Of all the mineral resources considered as potential targets for deep-sea mining, polymetallic nodules (also commonly called manganese nodules) are probably the most likely commodity to be developed into a commercial operation. As well as containing commercially attractive (though variable) levels of metals such as nickel, copper and cobalt, their occurrence on the seafloor surface presents a relatively straightforward engineering challenge in terms of their extraction when compared to some other metal deposits in the deep-sea. Polymetallic nodules are rounded lumps of manganese and iron hydroxides that cover vast areas of the seafloor, but are most abundant on abyssal plains at water depths of 4000-6500 metres (see the definition of topographic features for abyssal plains).The nodules of greatest commercial interest occur in the Clarion-Clipperton Zone in the equatorial Pacific Ocean (CCZ) and in the Central Indian Ocean Basin (see definition for CCZ).” (MIDAS, n/d) As with all other benthic ecosystems (see definition for benthic flora and fauna and benthic layer), it is difficult to assess exactly to what extent mining these nodules will impact the local deep-sea ecosystems, because very few scientific investigations have taken place so far. Many endemic (native) species have already been discovered, who depend on the nodules to survive. It is also known that recovery and recolonization rates are extremely slow.