An unprecedented marine heat wave had long-lasting negative effects on both survival and birth rates at the iconic dolphin population in Shark Bay, Western Australia. Researchers at UZH have now documented that climate change can have more far-reaching consequences for conservation of marine mammals than previously assumed.
Shark Bay in Western Australia in early 2011: A heat wave causes the water temperatures to rise to more than four degrees above the annual average. The extended period caused a significant loss of seagrass, which drives the Shark Bay ecosystem in this coastal area, a UNESCO World Heritage Site.
Researchers from UZH have now investigated how this environmental damage has affected the survival and reproduction of dolphins. They used long-term data on hundreds of animals collected over a ten-year period from 2007 to 201
The negative influence of the heat wave is unprecedented
"The prevalence of the heat wave's negative influence surprised us," says Sonja Wild, former PhD candidate at the University of Leeds and first author of the study. "It is particularly unusual that women's reproductive success does not seem to return to normal levels even after six years." There are several possible explanations for this phenomenon, e.g. Neglect of calves, increased newborn mortality, delayed sexual maturity or a combination thereof, but researchers have not yet been able to examine them in detail.
Tool-using dolphins are less affected
Interestingly, the heat wave did not have the same effect on all dolphin groups. Dolphins that use sponges as tools – a socially learned feeding technique that helps dolphins to locate food in deep water – were not as badly affected as those who do not use this technique. "Nevertheless, our work raises concerns that such sudden events may have quite negative long-term effects even in groups of marine mammals known to adapt normally to new environmental conditions," says Sonja Wild.
Dire news for whole oceanic ecosystems?
In their study, the UZH researchers show for the first time that marine heat waves do not only affect organisms at lower levels in the food chain, but can also have significant long-term consequences for animals at the top, such as dolphins. "Marine heat waves are likely to occur more frequently in the future due to climate change," says study director Michael Krützen, professor at the Anthropological Institute at UZH. "This is worrying not only for the long-term prospects for marine mammal populations but also for entire oceanic ecosystems."
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