Invertebrates, Marine, Overview PJD Lambshead, The Natural History Museum, London, UK PH Schalk, ETI, Universiteit van Amsterdam, Amsterdam, Netherlands r 2001 Elsevier Inc All rights reserved This article is reproduced from the previous edition, volume 3, pp 543–559, r 2001, Elsevier Inc Glossary Benthic That connected with the bed of the sea or a freshwater lake, river, or stream Deep sea The seabed and immediately overlying water covered by seas at least 200 m deep Disturbance A biological or physical factor that impacts a population or community by causing death, reduced reproduction, or increased emigration Infauna Animals living within sediments Physical Characteristics of The Oceans The world ocean covers more than two-thirds of the surface of the earth and as much as 90% of the habitable volume It is the largest habitat on earth and about one billion people depend on the oceans for their primary protein needs Yearly, well over 90 million tons of fish and shellfish are harvested Only 10% of the oceans’ area could be classed as shallow water and this is mostly located around the continental margins Seas deeper than 2000 m cover half the earth’s surface The seashore zone, the area covered and exposed by tides, corresponds to the ecological littoral region Shallow seas make up the sublittoral zone, also called the continental shelf, which ends at the shelf break, usually at around 200 m The continental slope marks the boundary between the continental and ocean floor crusts It extends from the shelf break down to about 1500 m, so it roughly corresponds to the ecological bathyal region, 200 m to 2000 m The continental slope falls away into the continental rise, which extends down to a depth of about 4500 m Beyond this is the abyssal plain at depths of between 5000 to 6000 m The continental rise and the abyssal plain roughly correspond to the ecological abyssal region, 2000 to 6000 m Other features of the seafloor are rocky seamounts and ridges, which may be of a considerable size, and deep trenches down to 11,000 m or more Trenches are usually a feature of subduction zones where the seafloor buckles and deepens beneath a continental crust Deep trenches correspond to the ecological hadal region The continental rise and abyssal plain tend to be relatively flat Geological features such as terraces and submarine canyons, however, sculpture the continental slope Pressure increases down the water column at the rate of one atmosphere per 10 m Much of the seafloor is covered in sediments; bare rock is rather rare Near the coast these sediments are of terrigenous origin and may be coarse (e.g clay, sands, or pebbles) Terrigenous material may be found down to the continental rise and vast areas of the seafloor consist of clay sediments or, in Encyclopedia of Biodiversity, Volume Invertebrate All animals that lack a backbone (vertebrae)Fthat is, most of the animal kingdom Pelagic That connected with the water column Planktonic Organisms of many different phyla that float in and are carried by water masses in the pelagic of the sea or freshwater Production The increase in biomass of an individual, population or community as it grows by converting energyfood into biomass productive areas, biogenic oozes mainly from diatoms, radiolarians, and Foraminifera The temperature of the water declines rapidly with depth until it stabilizes at about 1C, which takes place at approximately 1000 m, depending on latitude This phenomenon is known as the permanent thermocline At greater depths, the temperature declines slowly Water currents are too complex to be discussed here in detail but, broadly speaking, deep water is formed by the sinking of dense, cold saline water in the Antarctic and Arctic This dense water spreads out across the world ocean, eventually returning to the surface In general, marine water is well oxygenated, often at values near saturation There are areas where rapid seasonal blooms in the upper water column deoxygenate the water leading to oxygen minimum zones Oxygen concentration falls rapidly with sediment depth, especially in littoral muds and sediments under shallow enclosed seas The open ocean or pelagic realm has no obvious boundaries such as the mountain ranges or large water masses (rivers, seas, or oceans) that are so important in driving speciation on land, although to a certain extent the three oceanic basinsFAtlantic, Indian, and PacificFare partially separated by landmasses The world ocean is essentially a continuum and the most important environmental factors are temperature and salinity, which translate primarily into latitude and depth However, despite the lack of obvious barriers, speciation has and does occur in the pelagic environment The geographic species distribution of modern plankton is the product of the geological history of the oceans and continental barriers, limitations of species in adapting to biotic and abiotic environmental factors, and the degree of organism mobility The pelagic realm is divided by depth into zones Light, temperature, and salinity are responsible for the major vertical biodiversity gradients In the upper 200 m, the epipelagic, sufficient light is available to sustain photosynthetic processes This is the primary production zone where light and carbon dioxide is converted into carbohydrates, the principle energy (food) source for all open ocean inhabitants The mesopelagic http://dx.doi.org/10.1016/B978-0-12-384719-5.00078-2 379