Benthic Foraminifera from the Chuuk Lagoon Atoll System (Caroline Islands, Pacific Ocean)

The Chuuk Lagoon Atoll in the Caroline Islands system is located near the hotspot of tropical marine shallow-water diversity and adjacent to the global reef carbonate production center. It consists of a set of larger islands and smaller islets that are arranged in a triangular lagoonal atoll system surrounded by a protective reef barrier. This area constitutes an important biogeographic link between the Coral Triangle and other eastern Pacific Islands chains such as the Society, Marshall, Gilbert or Cook Islands. The Chuuk Islands also represent an area from which modern benthic foraminifera are virtually unknown. This study documents benthic foraminiferal assemblages from lagoonal habitats within the Chuuk Atoll to complete the record along the W-E Pacific biodiversity gradient and to assess their biogeographic relation to adjacent faunal provinces. Our analysis and systematic survey documents that shallow-water lagoonal sediments harbour diverse assemblages of at least 104 species of benthic foraminifera. The complete fauna is identified to species level and fully illustrated by scanning electron microscopy. Faunal comparisons of larger symbiont-bearing taxa with neighbouring biogeographic regions indicates that the foraminiferal assemblages from the Chuuk Island Lagoon represent a transitional biogeographic region between the high diverse Coral Triangle and East Pacific island chains. These findings are consistent with species richness patterns observed in zooxanthellate bearing reef corals, where diversity progressively drops off from the Coral Triangle towards the eastern Pacific.