 For example, pteropods are "a key prey item of a number of higher predators – larger plankton, fish, seabirds, whales".The rise in agriculture of the past 400 years has increased the exposure rocks and soils, which has resulted in increased rates of silicate weathering.In turn, the leaching of amorphous silica stocks from soils has also increased, delivering higher concentrations of dissolved silica in rivers.