BULLETIN OF MARINE SCIENCE, 85(1): 27–43, 2009 27 Bulletin of Marine Science © 2009 Rosenstiel School of Marine and Atmospheric Science of the University of Miami DISTRIBUTION OF MANGROVES ALONG ENVIRONMENTAL GRADIENTS ON SAN ANDRéS ISLAND (COLOMBIAN CARIBBEAN) Ligia E. Urrego, Jaime Polanía, Maria F. Buitrago, Luisa F. Cuartas, and Alvaro Lema ABSTRACT Species richness and distribution along environmental gradients in mangroves have been linked to abiotic and eco-physiological factors. e small surface area of San Andrés Island, Colombia, the relatively low environmental variability, as well as the lack of permanent freshwater courses may prevent the formation of a zonation pattern, leading to a homogeneous composition and structure of the forests. e goal of this study was to evaluate the mangrove types, including their structure and ﬂoristic composition under the inﬂuence of ﬁve environmental factors. e primary relationships among tree species and ﬂooding levels, salinity, pH, soil depth, and soil texture were investigated along 86, 500-m 2 plots established across 20 transects throughout the San Andrés Island shoreline. Canonical Correspondence Analysis identiﬁed four mangrove groups, with the ﬁrst two canonical axes explaining 65% of the variation in the data. e grouping of species along those axes was mainly associated with inundation level and soil depth. Two mangrove groups were classiﬁed as fringe mangroves that grow on highly saline and relatively shallow soils under the direct inﬂuence of tides. e remaining two were classiﬁed as riverine mangroves that grow on lower salinity soils inﬂuenced by sporadic freshwater ﬂows and isolated from direct tidal inﬂuence. Rhizophora mangle L. was present in the four mangrove groups but, on the highest saline soils where fringe mangroves grew, Avicennia germinans (L.) L. was dominant. In riverine mangroves, Laguncularia racemosa (L.) Gaertn., and Conocarpus erectus L. were the most important species. Mangroves, or mangrove forests, are associations of trees and shrubs, with mor- phological, physiological, and reproductive adaptations that allow them to grow in a complex environment that includes high salinity water, waterlogged soils, and peri- odic inundations by tides (Hogarth, 2007). Mangrove species tend to form discrete zones or bands perpendicular to the shoreline in response to physical gradients cre- ated by the interaction of these environmental factors. ese bands have been ob- served as far back as the 1940s (see Davis, 1940), especially for Caribbean mangrove ecosystems. Species richness, vegetation structure, and mangrove distribution either in these zones or along environmental gradients have been linked to abiotic and eco-physio- logical factors (Smith III, 1992; Krauss et al., 2008). e main abiotic factor, salinity, co-varies with many other environmental variables at diﬀerent spatial scales includ- ing geomorphology, height and amplitude of tides, hydrology, freshwater seepage, lo- cal topography, and drainage (om, 1967; Lugo and Snedaker, 1974; López-Portillo and Ezcurra, 1989; Ball, 1998; Matthijs et al., 1999; Dahdouh-Guebas et al., 2002a; Satyanarayana et al., 2002; Krauss et al., 2006). Propagule distribution and predation, population dynamics, and succession processes can be considered eco-physiological factors (Hogarth, 2007; Krauss et al., 2008). Besides additional factors such as tem- perature, CO 2 and sea level rise recently have been highlighted as important drivers for mangrove establishment and persistence (Krauss et al., 2008).