This dataset consists of two data files (spreadsheets) from a 15 days experiment simulating the combined effects of climate change (manipulated temperature and pCO2 from present days and predicted for 2050 and 2100) and diuron contamination. Photosynthetic parameters were used to evaluate the physiological responses of Halimeda opuntia.

Endpoints related to photosynthesis have high ecological relevance, once this physiological process is pivotal for algae health and survival. PAM fluorometry is reliable tool to evaluate toxicological effects of PSII herbicides and many other toxicants and stressors. Photochemistry parameters derived from PAM fluorometry and the direct measurement of photosynthesis by oxygen production will enable an evaluation of the species fitness in response to multiple stressors, and contribute to the knowledge regarding risks posed by herbicides, and how contaminants toxicity thresholds are affected by future climate change scenarios.

Methods:

Fragments of the calcareous green algae Halimeda opuntia were collected from SeaSim mesoscosm tanks (MOS system, Evolution 21 Project, more information on < https://www.aims.gov.au/evolution- 21>). These organisms were kept, for at least 8 months, in tanks simulating three climate scenarios: ambient condition (average temperature of 28°C and pCO2 410 ppm), 2050 (average temperature of 29°C and pCO2 680 ppm) and 2100 (average temperature of 30°C and pCO2 940 ppm).

After this acclimatization period, fragments were transferred to 1.5L chambers kept in the same scenarios, but also receiving seawater with six levels of diuron. The nominal diuron concentrations were 0, 0.3, 1, 3, 10 and 30 µg,L-1. A total of 54 chambers were used, three for each climate scenario/diuron combination, containing six Halimeda fragments each.

After 15 days exposed to these combined stressors, the photosynthetic efficiency, expressed as the effective quantum yield (light adapted yields) was estimated from chlorophyll fluorescence measurements of three Halimeda fragments from each chamber (six for the ambient condition, to increase sample size at the reference/control condition). These measurements were taken with an Imaging-PAM chlorophyll fluorometer (I-PAM, Walz GmbH, Germany).

One fragment from chamber were used in incubations to assess oxygen production (two for the ambient condition, to increase sample size at the reference/control condition). One hour incubations under the experimental light levels were performed, using a manual OD meter to record oxygen concentration before and after the incubation. Blanks were run in parallel. Oxygen production was normalized by the volume of seawater used in incubations, time and fresh weight of the algae fragment.

Format:

This dataset consists of two csv spreadsheets, containing the climate change scenario (Ambient, 2050 and 2100), the diuron concentration and the respective responses of two endpoints, the photosynthetic efficiency (light adapted yields, “Light_Yields” column, on “dataPAM.csv” file) and photosynthesis (mg of oxygen produced per hour of incubation per fresh weight, “O2_prod” column, on “dataProd.csv” file).

Data Dictionary:

dataPAM.csv - Each row represents one Halimeda fragment.

CLIMATE_CONDITION: Ambient, 2050 and 2100.

DIURON_NUMERIC: Nominal diuron concentrations (0, 0.3, 1, 3, 10 and 30 µg.L-1).

CHAMBER: Identification of the chamber each fragment was kept in.

LIGHT_YIELDS: Effective quantum yield (light adapted yield) measured by an Imaging Pulse Amplitude Modulated (I-PAM) fluorometer. Three fragments from each chamber were used (six for the ambient condition, to increase sample size at the reference/control condition).

dataProd.csv - Each row represents one Halimeda fragment.

CLIMATE_CONDITION: Ambient, 2050 and 2100.

DIURON_NUMERIC: Nominal diuron concentrations (0, 0.3, 1, 3, 10 and 30 µg.L-1).

CHAMBER: Identification of the chamber each fragment was kept in.

O2_PROD: Photosynthetic rates measured as oxygen production after one hour of incubation under experimental treatment light level (units are ‘mg of oxygen produced per hour of incubation per fresh weight’), measured after 15 days of exposure. One fragment from each chamber was used because of logistical reasons related to time required to complete incubations for all treatments (two for the ambient condition, to increase sample size at the reference/control condition).

Data Location:

This dataset is filed in the eAtlas enduring data repository at: data\custodian\2016-18-NESP-TWQ-2\2.1.6_Cumulative-impacts\data\Halimeda