Community structure and primary productivity of phytoplankton in three contrasting coastal waters of the Korean Peninsula

Abstract

Seasonal variations of primary productivity (PP) and community structure of phytoplankton were investigated in the eastern, western, and southern coastal waters of the Korean peninsula. The three coastal areas are characterized by contrasting environmental conditions in terms of topographic, hydrodynamic, and biogeochemical features. Monthly and in situ measurements of PP and chemotaxonomic composition of phytoplankton were conducted. The purposes of the present study were (1) to highlight major factors controlling seasonal variability in PP; (2) main nutrient sources determining phytoplankton community composition; (3) spatial variation in annual PP of phytoplankton; and finally (4) to make conclusion of major processes characterizing spatiotemporal variation of phytoplankton blooms along the coastal systems of the Korean peninsula. Although the magnitude of PP and seasonal patterns of community compositions varied among areas, a summer phytoplankton bloom, along with early spring bloom in the eastern coast, was observed as a unique bloom characteristic in the three contrasting coastal waters. Subpolar front between the North Korean Cold Current (NKCC) and the Eastern Korean Warm Current along the eastern coast determined water-column structure and nutrient availability and thereby seasonal bloom of phytoplankton. This result highlights the importance of the southward advection of the NKCC to seasonal and spatial bloom dynamics of phytoplankton along the eastern coast. The western coastal waters were characterized by macrotidal and thus vertically well-mixed water-column conditions. The summer phytoplankton bloom was well associated with freshwater discharge by the monsoon rainfall. Estuarine dam discharge promoted PP during July–August, generating conspicuous blooms near the discharging site. Along the southern coast, seasonal cycles of PP and the succession of phytoplankton were uncoupled between the inside and the outside of the coastal embayment. Different hydrographic and nutritional conditions in the inner- and the outer-bay systems explained seasonally different patterns of phytoplankton developments in the southern coastal water. These findings highlight that although major determinants (i.e., hydrographic conditions, nutrient sources) driving the bloom dynamics of phytoplankton varied in the three contrasting coastal systems, the resulting summer phytoplankton blooms should be emphasized in relation to further development and production dynamics of higher trophic-level organisms.