This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Kelp forests, ecosystems formed by large brown seaweeds in coastal waters, provide habitats for numerous fish and invertebrates and are vital to coastal productivity and carbon cycling. However, in recent years, kelp forests have declined throughout Japan, alongside the spread of "isoyake," a phenomenon in which rocky reefs become largely devoid of large seaweeds.
This ecological shift has been primarily attributed to rising sea temperatures and intensified grazing by herbivorous fish. To identify the drivers behind this collapse, researchers investigated the causes of kelp forest decline by integrating more than 40 years of data on the biomass of Ecklonia cava (kajime kelp) and long-term surveys of kelp cover across approximately 200 km (124 miles) of the Izu Peninsula coastline. These data sets were combined with satellite-derived sea surface temperature and marine heat wave records, field surveys of herbivorous fish and laboratory experiments examining the thermal tolerance of E. cava.
The paper is published in the journal Global Change Biology. The study found that the Izu coast experienced a dramatic surge in warming and marine heat wave activity from 2017 to 2025, during the prolonged Kuroshio Large Meander event. Laboratory experiments demonstrated that the photosynthetic performance of E. cava declined rapidly at temperatures above approximately 29.5°C (85.1°F).
At the same time, warming extended the annual window of temperatures suitable for herbivorous fish grazing by up to 86 days. These findings suggest that the combination of heat-induced physiological stress and a longer grazing season has hindered E. cava recovery, ultimately contributing to widespread loss of kelp forests and the transition to "isoyake" conditions along the Izu Peninsula. Harvey et al., Unprecedented Warming and Increased Herbivory Drive Collapse of Japan's Kelp Forests, Global Change Biology (2026).
DOI: 10.1111/gcb.71106 Journal information: Global Change Biology Swati Mestri holds a bachelor's degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space. Full profile → Master's in physics with research experience.
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