International Journal of Marine Science, 2025, Vol.15, No.4, 199-208 http://www.aquapublisher.com/index.php/ijms 202 inhibition to reduce energy consumption. Long-term deep acidification will lead to a continuous low respiration rate of sea cucumbers, and insufficient oxygen supply will affect its vitality and other physiological functions (Wang, 2024). 4.2 Effects of acidification environment on digestive enzyme activity and nutrient absorption Seawater acidification not only affects the respiration of sea cucumbers, but also has a negative effect on their digestive and absorption functions. Studies have found that low pH stress significantly reduces the activity of digestive enzymes such as alkaline phosphatase in the intestine of sea cucumber (Wu et al., 2013). Alkaline phosphatases are involved in the decomposition and absorption of organophosphorus, and the decrease in enzyme activity means that sea cucumbers are less efficient in obtaining nutrients from food. In addition, acidification may disrupt the balance of the intestinal flora of sea cucumbers and damage the digestive tract epithelium, further weakening its digestive capacity. Due to the decrease in food interest and inhibition of enzyme activity, the absorption rate of nutrients of sea cucumbers decreases accordingly. Long-term experiments have confirmed that the intake and growth rate of sea cucumbers under acidification conditions have significantly decreased: the specific growth rate of citrus citrus decreased by nearly 20% compared with the control when the pH decreased by about 0.3 (Yuan et al., 2016). Inadequate nutritional intake forces sea cucumbers to use their own reserves, resulting in weight loss and tissue growth restriction, ultimately endangering their health and survival. 4.3 Redistribution of energy metabolism and increase in metabolic costs Faced with acidification stress, sea cucumbers often need to invest more energy to maintain their homeostasis, which leads to the redistribution of their energy metabolism. In order to regulate the acid-base balance of body fluids, sea cucumbers must strengthen ion transport, ammonia discharge and other processes to increase basal metabolic energy consumption. This means that the energy used for growth and reproduction is relatively reduced. Experimental evidence shows that under the combined action of acidification and other stresses (such as heating), the energy distribution of sea cucumbers has significantly changed: the digestion and absorption efficiency of citrus ginseng is reduced under acidification and heating conditions, and the proportion of feces excretion energy is significantly higher than that of the control group. This suggests that sea cucumbers use more energy intake to cope with environmental stresses and reduce the share of energy allocated to growth and reproduction (Yuan et al., 2016). In the long run, the increase in metabolic costs will lead to a decrease in weight in sea cucumbers, a decrease in reproductive investment, and may also be impaired in physiological functions such as immunity. Ocean acidification breaks the original energy distribution balance by increasing the energy expenditure of sea cucumbers to maintain life activities, and ultimately has a potential negative impact on population renewal and ecological functions. 5 The Effect of Marine Acidification on Sea Cucumber Behavior 5.1 Changes in feeding behavior Ocean acidification usually leads to a weakening of sea cucumber feeding behavior. Experimental observations show that the feeding rate of sea cucumbers decreased, the feeding interval was prolonged, and food intake was significantly reduced. Research on ginseng found that the intake of ginseng decreased under acidification treatment, and its growth rate decreased by nearly 20% compared with normal pH. Long-term diet reduction will directly affect the nutritional acquisition of sea cucumbers and further affect their metabolism and growth through insufficient energy intake. 5.2 Changes in activity and habitat selection In addition to feeding, the activity level and habitat of sea cucumbers are also affected by ocean acidification. Different species have different behavioral responses to acidification. For example, low pH significantly reduced the frequency of nocturnal activity of luminous snails in the same domain, but had little effect on the activity of sea cucumbers; after several days of domestication, the activity level of both returned to normal. This suggests that sea cucumbers have stronger behavioral tolerance than some invertebrates (Yuan et al., 2018). In the low-pH coral reefs formed by the CO₂ leakage in Papua New Guinea, a large number of sea cucumbers can still be
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