Impacts on Marine Environments

our blue planet, the oceans dominate the earth in a variety of ways. With an average depth of almost 4 km, they provide over 99 percent of the habitable space for life on earth (Woodard 2000:31). As human populations have grown exponentially over the past century, and with 60 percent of the world’s population living within 100 km of the coast, many have looked to the oceans as a source of hope and protein to feed the masses. Once thought to be nearly inexhaustible, many global fisheries have collapsed or are severely depleted (Jackson et al. 2001; Pauly et al. 2002; Roberts 2002; Worm et al. 2006). Pollution, habitat loss, global warming, and the introduction of exotic species also take an increasing toll on coastal and pelagic ecosystems (see Carlton et al. 1999; Earle 1995; Ellis 2003; Vitousek et al. 1997:495; Woodard 2000). We are only beginning to understand the larger ecological consequences of such impacts, including the wholesale collapse of many coral reef, kelp forest, estuarine, arctic, benthic, and other ecosystems—foundations of marine productivity that have nurtured human societies for thousands of years. These impacts are now global in scale, but humans have had the heaviest impact on nearshore and coastal areas (0–50 m in depth), substantial impacts on deeper continental shelf habitats (50–200 m), and comparatively less impact on the deeper oceans (Steele 1998). In the last few years, two national commissions have issued reports concluding that the world’s oceans and fisheries are in a state of crisis (Pew Oceans Commission 2003; U.S. Commission on Ocean Policy 2004). The management of fisheries and our understanding of the broader ocean crisis have been hampered by the shallow historical focus of policy makers and resource managers, who have based many decisions on ecological observations that span 10, 20, or 30 years, or on historic catch records that rarely span more than a few additional decades. Just over a decade ago, Daniel Pauly (1995) referred to this problem as the “shifting baselines syndrome,” where fisheries managers use recent historical baselines to manage fisheries that are depleted or collapsed. Such recent historical baselines are often fundamentally flawed because they fail to account for the abundance of key species prior to heavy fishing or hunting by indigenous peoples or early commercial harvests (Dayton et al. 1998; Jackson