Origins, maintenance, and loss of biodiversity in marine lakes
Background: Marine lakes are variously isolated bodies of water that formed after the Last Glacial Maximum as rising seas flooded inland valleys. Marine lakes provide novel opportunities for testing island theory that was developed primarily in terrestrial settings, such as the species-area relationship of the classical Equilibrium Model, and patterns of evolution such as the Island Rule. They also offer two perspectives on the emerging General Dynamic Model of oceanic island biogeography. On the one hand, marine lakes of different depths are different ages and therefore may represent modern analogs of stages in the formation of individual lakes; modern shallow lakes representing inception and early-developmental stages, and modern deep lakes representing mature stages; some shallow lakes may be filling-in and represent senescent stages. On the other hand, the sediment deposited in each lake may hold a record of thousands of years of community assembly, dynamics, and disassembly.
Questions: We are exploring how local and regional, biotic and abiotic, deterministic and stochastic processes, influence taxonomic, genetic, and functional diversity, and how these culminate in shared or unique attributes of modern communities.
Methods: Between 2003-2013 we inventoried microbes, macroinvertebrates, phytoplankton and fishes, and measured abiotic characteristics of marine lakes in Palau. We also collected sediment cores of up to 12 m length from 8 of these lakes, for which we are constructing age models and analyzing biotic proxies, biolipids, and micro- and macro-fossils. Here, we report on patterns in modern community diversity across 16 lakes, and preliminary analyses of community similarity through time within several lakes.
Species diversity in modern marine lakes is, in general, consistent with species-richness relationships such as the SAR. However, the relationship breaks down when considering lakes that are far inland and stratified: microbial diversity is elevated, and teleost diversity is reduced. These lakes appear to provide  novel categories of dysoxic and anoxic environments for microbes and  dramatically less oxygenated habitat for fishes than would be suggested simply by area or other metrics of overall lake-size. We discuss the potential for observing these transitions and corresponding effects on diversity through time using a combination of ITRAX, lipid biomarkers, and benthic macrofossils.