Nutrient imbalance-a mismatch in nutrient ratios between the available food supply and the demands of consumers-has the potential to be transported up food chains, exposing zooplankton to nutrient limitations. In this study, the response of Calanus sinicus (copepod), Moina mongolica (cladocera), and Brachionus plicatilis (rotifer) to nutrient-limited (no-limited, P-limited, and N-limited) food were evaluated from the perspective of growth, reproduction, and stoichiometric homoeostasis. The results indicated that the growth of three species was suppressed under nutrient-limited (especially P-limited) conditions. However, the effect of nutrient limitations on their reproduction was species-specific. For C. sinicus, the dietary UFA (unsaturated fatty acid) as a major phospholipid component affected their egg production and total FA supporting energy promoted the hatchability of eggs. Furthermore, excess carbon in the diet promoted egg production but reduced hatching success. For M. mongolica, nutritional (P and UFA) and energy (total FA) support affected their fecundity. B. plicatilis fecundity exhibited the same pattern of growth (no-limited>N-limited>P-limited). In terms of stoichiometric homeostasis, B. plicatilis's elemental compositions were less likely to be affected by nutrient limitations than M. mongolica. We suggest that the effects of nutrient imbalances could potentially become an evolutionary force affecting ecosystem structure and stability in eutrophic waters.

The phenomenon of nutrient maximums at 70~200 m occurred only in the region of the Canada Basin among the world oceans. The prevailing hypothesis was that the direct injection of the low-temperature high-nutrient brines from the Chukchi Sea shelf (<50 m) in winter provided the nutrient maximums. However, we found that there are five problems in the direct injection process. Formerly Jin et al. considered that the formation of nutrient maximums can be a process of locally long-term regeneration. Here we propose a regeneration-mixture process. Data of temperature, salinity, oxygen and nutrients were collected at three stations in the southern Canada Basin during the summer 1999 cruise. We identified the cores of the surface, near-surface, potential temperature maximum waters and Arctic Bottom Water by the diagrams and vertical profiles of salinity, potential temperature, oxygen and nutrients. The historical 129Ⅰ data indicated that the surface and near-surface waters were Pacific-origin, but the waters below the potential temperature maximum core depth was Atlantic-origin. Along with the correlation of nutrient maximums and very low oxygen contents in the near-surface water, we hypothesize that, the putative organic matter was decomposed to inorganic nutrients; and the Pacific water was mixed with the Atlantic water in the transition zone. The idea of the regeneration-mixture process agrees with the historical observations of no apparent seasonal changes, the smooth nutrient profiles, the lowest saturation of CaCO₃ above 400 m, low rate of CFC-11 ventilation and 3H-3He ages of 8~18 a around the nutrient maximum depths.

Hypoxia is increasingly reported off the Changjiang River Estuary with the confluence of multiple high volume nutrient sources. The Regional Ocean Modeling System coupled with a biological model was used to analyze the effect of different nutrient sources on the development of hypoxia off the Changjiang River Estuary. By comparing to observed data, our model suitably captured the regional dynamics of chlorophyll a, dissolved oxygen, and nutrient concentration. A series of sensitivity experiments were conducted to investigate the hypoxia response to the various nutrient sources, such as loading from the Changjiang River, Kuroshio and Taiwan Warm Current. Our model results indicated that nutrients from different sources significantly influenced the hypoxia off the Changjiang River Estuary, and it was mostly affected by nutrients sourced from the Kuroshio. The nutrients input from the Changjiang River had larger impacts on the hypoxia in the north of 30°N than that in the south of 30°N. The nutrients sourced from the Taiwan Strait had a least influence on the hypoxia off the Changjiang River Estuary.

According to historical mean ocean current data through the field observations of the Taiwan Ocean Research Institute during 1991-2005 and survey data of nutrients on the continental shelf of the East China Sea (ECS) in the summer of 2006, nutrient fluxes from the Taiwan Strait and Kuroshio subsurface waters are estimated using a grid interpolation method, which both are the sources of the Taiwan Warm Current. The nutrient fluxes of the two water masses are also compared. The results show that phosphate (PO₄-P), silicate (SiO₃-Si) and nitrate (NO₃-N) fluxes to the ECS continental shelf from the Kuroshio upwelling water are slightly higher than those from the Taiwan Strait water in the summer of 2006. In contrast, owing to its lower velocity, the nutrient flux density (i.e., nutrient fluxes divided by the area of the specific section) of the Kuroshio subsurface water is lower than that of the Taiwan Strait water. In addition, the Taiwan Warm Current deep water, which is mainly constituted by the Kuroshio subsurface water, might directly reach the areas of high-frequency harmful alga blooms in the ECS.

