WESTERN AUSTRALIA - In 2011, a heatwave caused the waters of Shark Bay to rise to over 4 degrees above its annual average temperature. Shark Bay, a UNESCO world heritage site, has suffered a substantial loss of seagrass, greatly affecting the ecosystem in the area. The 5.4-million-acre protected site is located in Gascoyne, Western Australia.
Long term data collected from 2007 to 2017 were analyzed by researchers in their attempt to investigate the effects of the heatwave to the survival of dolphins. According to the data, the researchers found out that following the said heatwave in 2011, the survival rate of the dolphins has dropped by 12%. Data collected until 2017 also shows that female dolphins are giving birth to fewer calves since then.
Sonja Wild, the first author of the study and a former Ph.D. candidate at the University of Leeds, explained how unusual it was that the reproductive success of the female dolphins has not yet returned to normal. The data collected within the period of time suggest that the negative influence of the heatwave is still affecting marine life. Researchers are still investigating the matter in detail.
Wild stated that the lower reproduction rates could also possibly be the result of different factors such as increased newborn mortality, neglect of calves, delayed sexual maturity, or it can also be a combination of the said factors.
The extents of the effects of the heatwave are yet to be investigated as some dolphin groups were not affected severely affected by the higher water temperature. Dolphins that locate food in deep water using sponges as tools seem to be not as badly affected than those who do not use the said technique.
The team raised their concern that a phenomenon such as a heatwave could have long-term negative effects even to living organisms with high adaptability such as marine mammals.
Wild emphasized the long-term consequences that drastic changes in the ecosystem could hurt not only small organisms but also those at the top of the food chain. In this case, it is the loss of seagrass from the lower levels of the food chain and the dolphins at the top.
Michael Krützen, a professor at the Department of Anthropology at UZH, have warned that heatwaves are likely to occur more often because of climate change, adding that the long-term effects of these heatwaves could affect the entire oceanic ecosystem and not only marine mammal populations.
