Hidden Impacts of Plastic Chemical Pollution on Coral Embryos

Abstract

Successful embryonic development is critical to coral reef persistence, but coral embryos are increasingly exposed to plastic-derived contaminants in coastal environments. Polyvinyl chloride (PVC) releases complex mixtures of endocrine-disrupting chemicals as it degrades, yet the impacts of PVC leachate on coral early life stages remain poorly understood. We investigated the ecotoxicological responses of three levels of PVC leachate (0.01, 0.1, and 1 mg/L) during the first 14 hours post fertilization (hpf) of embryonic development in the coral Montipora capitata. PVC leachate did not affect embryo survival or the prevalence of morphological abnormality; however, we did detect subtle changes in accelerated developmental timing at the 14 hour-post fertilization stage in the moderate PVC leachate treatment samples. Furthermore, RNAseq analysis identified 130 differentially expressed genes (DEGs) responsive to PVC leachate treatments. Gene expression responses to leachate exposure were strongest at low (0.01 mg/L) and moderate (0.1 mg/L) levels, and during the earliest developmental stage (cleavage, 4 hpf), indicating a low-dose response pattern and suggesting sublethal effects of low-dose PVC leachate exposure in developing Montipora capitata embryos. Additionally, 16S rRNA gene microbiome analysis (V3-V4 region) identified 9 bacterial taxa and 17 predicted microbial functional pathways that were altered by PVC leachate, with differences in abundance and/or prevalence compared to controls. Our findings indicate that current environmental levels of PVC pollution are likely to influence developmental timing, gene expression, and microbiome assembly in coral embryos as early as 4 hours post-fertilization, in the absence of overt morphologic embryonic abnormalities or elevated mortality. This study provides insight into how sublethal, plastic-derived chemical pollution may affect coral early life stages, a critical but under-explored phase impacting reef resilience and recovery.