INDICATORS OF CHANGING LAND USE: STABLE CARBON AND NITROGEN ISOTOPES IN OCTOCORALS FROM BERMUDA (1876-2010)

In small island nations, like Bermuda, human populations have had a dramatic effect on land use, which in turn, has affected near shore coral reef environments. As dominant filter feeders on reefs throughout the Caribbean, including Bermuda, octocorals (or soft corals) incorporate indicators of water quality into their tissues and skeletons as they feed and grow. Stable carbon and nitrogen isotopes were measured in seven different octocoral species collected in 1876, 1888, 1951, 1956, and 1960 and preserved in dry museum collections. These were compared to values from the same species collected directly from reefs in 2008, 2009, and 2010. Interestingly, preliminary results indicate that there was only ~1.5‰ variation in both the stable carbon and nitrogen isotopic values between 1888 and 1960. This is in contrast to a 3‰ variation for carbon and 5‰ variation for nitrogen between 2008 and 2010 that reflected significant near shore environmental impacts. The distinction between near shore and offshore marine environments is likely a more recent phenomenon that was not apparent prior to 1960. The landscape of Bermuda transitioned from one dominated by endemic terrestrial flora (1876, 1888) to a more biodiverse non-native terrestrial landscape (1951, 1956, 1960) with moderate amounts of subsistence agriculture present through all five time periods. More recently (2008-2010) Bermuda’s landscape is dominated by non-native invasive terrestrial flora and significant human development. This shifting land use has contributed to the greater variation in stable carbon and nitrogen isotopes in more modern octocorals.