Hidden underlying mechanisms for changes in mesozooplankton communities: Transport and eddy driven changes

Area of Science:

• Marine Ecology and Oceanography
• Climate Change Indicators
• Zooplankton Dynamics

Background:

• Mesozooplankton communities serve as sensitive indicators of climate change due to their rapid growth and environmental responsiveness.
• The East Sea/Japan Sea, particularly the Ulleung Basin, has experienced rapid surface water warming in recent decades.
• Understanding changes in mesozooplankton is crucial for assessing the impacts of climate change on marine ecosystems.

Purpose of the Study:

• To investigate modifications in mesozooplankton taxonomic composition over 14 years (2009-2022) in the Ulleung Basin.
• To correlate these changes with physical oceanographic factors such as transport-driven, eddy-driven processes, and marine heatwaves (MHWs).
• To analyze the influence of specific currents like the East Korea Warm Current (EKWC) and the Western Channel (V-west) volume on zooplankton dynamics.

Main Methods:

• Analysis of mesozooplankton community structure and abundance in the Ulleung Basin mixed layer from 2009 to 2022.
• Correlation of zooplankton data with physical oceanographic data, including EKWC direction, Ulleung warm eddy presence, V-west volume, and MHW occurrences.
• Identification of dominant zooplankton taxa and their relationship to observed environmental conditions.

Main Results:

• A slight overall increase in mesozooplankton abundance was observed from 2009 to 2022.
• Two significant abundance peaks occurred in 2015 and 2020, primarily driven by Noctiluca scintillans.
• The 2020 peak showed Pyrocystis pseudonoctiluca as the next dominant species, linked to strong V-west, eastward EKWC, and MHWs, unlike the 2015 peak.

Conclusions:

• Physical changes, including transport and eddy-driven processes, strongly influence dominant mesozooplankton taxa in the Ulleung Basin.
• The interplay of V-west volume, EKWC direction, and MHWs synergistically affects the increase of specific zooplankton groups during summer.
• This study underscores the complex interactions between marine ecosystems and physical oceanographic changes in a warming regional ocean.