Timescales of Growth Response of Microbial Mats to Environmental Change in an Ice-Covered Antarctic Lake

Abstract

Lake Vanda is a perennially ice-covered, closed-basin lake in the McMurdo Dry Valleys, Antarctica. Laminated photosynthetic microbial mats cover the floor of the lake from below the ice cover to >40 m depth. In recent decades, the water level of Lake Vanda has been rising, creating a “natural experiment” on development of mat communities on newly flooded substrates and the response of deeper mats to declining irradiance. Mats in recently flooded depths accumulate one lamina (~0.3 mm) per year and accrue ~0.18 µg chlorophyll-a cm−2 y−1. As they increase in thickness, vertical zonation becomes evident, with the upper 2-4 laminae forming an orange-brown zone, rich in myxoxanthophyll and dominated by intertwined Leptolyngbya trichomes. Below this, up to six phycobilin-rich green/pink-pigmented laminae form a subsurface zone, inhabited by Leptolyngbya, Oscillatoria and Phormidium morphotypes. Laminae continued to increase in thickness for several years after burial, and PAM fluorometry indicated photosynthetic potential in all pigmented laminae. At depths that have been submerged for >40 years, mats showed similar internal zonation and formed complex pinnacle structures that were only beginning to appear in shallower mats. Chlorophyll-a did not change over time and these mats appear to represent resource-limited “climax” communities. Acclimation of microbial mats to changing environmental conditions is a slow process, and our data show how legacy effects of past change persist into the modern community structure.

Growth of modern branched columnar stromatolites in Lake Joyce, Antarctica

“…Also, growth rates might have decreased through time following a reduction in primary productivity as lake level rise reduced illumination and placed the stromatolites below the photic zone. Even though these growth rate estimates are poorly constrained, they are similar to measured and modeled growth rates of microbial mats in other McMurdo Dry Valleys lakes (Hawes et al ., , ), which suggests that our interpretations of environmental change during stromatolite growth are consistent with observed lake level rise.…”

Microbial Mat Communities along an Oxygen Gradient in a Perennially Ice-Covered Antarctic Lake

“…Two distinct mats zones are recognized. Below the ice cover, where liquid water persists year round, mats are rich in lightharvesting pigments (12) and extracellular polysaccharides, are laminated (11), and often take the form of complex, three-dimensional structures (13,16,17). During summer, solar heating melts the shallow margins of most MDV lakes to some extent, creating shallow "moats" that seasonally alternate between ice free and frozen.…”

Kinneyia: A Flow-Induced Anisotropic Fossil Pattern from Ancient Microbial Mats

“…They are found in vastly variable environments, ranging from deep sea hydrothermal vents (Wolff, 1977) to the Antarctic (Friedmann and Weed, 1987;Hawes et al, 2013), sewage pipes, and even the human body (Hall-Stoodley and Stoodley, 2009). They represent, however, not only one of the most ubiquitous life forms on Earth but also one of the earliest.…”