International Journal of Marine Science, 2025, Vol.15, No.6, 292-302 http://www.aquapublisher.com/index.php/ijms 299 Figure 2 Conceptual diagram of the anthropogenic nitrogen pump (ANP) (Adopted from Jin et al., 2024) 8 Ecological Effects of Changes in the Marine Phosphorus Cycle 8.1 Impacts on food web structure and trophic transfer Changes in Marine phosphorus supply often spread throughout the food web by affecting primary producers. Insufficient phosphorus supply leads to a decrease in phytoplankton biomass or changes in community composition, and the number of zooplankton dependent on them also decreases accordingly, which in turn affects higher trophic food sources such as fish, and may cause attenuation of fishery resources and reduction of biodiversity (Boxhammer et al., 2018). On the contrary, eutrophication caused by excessive phosphorus input will lead to the abnormal reproduction of a few high-nutrient-tolerant algae, forming a single dominant population. This algal bloom outbreak disrupts the normal food web structure: a large number of algae sink and decay due to the lack of sufficient consumers, resulting in hypoxia at the bottom and massive deaths of benthic organisms and fish (Paerl et al., 2018); Even in the absence of extreme events, if the composition of phytoplankton in a high-phosphorus environment leans towards species with lower nutritional value, it will also reduce the efficiency of trophic level transfer. 8.2 Interactions and feedback mechanisms among phosphorus, carbon, and nitrogen cycles In the ocean, phosphorus is not a lone fighter; it is always entangled with its two old partners, carbon and nitrogen. For phytoplankton to absorb carbon dioxide, they need sufficient phosphorus as support. If there is not enough phosphorus, even if there is a lot of nitrogen, they won't be able to do the job, and the absorption of CO₂ will naturally be reduced. However, once there is an increase in phosphorus in the environment, such as the "easy delivery" input brought by dust, phytoplankton can immediately accelerate, fix more carbon, and then send it to the deep sea through the biological pump (Zhou et al., 2023). Phosphorus is also indispensable for nitrogen fixation. Those microorganisms that can "produce nitrogen" themselves require a large amount of energy, and phosphorus is precisely a key link in energy metabolism. Without it, the nitrogen fixation rate drops immediately, and the entire system's ability to "generate new nitrogen" weakens accordingly. The problem is that humans are discharging more and more nitrogen into the atmosphere, but the increase in phosphorus is not keeping up. As a result, the N:P ratio in the ocean surface is increased, nitrate accumulates and is unused, and is eventually released back into the atmosphere through processes such as denitrification (Hayat et al., 2025). From this perspective, phosphorus is somewhat like an invisible "gate", which precisely controls the ocean's response to greenhouse gases and also influences the balance of carbon and nitrogen in the sea.
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