International Journal of Marine Science, 2024, Vol.14, No.1, 6-13 http://www.aquapublisher.com/index.php/ijms 9 thrive and reproduce in different light environments, thereby affecting the species composition and diversity of the planktonic community. Light limitation and light saturation refer to the degree of impact of light on the growth and photosynthesis of phytoplankton. When light is insufficient, the photosynthesis of phytoplankton is limited, and their growth rate decreases. This situation typically occurs in deep-sea, nutrient-rich waters, or in areas covered by clouds or fog. On the other hand, when light intensity exceeds a certain threshold, the photosynthesis of phytoplankton reaches a saturation state, and further increasing light intensity has little effect on promoting growth. The presence of light limitation and light saturation can affect the ecological niche and competitiveness of phytoplankton, thereby influencing the overall structure and stability of the entire planktonic community. Some planktonic organisms in the ocean are mixotrophic, meaning they cannot perform photosynthesis and acquire energy and nutrients by ingesting other phytoplankton or organic debris. The presence and abundance of these mixotrophic organisms are directly influenced by light conditions. Furthermore, phytoplankton can adapt to different light conditions by adjusting their pigment composition. Different pigments have absorptive abilities for different wavelengths of light, allowing phytoplankton to adapt to varying light conditions. Pigment adaptation mechanisms play a significant role in the survival and competitive ability of phytoplankton and have an impact on the structure and function of the entire planktonic community. 2.2 The impact of temperature on surface planktonic communities Temperature is a crucial environmental factor in the marine planktonic ecosystem, and it has both direct and indirect effects on the physiology, ecology, and geographical distribution of planktonic organisms (Figure 2). Temperature directly impacts the physiological processes of planktonic organisms, and different species have different adaptability to temperature. Some planktonic organisms have a wide range of temperature tolerance, enabling them to survive and reproduce over a broad temperature range, while others are more sensitive to temperature fluctuations. Changes in temperature can affect key physiological processes of planktonic organisms, such as metabolic rates, respiration, enzyme activity, and photosynthesis. High temperatures can accelerate biological metabolism and growth rates, but excessively high temperatures can lead to protein denaturation, cell membrane damage, and death. Conversely, low temperatures can reduce biological metabolism and growth rates and can even result in freezing and cold damage. Therefore, the physiological adaptability of planktonic organisms to temperature directly influences their survival and reproductive capacity. Figure 2 Changes in ocean temperature distribution (Image source: https://cn.bing.com/)
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