ASSESSING ON-SHORE RUBBLE CORAL DEPOSITS FOR PALAEOECOLOGICAL REEF ANALYSIS IN THE BAY OF WRECKS, KIRITIMATI ISLAND

Storm-derived rubble deposits of reef building corals on Kiritimati Island are an abundant resource and important archive for paleoclimate reconstruction for the central tropical Pacific. The coral rubble deposits along the windward shore of the Bay of Wrecks extend back hundreds of meters, forming well defined ridges that date back to over 4,000 years old, providing a unique environment to understand reef evolution from the mid- to late Holocene. Most palaeoecological reef analyses assume the fossil coral deposits represent the reef ecology; however, this assumption is based on reef terraces where large portions of Pleistocene or Holocene reefs are preserved intact. Here, we aim to determine if the coral rubble deposits immediately adjacent to the shoreline represent the reef building corals in the Bay of Wrecks. We placed five transects each five meters long along the most modern ridge deposit in the Bay of Wrecks (radiocarbon dated to the modern time period or post 1950 CE). We took photographs of a 0.5 x 0.5-meter grid every half meter along both the landward and seaward sides of the transect. Each pixel in the photograph was prescribed a coral genus to calculate the percent coverage for direct comparison with modern coral reef survey data previously collected in 2007. Initial results show there is a bias in the preservation of more dense coral structures. Percent coverage data from the modern rubble field photos show genus Astreopora, an Acroporidae coral with a dense skeletal structure, occupying consistently more than 80% of the rubble field. Modern reef survey data show Astreopora only occupies 4-5% of the reef, while more brittle corals that are dominant on the reef, such as Acropora or Montipora, are vastly underrepresented or absent from the rubble deposits. This is likely due to a bias is preservation as the more brittle corals (branching and table shaped) are continually broken down through intense wave action on the windward side of the island, favoring the preservation of denser and more mound-shaped corals as they are moved onshore. This bias could potentially affect robust palaeoecological surveys from fossil coral rubble deposits.