The mangroves of the North Pacific of Costa Rica are among the most altered coastal ecosystems in the country. Scientific information about their physiology, ecology, structure, and geochemistry is limited. This study analyzed the structural complexity and species composition of Potrero Grande and Santa Elena mangrove forests. Two visits were carried out to each mangrove between May and June 2012. The Point-Centered Quarter Method was used to determine forest structure. Mangrove species, height, diameter at breast height, and canopy density were noted at multiple points along transects. Associated fauna and cover of epiphytic macroalgae were recorded when present. Interstitial water salinity was determined at each point. Basal area, dominance, importance value, and density were calculated for each mangrove species and complexity index for the forests. Rhizophora racemosa had the highest relative dominance and importance value at both sites. Santa Elena had the highest complexity index (CI=26.9), this could be due to the high density found. Potrero Grande mangrove is one of the best developed mangrove forests on the Pacific coast of Costa Rica, given its structural characteristics (relatively tall trees and high tree trunk diameters) and species composition. While Pelliciera rhizophorae was known to have reached its northern limit at the Potrero Grande mangrove; this study extends its distribution further north for the Pacific coast of Costa Rica. Unlike Potrero Grande, Santa Elena is not adjacent to a marine protected area, resulting in uncontrolled extraction and tourism activities within Santa Elena Bay. The creation of a marine protected area in Santa Elena Bay is recommended to provide enhanced protection to this ecosystem. Rev. Biol. Trop. 62 (Suppl. 4): 33-41. Epub 2014 Diciembre 01.

Keywords: Potrero Grande, Santa Elena Bay, forest structure, The Point-Centered Quarter Method