Global warming has caused the average temperature of the upper ocean to increase by 0.07°C per decade. These temperature increases affect marine species and ecosystems in several ways, including increased mortality of key habitat-forming species such as seagrasses, changes in species distributions, and greater incidence of disease.
Recently, a research team led by Professor ZHOU Yi from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) first reported the northward shift of the southern boundary of the iconic temperate Zostera seagrass. marina (eelgrass) on the east coast of China and revealed that global warming is the underlying reason.
The study was published in iScience July 13.
The researchers performed 16 transplants of adult eelgrass shoots and seeds at the historical southern distribution limit of eelgrass between 2016 and 2021. They also monitored the morphological performance, molecular traits, and environmental parameters of the eelgrass.
They found that high water temperatures caused Z. marina to fail to recover at the edge of its biogeographic range. Transplanted eelgrass was negatively affected by high water temperatures, and most shoots did not survive the first summer and none survived the second in shoot or seed transplants between 2016 and 2021.
Transplanted eelgrass that underwent heat stress exhibited decreased seagrass growth, lower shoot height, reduced energy storage capacity (rhizome diameters), and increased mortality rate.
In addition, the antioxidant enzyme activity of transplanted eelgrass changed with increasing water temperature, and heat shock protein (HSP)70 and luminal binding protein (BIP) were significantly up-regulated at increase under heat stress conditions. “High water temperature, which has been shown to be one of the direct causes of seagrass shoot mortality, poses a significant threat to seagrass restoration, especially at the edge of its range. increasing temperatures associated with global warming will likely continue to shift the range boundaries of eelgrass northward,” said XU Shaochun, first author of the study.
“Our study provides a strong body of evidence that the southern limit of Z. marina in China has shifted north. Although range shifts and tropicalization are widely reported, this is the first evidence of global warming causing a northward shift of suitable eelgrass habitat,” said Prof. ZHOU.