Almost a decade after the hit Finding Nemo made clownfish seem totally warm and lovable, environmentalists are now looking for a real-life sequel: Saving Nemo.  In the United States, a request has been made to extend the protections of the Endangered Species Act to marine species including the clownfish. But before you start shedding tears for Nemo and his buddies, keep in mind that this request is not based on any evidence of a decline in the clownfish population. Instead, what has sparked concern is the worsening health of coral reefs, which more than one million aquatic species including the clownfish depend on to thrive, even survive.  In ways it makes more sense to move to protect a species when its habitat declines rather than its actual population. The most important mission of the Endangered Species Act is the protection of species' habitats; without their habitats, there's almost no hope of saving endangered animals, except perhaps in a zoo.    Earlier this year, alarming news came about the world's largest coral reef system, Australia's Great Barrier Reef (GBR,). A study has shown the Reef is in sharp decline, with half of its coral cover gone in the past 27 years.      Katharina Fabricius, an Australian coral reef ecologist co-authoring the study, has been diving and working on the GBR since 1988--and has watched the decline. "There are still a lot of fish ... but not the same color1 and diversity as in the past," she said.    The study team used information from more than 2,000 surveys to determine the rate of decline between 1985 and 2012. That overall 50-percent decline, they estimate, is a yearly loss of about 3.4 percent of the Reef. If the trend continued, the coral cover could halve again by 2022.     Several main factors are responsible for the decline, the study found. Intense tropical cyclones  , believed to be fueled by global warming, have caused massive damage to reefs in the central and southern parts of the Reef. Meanwhile, population explosions of the coral-consuming crown-of-thorns starfish   have affected coral populations along the length of the Reef. Two severe coral bleaching   events, caused by ocean warming, have also had major damaging impacts in northern and central parts of the GBR. According to the article, all of the following factors contribute to the decline of Great Barrier Reef's coral cover except   _  .
the growing popularity of scuba  diving around the Reef stronger tropical cyclones fueled by global warming the rapidly growing population of type of coral-eating starfish coral bleaching caused by rising temperature of the ocean water