Search

Obvious spatiotemporal heterogeneity is a distinct characteristic of ecosystems in subtropical bays. To aid targeted management and ecological restoration in long and narrow semi-enclosed subtropical bays, we analyzed seasonal and regional differences in long-term changes (1980–2019) in the biomass and abundance of large mesozooplankton (LMZ; >505 µm) in Xiangshan Bay, Zhejiang, China. We found spatiotemporal heterogeneity in the historical changes of LMZ. Significant negative trends in LMZ biomass were found in the inner and middle bay during the warm season (summer and autumn), when the nutrient concentration (especially dissolved inorganic nitrogen) and temperature increased simultaneously. Nutrient changes in Xiangshan Bay began in the late 1980s or early 1990s, coinciding with large-scale fish cage development. A rapid decline in LMZ biomass occurred after 2005 when power plants commenced operation, accelerating the warming trend. Therefore, the joint stress of eutrophication and warming likely precipitated the decline in LMZ biomass. Conversely, a significant increase in LMZ biomass was found in the outer bay in spring. This trend was consistent with the trend of LMZ biomass near the Changjiang (Yangtze) River estuary, which indicates that the pelagic ecosystem in the outer bay was affected by water from the Changjiang River estuary during spring. Based on our results, ecosystem management and restoration in semi-enclosed subtropical bays should focus on internal waters, which have a poor capacity for water exchange. For Xiangshan Bay, the changes in the Changjiang River estuary ecosystem during the cold season (winter and spring) should also be considered.

In the present study, we report N2 fixation rate (15N isotope tracer assay) and the diazotroph community structure (using the molecular method) in the western tropical North Pacific Ocean (WTNP) (13°–20°N, 120°–160°E). Our independent evidence on the basis of both in situ N2 fixation activity and diazotroph community structure showed the dominance of unicellular N2 fixation over majority of the WTNP surface waters during the sampling periods. Moreover, a shift in the diazotrophic composition from unicellular cyanobacteria group B-dominated to Trichodesmium spp.-dominated toward the western boundary current (Kuroshio) was also observed in 2013. We hypothesize that nutrient availability may have played a major role in regulating the biogeography of N2 fixation. In surface waters, volumetric N2 fixation rate (calculated by nitrogen) ranged between 0.6 and 2.6 nmol/(L·d) and averaged (1.2±0.5) nmol/(L·d), with

Fast repetition rate fluorometry (FRRf) allows for rapid non-destructive assessment of phytoplankton photophysiology

Temperature increase caused by thermal discharge from power plants promotes phytoplankton growth and frequent bloom in eutrophic subtropical waters, particularly in cold seasons. Suspension filter-feeding bivalves show size-selective grazing on phytoplankton. Thus, we hypothesized that algal bloom under thermal stimulation could be controlled and that phytoplankton community was structured by oyster farming. Here, ten cruises were conducted in two oyster farms (OFs) and control areas (CAs) adjacent to the Ninghai Power Plant in the upper section of Xiangshan Bay during 2009-2015. We found that thermal discharge induced severe winter algal blooms. Phytoplankton abundance and chlorophyll a (chla) were significantly lower (46.3% and 28.3%, respectively) in OF than in CA, indicating a high filtration efficiency by oysters and the associated biofouling assemblages. In addition, oyster farming significantly increased species richness (by 26.3%), Shannon-Wiener diversity (by 38.3%), and Pielou's evenness indices (by 28.8%) and reduced suspended solids (by 12.2%), total organic carbon (by 18.4%), dissolved inorganic nitrogen (by 1.5%), and phosphorus (by 3.7%). Furthermore, oyster farming considerably reduced (increased) micro-chla contribution (pheophytin/chla) by 34.8% (71.1%), suggesting a strong size-selective grazing on phytoplankton. Analysis of similarity revealed a significant difference in phytoplankton community composition between OF and CA. However, after the removal of culture rafts, all the abundance, chla, species diversity, dominant species, size structure, and community composition of phytoplankton showed no significant difference. Our study demonstrated that oyster farming effectively alleviated eutrophication and algal bloom and enhanced phytoplankton diversity, which provides guidance for aquaculture and ecological restoration in subtropical coastal eutrophic waters.

