# Physiological and Epigenetic Responses of the Long‐Spined Sea Urchin Diadema antillarum Across a Spatiotemporal Gradient

## TL;DR

This study examines how sea urchins respond to environmental changes and offers insights for their restoration in the Caribbean.

## Contribution

The paper provides the first comprehensive characterization of epigenetic responses in Diadema antillarum.

## Key findings

- Urchin densities decrease with higher sedimentation, and righting response slows under elevated sedimentation.
- DNA methylation variation clusters by season, and righting response correlates with methylation patterns.
- Transplanted urchins acclimatize to new environments, but handling stress causes significant mortality.

## Abstract

Following catastrophic population declines in the 1980s and 2022, the keystone herbivore
Diadema antillarum
has become a focal species for Caribbean‐wide restoration initiatives. In the present work, we combined an 11‐month field survey across four reefs on the island of Culebra, Puerto Rico, with reciprocal transplants to evaluate physiological performance and DNA methylation responses of
D. antillarum
to seawater temperature, salinity, sedimentation, and nutrient gradients. Environmental parameters varied significantly across sites and seasons (GLM, p < 0.01). Urchin densities were negatively correlated with sedimentation, and righting response (a proxy for neuromuscular function) slowed under elevated sedimentation. Epigenetic analyses revealed extensive DNA methylation variation clustering by season rather than site. Righting response correlated significantly with DNA methylation patterns, suggesting a role of epigenetic regulation in physiological plasticity. Surviving transplanted urchins rapidly recovered normal righting behavior, indicating individual‐level acclimatization despite ~50% transplant mortality primarily attributed to handling stress rather than environmental incompatibility. Collectively, our results suggest that restoration efforts should prioritize low‐sedimentation sites (< 30 mg·cm−2·day−1) while implementing refined handling protocols and preconditioning strategies to enhance transplant success and minimize procedural mortality in suboptimal environments.

Following catastrophic population declines in the 1980s and 2022, the keystone herbivore Diadema antillarum has become a focal species for Caribbean‐wide restoration initiatives. In the present work, we combined an 11‐month field survey across four reefs in the island of Culebra, Puerto Rico, with a reciprocal transplant experiment to evaluate physiological and epigenetic responses to environmental gradients. Our results suggest that sedimentation and nutrient loading, alongside strategic population supplementation from stress‐adapted source populations, should be prioritized during coordinated habitat remediation strategies. This work provides the first comprehensive characterization of epigenetic responses in D. antillarum, providing molecular baselines with potential applications for species recovery programs.