The Manzanilla barrier beach at Cocos Bay has been undergoing marine erosion for decades due to its position against the high energy environment of the Atlantic Ocean. The barrier beach borders the Ramsar listed freshwater Nariva Swamp, offering protection from the marine environment whilst helping to maintain the delicate ecosystem in the wetland. Visible ongoing coastal erosion at this beach threatens the longevity of this internationally protected wetland. Previous studies of coastline erosion at this beach have been restricted to the analysis of beach profile data over short time periods. This paper examines the evolution of the coastline over a 36 year time period from 1958 to 1994. Digital analysis of shorelines from 1958 and 1994 aerial photographs permitted the identification of areas where erosion or deposition was the dominant process over a 36 year time period. Identification of these areas of coastal change, allowed for the lateral extent of erosion or deposition to be quantified using the Digital Shoreline Analysis System (DSAS 4.0). These calculations gave an insight into the long-term rates of erosion and deposition operating within the bay. Direct coastal measurements were also made in the short-term as a calibration of the rates of erosion and deposition from the longer-term GIS analysis. The long-term GIS analysis revealed much slower erosion rates than previously reported in short-term studies. Results indicate that analyzing short-term erosion rates alone may exaggerate the true rates of erosion at this bay.