title: Combined effects of temperature and the herbicide diuron on Photosystem II activity of the tropical seagrass Halophila ovalis.
abstract: Tropical seagrasses are at their highest risk of exposure to photosystem II (PSII) herbicides when elevated rainfall and runoff from farms transports these toxicants into coastal habitats during summer, coinciding with periods of elevated temperature. PSII herbicides, such as diuron, can increase the sensitivity of corals to thermal stress, but little is known of the potential for herbicides to impact the thermal optima of tropical seagrass. Here we employed a well-plate approach to experimentally assess the effects of diuron on the photosynthetic performance of Halophila ovalis leaves across a 25 °C temperature range (36 combinations of these stressors across 15-40 °C). The thermal optimum for photosynthetic efficiency (▵) in H. ovalis was 31 °C while lower and higher temperatures reduced ▵ as did all elevated concentrations of diuron. There were significant interactions between the effects of temperature and diuron, with a majority of the combined stresses causing sub-additive (antagonistic) effects. However, both stressors caused negative responses and the sum of the responses was greater than that caused by temperature or diuron alone. These results indicate that improving water quality (reducing herbicide in runoff) is likely to maximise seagrass health during extreme temperature events that will become more common as the climate changes.
authors.affiliation: College of Marine and Environmental Sciences, James Cook University, Townsville, Queensland, Australia.|Australian Institute of Marine Science, Townsville, Queensland, Australia.
authors.forename: Adam D
authors.initials: AD
authors.lastname: Wilkinson
authors.affiliation: College of Marine and Environmental Sciences, James Cook University, Townsville, Queensland, Australia.|Centre for Tropical Water &Aquatic Ecosystem Research (TropWATER), James Cook University, Cairns, Queensland, Australia.
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Collier
authors.affiliation: Australian Institute of Marine Science, Townsville, Queensland, Australia.
authors.forename: Florita
authors.initials: F
authors.lastname: Flores
authors.affiliation: Centre for Tropical Water &Aquatic Ecosystem Research (TropWATER), James Cook University, Cairns, Queensland, Australia.
authors.forename: Lucas
authors.initials: L
authors.lastname: Langlois
authors.affiliation: Climate Change Cluster (C3), University of Technology Sydney, New South Wales, Australia.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Ralph
authors.affiliation: Australian Institute of Marine Science, Townsville, Queensland, Australia.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Negri
mesh_terms: D004237:Diuron / Q000737:chemistry / Q000633:toxicity*; D006540:Herbicides / Q000737:chemistry / Q000633:toxicity*; D031321:Hydrocharitaceae / Q000378:metabolism*; D010788:Photosynthesis / Q000187:drug effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D013696:Temperature
chemical_list: D006540:Herbicides; D045332:Photosystem II Protein Complex; D004237:Diuron