Times of the Islands Fall 2023

green pages newsletter of the department of environment & coastal resources
Looking beneath the thick layer of mud, scientists discovered microbial mats underneath the cay’s tidal lagoon.
Although their individual constituents can’t be seen
with the naked eye, microbial mats boast a level of biodiversity
comparable to that of the Amazon rainforest.
They form at interfaces between land and water. They
range from a few millimeters to tens of centimeters
thick and contain several layers, each dominated by a
different type of microbe. The topmost organisms feed
on sunlight, while the next layer feeds on the top layer’s
byproducts, and so on, forming a self-sufficient food
chain within each mat. Most organisms secrete slime or
filaments, which hold the mat’s tiny inhabitants together
and provide structural integrity.
Microbial mats are some of the oldest living forms
of life for which there is substantial fossil evidence. The
oldest known microbial mat fossils are roughly 3.5 billion
years old. To put that in perspective, dinosaurs appeared
roughly 230 million years ago, and humans didn’t arrive
on the scene until 2 million years ago. Because they’re so
ancient, scientists think microbial mats may hold clues to
the origins of life on Earth—and possibly other planets.
That’s what brought Dr. Usha Lingappa, then a graduate
student at Caltech studying geobiology, and her
colleagues to the Turks & Caicos in 2017. While microbial
mats have likely sprung up elsewhere in TCI, Little
Ambergris Cay has the best conditions for mat growth.
The small island consists of a bedrock rim surrounding
a tidal lagoon, where rising and falling water levels promote
mat formation. The lagoon is protected from strong
waves that could wash mats away, and the lack of human
activity and large animals minimizes damage to the mats.
As a result, Little Ambergris Cay has “absolutely resplendent
microbial mats,” Lingappa says.
Lingappa’s team was interested in how photosynthetic
microbes, like the ones in microbial mats, have
shaped Earth’s environment over time. Some of their
research focused on determining how similar current
mats are to ancient mats, and using current mats to glean
information on how ancient mats evolved. “What’s cool
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