Deep Sea Paradigms: Old paradigm from 1870s-1960s: Deep-sea desert: H.N. Mosely of Challenger. Challenger proposed that the Mid-Atlantic ridge could be a sunken lost continent. (The Dover Sea floor). Just a few species present worldwide. Disproven by: more research showed that there are many species that couldn?t be detected by previous technology. Deep sea environment and organisms are uniform and monotonous. Disproven by: diversity increases with depth. Sparsely inhabited. Disproven by: there are many microscopic organisms such as protists and bacteria that are very abundant. Also, worms can burrow in very highly concentrated areas. No light so no primary production. Disproven by: primary producers include bacterial mats, plankton, and endosymbiots. Food scarce, sinks from surface. Disproven by: not all organisms feed on marine snow. Animals mostly small. Disproven by: giagantism due to slower metabolisms. Processes proceed slowly. Disproven by: vents are short lived and change quickly. Prior to 1977: Deep-sea organisms are adapted to cold temperatures and high pressure. Deep-sea organisms are dependent on photosynthetically generated food sinking from the surface. And are adapted to low food environment. Deep-sea organisms are mostly small. Abundance of deep-sea organisms decreases with depth. Diversity of deep-sea organisms increases with depth. Competitive Exclusion Theory: First theorized in 1920s and 1930s. Assumes a uniform habitat unchanging over time. A few superior species should dominate. Other species out-competed and go extinct. This would explain the Challenger findings. Disproven by: Grassle?s use of the box corer. Stability-Diversity Theory 1970s: Constancy of environment over a long period of time. Allows evolution of new species without forcing extinction of old species. Organisms adapt to each other as well as to their environment. This theory would explain Sanders and Hessler?s findings. It has not been disproven but is no longer the favorite theory. Scarce Resources Theory: Scarce resources favor biological innovation and diversification. Plentiful food: little advantage for a mutation that creates an alternative feeding niche. Scarce food: advantage for a mutation that creates an alternative feeding niche. Evidence against: Coral reefs are very diverse despite scare resources though. This could explain Grassle?s findings though. It has not been disproven but it also is not the favorite theory. Microhabitat Theory: A mosaic of oases make it diverse. Spatial heterogeneity: organisms shape their habitat. Temporal disturbances: seasons, storms, food falls. Organisms specialize in particular conditions. This theory is currently in favor because of new observations. Highly mobile scavengers and burrowing of animals visible by submersible or photography. Seasonal variability of food supply (photos and sediment traps). Small-scale habitat difference visible in box corer. Exploration of Mid-Ocean Ridges: Biologists avoided with trawls and sleds. Rocks snag gear. Few remote photos in 1960s. Geologists were interested because of new theories. Although the deep-sea was initially believed to be a desert, surveys of mid-ocean ridges reveal abundant life at vents. Bacterial Chemosynthesis: Chemosynthesis: the biological conversion of carbon molecules (usually carbon dioxide or methane) and nutrients into organic matter using inorganic molecules (e.g. hydrogen gas, hydrogen sulfide) or methane as a source of energy. This occurs at hydrothermal vents. Hydrothermal Vent Food Web: 3 types of primary producers: Mats (bacterial mats). Plankton. Endosymbionts. The discovery of vents altered existing paradigm of the deep sea being a desert: Disproved that all deep-sea organisms are adapted to cold temperatures. Disproved that all deep-sea organisms are small. Disproved that every part of the deep-sea was cold. Organisms grow and recolonize very rapidly at hot vents. Disproved that the sea floor is monotonous and unchanging over longs spans of space and time. There are seasonal food changes. There are also microhabitats. Vents are isolated in localized areas along rift valleys. Vents are very active and short lived.
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