Litter decomposition of cultivated macroalgae and its implications for water quality in the East China Sea
摘要
The decomposition of macroalgae litters is a critical marine ecological process. This study investigated the decomposition dynamics and nutrient release patterns of litters from three cultivated macroalgae species in the East China Sea: Sargassum vachellianum, Ulva pertusa, and Chondria tenuissima. Field experiments and laboratory simulations were conducted to examine decomposition rates, changes in the contents of C, N, P, acid insoluble matter, cellulose, and hemicellulose, as well as nutrient release into the water during decomposition. The results indicated that all three macroalgae species exhibited varying degrees of weight loss and reductions in C, N, P, acid insoluble matter, cellulose, and hemicellulose during decomposition. C. tenuissima decomposed at the fastest rate, showing the most rapid loss of nutritional components. Based on the Olson decay model, the mean daily biomass loss rates were 1.36% for S. vachellianum, 1.50% for U. pertusa, and 1.75% for C. tenuissima under field conditions, indicating clear interspecific differences in decomposition speed. Additionally, the decomposition significantly affected nitrogen and phosphorus concentrations in the water. The contributions of S. vachellianum, U. pertusa, and C. tenuissima to water nitrogen were 11.79, 14.88, and 13.23 mg·g⁻1, respectively, and their contributions to phosphorus were 7.95, 9.03, and 10.42 mg·g⁻1, respectively. These findings suggest that in high-density macroalgae farming areas, the decomposition of accumulated dead macroalgae can alter local nutrient conditions; therefore, timely management of macroalgal litter is recommended to reduce potential water-quality deterioration while considering that nutrient release may also provide short-term nutrient supplementation to cultured seaweeds.