Anoxia and hypoxia have been widely observed in estuarine and coastal regions over the past few decades; however, few reports have focused on the East China Sea (ECS). In June and August 2003, two cruises sampled at stations covering almost the entire shelf of the ECS to examine hypoxic events and their potential causes. In August, DO concentrations <2-3 mg l(-1) covered an area estimated at greater than 12,000 km(2) (or 432 km(3) volume). In contrast, water column DO concentrations exceeded 4 mg l(-1) throughout most of the shelf region. A sharp density gradient was observed under the mixed layer in August, restricting vertical re-aeration across this strong pycnocline. Oxygen depletion events, such as that described here for the ECS shelf, are fueled by decomposition of newly produced marine and river-borne biogenic substances (as well as older residual organic matter) deposited to the bottom waters.

Coral reefs are built of calcium carbonate (CaCO3) produced biogenically by a diversity of calcifying plants, animals, and microbes. As the ocean warms and acidifies, there is mounting concern that declining calcification rates could shift coral reef CaCO3 budgets from net accretion to net dissolution. We quantified net ecosystem calcification (NEC) and production (NEP) on Dongsha Atoll, northern South China Sea, over a 2 week period that included a transient bleaching event. Peak daytime pH on the wide, shallow reef flat during the nonbleaching period was ∼8.5, significantly elevated above that of the surrounding open ocean (∼8.0–8.1) as a consequence of daytime NEP (up to 112 mmol C m−2 h−1). Diurnal‐averaged NEC was 390 ± 90 mmol CaCO3 m−2 d−1, higher than any other coral reef studied to date despite comparable calcifier cover (25%) and relatively high fleshy algal cover (19%). Coral bleaching linked to elevated temperatures significantly reduced daytime NEP by 29 mmol C m−2 h−1. pH on the reef flat declined by 0.2 units, causing a 40% reduction in NEC in the absence of pH changes in the surrounding open ocean. Our findings highlight the interactive relationship between carbonate chemistry of coral reef ecosystems and ecosystem production and calcification rates, which are in turn impacted by ocean warming. As open‐ocean waters bathing coral reefs warm and acidify over the 21st century, the health and composition of reef benthic communities will play a major role in determining on‐reef conditions that will in turn dictate the ecosystem response to climate change.

Effects of temperature and substrate addition (glucose, ammonium or dissolved free amino acid) on bacterial growth were studied in short-term incubations of samples from north, mid and south Chesapeake Bay and a small salt marsh creek, in 1991 and 1992. Bacterial specific growth rates were exponentially and positively correlated with incubation temperature in all seasons studied. Relationships with temperature were consistently similar across different estuarine habitats and chlorophyll concentrations (2 to 5 0 pg I") at incubation temperatures ranglng from 3 to 25OC. Within this temperature range, the average Qlovalue for bacterial specific growth rates was 2.72 + 0.26. Substrate enrichment did not increase bacterial abundance, production and specific growth rate within 24 h when water temperature was <7 "C. At lugher temperatures (>20°C), substrate enrichment effects occurred after 3 h incubation although the effect was not consistent across study areas. Temperature-substrate interaction experiments showed that temperature was more effective in regulating bacterial production and specific growth rate than substrate when compared on the same time scale. The substrate enrichment effect on bacterial growth appeared to be temperature dependent. High temperature dependency and the lack of substrate effect on bacterial growth at temperatures < 20°C suggested that estuarine bacterial growth was not limited by substrate supply but by temperature during non-summer seasons. Response of bacteria to temperature was uniform across a range of time scales. There was no evidence of adaptation to in situ temperature by bacterial assemblages in different seasons. The seasonal cycle of bacterial growth rate can largely be explained as a physiological response to the in situ temperature by a eurythermal bacterial community.

The occurrence of extreme weather conditions appears on the rise under current climate change conditions, resulting in more frequent and severe floods. The devastating floods in southern China in 2010 and eastern Australia 2010–2011, serve as a solemn testimony to that notion. Accompanying the excess runoffs, elevated amount of terrigenous materials, including nutrients for microalgae, are discharged to the coastal ocean. However, how these floods and the materials they carry affect the coastal ocean ecosystem is still poorly understood. Yangtze River (aka Changjiang), which is the largest river in the Eurasian continent, flows eastward and empties into the East China Sea. Since the early twentieth century, serious overflows of the Changjiang have occurred four times. During the two most recent ones in July 1998 and 2010, we found total primary production in the East China Sea reaching 147 × 103 tons carbon per day, which may support fisheries catch as high as 410 × 103 tons per month, about triple the amount during non‐flooding periods based on direct field oceanographic observations. As the frequencies of floods increase world wide as a result of climate change, the flood‐induced biological production could be a silver lining to the hydrological hazards and human and property losses inflicted by excessive precipitations.

[1] Planktonic communities tend to flourish on the western margins of the East China Sea (ECS) fueled by substrates delivered largely from the Changjiang River, the fifth largest river in the world. To study the effects of the Changjiang River discharge on planktonic community respiration (CR), physical-chemical variables and key processes were measured in three consecutive summers in the ECS. Results showed that concentrations of nitrate and Chl a, protozoan biomass, bacterial production, as well as CR in the surface water were all negatively correlated with sea surface salinity, reflecting the strong influence of river discharge on the ECS shelf ecosystem. Moreover, mean values of nitrate, Chl a concentrations, and CR rates were proportionally related to the area of Changjiang diluted water (CDW; salinity 31.0 practical salinity units (psu)), an index of river discharge rate. Presumably, higher river flow delivers higher nutrient concentrations which stimulate phytoplankton growth, which in turn fuels CR. CR exhibited significant monthly and interannual variability, and rates appear to be dominated by bacteria and phytoplankton. Although the plankton community was relatively productive (mean = 0.8 mg C m À2 d À1) in the CDW, the mean ratio of production to respiration was low (0.42). This suggests that the heterotrophic processes regulating CR were supported by riverine organic carbon input in addition to in situ autotrophic production.