International Journal of Marine Science, 2025, Vol.15, No.4, 199-208 http://www.aquapublisher.com/index.php/ijms 199 Feature Review Open Access Effect of Ocean Acidification on the Metabolism and Behavior of Tropical Sea Cucumbers Zhen Liu, Yeping Han Institute of Life Science, Jiyang College of Zhejiang A&F University, Zhuji, 311800, Zhejiang, China Corresponding author: yeping.han@jicat.org International Journal of Marine Science, 2025, Vol.15, No.4, doi: 10.5376/ijms.2025.15.0018 Received: 03 Jul., 2025 Accepted: 10 Aug., 2025 Published: 19 Aug., 2025 Copyright © 2025 Liu and Han, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Liu Z., and Han Y.P., 2025, Effect of ocean acidification on the metabolism and behavior of tropical sea cucumbers, International Journal of Marine Science, 15(4): 199-208 (doi: 10.5376/ijms.2025.15.0018) Abstract In recent years, CO₂ emitted by human activities has continued to rise. The ocean absorbs these CO₂ and has caused seawater acidification. It is expected that the pH of the sea surface will drop by 0.3~0.4 by the end of this century. Tropical sea cucumbers are the "engineers" of the subsea ecosystem, promoting organic degradation and nutrient circulation through feeding disturbances. This study reviews the effects of marine acidification on the metabolism and behavior of tropical sea cucumbers. Studies have shown that under low pH conditions, sea cucumbers have increased respiratory metabolic pressure, digestive enzyme activity is reduced, and more energy is used to maintain the acid-base balance in the body, and their growth and reproduction are limited. At the same time, sea cucumber feeding rate and defense behavior are inhibited, and habitat distribution may change. These changes will have a chain effect on tropical ecosystems such as coral reefs, weaken the nutrient circulation function, and affect ecological balance. In-depth research on the impact mechanism of marine acidification on sea cucumbers will help predict the response of marine ecosystems under climate change and provide scientific basis for resource conservation and aquaculture management. Keywords Ocean acidification; Tropical sea cucumber; Metabolism; Behavior; Ecological impact 1 Introduction As humans emit large quantities of greenhouse gases such as CO₂, the concentration of atmospheric CO₂ continues to rise, and the ocean absorbs about 1/4 of the artificial CO₂, resulting in an increase in the acidity of seawater. The average pH of the ocean surface has dropped by about 0.1 compared with pre-industrialization, and is expected to drop by about 0.3~0.4 at the end of the 21st century under high emission scenarios (Sun, 2024). Ocean acidification has poses a threat to sensitive ecosystems such as tropical coral reefs, manifested as adverse effects such as coral calcification rate and reduced biodiversity. Tropical sea cucumbers play an important role in marine benthic ecosystems. As a typical “ecological engineer,” sea cucumbers feed on seabed sediments and organic debris and excrete them, allowing sediments to be tilled and oxidized, promoting organic matter decomposition and nutrient circulation (Wolfe et al., 2018). Sea cucumber activities help maintain the water quality of the coral reef base and provide nutrient sources for symbiotic algae. In addition, many sea cucumber species have economic value and are an important resource for coastal fisheries and aquaculture. Therefore, studying the impact of marine acidification on sea cucumbers is not only ecologically significant, but also helps in the management and protection of tropical marine resources. Currently, research on marine acidification on echinoderms focuses on highly calcified sea urchins and starfish, and relatively insufficient attention is paid to sea cucumbers with low calcification. There are only a small number of lime-like bone fragments in tropical sea cucumbers, which are believed to be less sensitive to acidification than calcified organisms such as reef-making corals. However, acidification may indirectly endanger its survival and ecological function by interfering with the metabolic balance and behavioral patterns of sea cucumbers. In recent years, trials have begun to focus on the physiological responses of sea cucumbers under acidified conditions, such as changes in respiration rate and feeding vitality (Sun, 2024). A deep understanding of the effects of ocean acidification on the metabolism and behavior of tropical sea cucumbers is of great significance to reveal the
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