Chronic oiling and long-term effects of the 1986 Galeta spill on fringing mangroves

In April 1986, more than 50,000 barrels of crude oil spilled into Bahia las Minas on the central Caribbean coast of Panama, oiling reef flats, sea grasses, coral reefs and mangroves. In August 1986, the authors began a five-year study on the red mangrove (Rhizophora mangle L.) fringe and the plants and animals that live attached to submerged prop roots. This habitat forms an important part of near shore, tropical nursery grounds. In three habitats (wave-washed open shores, channels and lagoons, and interior drainage streams), oil initially coated virtually the entire surface of submerged prop roots and sank more than 20 cm into sediments. Secondary re-oiling was heaviest in sheltered drainage streams where oil continuously leached from sediments, but also occurred on the open coast and in channels. Bivalves in channels and streams were heavily contaminated through at least May 1991. Results show this spill was a chronic source of oil contamination rather than a single point-source event. The epibiota of submerged mangrove roots had not recovered completely in any habitat after five years. Independent of this reduction, the structure of the mangrove fringe significantly changed after oiling, including decreases in the amount of shore fringed with mangroves and in the density and size of submerged prop roots. Overall, the surface area on submerged mangrove roots decreased by 33 percent on the open coast, 38 percent in channels and 74 percent in stream. The combination of chronic re-oiling, damage to epibiotic assemblages, and reductions in the biogenic substrate (submerged prop roots) has decreased the productivity of this tropical nursery area and suggests recovery will be a complex and prolonged process