Effects of an oil spill on some organisms living on mangrove (Rhizophora mangle L.) roots in low wave-energy habitats in Caribbean Panama

Abstract Following the discharge of more than 50000 barrels of crude oil into a tropical, mangrove-fringed estuary, we examined the effects of oiling on the epibiota of mangrove (Rhizophora mangle) prop roots. Using data taken four years before the spill and for a year after the spill, we assessed the possible value of four bivalves and one barnacle as indicators of damage from oiling. Quarterly comparisons of abundances at matched oiled and unoiled sites showed strong indirect evidence of population reductions in six of seven comparisons. However, the shells of only two species persisted long enough on roots (3–6 months) to be useful direct indicators of recent mortality. Knowledge of conditions four years before oiling was important in establishing the extent of damage from this oil spill. Population reductions were most striking in brackish streams, where intertidal and subtidal mussels and barnacles were quickly devastated at oiled sites and showed no recovery during the year after the spill, and for an intertidal oyster in channels and lagoons. All other species showed at least some negative effects of oiling, but the strength of the evidence varied over time and among species.