Rapid regeneration of Acropora millepora coral recruits after physical damage to the primary polyp

During October and November in years 2017 – 2019, approx.. 10 gravid adult colonies of Acropora millepora and A. tenuis were collected from 5 to 8 m depth from two inshore reefs of the central Great Barrier Reef. Colonies were transferred from Falcon and Magnetic Island reefs to the National Sea Simulator (SeaSim) to undergo spawning.Three experiments were conducted on A. millepora recruits at three different stages of early development (1, 3, and 5 d post settlement) to examine the level and type of effects physical damage had on recruit survivorship, growth, and the ability to uptake symbionts after 21 d post settlement.Larvae (n = 20/well) of 13 d age were added to 10 mL of filtered seawater (0.5 μm) in 6-well culture plates (n = 56 wells), each well containing three crustose coralline algae (CCA) chips (4 × 4 mm) of P. onkodes in the centre of the well. CCA chips were only used to induce settlement and after ~20 h were removed, and settlement was assessed. The settled recruits were 0.7–0.9 mm in diameter.Damage types included: a) Recruits were sliced once with a scalpel at a haphazard distance between the mouth (centre) and the edge of the recruit, resulting in a mean incision 20–30 μm thick. to create various levels of damageb) Sections of the recruit were removed using a scalpel to create various levels of damageRecruits were imaged at four time-points: before tissue damage, immediately after tissue damage, 1 day after tissue damage and 21 days after tissue damage (i.e., 3-weeks after settlement) using a Leica stereomicroscope fitted with a 14-MP microscope camera (CMOS C-Mount) shot at 1.25 × optical zoom.Recruits were considered alive if tissue covered the basal plate. Survivorship, horizontal growth and surface area analysis were conducted to examine the post-settlement survivorship