The impacts of fish cage culture and suspended oyster culture on macrobenthic communities were investigated in Xiangshan Bay, China, on a seasonal basis from January to October of 2015. Samples were collected from a fish cage farm, a suspended oyster farm, and two corresponding reference sites. Two-way ANOVA results showed that species richness, abundance, biomass, and Shannon-Wiener diversity differed significantly between the four different investigated areas, and different seasons as well. Cluster analysis showed that macrobenthic community composition in the fish and oyster culture areas significantly differed from that in the reference sites, respectively. Trophic structure of macrobenthos in the fish and oyster culture areas mostly clustered together owing to higher abundance and biomass of surface-deposit feeders and carnivores. The macrobenthic communities and feeding guilds correlated highly with environmental factors, such as bottom water chlorophyll a and nutrients, as well as sediment total organic carbon. Although integrated multi-trophic aquaculture is regarded as a suitable approach to coordinate desirable economic, social, and environmentally sustainable outcomes, coastal ecosystems may suffer from large-scale nutrient enrichment due to aquaculture and other human activities, which should not be considered in isolation.

Biogeochemical processes in the East China Sea are substantially affected by anthropogenic nutrient inputs. The dramatic decadal changes in nutrient concentrations were mainly due to the increases of DIN and DIP in the Changjiang (Yangtze) River since 1980s. As a result, phytoplankton abundance increased dramatically between 1958 and 2016 in both the Changjiang Estuary and the East China Sea. Before 1980s, chain-forming diatoms were dominant, while increasing of large-cell dinoflagellates is probably related to increasing DIN/silicate ratio. Increasing nutrient input and phytoplankton abundance greatly impact seasonal hypoxia condition in the East China Sea. Hypoxia is relatively sporadic and patchy before 2013. In 2016 and 2017, hypoxic events were more severe, occurring over larger areas with dramatically lower minimum values of dissolved oxygen. Notwithstanding, occurrences of bottom hypoxia in the East China Sea are highly dynamic and are significantly influenced by episodic events such as wind mixing.

Macrobenthos samples were collected from the Yellow and East China Seas in four seasons during 2011 to 2012. The seasonal distribution of macrobenthos and its relationship with environmental factors were analyzed. A total of 562 macrobenthic species were identified, with polychaetes and mollusks accounting for 67% of the total number of species. A similarity percentage (SIMPER) analysis showed that the dominant species were bivalve mollusks in the Yellow Sea and small-sized polychaetes in the East China Sea. A two-factor analysis of variance showed significant seasonal variations in species number, density and diversity index, and significant regional differences of biomass and density. Two-factor community similarity analysis also showed significant seasonal and regional differences in macrobenthic communities. Canonical correspondence analysis indicated that the main environmental factors affecting the macrobenthic communities were water depth, temperature, dissolved oxygen, and inorganic nitrogen. The results demonstrate significant regional differences and seasonal variations in macrobenthos in the two seas. Sediment properties and water mass characteristics are speculated to be the causes of regional differences.

Centropages abdominalis Sato, a common cold-water copepod that is distributed widely in the coastal waters of the North Pacific, appears seasonally in winter and spring as the key zooplankton in the Xiangshan Bay, a typical subtropical semi-closed bay in China. Here, we hypothesised that C. abdominalis could produce diapause eggs as an over-summering strategy in late spring as a response to the increasing temperature and day length. We conducted 11 cruises and in situ reproduction experiments from April 2017 to June 2018 to reveal the variation in the reproductive strategies of C. abdominalis and the related environmental factors. The results showed that the revival of diapause eggs in the inner and middle part of the Xiangshan Bay should contribute to the initial population recruitment in early winter. Sustaining subitaneous egg production supported the instantaneous population recruitment in later winter and spring, and diapause eggs were mainly produced at the upper thermal distribution of C. abdominalis (16.12–21.32 °C) to over-summer in late spring. Temperature was the essential environmental factor that affected the shift in reproductive strategy for C. abdominalis, with an optimum temperature of 19.51 °C for diapause egg production and 11.63 °C for subitaneous one in the Xiangshan Bay. Furthermore, the long-day photoperiod possibly acted as a seasonal change signal for C. abdominalis to produce diapause eggs in late spring in the Xiangshan Bay. The timing of diapause egg production for C. abdominalis could be earlier in lower-latitude waters with shorter day length, as an acclimatisation to warmer habitats. Besides, salinity and Chl a concentration had less effects on diapause eggs production of C. abdominalis in this case. Confronted with ocean warming, the diapause egg period of cold-water copepod (like C. abdominalis) would be prolongated, leading to a reduced population appearance period, especially in lower-latitude waters.

