title: Nutrient ratios and the complex structure of phytoplankton communities in a highly turbid estuary of Southeast Asia.
abstract: Phytoplankton diversity and abundance in estuarine systems are controlled by many factors. Salinity, turbidity, and inorganic nutrient concentrations and their respective ratios have all been proposed as principal factors that structure phytoplankton diversity and influence the emergence of potentially toxic species. Although much work has been conducted on temperate estuaries, less is known about how phytoplankton diversity is controlled in tropical, monsoonal systems that are subject to large, seasonal shifts in hydrology and to rapidly changing land use. Here, we present the results of an investigation into the factors controlling phytoplankton species composition and distribution in a tropical, monsoonal estuary (Bach Dang estuary, North Vietnam). A total of 245 taxa, 89 genera from six algal divisions were observed. Bacillariophyceae were the most diverse group contributing to 51.4 % of the microalgal assemblage, followed by Dinophyceae (29.8 %), Chlorophyceae (10.2 %), Cyanophyceae (3.7 %), Euglenophyceae (3.7 %) and Dictyochophyceae (1.2 %). The phytoplankton community was structured by inorganic nutrient ratios (DSi:DIP and DIN:DIP) as well as by salinity and turbidity. Evidence of a decrease in phytoplankton diversity concomitant with an increase in abundance and dominance of certain species (e.g., Skeletonema costatum) and the appearance of some potentially toxic species over the last two decades was also found. These changes in phytoplankton diversity are probably due to a combination of land use change resulting in changes in nutrient ratios and concentrations and global change as both rainfall and temperature have increased over the last two decades. It is therefore probable in the future that phytoplankton diversity will continue to change, potentially favoring the emergence of toxic species in this system.
authors.affiliation: Institute of Marine Environment and Resources (IMER), Vietnam Academy of Science and Technology (VAST), Haiphong, Viet Nam.
authors.forename: Thuoc Van
authors.initials: TV
authors.lastname: Chu
authors.forename: Jean-Pascal
authors.initials: JP
authors.lastname: Torréton
authors.forename: Xavier
authors.initials: X
authors.lastname: Mari
authors.forename: Huyen Minh Thi
authors.initials: HM
authors.lastname: Nguyen
authors.forename: Kha Thi
authors.initials: KT
authors.lastname: Pham
authors.forename: Thu The
authors.initials: TT
authors.lastname: Pham
authors.forename: Thierry
authors.initials: T
authors.lastname: Bouvier
authors.forename: Yvan
authors.initials: Y
authors.lastname: Bettarel
authors.forename: Olivier
authors.initials: O
authors.lastname: Pringault
authors.forename: Corinne
authors.initials: C
authors.lastname: Bouvier
authors.forename: Emma
authors.initials: E
authors.lastname: Rochelle-Newall
mesh_terms: D017377:Diatoms / Q000145:classification / Q000254:growth & development; D004141:Dinoflagellida / Q000145:classification / Q000254:growth & development; D004784:Environmental Monitoring; D063366:Estuaries; D009584:Nitrogen / Q000032:analysis; D010758:Phosphorus / Q000032:analysis; D010839:Phytoplankton / Q000145:classification / Q000254:growth & development*; D054712:Salinity; D012621:Seasons; D012623:Seawater / Q000737:chemistry; D013696:Temperature; D014744:Vietnam; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D014873:Water Pollutants; D010758:Phosphorus; D009584:Nitrogen