Identifying and assessing evidence for recent shoreline change attributable to uncommonly rapid sea-level rise in Pohnpei, Federated States of Micronesia, Northwest Pacific Ocean

Those parts of the northwest Pacific Ocean where sea level has been rising fastest over the past few decades include islands in the Federated States of Micronesia. To understand the possible effects of rapid sea-level rise, coastal surveys were undertaken within Pohnpei State in October 2014. The high volcanic island of Pohnpei was targeted along with 10 reef-edge island groups on its surrounding barrier reef as well as islands on Ant Atoll, 15 km southwest. Evidence of shoreline erosion attributable to sea-level rise is found only in a few places along the main island’s northeast (windward) coast. High rainfall has led to the accumulation of terrestrial sediment along the coast that is covered with mangrove forest 2–3 km broad in places shielding the island’s coast from wave erosion. A different picture is found on reef-edge islands around which erosion over the last few decades can mostly be explained by recent sea-level rise. Islands have disappeared within living memory, others drastically reduced in size in the past decade, while others – their sand cover washed away – are being reduced to a skeletal (boulders anchored by mangrove) state. The coasts of Ant Atoll appear little affected by erosion ascribable to sea-level rise. In summary, fewer effects than might be expected from recent sea-level rise were seen in Pohnpei, largely for reasons of natural coastal resilience or a lack of record, especially for reef-edge islands. The importance of mangrove conservation and an understanding of sediment dynamics on the broad reef-lagoon shelf surrounding the main island is manifest