Impacts of nutrients and related environmental factors on distribution and size structure of Noctiluca scintillans populations of the Eutrophic Tha Chin Estuary, Thailand

Abstract

This study aimed to analyze the impacts of nutrients and related aquatic factors on changes in the Noctiluca population of the Tha Chin estuary, a nutrient-rich estuary located in the inner Gulf of Thailand. Field surveys were carried out at 30 stations during November 2009 to August 2010. The results indicated high levels of dissolved inorganic nitrogen (DIN; 13.89-46.99 μmol/L) and PO(4)(3-)-P (0.20-3.05 μmol/L) where the Noctiluca red tide occurred, particularly during the high-loading period. Dense populations were usually found in the outer part of the estuary with comparatively high salinity (25-29 psu). The highest Noctiluca density was 72,333 cells L(-1) and the cell diameters ranged between 360 and 460 μm. Proportions of small-sized cells (P(s); less than 300 μm) varied over time. In this study, P(s) showed a positive correlation with levels of PO(4)(3-)-P, while the total population density was significantly affected by levels of NH(4)(+)-N and DIN (p < 0.05). Overall, PO(4)(3-)-P influenced the development of the Noctiluca red tide, with the limitation of PO(4)(3-)-P levels to below 1 μmol/L suggested for controlling Noctiluca red tide outbreaks at their origin. To support environmental conservation and maintain sustainable production in the estuary, the levels of PO(4)(3-)-P should be considered for the further effective development of water quality standards in estuarine zones.

MODIS-derived green Noctiluca blooms in the upper Gulf of Thailand: Algorithm development and seasonal variation mapping

“…Moreover, our findings showed that DN>60% blooms occurred mainly in estuaries and closer to the shore, which were more highly influenced by freshwater discharge than green Noctiluca blooms. This finding is consistent with the preferred salinity range of dinoflagellates such as Ceratium furca (12-27 psu) and green Noctiluca (22-33 psu) (Lirdwitayaprasit et al, 2006), as well as the correlation between high salinity (25-29 psu) and green Noctiluca abundance reported by Chuenniyom et al (2012). Thus, our results suggest that, in addition to contributing anthropogenic nutrients, river discharge may influence red tide distributions by regulating salinity levels.…”

“…Seasonal variability may result from the interaction between increased river discharge into the northern uGoT and the transfer of riverine nutrient inputs by eastward circulation generated by the monsoon along the northern coast (Buranapratheprat et al, 2002;Buranapratheprat et al, 2006;Yu et al, 2018). Chuenniyom et al (2012) examined the green Noctiluca population in the Tha Chin estuary (off the north coast of Thailand) and observed a dense population in the outer part of the estuary with relatively high salinity, as well as a red tide during the high loading period of river discharge from November to December 2009. Moreover, ammonium nitrogen and dissolved inorganic nitrogen concentrations influence the total green Noctiluca population density, whereas orthophosphate phosphorus regulates the development of green Noctiluca red tides (Chuenniyom et al, 2012).…”

“…Chuenniyom et al (2012) examined the green Noctiluca population in the Tha Chin estuary (off the north coast of Thailand) and observed a dense population in the outer part of the estuary with relatively high salinity, as well as a red tide during the high loading period of river discharge from November to December 2009. Moreover, ammonium nitrogen and dissolved inorganic nitrogen concentrations influence the total green Noctiluca population density, whereas orthophosphate phosphorus regulates the development of green Noctiluca red tides (Chuenniyom et al, 2012). Although the seasonal dynamics of green Noctiluca in northern coastal waters are related to an increase in riverine inputs and circulation induced by monsoons (Sriwoon et al, 2008;Chuenniyom et al, 2012), the overall dynamics of green Noctiluca and other red tides in the uGoT remain unknown.…”

“…Moreover, ammonium nitrogen and dissolved inorganic nitrogen concentrations influence the total green Noctiluca population density, whereas orthophosphate phosphorus regulates the development of green Noctiluca red tides (Chuenniyom et al, 2012). Although the seasonal dynamics of green Noctiluca in northern coastal waters are related to an increase in riverine inputs and circulation induced by monsoons (Sriwoon et al, 2008;Chuenniyom et al, 2012), the overall dynamics of green Noctiluca and other red tides in the uGoT remain unknown. This is attributed to a lack of continuous tracking of the spatial and temporal variations in phytoplankton populations.…”