Coral Reef Benthic Microbes in Relation to Their Geochemical Environment

Abstract

Coral reef sediment microbes are considered important parts of nitrogen cycling in coral reef ecosystems. Research in the past, however, has focused mainly on microbes found on the coral reef proper and overlooked microbes existing within the sediments. This research attempted to investigate the relationship coral reef sediment microbes have with the geochemistry of sediment porewater by determining if microbial abundances are correlated to oxygen, nitrogen, or organic matter content of the sediments. Porewater and sediment samples were taken from various depths at Checker Reef, Hawaii, and sediment from Kilo Nalu, Hawaii was used in an artificial microcosm set-up. Porewater profiles of O2, NH4 +, NO3 - , and NO2 - were measured from each sediment array along with organic matter content measurements and DAPI cell enumerations. Cell abundances were then graphically analyzed versus each geochemical parameter and tested for correlations using a two-tailed t-test with a 95% confidence interval. Cell abundance and NH4 + were found to significantly correlate in the microcosm sediments but not in the Checker Reef sediment arrays. Significant correlations were not found between cell abundances and organic matter content, O2, NO3 - , or NO2 - . Microbial abundances were also compared against cell abundances in silicate sands and muddy sediments, representing sediments of different material and grain size, respectively. Cell abundances of the carbonate sediment samples exhibited similar numbers to silicate sands and lower numbers than muddy sediments. Analyzing and comparing cell abundances in coral reef sediments with their geochemical environment is just the first step in understanding the impact coral reef sediment microbes have on the coral reef ecosystem.