Summary To examine the distribution of Trichodesmium relative to physicochemical factors during summer in the Changjiang (Yangtze River) Estuary and adjacent East China Sea shelf, three cruises were conducted separately in June 2009, July 2011, and August 2009. Trichodesmium species found were T. thiebautii , T. erythraeum , and T. hildebrandtii . The population was dominated by T. thiebautii , which accounted for >85% of the samples found. Most of them were free trichomes. Colonial forms were rarely observed (approximately 10% of our samples), occurring only in offshore waters. The depth integrated abundances of Trichodesmium were 308 × 10 3 , 1709 × 10 3 , and 3448 × 10 3 trichomes m −2 in June, July, and August, respectively. Trichodesmium was distributed abundantly in the southern or southeastern part of our study area, where nutrients were low and light penetration, temperature, and salinity were high, which were influenced by the Taiwan Warm Current (TWC) and Kuroshio. Trichodesmium was found in low abundance in inshore, eutrophic, low-salinity waters, which were mainly controlled by the Changjiang Diluted Water (CDW) and coastal current. These results suggest that spatiotemporal changes in the summer Trichodesmium distribution correlate highly with the variations in physicochemical properties that are primarily controlled by the TWC, Kuroshio, and CDW. The summer N 2 fixation rate of Trichodesmium was estimated at 12.3 μmol N m −2 d −1 in our study area, contributing >50% of biological N 2 fixation.

To evaluate the effects of different anthropogenic activities on zooplankton and the pelagic ecosystem, we conducted seasonal cruises in 2010 to assess spatial heterogeneity among the mesozooplankton communities of Xiangshan Bay, a subtropical semi-enclosed bay in China. The evaluation included five different areas: a kelp farm, an oyster farm, a fish farm, the thermal discharge area of a power plant, and an artificial reef, and we aimed to identify whether anthropogenic activities dominated spatial variation in the mesozooplankton communities. The results demonstrated clear spatial heterogeneity among the mesozooplankton communities of the studied areas, dominantly driven by natural hydrographic properties, except in the area near the thermal discharge outlet of the power station. In the outlet area, thermal shock caused by the discharge influenced the mesozooplankton community by decreasing abundance and biomass throughout the four seasons, even causing a shift in the dominant species near the outlet during summer fromAcartia pacificato eurythermal and warm water taxa. Unique features of the mesozooplankton community in the oyster farm may be due to the combined effects of oyster culture and the natural environment in the branch harbour. However, kelp and fish culture, and the construction of an artificial reef did not exert any obvious influence on the mesozooplankton communities up to 2010, probably because of the small scale of the aquaculture and a time lag in the rehabilitation effects of the artificial reef. Thus, our results suggested that the dominant factors influencing spatial variations of mesozooplankton communities in Xiangshan Bay were still the natural hydrographic properties, but the thermal discharge was an anthropogenic activity that changed the pelagic ecosystem, and should be supervised.

Coastal eutrophication and its associated harmful algal blooms have emerged as one of the most severe environmental problems worldwide. Seaweed cultivation has been widely encouraged to control eutrophication and algal blooms. Among them, cultivated kelp (Saccharina japonica) dominates primarily by production and area. However, the responses of water quality and phytoplankton community to kelp farming remain unclear. Here, thirteen cruises were conducted in the kelp farms and control areas in the turbid, highly eutrophic Xiangshan Bay of the East China Sea from 2008 to 2015. Results indicated that kelp cultivation slightly increased dissolved oxygen and pH, but reduced dissolved inorganic nitrogen and phosphorus. We estimated that kelp harvesting would remove 297 t of nitrogen and 42 t of phosphorus from this bay annually. Because of decreased flow velocity, turbulence, and sediment resuspension, kelp farming greatly reduced suspended solids and increased transparency, resulting in increases in phytoplankton chlorophyll a and abundance. Additionally, kelp farming appreciably increased phytoplankton species number, Marglef richness, and Shannon–Wiener diversity indices by 51.6%, 40.1%, and 13.1%, respectively. Analysis of similarity and similarity percentages demonstrated that phytoplankton community composition differed significantly between the farm and control area, which was mostly attributed to long-chained diatoms and single-celled dinoflagellates. However, after the kelp harvesting, all measurements of water quality and phytoplankton biomass, diversity, and community composition exhibited no significant difference. Our study highlights that kelp cultivation alleviates eutrophication and acidification and enhances phytoplankton diversity, thus providing guidance for macroalgal aquaculture and remediation in eutrophic waters.

