The hotels are full, Japanese tourists throng the designer stores of Waikiki, and the unemployment rate is a mere 3% of the workforce. So what could possibly knock Hawaii, the 'aloha' or 'welcome' state, off its wave? The answer is that Hawaii's 1.2million residents may one day get fed up with playing host to overseas visitors, 7million of them this year. Indeed, some residents are already fed up. KAHEA, an alliance of environmentalists and defenders of native Hawaiian culture, bemoans the pollution caused by the cruise ships and the risk posed by the tourist hordes to creatures such as the dark-rumped petrel and the Oahu tree snail, or to plants like the Marsilea villosa fern. KAHEA has a point, the US Fish ＆ Wildlife Service currently lists some 317 species, including 273 plants, in the Hawaiian islands as threatened or endangered--the highest number of any state in the nation. Even the state flower, the hibiscus brackenridgei, is on the danger list. The loss of species, says one government report, has been 'staggering'. As for the impact of tourism on Hawaiian culture, a KAHEA spokeswoman wryly notes the element of exploitation: 'Native Hawaiian culture is used as a selling point—come to this paradise where beautiful women are doing the hula on your dinner plate. ' So what else is new? Hawaii's environment and culture have been under threat ever since Captain Cook and his germ-carrying sailors dropped anchor in 1778. Foreign imports have inevitably had an impact on species that evolved over the millennia in isolation. Moreover, with up to 25 non-native species arriving each year, the impact will continue. But, as the US Geological Survey argues, the impact can add to biodiversity as well as lessen it. The real challenge, therefore, is for Hawaii to find a balance between the costs and the benefits of development in general and tourism in particular. The benefits are not to be sneezed at. The state's unemployment rate has been below the national average for the past two-and-a-half years. Economists at the University of Hawaii reckon that Hawaiians' real personal income rose by 2.8% last year, will rise by 2.7% this year and will continue through 2007 at 2.5%. According to the state's 'strategic plan' for the next decade, tourism should take much of the credit, accounting directly and indirectly for some 22% of the state's jobs by 2007, more than 17% of its economic output and around 26% of its tax revenues. The trouble is that the costs can be high, too. As one economist puts it, 'We have a Manhattan cost of living and Peoria wage rates. ' That translates into a median house price today on the island of Oahu, home to three-quarters of the state's population, of $ 500, 000, and a need for many workers to take on more than one job. What is the main idea of Paragraph 1?