Acute toxicity of photosystem II herbicides to tropical seagrass 2013. (NERP TE 4.2, AIMS and JCU)

This dataset shows the measured response of the photosystems of seagrasses to herbicides in experiments conducted in 2012-2013. The data is provided as a multi-sheet spreadsheet.

The aim of this study was to apply standard ecotoxicology protocols to quantify the concentrations of four priority PSII herbicides that inhibit photochemistry by 10, 20 and 50% (IC10, IC20 and IC50) over 72 hrs in two common seagrass species from the GBR lagoon.  This data will enable improved assessment of the risks posed by PSII herbicides to tropical seagrass for both regulatory purposes and for comparison with other taxa.

Methods:

Four seagrass species (H. uninervis, C. rotundata, T. hemprichii and Z. muelleri) were used in preliminary studies to determine the time taken for PSII herbicides to affect photosynthesis, while more detailed ecotoxicology studies were undertaken with two of these species (H. uninervis and Z. muelleri). H. uninervis, C. rotundata and T. hemprichii were collected from intertidal seagrass meadows (&lt;1 m) from Cockle Bay, Magnetic Island (19°10.88’ S, 146°50.63’ E) while Z. muelleri was collected from Pelican Banks, Gladstone, Australia (23°46.005’ S, 151°18.052’ E).

Halodule uninervis, Cymodocea rotundata Ascherson (Cymodoceaceae) and Thalassia hemprichii Ascherson (Hydrocharitaceae) are tropical seagrass species widely distributed throughout the Indo-West Pacific while Zostera muelleri Irmisch ex Ascherson (Zosteraceae), (syn Zostera capricorni) is a tropical to temperate species found in Australia and New Zealand.

Potted seagrasses were exposed to dissolved herbicides in static-replacement seawater (24 h water changes).

All experiments were conducted under 273 ± 17 µmol photons m-2 s-1 (12h light:dark photoperiods, Aqua Illumination LED). This light intensity was chosen as the median daily irradiance at the Magnetic Island collection site. The glass aquaria were placed into water baths and maintained at 25.8 ± 0.3°C (range), equivalent to the annual average temperature in the GBR.

Herbicide concentrations ranged from 0.1 to 300 µg herbicide l-1 depending on the potency of the herbicide. Duplicate tanks were used for each herbicide concentration and each tank contained individually potted seagrass plant of each species. 

Inhibition of photosynthesis was measured after 72 h exposure using pulse amplitude modulation (PAM) fluorometry. Two parameters were measured (effective quantum yield, deltaF/F’m and maximum quantum yield, Fv/Fm). The inhibition of photosynthetic yields relative to controls were plotted as dose-response curves by fitting inhibition data with measured concentrations using a 4 parameter logistic model (SigmaPlot 11).  The herbicide inhibition concentrations (ICxx) that inhibited deltaF/F’m and Fv/Fm by 10, 20 and 50% (IC10, IC20 and IC50, respectively) were determined from each curve.

Initially a series of pilot studies were performed to measure the time it takes for the four PSII herbicides to illicit 90% steady state (maximum) inhibition of effective quantum yield (deltaF/F’m) in Z. muelleri at single herbicide concentrations. These findings were used to ensure that the exposure duration of later dose-response curves was sufficient. The nominal herbicide concentrations used were 10 µg l-1 Diuron, 50 µg l-1 Atrazine, 10 µg l-1 Hexazinone and 400 µg l-1 Tebuthiuron. This data can be found in the “Kinetics” worksheet. 
We also exposed all four species of seagrass to 10 µg l-1 Diuron to examine the consistency of response times between species. Inhibition of deltaF/F’m by the herbicides compared with carrier controls were conducted at multiple times up to 24 h.  This data can be found in the “4 seagrasses at Diuron 10ug_L” worksheet.

Further information can be found in this publication:
Flores F, Collier CJ, Mercurio P, Negri AP (2013) Phytotoxicity of Four Photosystem II Herbicides to Tropical Seagrasses. PLoS ONE 8(9): e75798. doi: 10.1371/journal.pone.0075798  

Format:

Acute_seagrass_toxicity_data_(Flores_et_al_2013).xlsx is an Excel SpreadSheet containing multiple worksheets.

Each sheet has a description such as this:
- Tank Rep: tank replicate (two tanks A and B)
- deltaF/F’m: effective quantum (light adapted) yield measured by a Pulse Amplitude Modulated (PAM) fluorometer
- Fv/Fm: maximum quantum (dark adapted) yield measured by a Pulse Amplitude Modulated (PAM) fluorometer
- Solvent cont: no herbicide but contains less than 0.03% v/v ethanol carrier as per the treatments
- Halodule uninervis: a seagrass species
- Zostera muelleri: a seagrass species
- Thalassia hemprichii: a seagrass species
- Halophila ovalis: a seagrass species
- 72 h: the duration of the herbicide exposure in some experiments
- Time (hr): duration of exposure in hours

Tags: Atrazine, Diuron, Hexazinone, Tebuthiuron, herbicide, marine, seagrass
Organization: Australian Ocean Data Network