Cresswell, Jacquelyn Nicole (2019-09). Benthic Anchialine Habitat Variability in Karst Subterranean Estuaries over Space and Time. Doctoral Dissertation.
Thesis
Diverse benthic and pelagic habitats develop in coastal estuarine settings from land-to-ocean physicochemical gradients, such as variations in salinity, dissolved oxygen, nutrients like carbon, and water circulation. Understanding the environmental controls of benthic habitat variability and how flora and fauna in those habitats respond to external environmental pressures, is of great ecological interest. Karst subterranean estuaries (KSEs) are globally distributed along coastal carbonate platforms wherein anchialine ecosystems exist that populate unique habitats. However, the environmental drivers of benthic anchialine habitat variability within karst subterranean estuaries is poorly understood. This dissertation explores benthic foraminiferal distributions in modern surface sediments and sediment cores to identify benthic anchialine habitat variability over time and space. The first study presents evidence for modern benthic anchialine habitat variability within KSEs using benthic foraminiferal distributions in caves of Bermuda. Benthic foraminiferal communities are controlled by provenance of organic matter (i.e., marine vs. terrestrial), and secondarily by other physical variables (i.e., tidal exposure, sediment grain size, light). The next study identifies developmental succession of benthic anchialine habitats in response to Holocene sea-level rise and vertical migration of a karst subterranean estuary since the last ice age in Bermuda. This study illuminates how sea-level rise can force subsurface aquatic island fauna to experience a previously unknown bottleneck event. Finally, the last study reveals that benthic anchialine habitat development over the last 10,000 years is driven initially by water mass (meteoric lens vs. saline groundwater) and secondarily by organic matter quantity and quality. This provides further evidence that sea-level rise influences benthic anchialine habitat development within KSEs. Overall, findings from this dissertation provide multiple pieces of evidence that benthic anchialine habitat variability, over time and space, is present within KSEs. Importantly, anchialine benthic habitat variability should be considered within marine ecosystem risk assessments, as the coastal zone in particular will face dramatic changes from coastal urbanization and marine climate changes during the 21st century, which will impact coastal faunal.
