An 18-month reciprocal field transplant experiment was undertaken to examine the environmental and genetic drivers behind variation in survival, weight gain, heat tolerance and algal symbiont community between the reef flat and slope habitats.

Pocillopora damicornis colonies from Heron Island were used in a two-part experiment of a replicated RTE across depth habitats and a common garden stress test. Three vital traits were measured between March 2012 – August 2013., and then the relative heat tolerance was measured by exposing the surviving colonies to 14 days of ex situ experimental heat stress.

At each site and habitat, 23 – 26 colonies were collected (total n = 97) and fragmented into two halves. One half of each colony was places onto experimental rack in its habitat of origin and the other haps was transplanted to the reciprocal habitat within each site. 2 x 2 m wire mesh racks were installed approximately 0.5m above the substrate and fragmented coral colonies were attached across the rack with cable ties in a haphazard manner. This resulted in four treatment groups replicated at two sites: flat to flat (FF), flat to slope (FS), slope to flat (SF), and slope to slope (SS).

Partial colony mortality and weight gain were measured in the field four times between March 2021 and August 2013. A number of colonies were sampled for Symbiodiniaceae community in coral tissue per site and treatment group at two time points in April 2012 and March 2013.

At the end of the field transplant experiment on 17 August 2013, the remaining live colonies were transported to the Australian Institute of Marine Science in Townsville, and kept in outdoor 1000L tanks for 10 days. They were then further fragmented into single branches and acclimatized in indoor 30L flow-through tanks at 24°C. Treatment temperatures for the heat stress exposure included 24°C, 29°C, 30°C and 31°C. Between 3 and 20 replicate fragments per colony were exposed each temperature level, for a total of 14 days heat stress. Heat tolerance was quantified by proxy of the maximum quantum yield (Fv/Fm), measured with Pulse-Amplitude Modulation (PAM) fluorometry.

Analyses were conducted of Symbiodiniaceae community composition by source and transplant habitats (flat and slope) and physiological traits, percent partial mortality and percent cumulative weight gain. Heat stress analysis was also conducted among different temperatures and contrasts of treatment groups.

See published papers linked below for further details.