Fig 1.
A schematic diagram of the experimental setup.
A) The mineral accretion technique (MAT) and B) the Control treatment setup and C) a timeline of the study, indicating the measurements and the progression of a marine heatwave (based on NOAA’s Coral Reef Watch). During the first month of the study (23 December 2019 to 25 January 2020), both the MAT and Control tables (with the coral fragments attached) were connected to the electric grid to provide an anti-corrosion coating. On 25 January 2020, the Control tables were taken off the grid and moved 35 m away. To keep current densities at the appropriate level after the removal of Control tables, new structures (Pod MAT) were attached to the electrical grid, but these were not further considered during this study. One experimental table is enlarged to show its dimensions and the attachment of the four coral species. Artwork by Vrijlansier.
Fig 2.
The brightness of studied coral fragments over time.
Brightness (mean ± SE) is used as indicator for bleaching of the four studied coral species during (March to May 2020) and after (June) a heatwave, compared between the mineral accretion technique (MAT) and Control treatment (n = 9). Brightness is expressed on a scale from 0 (completely black) to 1 (completely white). The dashed orange and red lines indicate the brightness values above which corals are typically said to be paling and bleached, respectively. Significant (p < 0.05) differences in brightness between corals of the MAT and Control treatment are indicated by an asterisk (*) for each time point.
Fig 3.
The condition of studied coral fragments over time.
The percentage (mean ± SE) live coral tissue cover of the four studied coral species throughout the 1-year experiment, compared between the Mineral Accretion Technique (MAT) and Control treatment (n = 9). Significant (p < 0.05) differences in live coral tissue cover between MAT and Control are indicated by an asterisk (*) for each time point. During the study a heatwave occurred between the months March and May.
Fig 4.
The growth of studied coral fragments over time.
The mean (± SE) Specific Growth Rate (SGR) of the four studied coral species throughout the 1-year experiment, compared between Mineral Accretion Technique (MAT) and Control treatment (n = 9). Significant (p < 0.05) differences in coral growth rates between the MAT and Control treatment are indicated by an asterisk (*) for each time point. During the study a heatwave occurred between the months March and May, which killed all fragments of Pocillopora verrucosa.
Fig 5.
Hard coral recruits on studied structures.
Mean (± SE) number of hard coral recruits (split per genus) settling on tables of the Control and Mineral Accretion Technique (MAT) treatment (n = 9). Recruits (0.5–5 cm) were counted 14 months after the structures were placed. The surface area of one table was 0.52 m2.