Algal mat is one of many types of microbial mat formed on the water surface or on the surface of rocks. It is made out of blue-green cyanobacteria and sediments. It is formed by having alteration layers between the blue-green bacteria and sediments, creating dark-laminated layers. Stromatolites are prime examples of algal mat. Algal mats played an important role in the Great Oxidation Event on Earth some 2.3 billion years ago. Overpopulation of algal mat may be an ecological problem, when mats disrupt the other underwater marine life by blocking the sunlight.
Cyanobacteria forming algal mats
Cyanobacteria found in sedimentary rocks shows that the bacteria started life on Earth during the Pre-Cambrian age. Fossilized cyanobacteria are commonly found in rocks that date back to Mesoproterozoic. Cyanobacteria are photoautotroph in nature; meaning they convert carbon dioxide and absorbed sunlight into food and energy via photosynthesis. They are also able to fix atmospheric nitrogen and convert it into the biologically-usable form (Paerl, Pinkney and Steppe, 2000). This gives them competitive advantage over other organisms that may be limited by the shortage of biologically available nitrogen. The cyanobacteria colonies contain two types of cells, the regular cells with chlorophyll carrying out the photosynthesis, and heterocysts which fix nitrogen. Heterocysts have thick walls and lack chlorophyll, both of which limits the exposure of heterocysts to oxygen which presence inhibits nitrogen fixation. For the same reason nitrogen fixation may be limited to night time when with the shutdown of photosynthesis in the photosynthetic cells, oxygen is no longer produced and therefore does not interfere with nitrogen fixation.
Stromatolites are alternating layers of cyanobacteria and sediments. The grain size of sediment portion of stromatolites is affected by the depositional environment. During the Proterozoic, the stromatolite’s compositions were dominated by micrite and thinly laminated lime mud, with thickness no more than 100 microns. Modern stromatolites are characterized by their thicker and irregular laminations due to coarser grain size. Stromatolites trap sediment particles when the particles come to a rest from wave agitation. Trapping is separate process where filaments of bacteria traps the particle, provided the angle of the filaments are still within the limits before the grain rolls off due to overcoming the friction of the film. The same authors found that the length of the filaments played an important role in deciding the grain size trapped. Many of these bacterial mats are found in extreme environments because of evolution of oxygen and competition. Paerl, Pinkney and Steppe (2000) commented that these bacterial mats were marked by geochemical areas, such as volcanism and tectonics. They favour harsh environments that are either nutrient-depleted or have high salinity levels. In another article, the authors mentioned the autotrophic lifestyle of the bacteria enabled them to thrive in variety of regions with harsh surroundings. Stromatolites can be found in places with ranging temperature such as in the marine, limnic and soil 
The importance of algal mats in the past
Algal mat mostly consist of filaments made of autotrophic bacterial and fine-grained particles. These bacterial are well known for the formation of stromatolites. Based on an article by Paerl, Pinkney and Steppe (2000), phototrophic bacteria such as cyanobacteria is an evolutionary organism responsible for increased oxygen level during the Proterozoic age. The event was known as The Great Oxidation Event, which was the creation and blooming of complex eukaryotic life form, which was left behind by these cyanobacteria. Preserved stromatolites are called stromatoliths. It can be easily recognized by its crystallized thinly laminated layers and its domed, columnar or conical shaped. However, the same cannot be said to stromatolites that were not crystallized. According to Frantz, Petryshyn, and Corsetti (2015), many of the stromatolites could not be preserved due to a process known as diagenesis. Diagenesis is a weathering process where newly deposited sediments lies on top of the old sedimentary bed, buried and compacted, lithified and uplifted to the surface as sedimentary rocks.
