Collaborative Research: Biologically-driven island-building during sea-level rise and its implications for promoting resilient coastlines

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Coastal regions are at high risk for flooding and erosion due to climate change. Mangroves help protect coastlines by trapping small sediment called mud. The accumulation of mud layers counteracts sea-level rise. This project will examine sediment trapping by microbial mats, layered communities of microorganisms. Microbial mats are common in mangrove ecosystems and previous research has shown that microbial mats can trap larger sediment than mangroves. The PIs hypothesize that microbial mats may be playing an important but under-appreciated role in trapping sand-sized sediment. This will be tested using field observations and modeling to understand whether microbial mats helped build emergent land in three study sites. Results will be used to evaluate whether it is useful to consider microbial mats in coastal management practices more broadly. A short educational film featuring the key conclusions of this project will be shared with local communities and the broader public. This project will also provide training to high school and graduate students.The PIs will test the hypothesis that microbial mats can augment grain-trapping effects of mangroves, resulting in the accumulation and early cementation of coarse sediment that makes coasts resilient to sea-level rise and increased hurricane intensities. The primary study site is Little Ambergris Cay (LAC), an uninhabited island in the Turks and Caicos Islands that accreted over approximately the last 10,000 years, characterized by thick microbial mats, carbonate-cemented hardgrounds, and mangrove thickets with underlying sediment dominantly composed of ooids, carbonate sand grains that form via precipitation from seawater. The project will apply a multidisciplinary approach to examine how biology contributed to the construction of emergent topography during sea-level rise and evaluate how the processes involved could be applied to enhance coastal resiliency in other areas. The project will consist of four components: (1) real-time observations of rates and mechanisms of sediment stabilization by microbial mats; (2) analysis of a 10,000 year, Holocene, depositional record to assess rates and spatial variations in sediment accumulation; (3) sediment transport modeling to reconstruct island development to test whether local hydrodynamics and inorganic cementation are sufficient to create the emergent topography observed or, alternately, if biological influence is required; and (4) comparing LAC microbial community and sediment accumulation patterns with two contrasting coastal systems (one in the Florida Keys and one in Belize) to identify how the unique ecology of LAC relates to other coastlines. In addition to evaluating whether the interactions of microbial mats with mangroves and sediment transport dynamics affect sediment accumulation in coastal regions at risk from rising sea-level, this project will also contribute to understanding of the diversity, activity, and morphology of mangrove-associated microbial communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.