Effects of copper and cadmium on physiology and antifouling defense of the marine macroalga Ulva reticulata

Abstract

Heavy metals are major stressors for benthic macroalgal communities in marine ecosystems. In this study, the effects of copper and cadmium on some physiological parameters along with antifouling defense of the marine macroalga Ulva reticulata were assessed under laboratory conditions. Macroalgal samples were treated with three concentrations (1 mg l−1, 3 mg l−1 and 5 mg l−1) of copper and cadmium for 2 and 7 days. After treatment, algal samples were analyzed for chlorophyll-a, carotenoid, total polyphenol and total antioxidant capacity. Also, algal extracts were tested against biofilm-forming bacteria strains to understand differences in antifouling activity. The results indicated that exposure of U. reticulata to copper and cadmium, on the one hand, induced protective mechanisms such as total phenol production and antioxidant capacity against metal stress and, on the other hand, reduced photosynthesis. While the extract obtained from control algal samples showed a strong inhibitory effect on the growth of biofilm-forming bacteria, treatment with heavy metals resulted in reduced antibiofilm activity. In general, the results revealed that exposure of macroalgae to heavy metals can affect antifouling defense traits in addition to changes in photosynthetic pigment content.

Effects of Cadmium on Biochemical Parameters, Viability and Bioaccumulation of Kappaphycus alvarezii

“…Meanwhile for Chl t content, exposure days had a significant influence (p<0.001) but not Cd concentration and their interaction. Similar decreasing trends in chlorophyll contents have been documented in many previous studies including in Cd-exposed macroalgae, G. domingensis (dos Santos et al, 2012), Sarcodia suiae (Han et al, 2020) and Ulva reticulata (Al-Khaldi et al, 2021) as well as in microalgae, C. vulgaris (Cheng et al, 2016) and C. sorokiniana (Carfagna et al, 2013). When exposed to Cd concentrations similar to the current study but for a longer duration, ranging from 100 to 300 μM, the agarophyte G. domingensis had decreased Chl a levels after being exposed for 16 days (dos Santos et al, 2012).…”

“…In other study with lower Cd concentration and short exposure time of 5 mg/L (44.6 μM) Cd for up to 24 h, the Chl a content in the red alga S. suiae was found to be decreased compared to ambient cadmium levels (Han et al 2020). In a similar study but at longer duration, exposure of U. reticulata to 5 mg/L (44.6 μM) Cd for 2 days exhibited a decrease in Chl a content (Al-Khaldi et al, 2021). Nevertheless, none of these studies on macroalgae were statistically significant compared to control algal samples, which are unlike the current study.…”

“…In another study using the same concentration of Cd but much longer exposure of 7 days, U. reticulata exhibited similar increasing trend of Cd uptake. A significant increase in metal content was observed with increasing treatment concentrations and exposure duration (Al-Khaldi et al, 2021). A study on the effect of Cd exposure to a much lower concentration (10 μM) on tissue accumulation in two marine macroalgae, Fucus vesiculosus and U. lactuca, revealed that the metal accumulation was significantly higher for both species.…”

“…Similar to plants, high levels of Cd may cause toxicity in algae. Cd was reported to suppress the growth rate, decrease the photosynthetic performance and relative electron transport rate, decrease the content of the photosynthetic pigments, negatively affect the ultrastructure of chloroplasts, change antioxidant enzyme activities, cause lipid peroxidation, and reduce antibiofilm activity (dos Santos et al, 2012;Wickramasinghe et al, 2017;Al-Khaldi et al, 2021). Algae possess several mechanisms to manage heavy metal toxicity in order to preserve their metabolic activities.…”