Time-series response of water column phytoplankton and periphyton on attachment plates following nutrient addition during summer in mesocosms

Abstract

A large amount of nutrients and anthropogenic pollutants including plastics, introduced particularly in rainy seasons to coastal waters through river discharge, can have a significant impact on marine ecosystems. The combined effects on microalgal communities of plastic debris and nutrients introduced into coastal waters are poorly documented. In this study we used large scale mesocosms (1000 L) to investigate a water column phytoplankton bloom and periphyton communities on polypropylene (PP) attachment plates, emulating marine plastic debris (MPD), under three nutrient scenarios: natural seawater as a control; low nutrient (LN) conditions and high nutrient (HN) conditions. In the water column the concentrations of nutrients added in both the LN and HN treatments were rapidly decreased along with flourishing diatoms and were mostly depleted after 6 days. The centric diatom Leptocylindrus danicus dominated at the beginning of the experiment, but later shifted to other diatom species, dependent on the nutrient levels. Although the abundance of the diatom Chaetoceros spp. significantly increased before nutrient depletion, it shifted to small diatoms including Pseudo-nitzschia spp. and Cylindrotheca closterium at the end of the experimental period. On the PP attachment plates the periphyton C. closterium, Nitzschia longissima, Frustulia sp., and Navicula sp. were observed during the experimental period. The dominant species was C. closterium, which comprised > 80% of the community from the middle to the end of the experimental period when nutrients were depleted. In both the planktonic and periphyton communities, C. closterium was a key species under low nutrient conditions. Our findings suggest that the introduction of nutrients and land-based plastic debris into coastal waters is ecologically important as it can affect microalgal community and the dispersal of harmful periphyton. © 2023, The Author(s), under exclusive licence to Springer Nature B.V.