Human impact on the marine environment

This chapter deals with the major human impacts on the marine environment, which affects the sea by adding materials to the sea (pollution), and indirect effects on the oceans through human-induced changes in the world's atmosphere. Modern technology has resulted in a huge increase in the ability to catch, and store edible marine species. Many or most important fishery stocks are now being exploited at levels considered to be at or over the maximum sustainable level. Marine pollutants find their way into the sea not only through deliberate routes such as sewage discharges, and dumping. A great variety of objects and substances finds its way into the sea through shipwrecks and lost cargoes, from plastic ducks, and sneakers to potentially lethal chemicals. The long-term effects of waste disposal at sea must obviously depend upon the length of time taken for material to be broken down to a harmless form. There are now a number of international and national regulations, enforcement, and compliance. Some rubbish can be beneficial to marine life. Pesticides enter the sea from agricultural runoff, rivers, and by airborne transfer. Radioactive materials may enter the sea from two main sources, namely, weapon testing via atmospheric fallout, and atomic power industries. Warm effluents discharged into bays, and estuaries may raise the water temperature. Global warming of 2–4 °C affect sea levels in two main ways; through melting of polar land ice, and through expansion of seawater as it warms up, and it also destroys the coral reefs.