The Galeta Oil Spill. I. Long-term Effects on the Physical Structure of the Mangrove Fringe

In April 1986, more than 75 000 barrels (1•5 × 107 l) of medium-weight crude oil spilled into Bahía las Minas on the central Caribbean coast of Panamá. Fringing mangroves were oiled on the adjoining open coast and in channels, lagoons, creeks and small man-made waterways within the bay. Changes in the physical structure of the mangrove fringe after oiling were documented over time. These included defoliation, limb loss and eventual collapse of dead trees. By 5 years after the spill, the length of shore fringed by mangroves was reduced at oiled sites relative to unoiled sites. Surviving trees at oiled sites had fewer and shorter submerged prop roots and a higher proportion of dead roots than trees at unoiled sites. These changes reduced the surface area of submerged prop roots by 33% on oiled open coast, 38% in channels and 74% in streams. Submerged prop roots serve as settlement surfaces for a diverse group of attached epibiota in an otherwise soft-bottom environment. Oil-induced reductions to this biogenic substratum thus negatively affected epibiotic communities of the mangrove fringe 5 years after the spill independently of any effects of hydrocarbons on the organisms themselves.