The optimal realized niches of the diatom Paralia sulcata in the Yellow Sea and its environmental implication

The observational and paleo-ecological records on some shelves (e.g., North Sea, Yellow Sea) have indicated that the proportion of Paralia sulcata in the diatom community has been increasing since the 1980s. Because of its heavily-silicified frustules, this species is considered as an important siliceous organism, which can impact the recycling efficiency of biogenic silicon in the ocean. However, the specific environmental factors driving the increase of P. sulcata remain unclear. In this study, based on seasonal in-situ observations and historical literature in the Yellow Sea, we statistically assessed the importance of different environmental factors in determining P. sulcata abundance. Further, we quantified its optimal realized niches, using the maximum entropy and generalized additive models to predict the fate of this species. P. sulcata indicates a preference for environments with cold temperatures and high nutrient levels. The contribution of sea temperature on cell abundance reaches up to 37.2 %, which is higher than that of the nutrient concentrations (∼ 20.5 %) and salinity (∼ 17.1 %). The optimal realized niches are defined as sea temperature at 6.25 ± 3.50 °C, salinity at 32.8 ± 0.52, the concentrations of dissolved inorganic nitrogen, phosphorus, and silicate at 8.38 ± 5.42 μM, 0.42 ± 0.29 μM, and 5.87 ± 3.53 μM, respectively, and ammonium/nitrate ratio at 1.32 ± 0.19. Based on the multivariate statistical methods, the optimal realized niches indicate that the increased sea temperatures in winter and spring, combined with nitrogen enrichment, especially ammonium enrichment, are key environmental drivers for P. sulcata proliferation in the Yellow Sea.