To explore the effects of coastal eutrophication and warming on phytoplankton biomass and cell size, we analyzed current and historical data for size-fractionated chlorophyll a (chla) in Xiangshan Bay, China. Results showed that micro- and nanophytoplankton overwhelmingly dominated (>84%) in all seasons. The contribution of micro-chla was significantly lower in warm than in cold seasons, whereas contribution of pico-chla showed the opposite result. Overall, the micro-chla contribution increased with decreasing pico-chla contribution from the stable, clear, eutrophic upper bay to the turbulent, turbid lower bay, indicating that phytoplankton size structure on a spatial scale was largely shaped by water column stability and light rather than by nutrients. Since the 1980s, phytoplankton biomass, primary productivity, and micro-chla contribution in Xiangshan Bay have increased sharply with increasing nutrient amounts and temperature. Additionally, it seems that algal bloom seasonality has shifted forward from spring to winter since the power plant operations in 2006.

Benthic macrofaunal communities along an estuarine gradient of a macrotidal estuary of the Jiaojiang River, China were analyzed to reveal spatial variations in those communities and their relationships with environmental variables. Benthic macrofauna were collected from 15 sampling stations in May and October 2010. Polychaetes and Mollusks are the dominant taxonomic groups. The species richness, density and Shannon diversity index generally tended to increase as one moved away from shore toward the outer stations of the estuary. Cluster analysis and multidimensional scaling ordinations indicated the presence of three distinct zones of macrofaunal communities in the estuary. Multivariate analyses showed a strong relationship exists between the macrofaunal communities and the environmental parameters in the Jiaojiang River estuary. Aside from salinity, dissolved inorganic nitrogen and soluble reactive phosphate contents were also the major factor affecting the structure of the macrofaunal communities. The results demonstrated the important effects of nutrient-load on the distributional patterns of benthic macrofaunal communities in nutrient-rich estuaries.

To explore the distribution and composition of phytoplankton community and their responses to environmental changes, summer net-collected phytoplankton and physicochemical parameters in the Hangzhou Bay during 2004–2010 were investigated. A total of four phyla and 84 species were identified, including 67 diatom and 12 dinoflagellate species. The dominant species constantly consisted of the diatoms, although the dominance of dinoflagellate and cyanobacteria increased recently. Due to great spatio-temporal variations in environmental factors (salinity, suspended solids, and nutrient concentration), significant heterogeneities in community compositions among different years and subregions (inner and middle sections, and bay mouth) were found based on the analyses of multidimensional scaling and similarity. Canonical correspondence analysis showed that salinity and Si/N were the main variables associated with algal assemblage. Compared with the historical data since the 1980s, eutrophication (N, P, and N/P increased with decreasing Si/N) was exacerbated drastically. Moreover, climatic forcing and human activities resulted in a series of physical alterations, including sediment retention, temperature increase, and salinity decrease as well as reduction in water exchanges. All these changes induced obvious increases in cell density and Chl-a while decreases in species diversity and diatom-dinoflagellate ratio as well as the shifting of dominant species. Therefore, the long-term phytoplankton variations were closely related to anthropogenic and climatic perturbations in the Hangzhou Bay.

