LIVE/DEAD AGREEMENT OF LACUSTRINE OSTRACODE ASSEMBLAGES DECLINES WITH INCREASING HUMAN IMPACT: A NEW TOOL FOR CONSERVATION PALEOBIOLOGY

Geohistorical are playing an increasingly important role in conservation by providing natural baselines of pre-human ecosystem conditions and variability against which current environmental change can be assessed. Live/dead discordance in mollusk assemblages can indicate human impact in marine environments, but new tools are needed to identify human impact in lacustrine habitats. Here we tested whether live/dead agreement is lower in lakes under current anthropogenic stress due to environmentally-induced changes in the composition of the living community within the window of time-averaging. This hypothesis was investigated at two spatial scales, using three pairs of physically-similar impacted and “pristine” lakes on each of three Bahamian islands. These islands themselves constitute a regional gradient of anthropogenic impact as judged by human population: New Providence (greatest impact, 250,000 people), San Salvador Island (intermediate impact, ~1,100 year-round residents), and Rum Cay (least impact, ~60 year-round residents). At the single island scale, we expected live/dead fidelity will be lower in the human-influenced lake of each pair, and at the regional scale, we expected live/dead fidelity will be lower on islands with highest human populations. In each of the eighteen lakes, living communities and associated death assemblages were sampled at five, ten, fifteen, and twenty meters from shore along two transects perpendicular to the shore, yielding sixteen samples per lake. We found that all six of the impacted lakes sampled on New Providence and San Salvador had lower live/dead rank-abundance correlation and taxonomic similarity than their counterpart pristine lakes, whereas only some of the three impacted lakes on lightly populated Rum Cay had lower fidelity. Overall, live/dead agreement of both impacted and “pristine” lakes was lowest on New Providence and higher on Rum Cay, where the difference in live/dead fidelity was smallest between “pristine” and impacted lakes. This test thus establishes the reliability of ostracode live/dead discordance as a tool for recognizing the ecological impacts of humans in lake environments, both among lakes on a single island and on a regional, inter-island scale.