Effects of Climate Change on Marine Fisheries

George, Grinson and Ratheesh Kumar, R and Kishore, Nanda (2026) Effects of Climate Change on Marine Fisheries. In: Beyond Blue Horizons Training Manual for BSc (Agri) students of Kerala Agricultural University. ICAR- Central Marine Fisheries Research Institute, Kochi, pp. 54-62.

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Abstract

Climate change is one of the most serious environmental challenges facing the oceans today. Human activities such as burning fossil fuels, deforestation, and industrial growth have increased the concentration of greenhouse gases (GHGs) like carbon dioxide (CO₂), methane (CH₁₄), and nitrous oxide (N₂O) in the atmosphere. These gases trap heat and drive global warming. Since the pre-industrial era, CO₂ levels have risen from about 280 ppm to over 420 ppm by 2024, surpassing what natural systems on land and in the ocean can absorb. The oceans play a major role in regulating the climate by absorbing approximately one-third of the excess CO₂ and most of the heat generated, but this has put the oceans and their life under significant stress. The ocean is warming, becoming more acidic, and losing oxygen in many areas. Rising sea levels, changing rainfall patterns, and more frequent extreme events such as marine heatwaves, cyclones, and floods add more pressure. These changes do not happen in isolation; instead, they interact with each other, causing widespread impacts on marine ecosystems. Coral reefs, plankton, fish, and other organisms are affected, leading to habitat loss, declining biodiversity, and shifts in species distribution. At the base of these ecosystems are microbial and algal communities, which drive primary production and nutrient cycling. Even small changes in temperature, acidity, or salinity can upset their balance. Warmer waters can accelerate growth and increase the risk of harmful algal blooms (HABs). Acidification reduces the ability of calcifying algae to form shells and also alters microbial processes that recycle nutrients. In estuarine and coastal areas, fluctuating salinity reshapes community structures, favoring species that can tolerate such stress. Extreme weather events introduce excess nutrients into coastal waters, triggering algal blooms and creating low-oxygen zones that threaten fish and other aquatic life. These ecological disruptions directly affect fisheries and aquaculture. Changes in plankton composition alter the food available to fish, while HABs and hypoxic conditions damage habitats and reduce fish stocks. For coastal communities, especially in tropical regions, this leads to lower catches, economic losses, and threats to food security.

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