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To figure out why native forests help manta rays thrive, McCauleyand his colleagues made careful measurements of Palmyra s marineand terrestrial ecosystems. They started with sea birds such asred-footed boobies, which fly over the ocean to catch fish. Thebirds then return to the islands to make nests in the trees. Whenthe scientists surveyed Palmyra s birds, they found that thenative forests had five times more birds than the palm forests. The difference lies in the architecture of the trees. Palm treesare essentially pillars, with tufts of leaves on top that whip backand forth in the wind. Palmyra s native trees, by contrast, formdense, thick canopies where birds can find stability andprotection. Nesting in the trees, the birds drop lots of guano on the ground.The guano is rich in nitrogen; the scientists found that the soilsof the native forests have nitrogen levels five times higher thanthose found in palm forests. The guano thus fertilizes the trees,which build up a greater concentration of nitrogen in their leaves.The leaves then fall to the ground and create a deep, rich soil. To track the fate of the nitrogen, McCauley and his colleagues tookadvantage of a quirk of guano. Nitrogen atoms come in differentisotopes (with different number of neutrons in their nucleus).Guano happens to be rich in one isotope known as nitrogen-15. Weused the chemistry to link Runoff from native forests had 18 times more nitrogen than that ofplanted palm forests. each one of these interactions one to the other, said McCauley. The soil and leaves in native forests are high in nitrogen-15 aswell. When the rain comes to Palmyra, it washes that guano-derivednitrogen along with other nutrients from the rich soil outinto the ocean. The runoff from the native forests had 18 timesmore nitrogen than that of palm forests, the scientists report. That nitrogen influences life on the way from the land to the sea.Clams living in the intertidal zones on the coasts of nativeforests have elevated levels of nitrogen-15. So do sponges in thereefs further out at sea. The nitrogen and other nutrients flowingout from the native forests fertilize phytoplankton thesun-harnessing algae in the ocean much as it does the trees onland. McCauley and his colleagues also found that the zooplankton thetiny animals that graze on the phytoplankton was three timesmore abundant off the coast of native Palmyra forests than off thecoasts of palm forests. McCauley s study highlights why ecosystems on land and at sea canbecome linked. Nitrogen and other nutrients are often in scarcesupply, and living things are very good at concentrating them andmoving them from one place to another. Palmyra s birds draw outthe nitrogen from the ocean and concentrate it in the forests,which then deliver a rich supply of nitrogen and other nutrientsback to the ocean, ultimately providing manta rays with food. A similar process takes place in the northwestern United States,where streams are starved for nitrogen. Each year, vast numbers ofsalmon swim When we damage the links between land and sea, we can havesurprisingly big effects on ecosystems. from the Pacific into those streams, where they mate, lay eggs, anddie. We re all familiar with footage of bears feasting on salmon,but they re not the only ones to benefit from the migration of thefish. After the salmon die, the nitrogen in their bodies fertilizesthe streams and enriches the soil. Plants that grow aroundsalmon-choked streams have high levels of nitrogen 15 in theirtissues. These links between land and sea are particularly vulnerable, andwhen we damage them, we can have some surprisingly big effects onecosystems. When people in the Pacific cut down native trees toplant coconut palms, they doubtless have no idea that they areaffecting the lives of manta rays. And yet McCauley s researchsuggests that this is precisely what is happening. As the nativeforests shrink, so too does the prime ocean habitat for the mantarays. The disruptions can also flow the other way, from sea to land. Onthe Aleutian Islands in Alaska, for example, people introducedfoxes in the early 1900s to harvest their fur. The foxes proceededto attack the sea birds that nested on the islands, driving downtheir numbers. Since the birds ingested nitrogen-rich fish anddeposited the nitrogen on land, the smaller population of birdsdelivered a smaller supply of nitrogen to the islands. The soilbecame less fertile, and the island ecosystems shifted fromgrasslands to shrubs. Humans are also good at pumping nutrients between ecosystems.Farmers, for example, spread fertilizers on their fields, and thenitrogen and phosphates get washed into rivers and into the oceans.But this type of runoff is no cure for damaged land-to-sea links.It delivers too many nutrients in too little time. Instead ofstimulating healthy ecosystems, it can instead create so-called dead zones in places like the mouth of the Mississippi River. Leave it to us to overdo things, says McCauley. POSTED ON 17 May 2012 IN Biodiversity Business & Innovation Oceans Science & Technology Science & Technology Asia North America North America. The e-commerce company in China offers quality products such as China Wireless Serial Converter , China Serial Isolator, and more. For more , please visit Serial Device Servers today!
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