Some observers, including the 19th-century American poet James Russell Lowell, have described the oceans as "monotonous." And to the untrained eye, gazing out over a seemingly endless expanse of seas, it can all look pretty much the same. Yet beneath the surface, all patches of ocean are not created equal: Tremendous variation can be found in temperature, seafloor topology, species abundance, and diversity.
Marine biologists now believe there are "biodiversity hotspots" in pelagic (open ocean) zones. These zones serve as gathering grounds for a dense array of life and are comparable to terrestrial hotspots now designated as prime targets for conservation. Pelagic hotspots identified to date—found off the coasts of Australia, Sri Lanka, Hawaii, Florida, and the Carolinas—lie in mid-latitude regions where warm and cold water masses converge and are close to coral reefs, seamounts (volcanic protrusions that form on the ocean floor), and "shelf breaks" at the edge of the continental shelf. Due to the abundant food supply predatory fish such as tuna, swordfish, and sharks, tend to concentrate in these same regions. Since many of these hotspots lie within national waters, conservationists believe it will be easier to protect them by creating reserves in which fishing is stringently regulated or banned.
Investigators have identified 10 coral reef hotspots closer to shore. These 10 reef systems comprise just 15% of the world's coral reefs, yet provide home to roughly half the world's most vulnerable marine species. Further reef stress from overfishing could lead to serious depletion if not outright extinction within the hotspots. With many organisms restricted to such a small range, any local impacts could result in global losses.
Eight of the 10 reef hotspots abut terrestrial hotspots, and many also adjoin pelagic hotspots. Consolidated conservation zones, extending from land to sea, could safeguard a significant fraction of the planet's most threatened biota.
A single bluefin tuna, which can weigh more than 1,000 pounds, often fetches more than $10,000 in today’s market, and that financial incentive has contributed to the fish’s demise.