Quantitative and precise observation of the phytoplankton is required for biogeochemical and environmental monitoring in coastal seas. However, phytoplankton data may vary greatly depending on the sampling methods. Net and water collection methods are widely adopted for obtaining marine phytoplankton in China; yet, exact differences and relationships between water- and net-collected phytoplankton communities remain poorly understood. Here, annual phytoplankton surveys in the southern Yellow Sea were conducted using these two sampling methods. Compared with water collection, net collection resulted in the loss of numerous noncolonial small-celled species, particularly cryptophytes and coccolithophores, and reduced phytoplankton depth-averaged abundance (DAA) by 1–2 orders of magnitude. However, through net collection, some scarce, large, or colonial species with low abundances were obtained, and the net-collected DAA distribution was highly consistent with the water-collected DAA distribution in each season. Moreover, DAAs of planktonic large-celled or long-chained dominant species, belonging to diatom, dinoflagellate, and cyanobacteria, were comparable in net- and water-collected samples. Regression analysis showed highly significant regression coefficients between net- and water-collected DAAs of phytoplankton, diatom, and diatom plus dinoflagellate, suggesting that net-collected data could be roughly derived from water-collected results. Non-metric multidimensional scaling and analysis of similarity indicated that phytoplankton community composition significantly differed between net- and water-collected samples. Similarity percentages confirmed that this difference was largely attributed to small-sized benthic and meroplanktonic diatoms, unidentified cryptophytes and coccolithophores, and single-celled dinoflagellates. Our results suggest that the sampling method profoundly influences phytoplankton analysis in terms of species information, abundance, dominant species, and community composition.

We analyzed the composition and distribution of phytoplankton in relation to physicochemical factors in the Changjiang (Yangtze River) Estuary and adjacent East China Sea shelf in June and August 2009. Diatoms and dinoflagellates dominated the community, particularly in eutrophic inshore waters controlled by the Changjiang Diluted Water (CDW), coastal current, and upwelling. However, high densities of cyanobacteria and cryptophytes were observed in the oligotrophic offshore waters influenced by the Taiwan Warm Current (TWC) and Kuroshio. In June, the northeastward CDW plume combined with the Yellow Sea Coastal Current induced algal bloom in the northern part of the CE. In August, the enhanced CDW formed two narrow, low-salinity tongues that extended eastward and southward (associated with the upwelling and coastal current), resulting in phytoplankton blooms off the CE and in the Zhejiang coastal waters, respectively. Phytoplankton abundance in August was considerably higher than in June, with increased solar radiation, CDW, and upwelling. The maximum abundance occurred on the surface in inshore turbid waters and on the subsurface (5–30 m) in offshore clear waters with increased stratification. Based on multidimensional scaling and cluster analysis, we found appreciable spatio-temporal variations in algal community composition. Different ecological groups corresponded with hydrographic distributions. Canonical correspondence analysis showed that nutrients, salinity, temperature, and suspended particulate matter were the main variables associated with community distribution. We suggest that the variations in summer phytoplankton community are highly correlated with the significant monthly and spatial variability in physicochemical properties, which are primarily controlled by the CDW and TWC.

Trichodesmium spp. is probably the most important diazotroph in oligotrophic tropical and subtropical seas. Their N fixation relieves the restraining of N limitation to the marine primary production, and promotes the absorption of CO2. Therefore, their distribution and N fixation are paid more attention on the condition of global warming in recent years. We summarize the studies on Trichodesmium spp. in China marginal seas and other global seas/oceans, including population structure, distribution pattern, sampling methods, restriction factors, N fixation rate, and their contribution to primary/new production and N input, as well as their function in oceanic C and N biogeochemical cycles. Finally, we point out the future research directions in China marginal seas.

Trichodesmium abundance was measured in the northern East China Sea (ECS) from 2006 to 2007 including four seasons. Our results showed an obvious seasonal variation of Trichodesmium that the abundance was very low in spring (0.96×103 trichomes/m3) and increased quickly to the highest value in summer (35.7×103 trichomes/m3), then declined successively in autumn (16.26×103 trichomes/m3) and winter (3.17×103 trichomes/m3). The horizontal distribution patterns of Trichodesmium were quite different among the four seasons. The seasonal variation may be mainly affected by seawater temperature. The horizontal distribution of Trichodesmium may be affected by multiple environmental factors jointly, while salinity seemed to play a more important role in shaping a horizontal distribution pattern of Trichodesmium than water temperature. Furthermore, neither the N-nutrient nor the P-nutrient was considered as a limiting factor for Trichodesmium. Comparison with adjacent areas showed that seasonal variation in this study area was similar to that in the southern ECS and the South China Sea (SCS) but different from that in Kuroshio. An estimation of N2 fixation rate by Trichodesmium abundance indicated that Trichodesmium might be an important source of biological N2 fixation in the shelf area of ECS.

