Effects of nanostructure antifouling biocides towards a coral species in the context of global changes

Abstract

Biofouling prevention is one of the biggest challenges faced by the maritime industry, but antifouling agents commonly impact marine ecosystems. Advances in antifouling technology include the use of nanomaterials. Herein we test an antifouling nano-additive based on the encapsulation of the biocide 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT) in engineered silica nanocontainers (SiNC). The work aims to assess the biochemical and physiological effects on the symbiotic coral Sarcophyton cf. glaucum caused by (1) thermal stress and (2) DCOIT exposure (free or nanoencapsulated forms), in a climate change scenario. Accordingly, the following hypotheses were addressed: (H1) ocean warming can cause toxicity on S. cf. glaucum; (H2) the nanoencapsulation process decreases DCOIT toxicity towards this species; (H3) the biocide toxicity, free or encapsulated forms, can be affected by ocean warming. Coral fragments were exposed for seven days to DCOIT in both free and encapsulated forms, SiNC and negative controls, under two water temperature regimes (26 °C and 30.5 °C). Coral polyp behavior and photosynthetic efficiency were determined in the holobiont, while biochemical markers were assessed individually in the endosymbiont and coral host. Results showed transient coral polyp retraction and diminished photosynthetic efficiency in the presence of heat stress or free DCOIT, with effects being magnified in the presence of both stressors. The activity of catalase and glutathione-S-transferase were modulated by temperature in each partner of the symbiosis. The shifts in enzymatic activity were more pronounced in the presence of free DCOIT, but to a lower extent for encapsulated DCOIT. Increased levels of oxidative damage were detected under heat conditions. The findings highlight the physiological constrains elicited by the increase of seawater temperature to symbiotic corals and demonstrate that DCOIT toxicity can be minimized through encapsulation in SiNC. The presence of both stressors magnifies toxicity and confirm that ocean warming enhances the vulnerability of tropical photosynthetic corals to local stressors.