Effects of Seawater Polyphenols from Gongolaria usneoides on Photosynthesis and Biochemical Compounds of the Invasive Alien Species Rugulopteryx okamurae (Phaeophyceae, Heterokontophyta)

Abstract

Gongolaria usneoides is a native brown alga in Europa, known for its high release of phenolics into the water. Rugulopteryx okamurae is a native brown macroalga from Asia but invasive in Europe, causing significant environmental and socioeconomic impacts. It has been observed that in some regions where Gongolaria is present, there is less biomass of Rugulopteryx, and they are often epiphytized by red filamentous algae. The present study aimed to analyze whether phenolics released in the seawater by G. usneoides affect the photosynthetic and biochemical responses in R. okamurae. To analyze the resilience of R. okamurae, algae were cultivated for 5 days in water with different percentages of phenolics released by G. usneoides (exposure phase) (0, 75, 150, 225 and 300 µg mL−1) in laboratory (20 °C, a 12:12 photoperiod, and PAR 190 µmol photons m−2 s−1 for a period of 115 h) and a period in the sun (4 h), followed 2 days cultured under phenolic-free water (recovery phase). Photosynthetic characteristics (Fv/Fm and ETR) and biochemical composition (phenolic, antioxidant activity, C, N and S) were measured (R. okamurae showed considerable photosynthetic declines without recovery when exposed to high concentrations of phenolics (225 and 300 µg mL−1). It can be inferred that the presence of G. usneoides in nature and the release of phenolic compounds by this alga may be affecting the invasive alga R. okamurae, potentially serving as a natural means to decrease or weaken the invasive species.