In Japan, decrease of important seaweed beds has been noticed by fishermen for more than a century and called isoyake.

In the modern context, isoyake (e-so-ya-kay) is defined as decrease or disappearance of upright seaweed beds resulting in the formation and maintenance of poorly vegetated area on the shallow bedrock and stony beds, other than seasonal and slight yearly fluctuations. Seaweeds decrease when they were grazed or browsed by herbivores (e.g., sea urchins and/or herbivorous fish), withered in waters with high water temperature, and grow by sedimentation, and or detached in storms.

Some are natural, but the others are highly anthropogenic. The resultant poorly vegetated areas occur most often offshore of seaweed beds, sometimes zoned between shallow and deep beds or patched among the beds.

Isoyake has increased during the 20th century; now most of coastal prefectures have more or less isoyake areas. The restoration of seaweed beds has often been unsuccessful because of drastic changes in coastal environments, a misunderstanding of isoyake, and inappropriate selection of restoration method, a decrease of young fishermen, etc.