Area-normalized chlorophyll a concentration for Acropora aspera corals collected from Shell Island, Kimberley, in April and November 2016

Coral tissue chlorophyll a concentrations were measured to assess how corals in the Kimberley region, NW Australia, were impacted by and recovered from the 2016 mass bleaching event documented at this location. The corals were collected at Shell island (Shenton Bluff), Cygnet Bay, in both the intertidal and subtidal reef zone. Tissue samples were collected from tagged colonies of the dominant coral species at this location, Acropora aspera, in April 2016 (peak bleaching) and 7 months after peak bleaching in October 2016. The health status of all tagged colonies was assessed in April 2016 and after 7 months of recovery in November 2016 using the Coral Watch Coral Health Chart where a change of two units in brightness indicates a significant change in symbiont density and chlorophyll a content (Siebeck et al., 2006). Colonies were considered either “healthy” (brightness scale, 3.6–6) or “bleached” (brightness, 1–3.5). Corals were stored at -80°C prior to processing. To quantify bleaching, chlorophyll a concentration was determined spectrophotometrically (Jeffrey and Humphrey, 1975; doi:10.1016/S0015-3796(17)30778-3) and used as a proxy for bleaching susceptibility. Tissue was removed from a branch tip using an airbrush and separated into animal and symbiont fraction via centrifugation (2 x 10 min at 3,000 g). Chlorophyll a from the symbiont fraction was extracted in 100% acetone in the dark at 4°C for 24 h and the concentration determined spectrophotometrically (Jeffrey and Humphrey, 1975) and then standardized to surface area. Surface area was calculated using the relationship between skeletal mass (x, in g) and the respective computer tomography (CT)- determined surface area (y, in cm2) of A. aspera skeletons from our study site (y = 9.4871x0.7729, n = 6, R2 = 0.99)