Landslide-related impulse waves are catastrophic but accidental, so limited data on field measurements are available; scaled physical experiment is therefore a functional method to simulate and analyze this phenomenon. A large-scale physical Froude-similar model to produce impulse waves was constructed based on the Chinese Gongjiafang landslide, which occurred on the main stream of Three Gorges after the impounding in the reservoir in China. With a scale of 1:200, the model had the dimensions of 24, 8, and 1.3 m. Four water levels, 145, 156, 172.8, and 175 m, were modeled for the experiments, and marble coarse sands were used to imitate the actual cataclastic rock mass. Wave height gauges, high-speed cameras, and run-up measuring instruments were used to monitor wave fluctuations in the model. Among the experiments, the ones modeled using a water level of 172.8 m best confirmed the actual conditions in the Gongjiafang landslide, representing a good validation of the experiments. This study obtained, for the first time, specific data on the reproduced impulse waves’ convergence and superposition during propagation, and of the energy change between impulse waves and reflected waves. The test data describe a rapid decaying and gradual decaying rule for the wave heights and run-ups. The Froude-similar experiments presented in this article help us to understand the whole procedure of impulsive wave generated by cataclastic rock mass failure, and the results acquired contribute to studies of impulse waves caused by similar bank destabilizations worldwide.

The distributions of N utilizing bacteria (denitrifying bacteria and ammonifying bacteria), P utilizing bacteria (organic phosphobacteria and inorganic phosphobacteria) and heterotrophic bacteria in the Changjiang Estuary, and the roles of main environmental factors in distributing bacteria, are explored with observations from two cruises in June and August 2006. Comparisons between the two important periods of initial hypoxia phase (June) and developed hypoxia phase (August) show differences in both bacterial distributions and the associated main environmental factors. First, the primary group of ammonifying bacteria has larger magnitude with spatial maximum value in the hypoxic stations related to sediment in August. The phosphobacterial abundance and detection rates in August are much lower than those in June, but the denitrifying bacterial abundance becomes greater in August. However, the difference of heterotrophic bacterial abundance between June and August is not obvious. Second, main environmental factors influencing bacteria vary from initial hypoxia phase to developed hypoxia phase. Two parameters (salinity and NO3−) in surface water and five environmental parameters (pH, salinity, PO43−, NO3− and temperature) in bottom water and surface sediment play major roles in the bacterial abundance in June, while different parameter combinations (salinity and PO4−) in surface water and different parameter combinations (DO, DOC, NO3−, PO43− and pH) in bottom water and surface sediment play major roles in August. Moreover, the bottom bacteria distributions in area south of 31°N are related to the position of the Taiwan Warm Current in June. The bacterial abundance and distribution may respond to the environmental change in the hypoxia processes of initial phase and developed phase. During the hypoxia processes, the whole structure of bacterial functional groups probably turns to different states, causing the recycling of nutrient regeneration and aggravating hypoxia regionally.

Based on the field survey data of four cruises in 2011, all phytoplankton communities in the southern Yellow Sea (SYS) were investigated for the species composition, dominant species, abundance and diversity indices. A total of 379 species belonging to 9 phyla were identified, of which the most abundant group was Bacillariophyta (60.9%), followed by Pyrrophyta (23.7%) and Haptophyta (6.9%). The seasonal distribution of abundance was: summer (4137.1×103 ind m−3) > spring (3940.4×103 ind m−3) > winter (3010.6×103 ind m−3) > autumn (340.8 ×103 ind m−3), while the horizontal distribution showed a decreasing tendency from inshore to offshore regions. The dominant species of phytoplankton varied in different seasons. The dominant species were Thalassiosira pacifica, Skeletoema spp. and Chaetoceros cinctus in spring, Chaetoceros debbilis, Chaetoceros pseudocurvisetus and Chaetoceros curvisetus in summer, Thalassiosira curviseriata, Alexandrium catenella and Ceratium fusus in autumn, Paralia sulcata, Phaeocystis sp. and Bacillaria paradoxa in winter, respectively. In SYS, the group of temperate coastal species was the major ecotype, and the groups of the central SYS species and oceanic species were also important constituents. The average values of Shannon-Weaver diversity index (H’) and Pielou evenness index (J) were 2.37 and 0.65 respectively. The indices H’ and J in the open sea were higher than those in coastal waters. Obvious co-variation tendencies between H’ and J were observed in all but the summer cruise of this survey.

