Herbicide effects on the growth and photosynthetic efficiency of Cassiopea maremetens

Abstract

Herbicides from agricultural run-off have been measured in coastal systems of the Great Barrier Reef over many years. Non-target herbicide exposure, especially photosystem II herbicides has the potential to affect seagrasses and other marine species. The symbiotic benthic jellyfish Cassiopea maremetens is present in tropical/sub-tropical estuarine and marine environments. Jellyfish (n = 8 per treatment) were exposed to four separate concentrations of agricultural formulations of diuron or hexazinone to determine their sensitivity and potential for recovery to pulsed herbicide exposure. Jellyfish growth, symbiont photosynthetic activity and zooxanthellae density were analysed for herbicide-induced changes for 7 days followed by a 7 day recovery period. Both the jellyfish and endosymbiont were more sensitive to diuron than hexazinone. The 7-day EC for jellyfish growth was 0.35 μg L for Diuron and 17.5 μg L for Hexazinone respectively. Diuron exposure caused a significant decrease (p < 0.05) in jellyfish growth at 0.1 μg L, a level that is below the regional Great Barrier Reef guideline value. Jellyfish recovery was rapid with growth rates similar to control animals following removal from herbicide exposure. Both diuron and hexazinone caused significant decreases in photosynthetic efficiency (effective quantum yield) in all treatment concentrations (0.1 μg L and above) and this effect continued in the post-exposure period. As this species is frequently found in near-shore environments, they may be particularly vulnerable to herbicide run-off.

Upside-Down but Headed in the Right Direction: Review of the Highly Versatile Cassiopea xamachana System

“…Studies conducted on different life stages of Cassiopea exposed to copper or zinc demonstrated measurable effects at environmentally relevant concentrations (Templeman and Kingsford, 2015). In other studies, agricultural formulations of diuron and hexazinone at ecologically relevant concentrations caused measurable inhibition with respect to Cassiopea growth, photosynthetic efficiency, and symbiont density within 7 days of exposure (Rowen et al, 2017). A study looking at interactive responses between herbicides and salinity demonstrated that reduced salinity increased herbicide toxicity (Klein et al, 2016a).…”

Use of a Thermophile Desiccation-Tolerant Cyanobacterial Culture and Os Redox Polymer for the Preparation of Photocurrent Producing Anodes

“…Both inhibitors do not show strong light absorbance or interaction with the electrodes at this potential, or have the possibility to shuttle electrons (Hasan et al, 2014(Hasan et al, , 2017Hamidi et al, 2015). Diuron is known to irreversibly block quinone A and B from photosystem II, hindering electron flow into plastoquinone (Rodea-Palomares et al, 2015;Rowen et al, 2017), whereas paraquat inhibition is known to take place at photosystem I, generating radical oxygen species (hydroxyl, superoxide, etc.) and finally damaging chloroplast structure and disrupting photocurrent density (Hupp and Meyer, 1989).…”

Polyps of the Jellyfish Aurelia aurita Are Unaffected by Chronic Exposure to a Combination of Pesticides

“…The exposure concentrations used in that experiment, however, greatly exceeded (by 4 orders of magnitude) those detected in the environment (Shaw et al 2010), such that the environmental relevance of the findings is limited. Another study, by Rowen et al (2017), used concentrations of 2 herbicides, diuron and hexazinone, that align with current water quality guidelines (Great Barrier Reef Marine Park Authority 2010) and described adverse effects on growth and photosynthetic efficiency in the zooxanthellate jellyfish C. maremetens . In our study, exposure to guideline concentrations for atrazine and chlorpyrifos did not cause any effect on the measured endpoints.…”

“…Only 3 studies have examined the effects of pesticides on jellyfish (Costa et al 2015; Klein et al 2016; Rowen et al 2017). Although these studies used a wide range of pesticide concentrations, exposure duration never exceeded 7 d, and none investigated potential interactions between pesticides.…”

“…Costa et al (2015), reported that high concentrations (5−50 mg/L −1 ) of the pesticides eserine and chlorpyrifos inhibited pulsation and the mobility of Aurelia aurita ephyrae, but the interactions between the pesticides were not examined. Rowen et al (2017) observed reduced growth, photosynthetic efficiency, and zooxanthellae density after Cassiopea maremetens medusae were separately exposed to the pesticides diuron and hexazinone at environmentally relevant concentrations. Klein et al (2016) have published the only study to consider how responses to pesticides may interact with changing environmental conditions, by testing the individual and combined effects of the herbicide atrazine and salinity.…”