Coastal surge: ecosystems likely to suffer as more people move to the shores.

The population of the United States in 2002 was about 288 million, up from nearly 249 million in 1990. That increase could spell trouble for ecosystems in coastal areas because population densities are increasing at faster rates in those places than elsewhere, says Kristen Crossett of the National Oceanic and Atmospheric Administration in Silver Spring, Md.

If this trend continues, coastal ecosystems, which include hundreds of plants and animal species, will experience shrinking habitats. Furthermore, increased runoff of fertilizers and other nutrients will probably stimulate harmful algal blooms in some areas.

Right now, about 96 million people live in the 330 counties or equivalent geographic units that border on the Atlantic and Pacific Oceans, the Gulf of Mexico, and the Great Lakes. According to census data, the overall population of coastline counties jumped more than 13.3 percent between 1990 and 2002, and the number of housing units there increased more than 12.3 percent during the period. On average, those counties host more than 400 residents per square kilometer, more than triple the population density in non-coastal counties.

Nine of the 10 counties with the fastest growth since 1990 lie along the Atlantic Coast; the exception is California's San Francisco County, a location bordering the Pacific Coast.

Rachel S. Franklin of the U.S. Census Bureau in Washington, D.C., reported these data last week in Philadelphia at the annual meeting of the Association of American Geographers (AAG).

In addition to the inhabitants of the ever-more-populous coastline counties, roughly 56 million people live in 343 counties where, in significant portions of the area, precipitation drains directly into the ocean.

Between 1980 and 2002, the increases in population density in these counties together with the coastline counties were about 4.5 times as great as those elsewhere in the nation, Crossett noted at the AAG meeting. In all, more than half of the nation's population lives in these 673 coastal counties, which make up only 17 percent of the nation's land area.

Economic projections suggest that coastal populations will jump another 11 million by the year 2008, says Crossett. Much of that growth will occur along the Pacific coast, where another 2.5 million residents will boost the overall population density about 6.5 percent. In the same period, an extra 2 million people along the Atlantic coast between Virginia and Maine will hike the population density there about 3.6 percent. Gulf of Mexico and Southeastern Atlantic coastal counties will see their population densities rise by 1.5 million, or 8 percent, and 1.3 million, or 9 percent, respectively.

All this development and its ecological impacts will pose immense challenges for coastal communities, including increased demands on energy, infrastructure, and the supply of fresh water.