Cumulative effects of suspended sediments and climate change on coral development prior to settlement (NESP TWQ 2.1.6, AIMS, JCU and AIMS@JCU)

This dataset contains data from experiments testing the survival of fertilised Acropora millepora gametes before and after settlement in different climate and sediment treatment conditions. One datafile shows the development and survival until competency for settlement, which has been tested at the National Sea Simulator. A second file demonstrates the settlement success after development in these treatments.

Successful recruitment is crucial for the survival and repopulation of coral reefs. Studies have shown that the different phases from gamete release, fertilisation and larvae development may be affected by suspended sediments, increasing temperatures or ocean acidification. To date, the cumulative impact of all three stressors has not been evaluated. Note that the gametes were exposed to the climate and sediment treatments after fertilisation.

Methods:
The cumulative effect of suspended sediment and climate stress on the larvae development of Acropora millepora was tested in this experiment. A. millepora colonies containing eggs were collected in the reefs surrounding Falcon Island, GBR (Permit: G12/35236.1, Location: S18°46'15", E146°31'57") about one week prior to the annual spawning event in late November / December 2017. Gametes were collected, and fertilisation initiated on 14.12.2017. After 45 minutes, the fertilised eggs were rinsed with filtered seawater and transferred (n = 60) into twelve 500 mL Schott glass bottles.

Sediment was added (Middle Reef, ~ 10µm) (Table 1), the bottles sealed, and they were then placed onto half-submerged roller tables in three different treatments resembling current (10-year historic daily mean reef temperature at Davies Reef, ~27°C) and predicted mid and end century climate conditions.

Climate conditions:
Today: +0°C Temp, 440 ± 50 PCo2 [ppm], sediment [mg/ml-1] 0, 10, 30, 100
Mid Century: +1°C Temp, 660 ± 50 PCo2 [ppm], sediment [mg/ml-1] 0, 10, 30, 100
End Century: +2°C Temp, 940 ± 50 PCo2 [ppm], sediment [mg/ml-1] 0, 10, 30, 100

To achieve a constant pCO2 within each bottle, they were kept closed, while the water-baths regulated their temperature. Since stagnant water may cause lethal larval aggregation at the water surface, the bottles were in continuous motion on half-submerged roller tables.

The coral larvae development and mortality in the bottles was documented every day for a seven-day period. At the end of each day, the water was exchanged to provide consistent water quality across all treatments during the entire experiment. At the same time point the sediment was replaced with fresh material, since it aggregated and deposited on the bottom of the bottles within approximately 12 hours (e.g. for 100 mg ml-1 t0: 100 mg ml-1, t12: ~0 mg ml-1). The aggregation to sticky flocs was likely caused by mucus production of the larvae and introduced organic matter due to mortality (Fabricius and Wolanski 2000; Ricardo et al. 2016b). By exchanging the material, a daily sediment resuspension event was simulated.

Coral larvae require cues to induce their settlement and subsequent metamorphosis to a coral polyp (Harrington et al. 2004). To identify how many days after fertilisation the highest settlement competency is achieved, settlement assays using CCA chips (Hydrolithon onkodes, size: 4 x 4 mm) and A. millepora larvae from ambient condition were performed, starting three days after fertilisation. After seven days, no increase in settlement success (90%) was detected. Therefore, the larvae developed under different sediment and climate scenarios were exposed to CCA chips after seven days and their settlement success documented 24 h later.

Format:

Brunner_Larvae_count.csv
It provides age, sediment concentration, climate treatment and the total count (initially n = 60) of alive larvae.

Brunner_CCA_Settlement.csv
The file provides count data of settled recruits (out of 10 exposed larvae) originating from different sediment and climate treatments.

Data Dictionary:

Brunner_Larvae_count.csv
DATE: The date larvae survival was documented and the water together with the old sediment was changed.
AGE: Days after fertilisation.
BOTTLE_NO: Bottle number in the respective climate.
CLIMATE: Climate treatment (Temperature and acidification as described in the methods).
SED_CONC: New sediment (mg L-1) added to the bottles on each 'Date'.
COUNT: Total number of living larvae (max 60) at the point in time specified by 'Date'.

Brunner_CCA_Settlement.csv
DATE_SET: Date larvae were exposed to CCA chips (Hydrolithon onkodes) for settlement.
DATE_COUNT: Date settled larvae were counted.
CLIMATE: Climate treatment (Temperature and acidification as described in the methods).
SED_CONC: Sediment concentration (mg L-1) the larvae were exposed to during their development.
SET: Number of larvae that successfully settled on the bottom or CCA chip.
TOTAL: Total number of recruits that were found during the counts (Initially n = 10).

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\larvae-development