Reef-building corals act as long-term sink for microplastic.

Area of Science:

• Marine Biology
• Environmental Science
• Oceanography

Background:

• Marine microplastic pollution is a pervasive global issue.
• A significant portion of microplastics entering oceans is unaccounted for, termed the "missing plastic" phenomenon.
• While sediments are known sinks, the role of coral reefs as long-term microplastic sinks remains underexplored.

Purpose of the Study:

• To investigate whether reef-building corals function as living, long-term sinks for microplastics.
• To quantify microplastic deposition within coral tissues and skeletons.
• To understand the processes governing microplastic accumulation in coral structures.

Main Methods:

• Four species of reef-building corals were exposed to polyethylene microplastics (200 particles L⁻¹) for 18 months in a laboratory setting.
• Microplastic presence and quantity were analyzed in coral tissues and skeletal structures.
• Correlation between microplastic accumulation and coral skeletal growth was assessed.

Main Results:

• Microplastics were detected in all coral specimens studied.
• Significantly higher microplastic concentrations were found in coral skeletons (up to 84 particles cm⁻³) compared to coral tissues (up to 2 particles cm⁻²).
• Accumulation in skeletons correlated with coral skeletal growth, indicating a stochastic deposition process.

Conclusions:

• Coral reefs serve as permanent biological sinks for microplastic pollution.
• Reef-building corals can sequester a measurable percentage (0.09%-2.82% annually) of bioavailable microplastics from tropical waters.
• This research underscores the ecological importance of coral reefs in mitigating microplastic pollution and highlights the need for their conservation.