In the absence of sunlight, many deep sea fish create lights of their own, in the form of bioluminescent symbiotic bacteria that dangle as lures or shine a path ahead like headlights. Marine invertebrates burrow through the silt of the seabed itself.
Seamounts, underwater mountains that climb 1,000 meters or more from the ocean floor, often have complex surfaces of terraces, pinnacles, ridges, crevices and craters, and their presence diverts and alters the currents that swirl about them; the net effect is to create a variety of living conditions, providing habitat for rich and diverse communities. There are believed to be in excess of 100,000 seamounts of 1,000 meters or higher, although only a fraction has been studied.
Perhaps most unique and remarkable of all are the ecosystems that surround hydrothermal vents and cold-water seeps. Hydrothermal vents occur in volcanically active areas of the seafloor, where super-heated gases and chemically-rich water erupt from the ground at temperatures of up to 400 degrees C. Microbial organisms are able to withstand these extreme temperatures to create energy from the chemical compounds being forced up through the floor. Some of these microbes live symbiotically inside tubeworms, while others form large mats, which attract progressively larger organisms that graze on them. So far, over 500 species have been discovered that live only at hydrothermal vents; it is possible that these communities are the oldest ecosystems on Earth, and that vents are where life began.
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