Contents lists available at ScienceDirect Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind Functional potential of coral assemblages along a typical Eastern Tropical Pacific reef tract Rafael A. Cabral-Tena a , Andrés López-Pérez b, ⁎ , Lorenzo Alvarez-Filip c , F. Javier González-Barrios a,c , Luis E. Calderon-Aguilera a , Cuauhtémoc Aparicio-Cid d a Departamento de Ecología Marina, Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California, México b Departamento de Hidrobiología, Universidad Autónoma Metropolitana – Iztapalapa, Ciudad de México, México c Biodiversity and Reef Conservation Laboratory, Unidad Académica de Sistemas Arrecifales, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Puerto Morelos, México d Ecosistemas Costeros y Marinos A.C., Huatulco, Oaxaca, México ARTICLE INFO Keywords: Huatulco Structural complexity Reef functional index Coral calcification rate Functional traits Coral reefs ABSTRACT Coral reefs are considered to be valuable ecosystems due to the goods and services that they provide. However, these ecosystem services are highly dependent on the physical structure of the reef, which in turn depends on the species composition of hermatypic corals. In this study, we explored the functional potential of reefs with a new index that takes into account coral cover, the calcification rate, rugosity, and the height of each species. In June 2019, we surveyed 11 reefs from the southern Mexican Pacific (15°40′N, 96°29′W-15°45′N, 96°5′W) to estimate coral cover and collect quantitative morphometric data of ~15 haphazardly selected coral colonies per site (N = 102). We estimated the calcification rates and structural complexity of the species present and then calculated the Reef Functional Index (RFI), which estimates the species-specific functional contribution of the corals in reef systems by integrating their capacity to create complex three-dimensional structures through calcium carbonate precipitation with morphological complexity. We modelled the effects of shifting species compositions through a permutation approach with 6435 possible combinations. We found a mean coral cover of 48.5 ± 18.09% ( ± SD) dominated by Pocillopora damicornis, Pocillopora verrucosa, and Pocillopora capitata and low abundance of Porites panamensis and Pavona gigantea. The mean RFI was 0.71 ± 0.1. The permutation model showed that the RFI was very close to its maximum potential (96%) when the relative abundance of pocilloporids was ≥60% and decreased as the relative abundance of massive corals increased. At maximum evenness, the RFI value was at 92% of its maximum potential. Our data highlight the importance of pocilloporids to the functioning of reefs in the Eastern Tropical Pacific (ETP) and confirm that P. damicornis is the primary reef builder in the region. Nevertheless, our findings also highlight the vulnerability of these reefs given that branching corals are more susceptible to environmental disturbance than slow-growing massive corals. In a rapidly changing environment, the future of ETP reefs depends not only on the survival of pocilloporids but also on the ability of coral reefs to withstand highly variable oceanographic conditions as complete ecosystems. 1. Introduction Coral reefs are socially, economically, and ecologically valuable, providing environmental services worth more than US $352,000 ha -1 year -1 (Costanza et al., 1998; de Groot et al., 2012). Coral reefs develop thanks to the ability of stony corals to deposit calcium carbonate while building their skeletons and form complex three-dimensional structures as they grow (Carricart-Ganivet et al., 2012; Norzagaray-López et al., 2015). Moreover, corals contribute to a range of critical ecosystem functions, which may be redundant (i.e., shared by more than one species), including providing structural complexity and habitats, nutrient cycling, and energy production (Veron, 2000; Hughes et al., 2018; González-Barrios and Álvarez-Filip, 2018; McWilliam et al., 2018). While species diversity or abundance analyses cannot be reliably used to understand community responses to a given disturbance, a functional trait-based approach can help to quantify, predict, and better anticipate the ecological impacts of dis- turbances (McGill et al., 2006; Villéger et al., 2011; Mouillot et al., 2013). The identification of functional traits and groups can help re- searchers understand and measure functionality in a reef environment https://doi.org/10.1016/j.ecolind.2020.106795 Received 26 June 2020; Received in revised form 26 July 2020; Accepted 30 July 2020 ⁎ Corresponding author. E-mail address: alopez@xanum.uam.mx (A. López-Pérez). Ecological Indicators 119 (2020) 106795 1470-160X/ © 2020 Elsevier Ltd. All rights reserved. T