# Feeding and Growth in the Ephyra Stage of Aurelia coerulea: An In Situ Study

## TL;DR

This study examines how young jellyfish feed and grow in their natural environment, finding that food availability and environmental experience influence their growth and potential to form large blooms.

## Contribution

The study provides empirical in situ data on feeding and growth rates of Aurelia coerulea ephyrae, revealing how environmental factors and prey availability modulate their development.

## Key findings

- Field-collected ephyrae had higher clearance rates and grazing carbon than lab-reared ones.
- Growth rates peaked at intermediate prey concentrations, not at extremes.
- Environmental history and prey availability modulate ephyra feeding and growth.

## Abstract

Jellyfish often form large groups, called blooms, which can affect the health of coastal waters and the animals living there. One stage in the jellyfish life cycle, called the ephyra, is very small and hard to study in the wild, but is important because it can shape how large a bloom will become. In this study, we collected young jellyfish from two coastal bays in Korea and measured how much food they ate and how fast they grew in their natural environment. We found that jellyfish which started life in the wild ate more and grew more than those raised in the lab, and that jellyfish grew best when food was available at just the right level: not too much or too little. These findings show that the success of jellyfish blooms depends on both natural food conditions and the jellyfish’s own experience in their environment. Understanding how young jellyfish feed and grow in nature will help scientists and managers predict and possibly control jellyfish outbreaks, which can affect fishing, tourism, and marine life.

The ecological role and in situ feeding potential of Aurelia coerulea ephyrae remain poorly quantified. We conducted in situ chamber experiments in Geoje and Jaran Bay, Korea, to evaluate clearance rates, specific growth rate (SGR), and grazing carbon among ephyrae of different sizes and origins. Larger field-collected ephyrae had higher clearance rates (4.2 ± 0.8 mL ind−1 h−1) and grazing carbon (17.2 ± 1.0 μg C ind−1 d−1) than smaller individuals (1.6 ± 0.5 mL ind−1 h−1; 5.2 ± 1.1 μg C ind−1 d−1), though the differences were not statistically significant (p > 0.05). Field-collected ephyrae exhibited significantly greater clearance (p < 0.05) and grazing carbon (p < 0.01) than laboratory-reared ephyrae, while laboratory-reared ephyrae had higher SGR (p < 0.01).Grazing efficiency did not differ significantly between groups (p > 0.05). SGR peaked at intermediate prey concentrations (0.189 ± 0.013 d−1, p < 0.05), with reduced growth at both lower and higher concentrations. These results indicate that in situ feeding and growth rates are lower than laboratory rates, and that early-stage predation by ephyrae is modulated by prey availability and environmental history. Such findings provide essential baseline data for predicting the bloom dynamics and ecological impacts of Aurelia in temperate coastal environments.