Microplastic (MP) pollution is a rapidly increasing stressors for corals and reef ecosystems. While MP exposure leads to increased photosynthetic efficiency of the coral-associated photosymbiont, its interaction with heterotrophic feeding, the second source of coral energy, is less well explored. To address this knowledge gap, we studied the responses of two reef-building coral species (Pocillopora verrucosa and Stylophora pistillata) ina six-week MP aquarium experiment with different feeding regimes: CF (twice-weekly feeding of the microplastic-free control group), MP + CF (400 ppl mix of MP types + control feeding), and MP + HF (400 ppl MP + high, daily feeding). To assess the interactive effects of MP and feeding regime, we measured coral growth, photosynthetic efficiency, and photosynthesis and respiration rates. Surprisingly,  coral growth was similar under all feeding and microplastic treatments. However, high feeding modulated the effects of MP on the photosymbiont of Pocillopora verrucosa, with increased photosynthetic efficiency and respiration in the MP + CF treatment compared to the other treatments. In contrast, Stylophora pistillata was not affected by MP exposure alone, but when combined with high feeding photosynthetic efficiency decreased. This decrease could be explained by an increase in their heterotrophic activity. These findings highlight that the feeding regime has an effect on the corals response to MP. Thus, future studies should consider the interactive effects of MP pollution and food availability to better mimic the natural environment.

Primary Presenter: Maria Lopez, Justus Liebig University (maria.a.lopez@allzool.bio.uni-giessen.de)

Authors:

María Antonieta López, Justus Liebig University  (Maria.A.Lopez@allzool.bio.uni-giessen.de)

Vanessa Tirpitz, Justus Liebig University  (vanessa.tirpitz@allzool.bio.uni-giessen.de)

Jessica Reichert, Justus Liebig University  (jreichert.sci@gmail.com)

Maren Ziegler, Justus Liebig University  (maren.ziegler@bio.uni-giessen.de)