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

<i>Gongolaria usneoides</i> is a native brown alga in Europa, known for its high release of phenolics into the water. <i>Rugulopteryx okamurae</i> 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 <i>Gongolaria</i> is present, there is less biomass of <i>Rugulopteryx</i>, and they are often epiphytized by red filamentous algae. The present study aimed to analyze whether phenolics released in the seawater by <i>G. usneoides</i> affect the photosynthetic and biochemical responses in <i>R. okamurae</i>. To analyze the resilience of <i>R. okamurae</i>, algae were cultivated for 5 days in water with different percentages of phenolics released by <i>G. usneoides</i> (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 (<i>Fv</i>/<i>Fm</i> and ETR) and biochemical composition (phenolic, antioxidant activity, C, N and S) were measured (<i>R. okamurae</i> 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 <i>G. usneoides</i> in nature and the release of phenolic compounds by this alga may be affecting the invasive alga <i>R. okamurae</i>, potentially serving as a natural means to decrease or weaken the invasive species.