Chemosynthesis is the process by which organisms use chemical energy to create organic molecules. Unlike photosynthesis, which converts sunlight into energy, deep ocean organisms utilize chemosynthesis to manufacture carbohydrates and other molecules from the oxidation of sulfates. Chemosynthesis occurs in hydrothermal vents in the deep ocean floor at elevated temperatures and total darkness. A hydrothermal vent forms when magma and lava seep through cracks in the Earth's crust, releasing chemical-rich compounds that are used by bacteria to produce organic molecules which can sustain life.
In the past decades, scientists, utilizing submersibles and remote sensing technology, explored the farthest limits of the ocean for the first time. They discovered rich clusters of life flourishing in the deep dark ocean floor which were activated not by the sun;s radiation but by the oxidation of chemical compounds seeping from the Earth's crust. These organisms, most of them bacteria, were found around hydrothermal vents on the ocean floor. Hydrothermal vents are cracks in the Earth's deep ocean floor, through whichmagma and lava seep.
Organisms that use chemosynthesis are known as extremophiles. Extremophiles are organisms that can live in in physical or geothermically extreme conditions that are considered detrimental to most life on Earth. These organisms engage in parasitic or symbiotic relationships to survive. Ecosystems based on chemosynthesis develop around Deep Ocean hot springs, where hydrogen sulfide, methane, and other hydrocarbon-rich compounds emerge out of the Earth's crust. Bacteria, covering the rocks around the vent in thick orange and white mats, use hydrogen sulfide streaming from the vents and oxidize it into sulfur; they utilize the energy released to combine carbon, hydrogen and oxygen into hydrocarbons.
An entire ecosystem develops from this simple reaction. Animals, such as clams, snails, mussels, and many other grazing animals feed on the bacteria. Bigger animals, including shrimp and crabs, consume the grazers, and these in turn are devoured by larger animals, such as fish and octopi. Tube worms and giant clams have developed a mutualistic (symbiotic) relationship with the bacteria that lives within them. Tube worms, which lack a mouth or digestive system, absorb dissolved gases from the vent or ocean water and deliver them to the bacteria, which convert them into organic matter to be used as food for both the bacteria and the tube worm.
Communities based on chemosynthesis are interconnected by food webs. Each layer in the food web represents hierarchical progressive movement of organic energy within the community. All the diversity of life depends on the primary producers (bacteria); primary consumers (clams, snails, mussels) obtain energy from primary producers by feeding on them; first order carnivores (shrimp, crabs) feed on primary consumers, and at the top of the food web are other carnivores (fish, octopi) which feed on all animals below the feeding layers. These animals are rarely eaten by other organisms.
Animals that live in the deep ocean floor must be adapted to withstand not only the extremely cold environment of the deep ocean floors, but also the tremendous pressure from the tons of ocean water above them. The lack of sunlight in the ocean floor has led many sea animals to develop bioluminescence, as well as highly refined senses to protect themselves from predators. Hydrothermal vents usually last for a few months or even years. Soon after, bacteria (primary producers) die and all life forms which were sustained by them either have to migrate or perish.
Hydrothermal vent life, despite the adverse living conditions, is very diverse. More than 300 animal species have been found at hydrothermal vents, most of them not found anywhere else in the planet. Other communities that use chemosynthesis to sustain life in the ocean, other than hydrothermal vents, are known as cold-seeps. Cold-seep ecosystems occur around petroleum deposits, and around fissures on the seafloor produced by tectonic activity. Bacteria use methane, hydrogen sulfide and other hydrocarbon-rich compounds to make organic molecules for the sustainability of a food web of symbionts, carnivores and scavengers.