Spatiotemporal variability in the biochemical characteristics of phytoplankton and zooplankton in the coastal waters of the Yellow and East seas

Abstract

The coastal waters are dynamic ecosystems influenced by seasonal temperature fluctuations, riverine inputs, and upwelling, which drive sensitive responses among lower trophic-level organisms. The biochemical composition of phytoplankton and zooplankton plays a critical role in determining energy flow and food web structure, yet their spatiotemporal variability remains underexplored. This study investigated spatiotemporal variability in the biochemical composition of phytoplankton and zooplankton in the Yellow Sea (YS) and East Sea (ES), focusing on environmental and biological drivers. Field surveys were conducted in spring (May) and summer (August) of 2023 (YS) and 2024 (ES), quantifying phytoplankton macromolecular composition—carbohydrates (CHO), proteins (PRT), and lipids (LIP)—and zooplankton proximate composition (PRT, LIP, and ash), and various environmental parameters. In the YS, phytoplankton LIP content was negatively correlated with nutrient concentrations, suggesting nutrient-driven biochemical shifts. In the ES, phytoplankton exhibited significant seasonal changes, with PRT decreasing and CHO increasing, reflecting metabolic adaptation to temperature stress and nutrient limitation. Zooplankton biochemical composition reflected these regional contrasts: in the YS, variability was largely influenced by community structure, while in the ES, it was more strongly regulated by phytoplankton nutritional quality. Under nutrient-limited conditions, diatom growth slows and cell wall synthesis may increase frustule thickness. These changes could reduce food palatability, which may help explain the observed pattern in the ES, including decreased zooplankton PRT content and increased LIP storage. A positive correlation in PRT content between phytoplankton and zooplankton in the ES indicated a stronger biochemical trophic linkage under stable copepod dominance, whereas weakened coupling in the YS reflected grazer diversity and variable feeding selectivity. These findings highlight how environmental conditions and community composition regulate biochemical properties and trophic connectivity in Korean coastal marine ecosystems.