Spatio-temporal variability of phytoplankton assemblages and its controlling factors in spring and summer in the Subei Shoal of Yellow Sea, China

The Subei Shoal is a special coastal area with complex physical oceanographic properties in the Yellow Sea.In the present study,the distribution of phytoplankton and its correlation with environmental factors were studied during spring and summer of 2012 in the Subei Shoal of the Yellow Sea.Phytoplankton species composition and abundance data were accomplished by Utermohl method.Diatoms represented the greatest cellular abundance during the study period.In spring,the phytoplankton cell abundance ranged from 1.59×10^3 to 269.78×10^3 cell/L with an average of 41.80×10^3 cell/L,and Skeletonema sp.and Paralia sulcata was the most dominant species.In summer,the average phytoplankton cell abundance was 72.59×10^3 cell/L with the range of 1.78×10^3 to 574.96×10^3 cell/L,and the main dominant species was Pseudo-nitzschia pungens,Skeletonema sp.,Dactyliosolen fragilissima and Chaetoceros curvisetus.The results of a redundancy analysis(RDA)showed that turbidity,temperature,salinity,pH,dissolved oxygen(DO),the ratio of dissolved inorganic nitrogen to silicate and SiO4-Si(DIN/SiO4-Si)were the most important environmental factors controlling phytoplankton assemblages in spring or summer in the Subei Shoal of the Yellow Sea.

Landscape changes and their ecological eff ects of Miaodao Archipelago with human disturbances and under natural conditions in the past 30 years

The modern landscape patterns of islands usually show obvious spatial heterogeneity and complex ecological effects due to the vulnerability of ecosystems with natural characteristics under increasing human activities.In this work,we studied the variation in landscape pattern of the Miaodao Archipelago in Bohai Sea,North China,from 1990 to 2019,and an evaluation index system was established to explore the impacts of natural conditions and human disturbances on the ecological effects in the pressure-state-response(PSR)framework.Empirical analysis was conducted on the natural conditions,human disturbances,and ecological effects.The results show that forest was the main component of the landscape pattern in the archipelago.Both of the areas offorest and construction land were increasing,and the areas of cropland and grassland were declining.Other landscape types changed slightly,and the landscape fragmentation was increasing.The natural condition exhibited positive effects while human disturbance showed negative effects on the local ecology.Human disturbances come mainly from shoreline use while the natural conditions were mainly from the elevation change.The ecological effects were resulted mainly from the net primary productivity and water yield.

Degeneration of foundation cushion species induced by ecological constraints can cause massive changes in alpine plant communities

Foundational cushion plants can re-organize community structures and sustain a prominent proportion of alpine biodiversity,but they are sensitive to climate change.The loss of cushion species can have broad consequences for associated biota.The potential plant community changes with the population dynamics of cushion plants remain,however,unclear.Using eight plant communities along a climatic and community successional gradient,we assessed cushion population dynamics,the underlying ecological constraints and hence associated plant community changes in alpine communities dominated by the foundational cushion plant Arenaria polytrichoides.The population dynamics of Arenaria are attributed to ecological constraints at a series of life history stages.Reproductive functions are constrained by increasing associated beneficiary plants;subsequent seedling establishment is constrained by temperature,water and light availability,extreme climate events,and interspecific competition;strong competitive exclusion may accelerate mortality and degeneration of cushion populations.Along with cushion dynamics,species composition,abundance and community structure gradually change.Once cushion plants completely degenerate,previously cushion-dominated communities shift to relatively stable communities that are overwhelmingly dominated by sedges.Climate warming may accelerate the degeneration process of A.polytrichoides.Degeneration of this foundational cushion plant will possibly induce massive changes in alpine plant communities and hence ecosystem functions in alpine ecosystems.The assessment of the population dynamics of foundation species is critical for an effective conservation of alpine biodiversity.