The Influences of Additional Nutrients on Phytoplankton Growth and Horizontal Phytoplankton Community Distribution during the Autumn Season in Gwangyang Bay, Korea

Abstract

In order to estimate the effect of additional nutrients on phytoplankton growth and horizontal phytoplankton community distribution during the autumn season in 2010 and 2011, we investigated the abiotic and biotic factors of surface and bottom 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.15~20 where in influenced by the surface warm water current from offshore of the bay. On the other hand, nano-and pico-sized Chl. a were gradually increased towards the outer bay and their trends were significant in 2011 than in 2010. The cryptophyta species occupied more than 85% of total phytoplankton assembleges in 2010, whereas their abundance in 2011 remainds to be 1/10 levels of 2010. Following the cryptophata species, the diatom Chaetoceros spp. and Skeletonema-like spp. were found to be dominant species. Further the biosaasy experimental results shows that the phytoplankton biomass in the + + N and + + NP treatments was higher compared to control and + + P treatments and its trend was significant at St.8 and St.20 where nutrient concentration were low. Based on the bioassay and field survey, providing the high nutrients may have stimulated to 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.

Different Roles of Top-Down and Bottom-Up Processes in the Distribution of Size-Fractionated Phytoplankton in Gwangyang Bay

“…An increase in phosphate levels leads to cryptophyte blooms in the Krka River estuary in the eastern Adriatic Sea [38]; however, how their dynamics are associated with nutrient limitations is not well known. In Gwangyang Bay, cryptophyte growth appears to be favored in the fall when weakened stratification propagates water column mixing [35] or tides transport cryptophytes from the Seomjin River estuary to the Yeosu Channel [28]. In the study region, P-deficiency (i.e., DIP < 0.2 µM; Dortch and Whitledge [39]) was not detected, but P-limitation was enhanced in the summer during the nanoplankton bloom.…”

“…and Eucampia zodiacus were the bloom causative species in the summer and winter, respectively (Unpublished data). Although cryptophytes mainly reside in freshwater ecosystems [34], they conventionally cause blooms in Gwangyang Bay [28,35,36]. Klaveness [37] determined that as opportunists, cryptophytes can proliferate at a fast rate when the growth of competing algae is not favored.…”

Mesocosm experiments of temperate marine coastal waters: timing of changes in phytoplankton communities and attachment to plastic plates after nutrient addition

“…Spring blooms are primarily triggered by increases in water temperature and light intensity and an enrichment of nutrients from increased mixing of the water column; autumn blooms are triggered by replenishment of nutrients in the euphotic zone, which had a depletion of nutrients during summer months (Cushing 1989;Carstensen et al 2015;Wihsgott et al 2019). For example, the autumnal enrichment of nutrients in Korean coastal waters (KCWs) leads to an increase of diatoms and cryptophytes, and a gradual collapse of dino agellates, organisms that dominate through diel vertical migration under conditions of nutrient depletion (Bae et al 2014;Lim and Baek 2017;Lim et al 2022b).…”