"They can feed on everything from really tiny copepods that you can barely see to big shrimp, and even fishes," Stewart said. Mantas were known to feed primarily on tiny marine organisms called zooplankton, filtering them from seawater with specialized gill plates, but tissue analysis of the rays revealed that their diets are broader than scientists had expected. "Some months, they were close to the surface, and some months, they were much deeper, which correlates to where we think different types of food may have been available." "The tags also record where in the water column they are," he said. So why don't mantas seasonally roam the oceans as other massive predators do? Greater flexibility in their diet might be the answer, Stewart suggested. And their genetic analysis confirmed that mantas in the different sample sites were not, in fact, the same individuals traveling from place to place, but rather established groups that staked out their ranges and stayed put. But every tag they deployed after that returned the same results over a six-month period. Stewart said their initial reaction was, "Well, that's interesting," though they needed to collect more data to be sure. In the very first batch they collected, Stewart and his colleagues noticed something unexpected: The tags popped off within about 62 miles (100 km) from where they were originally attached, and when the scientists mapped the mantas' movements over months, they found that the tags remained in largely the same area. (Image credit: Scripps OceScripps Oceanography / Joshua Stewart) The tags were programmed to detach after six months and then float to the ocean surface, where scientists could retrieve them.Ī giant manta ray swims in the Revillagigedo Archipelago, about 300 miles off Baja California, Mexico. Tagging technology has been used by oceanographers for more than two decades, but recent innovations have made devices much more robust and reliable, with a recovery rate of 80 to 90 percent, Stewart said. The researchers set out to tag and sample manta-ray populations at four sites that were up to 8,000 miles (13,000 kilometers) apart, to find out how far the rays traveled. They're certainly big enough and capable enough."
"So we thought the mantas were migratory, too. "If you look at every other big animal that lives in remote pelagic environments, they're making long, epic migrations," Stewart said. And because mantas are so big, it was thought that they were simply doing what large migratory ocean creatures such as whales, leatherback turtles and bluefin tuna do - following their food. And in some locations, researchers would see the mantas for a few weeks or months, but they wouldn't find any at all for the rest of the year. In turn, plankton-feeding giant manta rays prefer waters near native forests instead of near the coconut groves, McCauley and his colleagues report online May 17 in Scientific Reports.Stewart, who is also the associate director of the nonprofit conservation organization Manta Trust, explained that individual mantas can be identified by unique patterns of spots on their bellies photos of mantas captured by researchers, dive tours and citizen scientists were used to track mantas over time.īut sometimes, nearly two decades would elapse between sightings, Stewart said. Tiny plankton in the sea flourish on this nitrogen boost. The nesting seabirds enrich forest soil with their droppings and carcasses, and water washing out of this rich forest carries about 26 times as much nitrogen as runoff from palm forests. It turns out that the birds’ real estate decisions affect where big fish feed off the coast. The birds tend to avoid the branch-poor, bendy coconut palms that were planted when people reached the far-flung atoll. Red-footed boobies, black noddies and other seabirds that feast on fish nest in the islands’ sturdy, many-branched native trees, says ecologist Douglas McCauley of the University of California, Berkeley. SURF AND TURF The nesting preferences of birds such as black noddies (left) have implications for the feeding habits of giant manta rays (right) on the Pacific atoll of Palmyra, a new study finds. By following a pinball cascade of ecological consequences, researchers have traced the far-flung influences of preserving bird-friendly native forests versus replacing those forests with coconut palms on the Pacific atoll of Palmyra.
0 kommentar(er)