In the present study, a microcosm experiment was conducted for 12 days during the spring near Dongtou Island in the East China Sea with the aim of investigating the effects of different nitrogen-phosphorus (NIP) ratios (1N:1P, 4N:1P, 16N:1P, 64N:1P, and 256N:1P) on phytoplankton community growth and succession. The results indicated that the cell abundance, chlorophyll a (chl a) concentration, specific growth rate, diversity indices, and species composition of the phytoplankton community varied significantly with the N/P ratios. A higher growth rate (evaluated based on cell abundance and chl a) of the phytoplankton community was observed during the early phase of test (days 1 to 4) with high N/P ratio treatments and with low N/P ratio treatments during the late phase of test (after day 6). The H' was most the sensitive among the diversity indices we used in the present study, and it decreased significantly in the low N/P ratio treatments on day 4 but increased in the low N/P ratio treatments on day 8 and day 12. On the other hand, a definite community succession order from diatoms (Skeletonema costatum) to dinoflagellates (Protoperidinium bipes and Prorocentrum donghaiense) was observed in all treatments. However, the proportion and occurrence time of the dominant species varied with different N/P treatments. (C) 2012 Elsevier B.V. All rights reserved.

Recent oil spillage accidents around the world greatly increase harmful risks to marine ecology. This study evaluated the influences of petroleum water accommodated fraction (WAF) on 15 typical species of marine copepods collected from a subtropical bay in East China Sea at different seasons. Copepods showed impaired swimming ability, restlessness, loss of balance, anoxic coma, and even death when they were acutely exposed to the crude oil WAF under laboratory conditions. The LC(50) values (expressed in total petroleum hydrocarbon concentration) indicated that the tolerances of copepods to WAF decreased significantly (P 0.05) with increased exposure duration and natural water temperatures (acclimatization temperature). The sensitivity of the copepods was species-specific (P 0.01), and there was a significant (P 0.05) positive correlation between the 48-h LC(50) and body size. Therefore, the small copepod species confront more survival challenges under oil contamination stress, especially in the warm months or regions.

There is concern about the impact of expanding coastal aquaculture activity, particu- larly in China, with the biggest aquaculture industry in the world. We conducted 3 cruises to the oyster, kelp and fish farms of the Xiangshan Bay during the winterspring transition (02/2009), winter (01/2010) and spring (04/2010). Our aim was to explore the spatial heterogeneity of the phytoplankton community in different culture habitats and evaluate the effects of mariculture on phytoplankton. Different culture types formed unique small-scale habitats that exhibited various en vironmental gradients and forms of phytoplankton community patchiness. Both environmental (i.e. temperature, salinity, transparency, suspended solids, dissolved oxygen, pH, dissolved inor- ganic nitrogen, PO4-P, SiO3-Si, N/P, and total organic carbon) and phytoplankton (i.e. cell density, chlorophyll a, species richness, main dominant species, and community structure) parameters were significantly different among the 3 culture habitats. Canonical correspondence analysis showed that phytoplankton distribution was mainly influenced by temperature, nutrition, salinity and suspended solids. Oyster and kelp farming effectively alleviated coastal eutrophication and also increased species richness and diversity; fish farming did not. Temperature elevation caused by the thermal discharge from a power plant induced phytoplankton blooms during the winter and winterspring transition. Nevertheless, the filtering effect of suspended oysters dramatically reduced microalgal biomass. The kelp and oyster farms were much better than the fish farm in terms of water quality, phytoplankton composition, and habitat restoration function. These results provide guidelines for future policy-making in aquaculture as well as eutrophication control and management.

