The effect on phytoplankton dynamics of nutrient inputs from rivers within the highly eutrophic Pearl River Estuary (PRE) in China is well understood. However, the role that typhoons play in enhancing or reducing phytoplankton blooms is less well known. The primary factors controlling phytoplankton dynamics in the PRE in June-July 2009 were determined by coupling satellite remote sensing data with field observations during two successive typhoons: Nangka and Soudelor. The results revealed that the magnitude of chlorophyll a concentration (Chl) near the PRE was controlled by several key factors.(1) Vertical mixing of seawater induced by Typhoons Nangka and Soudelor led to a sudden decrease in Chl and phytoplankton abundance near the PRE, especially in picophytoplankton. (2) Following the typhoon events, increased nutrient availability associated with significant freshwater runoff promoted phytoplankton (especially Synechococcus) growth, recovery, and blooms in and near the PRE. (3) Increased freshwater input or easterly winds enhanced the extension of highly abundant phytoplankton with brackish water from the estuary into the adjacent nearshore water. (4) Phycocyanin-rich Synechococcus was endemic and a dominant picophytoplankton group in the estuarial brackish water. We propose a mechanism that describes the interactions of vertical mixing, terrestrial precipitation, freshwater discharge, nutrient inputs, and winds on short-term phytoplankton dynamics in and near the PRE during typhoon season.

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A high sedimentation event caused by dredging and dumping of sediment was recorded on Xiaodonghai Reef in Yulin Bay, southern Hainan Island, China. Significantly high sedimentation and constant light shading were observed during the sediment dumping event (SD Event). Using long-term video transects, we quantified coral community changes and responses to the SD Event between 2008 and 2010. The SD Event caused severe coral mortality on Xiaodonghai Reef at a depth of 6 m, while corals at 3 m were less affected. Total live coral cover at 6 m decreased from 54.3% to 14.8%, and Diploastrea heliopora replaced Galaxea fascicularis as the dominant coral species at 6 and 9 m. The density of juvenile corals also declined after the SD Event, especially for the genera Galaxea and Platygyra. However, the density of juvenile Porites and Pocillopora spp. slightly increased. Monitoring for 11 months after the SD Event indicated no recovery of coral communities on Xiaodonghai Reef. Long-term video transect data also revealed that mean live coral cover dramatically declined, from 30.5% in 2008 to 9% in 2010, while the dominant corals in Yulin Bay shifted to more tolerant coral species, such as massive Porites spp. and D. heliopora. The rapid coral community degradation in Yulin Bay between 2008 and 2010 was probably caused by high sediment deposition resulting from intensive dredging and land-clearing activities. These results highlight the necessity for an integrated watershed management to control sediment deposition on near-shore coral reefs. Of the 704 scleractinian coral species that could be assigned conservation status, 32.8% are in categories with elevated risk of extinction [3]. Scleractinian coral communities are sensitive to many disturbances, such as thermal stress [4,5], ocean acidification [6], outbreaks of crown-of-thorns starfish (COTS; Acanthaster planci) [7,8], overfishing [9], typhoon damage [9] and terrestrial pollution [10]. Coral bleaching and ocean acidification resulting from climate change have become the main threats to coral reef on a global scale, whereas on regional scales, terrestrial pollution (especially heavy sedimentation) has become the main threat to inshore coral reefs [6,11,12]. Heavy sedimentation may result in light shading, sediment abrasion on the coral surface, smothering of coral tissues and may eventually lead to its death [13,14]. Heavy sedimentation results in fewer coral species, less live coral, lower coral growth rates, reduced coral recruitment, decreased calcification, decreased net productivity of corals, and slower rates of reef accretion