Large scale damage to mangrove forests following two large oil spills in Panama

Mangrove forests of Bahía Las Minas on the Caribbean coast of Panama were affected by large oil spills twice over the last 30 yr. Lethal and sublethal damage to these mangroves by the two spills was assessed on aerial photographs and in the field. The first spill occurred in 1968 when the tanker Witwater broke-up and sunk, releasing 2.8-3.8 million liters of diesel oil and Bunker C fuel oil, and killing 49 ha of mangroves or 4 percent of mangroves in the bay. The second was in 1986 when a land tank at the Refinería Panamá ruptured, releasing at least 8 million liters of crude oil, and killing 69 ha of mangroves or 6 percent of those in the bay. In each case, the areas affected most were the low to mid intertidal zone dominated by Rhizophora mangle. The extent and location of deforestation was site- and spill-specific, notably influenced by prevailing wind and tidal conditions. Some areas were deforested twice. Possible sublethal damage to surviving forests was assessed for the 1986 spill, noting that areas of unusually 'open' canopy exceeded 307 ha. Field studies, reported elsewhere, confirmed that canopy leaf biomass decreased in 'open' canopy sites where oil concentrations in surrounding sediments increased. Therefore, in 1986, a further 34 percent of mangrove forests in the bay probably suffered damage from oiling, and the sum of these partially damaged forests plus the deforested areas more closely represents the total area of damage. It appears that only 18 percent of trees oiled in this bay eventually died, and the total area of damaged mangroves after the large 1986 oil spill was 5-6 times greater than the deforested areas alone