International Journal of Aquaculture, 2025, Vol.15, No.6, 308-316 http://www.aquapublisher.com/index.php/ija 311 4 Ecological and Environmental Impacts of Porphyra Cultivation 4.1 Positive effects of cultivation on marine ecosystems porphyra farming has multiple positive effects on Marine ecology. On the one hand, porphyra absorbs nutrients such as nitrogen and phosphorus from seawater, which can effectively reduce the degree of eutrophication in nearshore waters and decrease the occurrence of algal blooms and red tides. On the other hand, porphyra fixes carbon dioxide through photosynthesis and has a certain "blue carbon" carbon sequestration effect (Zhao et al., 2015). Secondly, the laver farming facilities provide new habitats for Marine life. Many small fish and shrimp will avoid enemies and forage among the net structures, and the biodiversity in some local sea areas has increased, as if an artificial Marine ranch has been formed. It can be seen that under scientific management, porphyra cultivation not only does not pollute the environment, but also plays a positive role in purifying water quality, sequestering carbon and providing habitats, and is regarded as an environmentally friendly cultivation model. 4.2 Potential environmental risks: eutrophication and disease transmission Although porphyra cultivation is environmentally friendly, improper management may still cause environmental problems. If the stocking density is too high or chemical fertilizers are applied artificially, there may be an excess of nutrients in the seawater, which may instead breed algae and lead to deterioration of water quality. If there is a large amount of seaweed residue floating and rotting after harvest, it will also increase the organic pollution load. Therefore, the scale of aquaculture must be controlled and the residual algal bodies should be cleared in time to avoid local eutrophication (Reverter et al., 2020). Another hidden danger is the prevalence of diseases. High-density single-variety cultivation is prone to induce diseases such as "red rot" in porphyra, which can spread rapidly through water flow (Figure 1), potentially leading to reduced yields or even total crop failure in large areas of cultivation. In addition, if the introduction of porphyra varieties from other places is not properly managed, it may also cause the risk of genetic hybridization or ecological invasion. In this regard, it is necessary to strengthen disease monitoring, promote disease-resistant varieties, and implement crop rotation or temporary breeding in the breeding areas to reduce the probability of epidemic occurrence (Liu et al., 2024). Under standardized management, the environmental and biosecurity risks in porphyra cultivation are completely controllable. Figure 1 Global multi-antibiotic resistance (MAR) index calculated from aquaculture-derived bacteria (Adopted from Reverter et al., 2020) 4.3 Sustainable aquaculture and ecological restoration functions Under proper management, porphyra farming can even serve as an assistant for Marine ecological restoration. Through scientific planning and layout as well as model innovation, the breeding activities themselves achieve sustainability while also having a positive impact on the environment. For instance, promoting integrated farming of porphyra with shellfish, fish, etc., enables the waste from farming to be absorbed by porphyra and the shellfish to purify the water quality, achieving the effect of "treating aquaculture with aquaculture". Appropriately expanding the aquaculture area to offshore deep water can relieve the pressure of nearshore sea use (Bricker et al., 2018). The use of degradable aquaculture materials and the implementation of a rotational fallow system also help
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