Recently, the impact of petroleum pollution on marine plankton has been complemented by a great concern. This review summarizes the reports about toxic effects of oil water accommodated fraction (WAF) on marine phytoplankton, zooplankton and early life stage of animal. For the oil WAF, toxicants are mainly composed of the aromatic hydrocarbons, such as the benzene hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) with 2–5 rings. The oil WAF, especially the PAHs, can be accumulated in plankton due to their great lipophilic abilities, and thus elicites various deleterious effects. Toxicological tests show that marine plankton is very sensitive to the petroleum WAF, as the order of median effective/lethal concentration is merely μg/L or mg/L. There are species and developmental stages differences of plankton tolerance to petroleum WAF, and the toxicity of different oil WAF is various. Generally, its toxicity enhances with increasing carbonic chain length and benzene ring number. Many studies on the acute and sub-acute toxic effects of oil WAF have been done, however few researches on its chronic toxic effects has been carried out till now. Besides, most reports focused on the levels from molecule to individual, though very little work of petroleum toxic effects has ever been performed on the marine plankton population or community levels. Therefore, it is necessary to continue these studies in future.

The major objective of this study is to understand the upper thermal limits and potential impact of temperature elevation on copepods caused by coastal power plants. Laboratory experiments were designed to evaluate the upper incipient lethal temperature (UILT) and critical thermal maximum (CTMax) of eight coastal copepod species collected from a subtropical bay in spring and summer. The 48h-UILT of copepods acclimatized at 16.0, 20.0, 28.0 °C were 26.4–29.1, 27.3–30.1, 32.9–36.9 °C, respectively. And the CTMax of copepods acclimatized at 28.0 °C was 35.80–41.03 °C. The UILT of copepods increased significantly with rising acclimatization temperatures, but the difference values between UILT and acclimatization temperatures decreased, which indicated that the seawater temperature elevation induced the growing mortalities of copepods with increasing natural seawater temperatures from the thermal addition of power plants. The results also showed that estuarine copepods had more tolerances to the thermal stress than those from other more stable marine environments. As to the calanoid copepod species, there was a significant negative correlation between the CTMax and body length ( p

The tolerance of marine copepods to short-term thermal stress was measured by the median lethal temperature (LT50) tests in laboratory. Experiments on LT50 of copepods from different acclimation and acclimatization conditions collected from the Yueqing Bay were carried out under heat exposure for 15, 30 and 45 min. The LT50 of copepods decreased with increasing exposure time but increased with rising acclimation and acclimatization temperatures. However, the differences in copepod LT50 decreased with rising acclimatization temperatures, which suggested that entrained copepod mortality increased with raised water temperature due to the acute thermal stress of coastal power stations. Results also revealed that the thermal tolerance of Labidocera euchaeta was much higher than that of Calanus sinicus in spring. The thermal tolerances of different copepod species in summer were in the order, Pseudodiaptomus marinus, Acartia spinicauda, Acartia pacifica and L. euchaeta.

The phytoplankton community in the Changjiang Estuary is subject to intensive physical and chemical stresses because of human- and climate-driven changes. We obtained historical data on summer phytoplankton communities from 1959 to 2009 to explore responses to long-term environmental changes. The nitrogen (N) and phosphorus (P) concentrations and ratios (N/P and N/Si) increased because of persistent riverine loading, but silicon (Si) levels remained constant. Climatic changes and extensive water diversions and withdrawals (sediment retention) resulted in a series of physical alterations, including increased temperature, turbidity reduction, and river plume shrinkage. These changes induced a dramatic increase in microalgal biomass (cell density and chlorophyll a) with a decreasing diatom-dinoflagellate ratio, and exacerbated harmful algal blooms. In the past dominant net-collected species were usually chain-forming diatoms; however, more recently, large dinoflagellates and filamentous cyanobacteria dominate. This was not consistent with information from water samples (co-dominated by small dinoflagellates), because of the loss of solitary species collected using a 76-μm net. The dominant species shifted from temperate-subtropical/eurythermal to subtropical-tropical/eurythermal taxa in the warmer water caused by global warming and hydrographic changes. There was also an increased dominance of euryhaline/high-salinity species due to increase in Kuroshio transport and the northward Taiwan Warm Current and reduction in Changjiang Diluted Water. All these changes in phytoplankton communities appear to be closely related to an increase in anthropogenic activities and climatic changes.