Benthic Foraminiferal Assemblages from Kiritimati (Christmas) Island Indicate Increased Nutrification has Occurred on a Decadal Scale

Community assemblages of live and dead benthic foraminifera from Kiritimati (Christmas) Island, Kiribati, were used to investigate changes in nutrification before and after human occupation and the arrival of associated fishing impacts, which began in the ~1970s. Benthic foraminiferal assemblages have previously been shown to have strong empirical relationships with water quality and are dominated by mixotrophic, symbiont-bearing foraminifera in clear, nutrient-poor waters. As nutrification increases, heterotrophic and/or opportunistic foraminifera increase in prevalence. Compared with the dead assemblages, in the live, post-human occupation material the proportion of mixotrophic taxa decreased significantly at all sites. This indicates that nutrification occurred in Kiritimati over the scale of decades, possibly due to changes in trophic structure and nutrient cycling due to fishing. Sites with higher fishing pressure had larger increases in nutrification, as revealed by the change in foraminiferal assemblages. Because benthic foraminifera are preserved in the fossil record, there is potential for application to tropical locations which have been occupied for much longer time periods to investigate if and when water quality declined due to human impacts.