Total volume of 3D small patch reefs reflected in aerial photographs can predict total species richness of coral reef damselfish assemblages on a shallow back reef

Ecol Res (2015) 30: 675–682 DOI 10.1007/s11284-015-1268-0 O R I GI N A L A R T IC L E Akihisa Hattori • Takuro Shibuno Total volume of 3D small patch reefs reflected in aerial photographs can predict total species richness of coral reef damselfish assemblages on a shallow back reef Received: 19 May 2014 / Accepted: 8 April 2015 / Published online: 22 April 2015  The Author(s) 2015. This article is published with open access at Springerlink.com Abstract Because fish have a high dispersal ability, an understanding coral reef fish metacommunity structure is vital for effective conservation. Coral reefs provide patchy habitat of various sizes and scales. We examined the species–area relationship (SAR) of damselfish (Pomacentridae) assemblages over 81 environmentally homogenous patch reefs ranging 0.07–45.4 m2 with low coral cover. Patch reefs were located in the shallow back reef (<2.5 m deep) off Ishigaki Island, Japan. Reef area was measured by performing image analysis of enlarged sections of a high-resolution (>1/2500) color aerial photograph used as a fine-scale seascape map. To assess the effects of three-dimensional meso-scale rugosity on species richness, we assumed that all reefs had a cylindrical shape and examined species by volume (area · height) relationships (SVR). Patch reef volume was a better determinant of species richness than area, and the regression functions of SVR provided better estimates of patch reef species richness. Neither the observed SVRs nor SARs, however, could be explained by a random placement model alone. Our results suggest that several small reefs are likely to have higher species richness than a single large reef of equivalent area in the shallow back reef where large patch reefs are flat. Thus, total patch reef volume (area · height) better reflects meso-scale rugosity and is a useful indicator of total species richness relative to the total amount of essential habitat in shallow back reefs. Keywords Meso-scale rugosity Æ Metacommunity Æ Seascape structure Æ SLOSS Æ Species–area relationships A. Hattori (&) Faculty of Liberal Arts and Education, Shiga University, 2-5-1 Hiratsu, Otsu, Shiga 520-0862, Japan E-mail: T. Shibuno Aquaculture Department, Southeast Asian Fisheries Development Center, 5021 Tigbauan, Iloilo, Philippines Introduction Unlike terrestrial animals, an understanding of metacommunity structure is vital for the conservation of sedentary marine animals because they have a dispersive larval phase that enables use of discrete habitat patches (Roff and Zacharias 2011). Coral reefs form patchy habitats for sedentary marine animals on various scales, and coral reef fish communities are among the richest animal communities in nature (Lowe-McConnell 1987; Sale 1991, 2002; Boström et al. 2011; Pittman et al. 2011). Although patterns of reef connectivity and patch dynamics are not well understood for reef fish (Christie et al. 2010; Mumby et al. 2011), evidence suggests that larval connectivity between habitat patches within a coral reef area is high (e.g., Almany et al. 2007; Planes et al. 2009; Pinsky et al. 2012). The back reef is an essential component of a coral reef, harboring many resident reef fish (Chave and Eckert 1974; Lowe-McConnell 1987). Back reefs are often less than 3 m deep and consist of numerous small patch reefs formed by coral heads and outcrops dispersed throughout the sandy bottom. These patch reefs of various sizes offer a valuable means of studying the metacommunity structure of coral reef fish on a small spatial scale. The species–area relationship (SAR) is a useful tool for terrestrial conservation because it allows an estimate of an important variable (species richness) to be made from another variable (area) that is easily measured (Rosenzweig 1995, 2004; Tjörve 2003; Dengler 2009; Smith 2010). Fahrig (2013) suggested that species richness does not increase in several small habitats relative to a single large habitat of equivalent area, but that total area, no matter how subdivided, is the crucial determinant of species richness. In contrast, Rosenzweig (2004) suggested that this single large or several small (SLOSS) debate may matter at small spatial scales because of edge effects and metapopulation dynamics. On very small 676 scales, superior competitors can avoid using patch edges where predation risk is higher (Ries and Sisk 2010), and superior dispersers or colonizers can move among habitat patches using small patches and patch edges to avoid interspecific competition (Tilman 1994; Lehman and Tilman 1997; Hattori 2002). Thus, multiple species with similar habitat requirements may coexist in a patchy habitat via interspecific trade-offs between dispersal/colonization and competitive abilities (Tilman 1994; Lehman and Tilman 1997). Marine ecologists examining the SAR in coral reef fishes across small patch reefs dispersed throughout a sandy bottom have found greater species richness in larger patch reefs (Sale and Steel 1986; McClanahan 1994; Ault and Johnson 1998; Acosta and Robertson 2002; Chittaro 2002). These findings suggest that high fish species richness on large reefs may be caused by high coral cover and topographic complexity in addition to the large area. Even if there are no differences in complexity between habitat patches, the random placement model holds that more species may be found on larger reefs simply because they may randomly accumulate larger numbers of settling species (Coleman 1981; Simberloff and Gotelli 1984). Belmaker et al. (2007) demonstrated clearly that, on a small scale, the observed SAR in coral reef fish can be reproduced using random placement model simulations (RPMS). In contrast, Harborne et al. (2012) highlighted the important influence of coral-generated meso-scale rugosity on reef fish species abundance and diversity, where tall reefs (>0.5 m) harbor more species than flat reefs. Accordingly, several small but tall reefs may harbor more species than a single flat (and short) reef of equivalent area. Moreover, interspecific trade-offs between dispersal and competitive abilities may affect the SAR in coral reef fish on very small spatial scales. Thus, the relationships among species richness, patch reef area (size distribution and total area), habitat complexity (coral cover and three-dimensional meso-scale rugosity) and the random placement model remains uncertain. To determine whether single large or several small patch reefs (both in the size-distribution and the total patch reef area) affect the total species richness of fish on shallow back reefs, Hattori and Shibuno (2010) examined SARs in damselfish (Pomacentridae) assemblages on 84 small patch reefs with similar levels of low coral cover off Ishigaki Island, Okinawa, Japan. They performed RPMS to compare SARs simulated with random placement with observed SARs. Species richness was found to increase linearly with log-transformed patch reef area, but observed species richness on the largest reefs was much lower than that ex (...truncated)