This study examined the effects of microhabitat features on the survival of Acropora tenuis spat in a year-long experimental field deployment of two types of artificial settlement devices.

Fragments of mature gravid Acropora tenuis (Dana 1846) colonies were collected from Backnumbers Reef on the central mid shelf of the Great Barrier Reef ahead of coral spawning in Nov 2018. The corals were transported back to the Australian Institute of Marine Science National Sea Simmulator (SeaSim) facility and kept in temperature controlled outdoor aquaria. Egg-sperm bundles were collected during spawning from six colonies and cross-fertilized. Larvae were maintained in the culture tank until used in the experiment.

Two types of experimental settlement devices—lattice-grids and grooved-tiles—were designed and manufactured to test larval settlement choice and post-settlement survival. Prior to settlement, all experimental devices were conditioned in the SeaSim for approximately 4 weeks to develop a biofilm and recruit crustose coralline algae (CCA) for larval settlement induction.

Eight days after fertilization larvae were left to settle on the devices for 4 days. Images of the lattice-grids and grooved-tiles racks were taken 9 and 11 days after larval introduction (approx. 5-7 days after settlement).

The settlement devices were then deployed at Backnumbers Reef onto three replicate racks on a shallow, central mid-shelf reef of the Great Barrier Reef. Survival of A. tenuis recruits was tracked by assessment of in situ images, taken on SCUBA, of the upper- and under-sides of each device. Images were taken at 41, 95, 185, 246, and 311 days and then imaged again upon retrieval from the field on 16th December 2019 at the final time point of 376 days post settlement.