OCEAN LIFE Volume 4, Number 2, December 2020 E-ISSN: 2580-4529 Pages: 51-62 DOI: 10.13057/oceanlife/o040201 Physicochemical factors influencing zonation patterns, niche width and tolerances of dominant mangroves in southern Oriental Mindoro, Philippines AARON FROILAN M. RAGANAS 1,♥ , DAMASA B. MAGCALE-MACANDOG 2 1 Department of Biological Sciences and Environmental Studies, College of Arts and Sciences, University of the Philippines Mindanao, Mintal, Davao City 8022, Philippines. Tel.: +63-82-293-0302, Fax.: +63-82-293-0312,  email: amraganas@up.edu.ph 2 Institute of Biological Sciences, College of Arts and Sciences/School of Environmental Science and Management, University of the Philippines Los Banos, College 4031, Laguna, Philippines Manuscript received: 9 June 2020. Revision accepted: 29 August 2020. Abstract. Raganas AFM, Magcale-Macandog DBM. 2020. Physicochemical factors influencing zonation patterns, niche width, and tolerances of dominant mangroves in southern Oriental Mindoro, Philippines. Ocean Life 4: 51-62. Physicochemical factors are known for having strong influence on the spatial patterns and structural complexity of mangroves. In this regard, we aimed to contribute to filling up this information gap in the six mangrove ecosystems on the southern coast of Oriental Mindoro, Philippines. In each of the six mangrove ecosystems, the dominant mangrove species were identified in four mangrove ecotypes - seaward, riverine, middle, and landward - using a stratified random sampling method for vegetation survey. Physicochemical parameters of water, air and soil were also obtained from these ecozones. Results of the Principal Component Analysis revealed that temperature and water salinity are the factors that show strong influence on the spatial distribution of the dominant mangrove species. Canonical Correspondence Analysis revealed that Avicennia marina, Sonneratia alba and Rhizophora apiculata, are species associated with a highly saline environment, while Xylocarpus granatum, Ceriops decandra, Avicennia rumphiana, and Rhizophora mucronata are species associated with low to optimum saline environment. Most of these dominant species preferred ecotypes with low to optimum salinity levels as revealed by their individual niche width and tolerances. The different adaptations and dominance of these mangrove species provide insights in the identification of appropriate species that could be used as planting materials for the rehabilitation endeavours of the respective mangrove ecosystem. Keywords: Dominant mangrove species, ecotypes, physicochemical factors, stratified random sampling, zonation patterns Abbreviations: CA: Correspondence Analysis, CCA: Canonical Correspondence Analysis, CI-III: Dendrogram clusters, cm: centimeter, DO: Dissolved Oxygen, lux: amount of illumination, LZ: Landward Zone, MZ: Middle Zone, PAST: Paleontological Statistics, PCA: Principal Component Analysis, pH: degree of acidity and basicity of soil and water, ppm: parts per million, psu: practical salinity unit, RH: Relative humidity, RZ: Riverine Zone, SA: Marine water category classified as “protected marine waters”, SZ: Seaward zone INTRODUCTION In many environmental settings, the physicochemical factors are among the most important parameters that regulate the structural characteristics of a plant community. In the mangrove environment, physicochemical factors have a great influence on the structural development and productivity of the ecosystem (Das et al. 2019). The physiological tolerance of different mangrove species to waterlogging, salinity, sulfides, nutrients, sedimentation, soil texture, nutrients, and redox potential have been linked with their structural and distribution patterns (Cardona and Botero 1998; Sherman et al. 1998; Das et al. 2019). The development of each mangrove species is influenced by the physicochemical characteristics of soil, which may compromise their growth and structure (Perera et al. 2013; Harahap et al. 2015; Bomfim et al. 2018). Perhaps, the soils and mangrove vegetation have a strong interaction with each other, resulting in the formation process of both the soil and the characteristic of the growing mangrove plants (Bomfim et al. 2018). Among the aforementioned physicochemical factors, salinity is considered as the limiting factor that has a critical role in the establishment and productivity of mangroves, aside from the influence inflicted by human and other biotic factors (Ball 2002; Feller et al. 2010; Kodikara et al. 2018). The variations in the salinity of water and the corresponding ability of different mangrove species to adapt in saline conditions have significant contribution to their growth and distribution patterns (Bomfim et al. 2018). Mangroves growing in habitats with lower salinity are likely to grow more rapidly than those living in the highly saline habitat (Perera et al. 2013). The differences in the mangrove environment conditions can result in the dominance of a particular species leading to their habitat differentiation. Water quality is also among the parameters that provide basic scientific information in understanding the physical and chemical influences in the mangrove environment (Mariappan et al. 2016). The patterns of tidal inundation in