Negative impacts of HABs
Damages such as environmental, economic and health are increasing in frequency, duration and in remote regions. These are caused by harmful algal blooms (HAB), also known as red tide or green tide. HABs have been known to produce a wide range of toxins, with newer toxins discovered frequently, which makes the task of understanding these phenomena increasingly difficult. HAB can be found in water of high importance for economic and environment; with salinity ranging from low to high such as in rivers and lakes to reservoirs and oceans. Toxins seeped into water column where it can get into water supply and affecting humans and livestock. Toxins can have either direct or indirect effect towards an organism. Some marine life is susceptible to toxins caused by HABs while others are affected through accumulation of toxins over a period of time; such as filter-feeding shell¬fish and secondary consumers. It has been estimated that there are thousands of human poisoning cases annually in Asia from toxic water. Single HAB fish-kill events in Korea have been estimated to have cost from $1–100 million in lost fish, while in Japan such events have been estimated to have resulted in losses of fish worth more than $300 million.
Moreover, some HABs are harmful to the ecosystem through their sheer biomass accumulation. Such biomass accumulation can lead to a multitude of negative consequences. For one, their accumulation can reduce the light penetration in the water column, thereby reducing habitat suitability for the growth of submersed grasses. Exceedingly high biomass can also cause fish gills to clog, leading to suffocation.40 High biomass blooms can also lead to the development of “dead zones.” 41 Dead zones are formed when the algae begin to die and their decomposition depletes the water of oxygen. Dead zones do not support (aerobic) aquatic life, and are responsible for losses of millions of dollars’ worth of fish annually.
Potential applications of algal mats
Third generation biofuels feedstock is represented by micro- and macro- algae, which present further advantages over the previous two. (The first generation biofuels are made from edible feedstock like corn, soybean, sugarcane, and rapeseed. Second generation of biofuels from waste and dedicated lignocellulosic feedstock shave advantages over those of first generation.) This marine biomass shows the prospect of high yields requiring no use of arable land. Major advantages of algae are: no competition with food crops for arable land, high growth rates, and low fractions of lignin which reduces the need for energy-intensive pretreatment and compatibility with biorefinery approach implementation. It has been proven that macroalgae can reach 2–20 times the production potential of conventional terrestrial energy crops However, some disadvantages such as the presence of high water content, seasonal chemical composition and the occurrence of inhibitory phenomena during anaerobic digestion, make algal biofuels not yet economically feasible although they are more environmental friendly than fossil fuels.
Algal mat is one of microbial mat made out of blue-green cyanobacteria and sediments. Cyanobacteria are photoautotrophs organisms and commonly found in rocks in fossilized form. And they are responsible for The Great Oxidation Event which accumulated the oxygen levels during the Proterozoic time and allowed complex life form to thrive (Schirrmeister, Vos, Antonelli, and Bagheri, 2013). However, due to water pollution with nutrient, algal mat can grow rapidly and affect the ecosystem negatively, which is known as Harmful Algal Blooms (HABs). In spite of that, with farther development in technology, it can be useful for efficient biofuel.
- BETTINA E. SCHIRRMEISTER, MURIEL GUGGER and PHILIP C. J. DONOGHUE (2015), CYANOBACTERIA AND THE GREAT OXIDATION EVENT: EVIDENCE FROM GENES AND FOSSILS, Palaeontology, Vol. 58, Part 5, 2015, pp. 769–785
- C. M. FRANTZ , V. A. PETRYSHYN , AND F. A. CORSETTI, (2015) Grain trapping by filamentous cyanobacterial and algalmats: implications for stromatolite microfabrics through time, Geobiology (2015), 13, 409–423.
- Hans W. Paerl, James L. Pinckney and Timothy F. Steppe (2000), Cyanobacterial-bacterial mat consortia: examining thefunctional unit of microbial survival and growth inextreme environments, Environmental Microbiology (2000) 2(1), 11-26
- Bettina E. Schirrmeister, Jurriaan M. de Vos, Alexandre Antonelli, and Homayoun C. Bagheri (2012), Evolution of multicellularity coincided with increased diversification of cyanobacteria and the GreatOxidation Event, DOI10.1073/pnas.1209927110
- Patricia M. Glibert (2013), Harmful Algal Blooms in Asia: an insidious and escalating waterpollution phenomenon with effects on ecological and humanhealth, ASIA Network Exchange.
- Montingelli, ME; Tedesco, S; Olabi, A G. Biogas production from algal biomass: A review, Renewable & Sustainable Energy Reviews43 (Mar 1, 2015): 961-972.