High Heterotrophic Plasticity of Massive Coral Porites pukoensis Contributes to Its Tolerance to Bioaccumulated Microplastics

Scleractinian corals have been observed to be capable
of accumulating
microplastics from reef environments; however, the tolerant mechanism
is poorly known. Here, we examined the response of Porites pukoensis to microplastic pollution by analyzing
algal symbiont density, energetic metabolism, and caspase3 activities
(representing the apoptosis level) in the coral–Symbiodiniaceae
association. The environments of three fringing reef regions along
the south coast of Sanya City, Hainan Province of China, were polluted
by microplastics (for example, microplastic concentrations in the
seawater ranged from 3.3 to 46.6 particles L–1),
resulting in microplastic accumulation in P. pukoensis (0.4–2.4 particles cm–2). The accumulation
of microplastics was negatively correlated to algal symbiont density
in the corals but not to caspase3 activities in the two symbiotic
partners, demonstrating that P. pukoensis could tolerate accumulated microplastics despite the decrease of
algal symbiont density. Furthermore, results from the carbon stable
isotope and cellular energy allocation assay indicated that P. pukoensis obtained energy availability (mainly
as lipid reserves) using the switch between heterotrophy and autotrophy
to maintain energy balance and cope with accumulated microplastics.
Collectively, P. pukoensis achieved
tolerance to microplastic pollution by maintaining energy availability,
which was largely attributed to its high heterotrophic plasticity.