The Role of Microbial Mats in the Biostabilization of Sediment Through Trapping and Binding

Layered microbial communities, called microbial mats, commonly form in the intertidal or shallow subtidal zone, particularly in areas protected from wave action and strong currents. These microbial mats can accrete by growing around sand-sized detrital mineral grains in a two-step process known as trapping and binding. We hypothesized that trapping and binding by microbial mats can promote the stabilization of sand-sized sediment and is therefore a process that should be considered as an important mode of biostabilization for sandy coastlines threatened by sea-level rise and increased storm intensity. To test this hypothesis, we designed a suite of in situ field incubation experiments to assess the amount of sediment microbial mats can trap if given a large sediment supply. These experiments, conducted on Little Ambergris Cay, Turks and Caicos Islands, focused on two of the most common morphologies of microbial mats (i.e., polygonal tufted mats and flat mats). We observed cyanobacterial filaments move around and on top of sand-sized grains within the first 24 h of each experiment, with increased movement related to environmental factors (duration of submergence, protection from tidal advection, and light availability). The results of our experiments show that polygonal tufted mats can stabilize twice the amount of sand-sized sediment than was naturally delivered over multi-month timescales, meaning these mats are sediment supply-limited and are capable of capturing more sediment. Furthermore, microbial mats have the capacity to trap and bind larger grains than seagrasses and mangroves. We recommend that microbial mats should be considered as part of nature-based management solutions for biostabilization of sand-sized sediment.