International Journal of Marine Science, 2025, Vol.15, No.4, 199-208 http://www.aquapublisher.com/index.php/ijms 201 Figure 1 Dissolution of natural marine CaCO3 grains after a minute in suspension in water (Adopted from Sulpis et al., 2022) 3.2 The role of protein and lipid metabolism in sea cucumber physiology The nutrients in sea cucumbers are mainly stored in the form of protein. The body wall of sea cucumber is rich in structural proteins such as collagen, accounting for a large proportion of the dry weight; during the peak season of feeding, sea cucumbers convert the organic matter intake into body wall and muscle protein for accumulation. When faced with high energy consumption stages such as hunger or reproduction, these protein reserves can be decomposed to provide energy (Zamora and Jeffs, 2015; Asha and Muthiah, 2018). In contrast, sea cucumbers have low fat content in their bodies, but lipids provide necessary energy for developing reproductive gonads during the reproductive period. High-protein baits can promote the growth and repair of sea cucumber tissue, while appropriate lipid levels help improve reproductive performance. 3.3 Metabolic regulation mechanism for environmental stress (temperature, salinity, acidification) Tropical sea cucumbers have evolved a series of metabolic regulatory mechanisms to deal with environmental stresses such as temperature, salinity and acidity. When the temperature is too high, sea cucumbers often reduce their activity and even enter dormant state to reduce energy consumption and oxidative damage. For example, ginseng stops eating and sleeping in summer when the water temperature is too high in summer, thereby protecting its own tissues from depletion (Li et al., 2021). When salinity changes drastically, sea cucumbers maintain body fluid balance through osmotic regulation: in a low-salt environment, their body cavity fluid Na⁺-K⁺-ATPase plasma pump activity is improved, and they actively ingest ions to stabilize the osmotic pressure (Jiang et al., 2024). Faced with the acidification stress of lowering seawater pH, sea cucumbers also show obvious physiological plasticity. Long-term exposure experiments show that adult sea cucumbers can adjust the ion composition of body fluids to stabilize the pH of the internal environment, and the pH of the body cavity fluid gradually returns to normal levels after the initial decrease. This shows that sea cucumbers have certain acid-base regulation capabilities and can withstand moderate environmental acidification. At the same time, research has found that increasing water temperature can offset the adverse effects of acidification on sea cucumber metabolism to a certain extent: for example, the feeding and growth rates of citrus citrus under heating conditions are higher than those of pure acidification conditions (Li et al., 2021). 4 Effects of Marine Acidification on Sea Cucumber Metabolism 4.1 Changes in respiration rate under low pH conditions The effect of ocean acidification on sea cucumber respiratory metabolism depends on the degree of acidification and exposure time. Under moderately intense acidification conditions, sea cucumbers can maintain near-normal metabolic levels through physiological regulation. Experiments showed that in an environment with a pH reduction of about 0.3, the oxygen consumption rate of pilosula was not significantly different from that of the control group, and its energy distribution pattern did not change significantly. This shows that the basal respiratory metabolism of sea cucumbers has a certain degree of toughness to moderate acidification and will not immediately cause disorders. When the acidification level exceeds the tolerance range, sea cucumbers may initiate metabolic
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