4/2/2023 0 Comments Kingdom new lands scythe![]() ![]() Microbes feast on the rotting vegetation, consuming oxygen. ![]() There, pollution from nutrients running off the land, such as synthetic fertilizer, sparks algae blooms. SCIENTISTS FOR YEARS have documented oxygen-starved dead zones in places like the Gulf of Mexico and the Baltic Sea. student at the University of Porto, subdues a blue shark, which will be fitted with sensors to study how ocean oxygen levels affect its behavior. Why would they head toward places with less oxygen? And what could it mean for the future of marine life as vast stretches of low-oxygen water grow bigger around the world? These open-ocean sharks are the Olympic sprinters of the marine world-makos are capable of bursts of up to 35 kilometers per hour. After affixing satellite-connected tags to a handful of the fish, he was mystified when the sharks seemed drawn to a large patch of water where northwest Africa bulges into the Atlantic, a region known to be low in oxygen. But the observation came back to him around 2011, when he was tracking blue and shortfin mako sharks traversing the eastern side of the Atlantic Ocean. The discovery was just a footnote in his catshark work. “It was really a classic case of decreasing oxygen clearly displacing the sharks from where they wanted to be,” Sims says. When Sims looked at data from tracking tags attached to the sharks, he saw the fish swam closer to the surface in summer, skirting a pocket of low oxygen. They worked in an inlet on the southwest Irish coast, where the deeper waters grew stagnant over the summer. He and several friends had spent years deciphering the feeding and mating habits of small-spotted catsharks, meter-long, cream-colored fish with cartoonishly large eyes. Sims first noticed a link between shark behavior and oxygen levels in the early 2000s. The lanky 53-year-old recounts these tales with a delight seemingly undiminished since, as a young child, he was enchanted by sharks that washed up on the beaches near his home on England’s southeast coast. He tangled with a feisty catshark that sprang from the water and latched onto his flashlight. He once led a boat in hot pursuit of what he thought was a school bus–size basking shark-only to find the wake he was following came from a lone salmon. He’s donned a chainmail suit to swim with 3-meter bull sharks. Marine Biological Association and the University of Southampton, has experienced his share of drama, disappointment, and occasional comedy over 3 decades of studying sharks. “Finally!” said David Sims, the bearded marine biologist heading the expedition. Hands slid back inside gloves removed after a false alarm an hour earlier. His announcement of a shark on the line jolted them into action. and Portuguese scientists took to the sea aboard Garcia Habas’s boat in November 2022. Sharks-fast-moving fish that burn lots of oxygen, sit at the top of food chains and crisscross huge ocean expanses-should be sensitive indicators of the effects. ![]() As global warming continues, the problem is sure to get worse, with disturbing forecasts that by 2100 ocean oxygen could decline by as much as 20%. But some researchers believe deoxygenation could ultimately pose a more significant threat, making vast swaths of ocean less hospitable to sea life, altering ecosystems, and pushing valuable fisheries into unfamiliar waters. Two other climate-related threats to the seas-ocean acidification and marine heat waves-get more attention from scientists and the public. Lena MuchaĬlimate change is leaching oxygen from the ocean by warming surface waters. Off Gran Canaria, one of the Canary Islands, a small fishing boat carried a team of scientists hoping to tag sharks swimming toward an expanding low-oxygen zone. ![]()
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