To Preserve Earth's Biodiversity, Study The Sea's Web of Life

THE next time you inhale, spare a thought for the ''grasses'' of the sea. These are the microscopic floating plants that supply much of the atmosphere's oxygen. They also sustain most of the ocean's rich diversity of life.

The National Academy of Sciences, acting through its National Research Council (NRC), says it's time for scientists to drop the traditional piecemeal approach to marine biology and begin a concerted effort to understand ocean life as a wonderfully diverse, yet integrated system. Scientists should do for the sea what they did years ago for the rain forest: Recognize that it's the health of the whole system that counts, not just the fate of a few species within it.

Since the ocean has literally been out of sight for most ecologists, it also has been out of mind as these scientists mobilized to preserve as much of Earth's biodiversity as possible. Yet the ocean is the biggest interconnected environment we have. Unless scientists understand how its living systems work, they won't know enough to protect the planet's biodiversity. Also, unless they know what's happening to the sea's ''web of life,'' they won't know how to manage declining fisheries effectively.

Overfishing is a major direct cause of that worldwide decline. But it's not the only factor involved. Fishing practices can have unintended side effects such as damaging sea-bed habitats or interrupting the food supply of fish. Such things contribute to decline of commercial species even without overfishing. Changing weather patterns and shifting ocean currents can also have drastic biological effects. The decline of marine life off North America's west coast, where overfishing is not involved, illustrates this.

In simplified terms, the sea has its deserts and lush pastures. Where nutrients such as nitrogen or phosphate are readily available, microscopic plants -- the phytoplankton -- burgeon. Like grass on land, they convert sunlight into energy-rich food for a variety of grazers. These grazers -- the so-called zooplankton -- are tiny animals, including fish larvae. They in turn feed larger predators. And so on up the food chain.

As the tiny plants and grazing animals die, their remains drift downward where bacteria decompose them to produce nitrogen and other nutrients. This is why areas rich in marine life tend to be areas where such nutrient-rich water wells up from below toward the surface.

Last month, John McGowan and Dean Roemmich with Scripps Institution of Oceanography at San Diego reported in Science magazine that, since 1951, many larger species of zooplankton off California have declined 80 percent. This has brought declines up the food chain, even affecting birds that feed off zooplankton.

The scientists point out that, during this period, surface water has warmed as much as 1.5 degrees in some places. This has reduced the upwelling of the nutrient-rich deeper water, starving the area's food chains at their phytoplankton base. The warming seems to be part of a long-term climate change.

The Scripps researchers note that they don't know if the warming is part of a natural cycle or a sign of theoretical man-made global warming. However, it dramatizes the point that scientists need to know the whole marine biology story if they are to assess what human activity is doing to ocean life. Blaming fishery declines simply on overfishing is too simplistic.

In making this same case, the NRC report issued March 21 isn't a plea for more research money, although funding will be needed. It is a wake-up call to marine scientists to face up to the problem of understanding biodiversity in the sea. They need to take all factors into account, including climate changes, even when studying a limited area like an estuary. And that means working in scientific teams that integrate the skills of specialists.

It would seem to be an obvious thing to do. But for marine biologists who tend to be specialized, that requires a culture change.

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