medium-density polypropylene filter tions. CAP, PERMANOVA, and PERMDISP using the media pads (Matala USA, Laguna Hills, CA) (Fig. 2a). Jaccard index were also run for comparison with Bray– This tier of plates is attached to a 35 cm 9 45 cm base Curtis similarity measures. While both Bray–Curtis 123 Author's personal copy Coral Reefs Fig. 1 Map of the south shore of O‘ahu, Hawai‘i, with autonomous reef monitoring structure (ARMS) deployment sites.