TOKYO -- A major amount of the kelp distributed along the northern coast of Japan is at risk of disappearing if global warming continues to heat waters around the country at their present rate, according to a research team at Hokkaido University.
Their findings were published in English in the Ecological Society of Japan's journal, Ecological Research, on Nov. 19. A member of the team said, "It's not just that there will be big changes for the seaweed bed, known as the "cradle" that rears marine life, but also that this will have a major effect on kelp farmers and others."
The team looked at 11 different types of kelp that grow in the northern Japan area, including Saccharina japonica, known as makonbu in Japanese, and Laminaria angustata. Based on 1,958 records of their distribution from the 1950s to the 1980s, they estimated the kelp species' distribution in the 1980s before warming began to accelerate.
They then predicted what the distribution of kelp would look like in the event that global average temperatures at the end of this century rise up to either 2 or 4 degrees Celsius higher than pre-industrial levels.
Their results showed that in the event that global average temperatures rise to 4 C, waters on the eastern coast of Hokkaido, Japan's northernmost prefecture, will be at most 10 C warmer than they were in the 1980s. This would bring them to about the same temperatures currently found in the ocean off the coasts of Tokyo and Chiba Prefecture, which are much farther south.
If the described conditions come to pass, the team expects the distribution of kelp across northern Japan to fall precipitously to between 0 and 25% of levels in the 1980s. All 11 types would be in a state of crisis, and six types found on the eastern coast of Hokkaido, including the Laminaria longissimi, are under possible threat of disappearing completely.
Even in the event that global average temperatures rise by 2 C, kelp distribution is expected to fall to between 30% and 51% of levels in the 1980s, and four types are in danger of disappearing.
Since the middle of the 20th century, changes in parts of the ecology of the northern Japan coast accompanied by rising sea temperatures can already be observed. For example, kelp species have been replaced by wakame seaweed and other types.
Masahiro Nakaoka, a member of the team and a professor in marine ecology at Hokkaido University, said, "To protect our fishing industries and food culture, it's important that we proceed with a plan against global warming."
(Japanese original by Ai Oba, Science & Environment News Department)