# Tephra-mediated manganese cycling shapes coral responses to coastal sedimentation

## TL;DR

Volcanic tephra increases manganese in seawater, helping corals resist sedimentation stress by boosting their photosynthesis.

## Contribution

Tephra's role in manganese cycling and coral resilience to sedimentation is newly demonstrated through experimental evidence.

## Key findings

- Tephra exposure increases coral photosynthetic efficiency under low light and sedimentation stress.
- Photosynthetic efficiency is logarithmically linked to seawater manganese concentration below 3 µg L−1.
- Tephra plays a key role in coastal manganese cycling and supports coral recovery after disturbances.

## Abstract

Terrestrial runoff from tropical volcanic islands impacts coral reefs by increasing turbidity and sedimentation. During explosive volcanic eruptions, large amounts of fragmented volcanogenic rock (tephra) are deposited, exacerbating sediment runoff for long periods of time. Nevertheless, tephra is an important, yet underestimated, source of the essential trace metal manganese (Mn), which promotes coral photosynthesis. Here, we show Mn leached from pristine and remobilised tephra increases resilience to sedimentation stress. Using coral culture experiments, microcolonies of Stylophora pistillata exposed to four tephra samples all showed rapid and sustained increases in photosynthetic efficiency (ΦPSII, rETR, Pn and Pgross), even under reduced light conditions. Photosynthetic efficiency is logarithmically correlated to seawater Mn concentration, with large increases at values < 3 µg Mn L− 1, and negligible changes at values > 10 µg Mn L− 1. Tephra exposure has a crucial role in coastal Mn cycling and potentially benefits stressed corals following environmental disturbances.

The online version contains supplementary material available at 10.1038/s41598-026-38388-9.