Award: OCE-1241255

This project surveyed the taxonomic, genetic, and functional diversity of organisms found in the marine lakes of Palau, with the intent of better understanding processes that change (increase or decrease) or stabilize biodiversity across space and through time. Marine lakes are intriguing places to conduct this work because they appear to present many, recent, replicated, independent natural experiments in ecology and evolution. Hypothetically, marine lakes formed as melting ice sheets raised sea level after the last glacial maximum, flooding inland valleys. In principal, therefore, marine lakes were most likely first inoculated with marine life from the surrounding sea during a period of great climatic and environmental change as the planet transitioned from a glacial to inter-glacial state. Foundational work on the project affirmed key elements of this scenario. Sediment coring and radiocarbon dating estimated lake ages between ~7000 to ~11,000 years (though the deepest and therefore oldest lakes are yet to be measured), measuring salinity and temperature profiles showed that physical structure and dynamics varied from lake to lake, and genetic analyses revealed populations of many organisms are isolated in each lake. Thus, marine lakes do constitute a suite of natural experiments for ecological and evolutionary studies. Through surveys of the microbes, algae, invertebrates, and fishes present in 20 marine lakes in Palau, we sketched a picture of how biodiversity differs with environmental conditions across modern marine lakes. We found, for example, that the number and abundance of species (microbes, invertebrates) in a lake is influenced by whether the lake is stratified, by its oxygen content, and by its distance from the ocean. However, microbial and invertebrate species richness are affected differently by these parameters. Therefore, it was intriguing, to also find that the types of microbial and invertebrate species present in lakes, a measure of community composition, responded in similar ways to changes in oxygen and salinity profiles across lakes. These findings indicate that a shared spatiotemporal and environmental context may generate parallel patterns of beta-diversity in microbes and macro-invertebrates, in spite of key trait differences between these organisms. This, in turn, raises the possibility that parallel processes also influence transitions among regional marine biotas beyond the marine lakes. We currently are continuing to analyze the data and samples collected in Palau to explore relationships that will clarify the mechanisms shaping detailed relationships that underlie the broad patterns described above. For example, we are interested in how community composition changes with depth gradients, how life history influences dispersal and population genetic differentiation, whether communities are random assemblages or somehow selected subsets of all possible species, and if deterministically assembled then whether this be related to particular functional traits? These questions, and the clarity that marine lakes have brought to some of these analyses so far, are reminiscent of the studies of oceanic islands that terrestrial biogeographers, ecologists, and evolutionists have been conducting for many decades. That marine lakes are consistent with the definition of habitat islands (pieces of livable environment surrounded by an unoccupiable matrix), that their formation has similarities to the formation of oceanic islands, and that some of the observed patterns of biodiversity are island-like is intriguing. The conception that studies of marine lakes may yield insight into general processes on other island and island-like marine systems, in a manner similar to the contributions of studies of oceanic islands to terrestrial biology, is novel and now stimulating considerable debate. The project has greatly increased the available data describing biodiversity in marine lakes and their dynamics, providing the first comprehensive description of benthic diversity as well as additional information on the plankton. These data are critical to informing decisions about management of marine lakes, which are economically and naturally valuable resources. Data are available through the BCO-DMO project page (http://www.bco-dmo.org/project/2238) and information is summarized on the lab website. During the project we helped grow the scientific workforce and public understanding by training a citizen scientist, five undergraduate students, two technicians, nine graduate students, two postdocs, and two overseas collaborators in biodiversity data collection and analyses. We additionally established national and international collaborations that now are advancing integrative ecological-evolutionary and cross-scale biodiversity analyses. Last Modified: 08/10/2019 Submitted by: Michael N Dawson