HUMAN DISTURBANCE FROM THE NINETEENTH CENTURY STILL INFLUENCES OSTRACODE COMMUNITY STRUCTURE AND TAPHONOMIC FIDELITY IN A BAHAMIAN BLUE HOLE

Geohistorical data, particularly from microfossils, plays an increasingly important role in conservation: including providing historical baselines and producing records of ecosystem variability. This project combines taphonomic and paleoecological data to understand the role of anthropogenic change in determining why two physically-similar blue holes have divergent biota today.

Lacustrine ostracode assemblages exhibit species sorting across a hydrological gradient on San Salvador Island, Bahamas, with different assemblages in lakes of differing salinity, dissolved oxygen, and alkalinity. Yet, two small, deep, brackish, well-oxygenated, and alkaline blue holes exhibit different patterns of taphonomic fidelity today. One blue hole, Blue Hole Five, has very low variability in ostracode assemblages and very high live/dead agreement, while the other blue hole, Watlings Blue Hole, has high variability in modern ostracode assemblages and a large variability in live/dead agreement. This variability in Watlings is unrelated to water depth, substrate, or distance from shore. Based on previous work showing low live/dead fidelity in mollusks due to human disturbance and the location of Watlings on a former plantation estate, we hypothesized that different histories of human disturbance (high in Watlings, low in Blue Hole Five) caused the divergent patterns in these two blue holes.

To test this hypothesis, we extracted sediment cores from both blue holes and quantified ostracode assemblages for both blue holes. We found that during the initial phase of plantation-style agriculture on San Salvador (~1800 A.D.), ostracode assemblages from Watlings exhibited an increase in evenness, with two opportunistic species increasing in abundance. We also found a corresponding decrease in community-aggregated size and an increase in community-aggregated degree of calcification, perhaps reflecting the fast growth rate of the opportunistic species. These community-level were either non-existent or much reduced in magnitude in Blue Hole Five. Our results show that human disturbance can leave legacies that are still visible long after the disturbance ends. Finally, our results can be generalized to help explain observed taphonomic mismatch and increased biotic variability in ecosystems today.