How Humans Are Hurting Our Oceans Chapter 13: Exploring the Oceans

What is an Estuary? o Estuaries are bodies of water and their surrounding coastal habitats typically found where rivers meet the sea. o They harbor unique plant and animal communities because their waters are brackish—a mixture of fresh water draining from the land and salty seawater. o Of the 32 largest cities in the world, 22 are located on estuaries.

Why Are Estuaries So Important? o Many animal species rely on estuaries for food and as places to nest and breed. They are often called nurseries of the sea. o Most fish and shellfish eaten in the United States, including salmon, herring, and oysters, complete at least part of their life cycles in estuaries. o Estuaries also help to maintain healthy ocean environments. They filter out sediments and pollutants from rivers and streams before they flow into the oceans, providing cleaner waters for marine life. o Estuaries provide habitat for more than 75 percent of the U.S. commercial fish catch!

Why Estuaries Are in Danger o The greatest threat to estuaries is, by far, their large-scale conversion by draining, filling, damming or dredging. These activities result in the immediate destruction and loss of estuarine habitats. o In the United States, 38 percent of the wetlands associated with coastal areas have been lost to these types of activities. In some areas, the estuarine habitat loss is as high as 60 percent. o Many are seriously degraded by pollution. People have historically viewed estuaries and waterways as places to discard the unwanted by-products of civilization. Pollution is probably the most important threat to water quality in estuaries. o The pollutants that have the greatest impact on the health of estuaries include toxic substances like chemicals and heavy metals, nutrient pollution (or eutrophication), and pathogens such as bacteria or viruses.

Water Contamination o In places like Chesapeake Bay, a major water quality concern stems from nutrient loading (increased levels of dissolved nitrogen and phosphorous). As water makes its way through a local watershed and eventually to the ocean, it is inevitably affected by how people use the land. o Runoff from fertilizers applied to agricultural fields, golf courses, and suburban lawns; deposition of nitrogen from the atmosphere; soil erosion; and discharge from aquaculture facilities and sewage treatment plants all contribute to increasing nutrient content in coastal waters. o Algae in the water feed off these nutrients and can bloom in excess when nutrient concentrations get too high. When they are overfed, they can do more harm than good. Decomposing algae can deplete dissolved oxygen in the water to dangerously low levels. This process, known as eutrophication, can result in fish kills and suffocation of other marine life. If enough oxygen is removed from the water, the area becomes a “dead zone,” where no aquatic life can survive.

The Effect of Humans on the Ocean

Ocean Acidification o What is pH? The pH scale measures how acidic or basic a substance is. It ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic. o o Corals, calcareous phytoplankton, mussels, snails, sea urchins and other marine organisms use calcium (Ca) and carbonate (CO 3 ) in seawater to construct their calcium carbonate (CaCO 3 ) shells or skeletons. o o As the pH decreases, carbonate becomes less available, which makes it more difficult for organisms to secrete CaCO 3 to form their skeletal material. o o CO 2 accumulation and lowered pH may result in acidosis, or a build up of carbonic acid in the organism's body fluids. This can lead to lowered immune response, metabolic depression, behavioural depression affecting physical activity and reproduction, and asphyxiation.

What Areas Will First be Affected by Ocean Acidification? o o The first areas to be impacted by ocean acidification are high-latitude regions and deep water areas, where the natural carbonate levels are lowest and closest to becoming undersaturated with respect to carbonate. o o Coral reef ecosystems in the warm waters of tropical and subtropical regions are among the most diverse and productive of marine ecosystems, supporting hundreds of millions of people directly through subsistence harvesting. It is estimated that by 2050, we may be losing more reef area to erosion than can be rebuilt through new calcification.

Our Acidic Oceans

Other Human Activities That Hurt Our Oceans o o Litter of all forms end up in the oceans due to careless beach visitors or garbage thrown overboard by ships, but by far the greatest source of marine litter is that which makes its way into the ocean from storm water drains, rivers and estuaries - particularly those near large urbanized zones. o o Thermohaline circulation…without the continual cycling of salt, nutrients, oxygen, carbon dioxide and energy, the face of the planet would change dramatically. The potential of one aspect of the global thermohaline circulation is threatening to shut down completely: The portion of the system in the North Atlantic, which includes the Gulf Stream, is showing signs of slowing down and cooling. The last time in the Earth's history when this occurred, most of Europe was thrown into what is known as 'The Little Ice Age'.

More Human Effects o o Pollution in the forms of oil spills, plastic and solid waste (debris), chemicals and sewerage from both land-based sources and ships have varying impacts (depending on the extent of the pollution), but cumulatively these forms of pollution create a highly degraded marine environment. o o The exploitation of marine resources - fish stocks, in particular - is a global problem, and a function of both a growing demand for food (by the growing global human population) and the competition between fisheries to capture the greatest possible market share. The two areas that need to be raised in this regard are overfishing and bad or 'dirty' fishing practices.