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Updated: Jan 20, 2026

Coral Reef Arks: An In Situ Mesocosm and Toolkit for Assembling Reef Communities
Published on: January 6, 2023
Effects of tourism-derived sewage on coral reefs: Isotopic assessments identify effective bioindicators
Liam Lachs1, Nur Arbaeen Mohd Johari2, Dung Quang Le2
1Marine Biology, Ecology & Biodiversity, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium; Institute of Oceanography and Environment, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia.
Abstract:
Pulau Redang and Pulau Tioman have experienced huge tourism growth over the last two decades, but minimal sewage treatment may threaten the resilience of their coral reefs. This study uses stable isotope techniques to identify suitable bioindicators of sewage nutrients (δ15N) at these islands by measuring macroalgae (Lobophora spp.), gastropods (Drupella spp.), scleractinian coral (Acropora spp.), and leather coral (Sinularia spp.). At tourist hubs using seepage septic tank systems, enrichment of Acropora δ15N (Redang, +0.7‰) and Sinularia δ15N (Tioman, +0.4‰) compared to pristine background levels indicate enhanced sewage nutrient discharge. Carbon isotopes and survey data suggest that sedimentation did not confound these δ15N trends. Potential damaging effects of sewage discharge on the coral reef communities at both islands are highlighted by strong correlations between Acropora δ15N and regional variation in coral reef community structure, and exclusive occurrence of degraded reefs at regions of high sewage influence.
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