Porites growth characteristics in a changed environment: Misima Island, Papua New Guinea

The construction in 1988 of an open-cut gold mine and ore-processing facili ty at Misima Island, Papua New Guinea, resulted in disturbance of the adjac ent fringing coral reef, mostly because of large increases in sedimentation . This provided an opportunity to examine whether growth characteristics of the major reef-building coral, Porites, changed in response to this sudden and sustained increase in sedimentation. Annual variation in skeletal dens ity was measured in 93 colonies variously affected by sedimentation. The co lonies provided data for average annual density, annual extension and annua l calcification covering the periods 5 y before and 5 y after mining operat ions began. The average depth of skeleton occupied by tissue (tissue layer thickness) was also measured for most colonies. There was high mortality of Porites in regions strongly affected by increased sedimentation. In coloni es that survived, density, extension and calcification tended to be less (i n some cases significantly) in the period after mining operations began com pared with pre-construction levels. However, these decreases were not linke d with proximity to the mine site and probably reflect a regional-scale res ponse of Porites growth to some other environmental change. This suggests t hat periods of high sedimentation may not be recorded by the growth charact eristics of massive Porites. Average growth characteristics of surviving Po rites from Misima Island were similar to those from inshore reefs of the no rthern Great Barrier Reef (GBR). Tissue layer thickness in Porites from the control areas at Misima Island were also similar to colonies from the nort hern inshore GBR reefs. However, tissue layer thickness significantly decre ased with increased proximity to the mine site at Misima Island.