Adaptation to no light

A community of tube worms "Riftia pachyptila" living around a hydrothermal vent.

Life in the darkness provides 2 fundamental problems to life in the deep sea. The first is that with no light there is no photosynthesis, this means there is no algae or photosynthesising organisms which are in most ocean environments the foundations of the food chain, so with no light energy must be sourced from elsewhere. The second problem is that with no light an organism cannot see anything, making it difficult to find prey or another individual to breed with. However like all problems these are over come in several ways.

Firstly the more immediate problem of food and energy, most organisms in the deep sea are scavengers that sniff out rotting carcases of fallen animals, most noticeably megafauna such as cetaceans. Fallen carcases (Jones 1998)attract thousands of animals in the deep sea as the rotting smell disperses in the water. Common species found are various hagfish species from the family Myxinidae that are perfectly adapted to feeding on corpses as they latch on using barbed teeth, and can then tie themselves in knots to remove as larger amounts of flesh as possible. There are also thousands of strains of bacteria that colonize the bones long after the flesh has all been eaten away, nothing is wasted. These carcasses are rare however, and so a lot of sessile animals exist to catch “Marine snow”. Marine snow is falling particles of biomass from the above water column, many organisms have evolved to feed off this falling debris such as deep sea copepods. All these methods rely on energy input from the sun however. The one’s that do not rely on the sun have remarkable ways to get energy.

Bathymodilus childressi, a deep sea mussel living on cold seeps.

Hydrothermal vents are formed on the sea floor where active tectonic plates are moving apart allowing magma to rise and heat the water around it forming vents that spew out compressed hot water and other chemicals. One such chemical is hydrogen sulphide, which is the apparent key to the vast abundance of life that is found surrounding these vents. Strains of bacteria have developed to use the hydrogen sulphide to form energy, a process known as chemosynthesis. Many other species are then feeding on these bacteria or developing symbiotic relationships with them such as Riftia pachyptila the giant tube worm (Minic 2004) which forms vast forests around these vents. In a similar fashion Bathymodiolus childressi forms a similar relationship with another strain of bacteria that performs a similar chemosynthesis from methane in biomes known as cold seeps. A cold seep is an area where methane and hydrogen sulphide seep out of the seabed forming brine pools and forms large communities much like hydrothermal vents.

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