Algal mats are one of many types of

microbial mat A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts ...

that forms on the surface of water or rocks. They are typically composed of blue-green

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

and sediments. Formation occurs when alternating layers of blue-green bacteria and sediments are deposited or grow in place, creating dark-laminated layers.

Stromatolites Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). Th ...

are prime examples of algal mats. Algal mats played an important role in the

Great Oxidation Event The Great Oxidation Event (GOE), also called the Great Oxygenation Event, the Oxygen Catastrophe, the Oxygen Revolution, the Oxygen Crisis, or the Oxygen Holocaust, was a time interval during the Paleoproterozoic era when the Earth's atmosphere ...

on Earth some 2.3 billion years ago. Algal mats can become a significant ecological problem, if the mats grow so expansive or thick as to disrupt the other underwater

marine life Marine life, sea life, or ocean life is the plants, animals and other organisms that live in the salt water of seas or oceans, or the brackish water of coastal estuaries. At a fundamental level, marine life affects the nature of the planet. M ...

by blocking the

sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...

or producing toxic chemicals.

Cyanobacteria forming algal mats

Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

found in sedimentary rocks indicate that

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

l life began on Earth during the

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

age. Fossilized cyanobacteria are commonly found in rocks that date back to

Mesoproterozoic The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), ...

.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 Cyanobacteria are photoautotrophs in nature; they convert carbon dioxide and sunlight into food and energy via

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

. Some species are also able to fix atmospheric nitrogen and convert it into the biologically-usable form of

nitrate Nitrate is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...

nitrite The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...

. 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 Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to a ...

carrying out the photosynthesis, and

heterocyst Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as '' Nostoc punctiforme'', ''Cylindrospermum stagnale'', and ''Anabaena sphaerica''. They fix nitrogen fr ...

s which fix the nitrogen. These heterocysts have thick walls and lack chlorophyll, both of which limits their exposure to oxygen, the presence of which inhibits nitrogen fixation. For the same reason, fixation may also be limited to nighttime when the light-dependent reactions photosynthesis are shut down, minimizing oxygen production.

Stromatolites Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). Th ...

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 Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

, stromatolites' compositions were dominated by micrite and thinly laminated lime mud, with thicknesses no greater than 100 microns.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. Modern stromatolites are characterized by their thicker and more 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 length of the cyanobacterial filaments plays an important role in deciding the grain size trapped. It has been noted 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. This resilience may also be due to the

autotrophic An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...

lifestyle of the bacteria, which enables them to thrive in a variety of harsh environments. 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 mats consist largely of filaments made of autotrophic bacteria and fine-grained particles. These bacterial are well known for the formation of stromatolites. Phototrophic bacteria such as cyanobacteria are evolutionary organisms responsible for the increased oxygen levels during the Proterozoic age. The event was known as The

, during which complex

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

life forms originated, potentially due to the increased oxygen availability.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 Preserved stromatolites are called stromatoliths. They can be easily recognized by their crystallized, thinly laminated layers and their domed, columnar or conical shapes. However, the same cannot be said for stromatolites that were not crystallized. The lack of many well-preserved stromatolites has been proposed as a consequence of ongoing

diagenesis Diagenesis () is the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. Increased pressure and temperature only start to play a ...

during formation. 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 algal mats

The rapid formation of algal mats can result in

harmful algal blooms A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are sometimes ...

(HABs), also known as

red tide A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural phycotoxin, algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are ...

s or green tides. 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. HABs can be found in water of high importance for economic and environment; with

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

ranging from low to high such as in rivers and lakes to reservoirs and oceans. Toxins can seep into the water column, from which they may be introduced into the local water supply, affecting humans and livestock. Toxins can have either direct or indirect effects on an organism. Some marine life is directly susceptible to toxins caused by HABs, while others are affected through accumulation of toxins over a period of time. This

bioaccumulation Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost or eliminated ...

process typically affects organisms such as filter-feeding shellfish 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 millions of dollars, and in Japan such events have been estimated to have resulted in losses of fish worth more than $300 million. Patricia M. Glibert (2013), Harmful Algal Blooms in Asia: an insidious and escalating water pollution phenomenon with effects on ecological and human health, ASIA Network Exchange. Moreover, some HABs are harmful to the

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

simply by their sheer

biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...

accumulation. Such biomass accumulation can lead to a multitude of negative consequences. For one, their growth and proliferation 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. High biomass blooms can also lead to the development of “dead zones”, formed when the algae begin to die and their decomposition depletes the water of oxygen. Dead zones are unable to support (aerobic) aquatic life, and are responsible for losses of millions of dollars’ worth of fish annually.

Potential applications of algal mats

Third generation

biofuel Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration (E ...

feedstocks are represented by both micro- and macro- algae, which present further advantages over the previous generations. (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.) Marine and aquatic biomass tentatively demonstrates high yield while requiring minimal 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.Montingelli, ME; Tedesco, S; Olabi, A G. Biogas production from algal biomass: A review, Renewable & Sustainable Energy Reviews43 (Mar 1, 2015): 961-972.

References

{{DEFAULTSORT:Algal Mat Aquatic ecology Algae