The variations in nutrients (molar ratios) and chlorophyll a in the Jiaozhou Bay were examined before and after a diatom bloom in a period that lasted from November 2003 to March 2004. Negative relationships between nutrient concentrations, Si/P, Si/N ratios and chlorophyll a content were found during the bloom, which reflected the relationship between nutrient concentrations, phytoplankton biomass and growth. Large increase in nutrient concentrations, particularly SiO₃-Si after the late autumn, is one of major reasons inducing the diatom bloom in winter, and the bloom was finally controlled due to SiO₃-Si depletion by phytoplankton. The bloom was mainly controlled by SiO₃-Si. Before 1998, relatively low level of SiO₃-Si kept ecological balance of eutrophication waters in the Jiaozhou Bay. In recent years, however, human activities have increased SiO₃-Si concentration, which is likely one of the primary cause for the increased diatom blooms in the Jiaozhou Bay. Therefore, it is necessary to control SiO₃-Si concentration in the Jiaozhou Bay.

A spatial and temporal variation in physiochemical parameters in the southeastern Yellow Sea (YS) is in vestigated in the spring and summer of 2009 to 2011. Nutrient show a strong negative relationship with chlorophyll a (Chl a) concentration in spring, and the subsurface chlorophyll a maxima (SCM) layer was associated with the nitracline in summer. In summer, the SCM was usually found within or above the pycnocline and at the depths of shoals from the open sea to the coastal sea due to tidal and/or topographical fronts in the southernmost study area. High Chl a concentrations were found in the central southern YS, where the YS cold water layer expanded under the pycnocline and encountered water masses during spring and summer. After a typhoonin the summer of 2011, Chl a concentration increased, especially in the central southern YS, where cold waters occurred below the pycnocline. The results suggest that the development of thermohaline frontsmay play an important role in the growth and accumulation of phytoplankt on biomass in the upper layer of the southeastern YS during spring and summer.

Marine ciliates play important roles not only in linking the microbial loop to the classic pelagic and benthic food chains but also in regenerating nutrients, yet how dietary nutrient imbalance impacts their nutrient regeneration has not been thoroughly addressed. The growth and physiological responses of Euplotes vannus to low dietary nitrogen (LN) and low dietary phosphorus (LP) conditions were studied, with the bacterium Pseudomonas putida as prey. Feeding on LN prey reduced the growth rate of E. vannus. Dietary nutrient limitation changed the types and quantities of nutrient recycling. Feeding on LP prey enhanced dissolved organic carbon excretion but reduced orthophosphate excretion, whereas feeding on LN prey generally resulted in decreases in the excretion rate in all N forms (ammonium, urea, and nitrate). In addition, the proportion of ammonium in regenerated N increased significantly under the LN condition. These findings indicate that a nutrient-imbalanced diet triggers E. vannus to retain limited macronutrients and promotes the recycling of excessive macronutrients, which may potentially form positive and negative feedback to ambient N and P limitations, respectively.

In June 2003 and 2006 concentrations of nutrient were determined in the Changjiang Estuary. The data indicated that phosphate and nitrate did not behave conservatively in the estuary, but silicate behaved conservatively. An important mobilization of phosphate and nitrate was observed from the river up to halfway in the estuary. Both input flux (from river to estuary) and output flux (from estuary to coastal zone) of phosphate, silicate and nitrate were calculated from statistical interpretations of the salinity profiles. There was a large discrepancy between input and output fluxes of phosphate and nitrate. The river fluxes of silicate, phosphate and nitrate (f_r) are augmented 5.3%, 28.9% and 36.6% in June 2003 and 1.0%, 62.5%, 31.7% in June 2006 by internal inputs (f_i). The phosphate and nitrate fluxes are enhanced through the estuarine process, while silicate flux is unaltered. The authors present some long-term data for nutrient concentrations and the ratios of silicon to nitrogen to phosphorus in the Changjiang Estuary. Silicate level falled in the last two decades, while concentration of nitrate increased. Phosphate concentration had no significant change.

General nutrient components including moisture,ash,crude protein,lipid and carbohydrate,inorganic elements,photosynthetic pigments,amino acids and fatty acids of Bangia sp.were analyzed and compared with Porphyra yezoensis.The results indicated that the content of protein,total amino acids and free amino acids accounted for 47.2%,42.6% and 3.3% in dried Bangia sp.,respectively,all essential amino acids were present in relatively high levels and desirable composition.Lipid was 1.8%,in which the eicosapentaenoic acid(EPA) reached 50.5%.In per 100 g dried material,the content of chlorophyll,carotenoids,phycoerythrin and phycocyanin accounted for 766,208,4 600 and 2963 mg,respectively.Inorganic elements necessary for human body were found to be abundant in Bangia sp.The results showed that the nutritive value of Bangia sp.was the highest among algae reported so far,and the industry of Bangia sp.was provided with significant economic importance and developing potential.

In the present study, the ecosystem-based water quality model was applied to the Pearl River (Zhujiang) Estuary. The model results successfully represent the distribution trend of nutrients and dissolved oxygen both in the horizontal and vertical planes during the flood season, and it shows that the model has taken into consideration the key part of the dynamical, chemical and biological processes existing in the Zhujiang Estuary. The further studies illustrate that nitrogen is in plenty while phosphorus and light limit the phytoplankton biomass in the Zhujiang Estuary during the flood season.