Physical and biological roles of mesoscale eddies in Japanese eel larvae dispersal in the western North Pacific Ocean

Yu-Lin K Chang,Yu-San Han,Jinyu Sheng,Mélanie Béguer-Pon,Kyoko Ohashi,Yasumasa Miyazawa

doi:10.1038/s41598-018-23392-5

Abstract

The physical and biological roles of mesoscale eddies in Japanese eel larvae dispersal are investigated using a three-dimensional (3D) particle-tracking method, with a focus on the Subtropical Counter Current eddies of the western North Pacific Ocean. Virtual eel larvae (v-larvae) movements depends on the 3D ocean currents and active swimming behavior, including vertical swimming (diel vertical migration), horizontal directional swimming toward settlement habitat, and horizontal swimming toward available food. V-larvae are able to remain in eddies passively due to mesoscale eddy nonlinearity and/or actively due to attraction to rich food supplies. Thus, both physical trapping and biological attraction to food contribute to the retention of v-larvae in eddies. Physical trapping dominates the retention of v-larvae whose swimming speeds are slower than the eddy propagation speed, whereas biological food attraction prevails in the retention of v-larvae swimming faster than eddy propagation. Food availability differs between warm (anti-cyclonic) and cold (cyclonic) eddies, with the latter providing a richer food supply. Fish larvae that are retained for longer durations in cold eddies (shorter durations in warm eddies) are able to obtain more food and potentially grow faster, which enhances survival rates.

Highlights

Mesoscale eddies play an important role in various biochemical and physical processes[1,4]
We explored the effects of mesoscale eddies on fish larvae dispersal, including eddies’ ability to physically trap and transport the larvae and to act as a food source, which has direct applications to Subtropical Counter Current (STCC) mesoscale eddies and Japanese eel larvae in the western North Pacific Ocean
A three-dimensional (3D) particle-tracking method was used in which v-larvae were set to swim horizontally and migrate vertically (DVM), in addition to being moved passively by ocean currents

Summary

Introduction

Mesoscale eddies play an important role in various biochemical and physical processes[1,4]. A recent study suggests that the rich nutrient supply in mesoscale eddies can lead to faster growth rates of larval coral reef fish and result in greater survival and settlement[19]. In addition to their biochemical roles, mesoscale eddies play a crucial physical function by transporting ocean mass. The observed presence of fish larvae in mesoscale eddies can be attributed to passive physical trapping and/or active biological behavior, the relative importance of each mechanism remains to be studied. The simulations in this study will focus on the dispersal of Japanese eel larvae in STCC eddies

Objectives

Results

Conclusion