Final 11

Final 11 - Study Guide - Chapter 11 - Sustaining Aquatic...

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Study Guide - Chapter 11 - Sustaining Aquatic Biodiversity Core Case Study: A Biological Roller Coaster Ride in Lake Victoria . Lake Victoria is a large shallow lake in East Africa in ecological trouble. In 1980 it contained 500 species of endemic (found no where else) cichlids, but today only 200 species survive. The factors causing this loss of biodiversity include: 1) introduction of Nile perch, a large predator, and 2) large algae blooms from agricultural and urban runoff . Poverty has increased in the local population due to mechanized fishing for Nile perch, which has put small-scale fishermen out of business, and has caused local forests to be depleted of firewood, which is used to smoke the perch. Now, the Nile perch is declining as its food supply diminishes. Anthropogenic changes that occur without a clear understanding of the dynamics of large aquatic ecosystems threaten another component of the world’s the biodiversity needed to sustain earth’s ecosystems. What are the major threats to aquatic biodiversity? Only 5% of the earth’s ocean has been explored and we know little about its biodiversity. Scientist have observed that: 1) coral reefs, estuaries and the deep-ocean floor have the greatest marine diversity, 2) biodiversity is higher near the coasts, and 3) because of greater habitat and food variety, the ocean floor has more biodiversity than the ocean surface . Habitat loss and degradation are the greatest threats to marine and freshwater ecosystems. Ocean fishes spawn in coral reefs, mangrove forests, coastal wetlands, and rivers. Unfortunately, these are the areas with the greatest human activity, and coastal habitats are disappearing 2-10 times quicker than tropical forests. Dredging operations and fishing boats that use trawls are degrading the ocean bottom. In the United Nations, an agreement to stop bottom trawling in the South Pacific has been reached, but enforcement will be difficult. In freshwater aquatic zones, dams and excessive water withdrawal from lakes and rivers disrupts flow and habitats. Today 51% of freshwater fish species are threatened with premature extinction. The deliberate or accidental introduction of harmful invasive species displaces many native species and disrupts ecosystem services. The Nature Conservancy has reported that 84% of the world’s coastal waters are being colonized by invasive species, and bioinvaders are blamed for 2/3 of the fish extinctions in the U.S. from 1900-2000. Two major sources of these invaders are ship ballast water and consumers, such as aquarium hobbyists that dump tanks into nearby streams and lakes, a particularly bad problem in Florida. We may be able to use biological controls to fight some invasive species seems, but these programs could just introduce another pest. By 2020, 80% of the world population will live in gigantic cities along marine coastlines, and this
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Final 11 - Study Guide - Chapter 11 - Sustaining Aquatic...

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