광양만에서 식물플랑크톤 계절별 분포와 영양염 첨가가 식물플랑크톤 군집에 미치는 영향

Abstract

The influences of additional nutrients on phytoplankton growth and seasonal characteristics of phytoplankton communities in Gwangyang Bay, Korea

Si Woo Bae

Department of Oceanography, Graduate School, Pukyoung National University, Busan, Korea

Abstract In order to estimate the effect of additional nutrients on phytoplankton growth and horizontal phytoplankton community distribution during the 2010 and 2011, we investigated the abiotic and biotic factors of surface waters at 20 stations of inner and offshore areas in Gwangyang Bay, Korea. Also, nutrient additional experiments were conducted to assess additional nutrient effects on phytoplankton assemblage using the surface water. In both years, the total nutrients were high at the enclosed inner bay and the mouth of Seomjin River, whereas it was low at the St. 15 ~ St. 20, which is influenced by surface warm water current from offshore of the bay. Diatoms had a high relative contribution to total phytoplankton biomass and the dominant species were Skeletonema costatum-like species and Thalassiosira nordenskioeldi, particularly in the winter and summer. Eucampia zodiacus and cryptophyta Cryptomonas spp. were dominant in spring and autumn, respectively, comprising more than 70% of the community. A relative contribution of size-fractionated phytoplankton was different in periods that the micro-sized was higher in summer and winter due to dominate the chain diatoms, but nano-sized was higher in spring and autumn by enormous Cryptophyta biomass. The high nano- and pico-sized biomass were observed by Seomjin river discharge at station 10. Based on the spring algal bio-assays, although maximum growth rate of phytoplankton communities at inner bay (St.8) were similar to those of outer bay (St.20), half-saturation constant (Ks) for phosphate at outer bay was slightly lower than those of inner bay. This implied that adapted cells in low nutrient condition of outer bay may have enough grown even the low phosphate and they also have a competitive advantage against other algal species under low nutrient condition. In particular, efficiency of N (+) addition in summer season was higher compared to control and P added experiments. In the bay, silicon was not a major limiting factor for phytoplankton growth, whereas nitrogen (N) was considered as a limiting factor during spring and summer. Based on the bioassay and field survey, providing the high nutrients may have stimulated phytoplankton growth such as S. costatum-like spp.. In particular, opportunistic micro-algae such as Cryptomonas spp. were able to achieve the high biomass under the relatively mid nutrient condition from bottom after break down of seasonal stratification in the Gwangyang Bay.

List of Figures

Fig. 1. Location of sampling sites in Gwangyang Bay, Korea. White open squares and circle indicates spring, summer and autumn bioassay stations. respectively. ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 7 Fig. 2. Seasonal and temporal variations rainfall from 2010 to 2011 in Gwagyang Bay. Arrows indicates sampling date. ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 9 Fig. 3. Horizontal distribution changes of temperature 2010(a) and 2011(b) in Gwangyang Bay. ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 10 Fig. 4. Spatial distributions of temperature in Gwangyang Bay. ∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 10 Fig. 5. Horizontal distribution changes of salinity 2010(a) and 2011(b) in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 12 Fig. 6. Spatial distributions of salinity in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 12 Fig. 7. Comparison of abiotic(a: secchi depth; b: dissolved oxgen; c: pH) 2010 and 2011 in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 13 Fig. 8. Seasonal and horizontal distributional changes in nutrients at sampling stations in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 16 Fig. 9. Spatial distributions of DSi in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 17 Fig. 10. Spatial distributions of DIN in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 17 Fig. 11. Spatial distributions of DIP in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 18 Fig. 12. Spatial distributions of Chl. a in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 20 Fig. 13. Percentages of the total Chl. a concentration for each size fraction (<3 µm, >3 µm and <20 µm, >20 µm) in 2011.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 21 Fig. 14. Seasonal and horizontal distributional changes in total phytoplankton abundances and their relative contribution in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 24 Fig. 15. Seasonal and horizontal distributional changes in diatom abundances and their relative contributions in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 25 Fig. 16. Change in in vivo fluorescence of phytoplankton community by algal bio-assay. These experiments are used the surface water of each station in the spring of 2010 in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 30 Fig. 17. Relationship between growth rate of phytoplankton communities and nutrient concentration of nitrate (a, c) and phosphateas (b, d).

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 31 Fig. 18. Growth response of phytoplankton assemblages by algal bio-assay. These experiments are used the surface water of each station in the summer of 2010 in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 32 Fig. 19. Comparision of N and P nutrient additional efficiency vs. control based on Figure 18.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 33 Fig. 20. Growth response of phytoplankton assemblage by algal bio-assay. These experiments are used the surface water of each station in the autumn of 2010 in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 34 Fig. 21. Comparision of N, P and NP nutrient additional efficiency vs. control based on Figure 20.

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List of Tables

Table 1. Pearson correlation coefficients (r) indicating the relationships between abiotic and biotic factors at 19-20 stations in 2010 (left lower part) and 2011 (right upper part) in Gwangyang Bay.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 27 Table 2. Nutrient limitation assessment in Gwangyang Bay based on two differents criteria (nutrient concentration and ratios) in winter. Bold words indicate the nutrient limitation.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 45 Table 3. Nutrient limitation assessment in Gwangyang Bay based on two differents criteria (nutrient concentration and ratios) in spring. Bold words indicate the nutrient limitation.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 46 Table 4. Nutrient limitation assessment in Gwangyang Bay based on two differents criteria (nutrient concentration and ratios) in summer. Bold words indicate the nutrient limitation.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 47 Table 5. Nutrient limitation assessment in Gwangyang Bay based on two differents criteria (nutrient concentration and ratios) in autumn. Bold words indicate the nutrient limitation.

∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙∙ 48