Highlights
•The combined effects of plastic pollution, ocean warming, and acidification on macrophyte decomposition were tested.
•High quantities of plastic slowed the decomposition of seagrass and kelp.
•Ocean warming increased the decomposition rates of seagrass and kelp.
•Ocean acidification did not significantly influence macrophyte decomposition.
•Reducing plastic pollution and CO2 emissions is likely the best approach for preserving detritus-based ecosystem processes.
Abstract
Plastic pollution and ocean change have mostly been assessed separately, missing potential interactions that either enhance or reduce future impacts on ecosystem processes. Here, we used manipulative experiments with outdoor mesocosms to test hypotheses about the interactive effects of plastic pollution, ocean warming and acidification on macrophyte detrital decomposition. These experiments focused on detritus from kelp, Ecklonia radiata, and eelgrass, Zostera muelleri, and included crossed treatments of (i) no, low and high plastic pollution, (ii) current/future ocean temperatures, and (iii) ambient/future ocean partial pressure of carbon dioxide (pCO2). High levels of plastic pollution significantly reduced the decomposition rate of kelp and eelgrass by approximately 27% and 36% in comparison to controls respectively. Plastic pollution also significantly slowed the nitrogen liberation from seagrass and kelp detritus. Higher seawater temperatures significantly increased the decomposition rate of kelp and eelgrass by 12% and 5% over current conditions, respectively. Higher seawater temperatures were also found to reduce the nitrogen liberation in eelgrass. In contrast, ocean acidification did not significantly influence the rate of macrophyte decomposition or nutrient liberation. Overall, our results show how detrital processes might respond to increasing plastic pollution and ocean temperatures, which has implications for detrital-driven secondary productivity, nutrient dynamics and carbon cycling.
Litchfield S. G., Schulz K. G. & Kelahera B. P., 2020. The influence of plastic pollution and ocean change on detrital decomposition. Marine Pollution Bulletin 158, 111354. doi:10.1016/j.marpolbul.2020.111354. Article (subscription required).
