Toxicity thresholds of nine herbicides to coral symbionts (Symbiodiniaceae)

Abstract

Over 30 herbicides have been detected in catchments and waters of the Great Barrier Reef (GBR) and their toxicity to key tropical species, including the coral endosymbiotic algae Symbiodiniaceae, is not generally considered in current water quality guideline values (WQGVs). Mutualistic symbionts of the family Symbiodiniaceae are essential for the survival of scleractinian corals. We tested the effects of nine GBR-relevant herbicides on photosynthetic efficiency (ΔF/Fm′) and specific growth rate (SGR) over 14 days of cultured coral endosymbiont Cladocopium goreaui (formerly Symbiodinium clade C1). All seven Photosystem II (PSII) herbicides tested inhibited ΔF/Fm′ and SGR, with toxicity thresholds for SGR ranging between 2.75 and 320 µg L−1 (no effect concentration) and 2.54–257 µg L−1 (EC10). There was a strong correlation between EC50s for ΔF/Fm′ and SGR for all PSII herbicides indicating that inhibition of ΔF/Fm′ can be considered a biologically relevant toxicity endpoint for PSII herbicides to this species. The non-PSII herbicides haloxyfop and imazapic did not affect ΔF/Fm′ or SGR at the highest concentrations tested. The inclusion of this toxicity data for Symbiodiniaceae will contribute to improving WQGVs to adequately inform risk assessments and the management of herbicides in tropical marine ecosystems.

Sentinels for future coral reef conditions: assessment of environmental variability and water quality in semi-enclosed inland bays in the southern Caribbean

“…This suggests that coral health may be reduced because coral-associated bacteria have many beneficial roles for different coral life stages (McDevitt-Irwin et al, 2017). The interim effectbased trigger value of the algal photosynthetic inhibition assay, on the other hand, was not exceeded at any site, indicating that there appear to be low risks of chemicals inhibiting photosynthesis, such as herbicides (Marzonie et al, 2021).…”

Environmental Concentrations of Herbicide Prometryn Render Stress-Tolerant Corals Susceptible to Ocean Warming

“…27,28 PSII herbicides inhibit photosynthetic electron transport by binding to the Q B binding site of the D1 protein in PSII, resulting in the generation of reactive oxygen species, subsequently interfering with Symbiodiniaceae photosynthesis, exacerbating oxidative damage, and ultimately compromising coral health. 29,30 However, it is still unknown whether environmental concentrations of PSII herbicides have physiologically relevant impacts on stress-tolerant corals, which in turn render them susceptible to ocean warming. The co-occurrence of PSII herbicide and ocean warming is anticipated to intensify in the forthcoming decades, and this can pose a substantial threat to reef corals at physiological levels.…”

“…Similarly, triazine herbicides, prometryn, simetryn and ametryn, were detected near the reef transect of Hainan Island, among which prometryn concentrations reached up to 0.4 μg L –1 . The presence of Irgarol 1051 in coral reefs in Bermuda, Eastern Africa, Hawaii, the Florida Keys, and the wider Caribbean poses a grave hazard to endemic coral reefs. − The concentrations of these herbicides exceed threshold values critical for safeguarding 99% of species, according to the pesticide risk metric. , PSII herbicides inhibit photosynthetic electron transport by binding to the Q B binding site of the D1 protein in PSII, resulting in the generation of reactive oxygen species, subsequently interfering with Symbiodiniaceae photosynthesis, exacerbating oxidative damage, and ultimately compromising coral health. , However, it is still unknown whether environmental concentrations of PSII herbicides have physiologically relevant impacts on stress-tolerant corals, which in turn render them susceptible to ocean warming.…”

Bisphenol A affects the development and the onset of photosymbiosis in the acoelSymsagittifera roscoffensis

“…The symbioses between animals and algae are the results of a precise balance involving different physiological and environmental factors, and are thus particularly susceptible to anthropogenic stressors. The peculiar nature of this relationship has boosted many scientific investigations, most of which have focused on the effects of environmental perturbations and pollutants on corals and their Symbiodinium symbionts (Bielmyer et al, 2010; Kuzminov et al, 2013; Marzonie et al, 2021; van Dam et al, 2015; Venn et al, 2008). It has been reported that some compounds can trigger bleaching events, i.e.…”