Acute heat stress drives abundance shifts in Chaetodon octofasciatus under turbid-water conditions: Evidence from Bintan Island

¹ Doctoral Program of Marine Science, Faculty of Fisheries and Marine Science, Institut Pertanian Bogor, Kampus IPB Darmaga, Bogor 16128, West Java, Indonesia.
² Department of Naval Architecture, Faculty of Engineering and Maritime Technology, Universitas Maritim Raja Ali Haji, Tanjungpinang, Kepulauan Riau, Indonesia.
³ Research Center for Biota Systems, National Research and Innovation Agency, Cibinong, Bogor 16911, West Java, Indonesia.
⁴ Marine Evolution and Ecology Group, Naturalis Biodiversity Center, 2300 RA Leiden, The Netherlands.
⁵ Department of Marine Sciences and Technology, Faculty of Fisheries and Marine Science, Institut Pertanian Bogor, Bogor 16680, West Java, Indonesia.
⁶ Department of Oceanography, Faculty of Fisheries and Marine Sciences, Diponegoro University, Semarang, Indonesia.
⁷ School of Environment and Natural Science, Newcastle University, England.School of Environment and Natural Science, Newcastle University, England.
⁸ Faculty of Fisheries and Marine Sciences, Riau University, Pekanbaru, Indonesia.
⁹ department of Masterof of Environmental Science, Universitas Maritim Raja Ali Haji, Tanjungpinang, Kepulauan Riau, Indonesia.

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Coral bleaching responses in reef fishes are predominantly documented from clear-water reefs, where coral loss reliably predicts declines in coral-associated species. Turbid reef systems may follow different trajectories because thermal exposure, benthic change, and water-column forcing covary with light, sedimentation, and productivity gradients. Here, we combined repeated observations of sea-surface temperature anomaly, benthic composition, water-column conditions, and Chaetodon octofasciatus abundance from ten reef stations on eastern Bintan Island, Indonesia, surveyed before, during, and after the 2016 global coral bleaching event. Mean sea-surface temperature anomaly increased from 0.11°C before bleaching to 0.88°C during bleaching and declined incompletely to 0.33°C one year later. Over the same period, C. octofasciatus abundance rose from 12.6 to 20.8 individuals 350 m⁻² and remained elevated at 20.1 individuals 350 m⁻² after bleaching. Although pooled abundance was positively associated with sea-surface temperature anomaly (Spearman ρ = 0.43, P = 0.024), paired station-level changes in abundance were not significantly related to paired thermal changes (ρ = 0.24, P = 0.410). Live coral cover alone did not explain the abundance increase, whereas multivariate benthic composition and water-condition structure shifted across sampling phases. These findings suggest that post-bleaching increases in coral-associated fish abundance may reflect short-term benthic–corallivore reconfiguration rather than ecosystem recovery, and that fish abundance alone is an unreliable indicator of reef resilience in turbid systems.