Characterization of the phytoplankton community in coastal waters of Kota Kinabalu, Sabah

• Main Author: Chong, Brian Wei Khong
• Format: Thesis
• Language: English; English
• Published: 2020
• Subjects: QK900-989 Plant ecology
• Online Access: https://eprints.ums.edu.my/id/eprint/40916/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/40916/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/40916/

Tropical coastal ecosystems are seemingly seasonally stable environments compared to temperate and boreal regions. However, tropical waters experience seasonal changes in environmental conditions brought about by the Northeast Monsoon (NEM) and Southwest Monsoon (SWM), which may influence the temporal variation of the phytoplankton community. This study aimed to: (i) determine the monsoonal changes of the phytoplankton community in relation to the environmental parameters; (ii) examine the monsoonal variation of the predominant harmful algal bloom (HAB) species; (iii) uncover the phytoplankton diversity using next-generation sequencing (NGS) technology; and (iv) compare the techniques of phytoplankton identification using light microscopy and NGS. Samples were collected off the coast of Kota Kinabalu at bi-weekly intervals from August 2017 to January 2019, covering the NEM (November to March), the SWM (May to September), and the inter-monsoon periods in April and October (IMPs). Samples for species identification were collected using a plankton net (5 μm mesh) while surface water was collected for cell counts, nutrient analysis, and molecular analysis. Concurrent measurements of temperature, salinity and dissolved oxygen were carried out. Light intensity was measured continuously with a logger affixed above the water surface. Mean sea surface temperature during the SWM (30.4 ± 0.7) was significantly higher (p < 0.05) compared to NEM (29.6 ± 0.9), while salinity was significantly lower (p < 0.05) in the SWM (28.9 ± 2.7) compared to the NEM (31.7 ± 1.5). Mean photosynthetic active radiation (PAR) was significantly lower (p < 0.001) during the SWM (1.0 × 103 μmol m-2 s-1) compared to the NEM (1.5 × 104 μmol m-2 s-1). Nutrient concentrations showed no significant differences (p > 0.05) between the monsoons. Nutrient ratios indicate that silica was not the main limiting nutrient, while the environment may shift between nitrogen and phosphate limitation. A total of 32 diatom taxa, 22 dinoflagellate taxa, and one silicoflagellate taxa were identified. HAB species from the genera Margalefidinium and Pyrodinium were only detected sporadically in low cell densities (3.48 ± 2.2 × 103 cells L-1 and 159 ± 75 cells L-1, respectively) throughout the study period. Total phytoplankton densities were significantly higher in the SWM with median cell densities of 1.12 x 104 cells L-1 compared to the NEM with 3.98 x 103 cells L-1. Hierarchical clustering analysis (HCA) based on genera abundance showed that there are four main clusters which corresponded to the transitioning periods of the monsoons. SWM1–NEM1 (Cluster III) was dominated by the dinoflagellates Protoperidinium spp. (8.83 ± 1.5 ×103 cells L-1) and Prorocentrum spp. (2.6 ± 1.1 × 103 cells L-1) and shifted to a diatom-dominant community (Cluster IV) (Dactyliosolen spp. with 7.55 ± 1.9 × 103 cells L-1). During SWM2 (Cluster II), the phytoplankton community was dominated by the diatom Chaetoceros spp. (2.96 ± 0.41 × 105 cells L-1). Cluster I was dominated by Pseudo-nitzschia spp. during the IMP in April 2018 (2.80 ± 2.0 × 103 cells L-1). The distribution of diatom-dominant and dinoflagellatedominant communities along the axes of the Canonical Correspondence Analysis (CCA) triplot showed that dinoflagellate-dominant communities were more affected by mean PAR and Si:N ratio whereas diatom-dominant communities were more affected by a combination of temperature, salinity and N:P ratio. Microscopy and NGS showed complementary results with more diatom taxa detected by microscopy whereas NGS detected smaller and rarer taxa. The results of this study implicate that tropical waters can experience significant changes in the environment which are associated to shifts in the dominant phytoplankton taxa between the monsoons, and the application of both microscopy and NGS methods in tandem can provide more comprehensive information about the phytoplankton diversity.