# Adaptation Strategy of the Planula Strobilation in Moon Jelly, Aurelia coerulea to Acidic Environments in Terms of Statolith Formation

## TL;DR

This study shows that moon jellyfish can adapt to acidic ocean conditions by changing their reproductive strategy to produce ephyrae with minimal but functional structures.

## Contribution

The study reveals that planula-strobilation in Aurelia coerulea is an adaptive strategy under acidification, enabling survival through modified statolith development.

## Key findings

- Planula-strobilation produces viable ephyrae at pH 6.8, while polyp-strobilation fails.
- At pH 7.8, both strobilation types result in smaller but more numerous statoliths.
- Planula-strobilated ephyrae have needle-shaped statoliths, indicating rapid crystallization.

## Abstract

Ocean acidification poses a significant threat to marine invertebrates with calcium-based structures. This study investigated the effects of low pH on two types of strobilation in Aurelia coerulea: polyp-strobilation (conventional asexual reproduction from polyps) and planula-strobilation (direct development from planulae). Experiments were conducted under pH 6.8, 7.8, and 8.1 conditions to observe morphological changes and statolith formation in ephyrae. Under the pH 6.8 condition, polyp-strobilation failed to produce normal ephyrae, while planula-strobilation succeeded in releasing morphologically normal ephyrae, albeit without statoliths. Under the pH 7.8 condition, both strobilation types produced ephyrae with altered statolith morphology. These statoliths were smaller in size but more numerous than those formed at pH 8.1 as normal pH, suggesting a compensatory mechanism that maintains total statolith mass and potentially preserves function. Planula-strobilated ephyrae had fewer but larger, needle-shaped statoliths, suggesting rapid statolith development. These findings suggest that planula-strobilation functions as a stress-adaptive reproductive strategy, producing the minimum necessary morphology and internal structures to ensure survival in a changing environment. The ability of Aurelia coerulea to adjust reproductive strategy and developmental traits under acidified conditions may contribute to its ecological success and persistence under future climate change scenarios.

Ocean acidification, caused by increased atmospheric CO2, threatens marine organisms that depend on calcium-based structures such as jellyfish statoliths. This study investigated the effects of low pH on the morphology and statolith formation of ephyrae in Aurelia coerulea, comparing two developmental pathways to form ephyra: polyp-strobilation and planula-strobilation. Under the pH 6.8 condition, polyps failed to produce viable ephyrae, whereas planula-strobilation succeeded in releasing ephyrae with normal morphology, though statoliths were absent. Under the pH 7.8 condition, both strobilation types produced normal-shaped ephyrae with reduced statolith size but increased statolith number compared with the control (pH 8.1), suggesting a compensatory response to acidification. Statolith morphology differed between pathways: planula-strobilated ephyrae had needle-shaped statoliths with high aspect ratios, indicating a rapid, early-stage crystallization process. Despite their minimal body size and statolith development, planula-strobilated ephyrae maintained the functional mass of statoliths necessary for survival. This rapid, morphologically minimized development suggests that planula-strobilation is an adaptive reproductive strategy in response to environmental stress. Our findings suggest that A. coerulea possesses a flexible life history strategy that may facilitate its resilience to ongoing ocean acidification scenarios.