Induction of coral larval settlement by coralline red algae: facilitators, inhibitors and possible mechanisms

Guillermo Diaz-Pulido¹, Muhammad Abdul Wahab², Steven D Melvin¹, Soren Schipper^1,2, Soyoung Jeong¹, Timothy Jackson¹, Luis A. Gomez-Lemos¹, Sophie Stephenson², Vilde Snekkevik², Guy McCutchan², Andrea Severati², Carly Randall², Andrew Negri²

¹School of Environment and Science, Nathan Campus, Griffith University, Brisbane, Queensland 4111, Australia

²Australian Institute of Marine Science, Townsville 4810, Queensland, Australia

Coral reef ecosystems are declining rapidly due to a multitude of natural and anthropogenic pressures. To decelerate this process, rapid action is required to reduce the impacts of climate change, ocean acidification, and local human activities. The implementation of intervention strategies such as the restoration of coral populations is also needed. A key aspect of reef restoration focusses on the production of coral spat in aquaculture settings, and this requires knowledge of the intimate relationship between coral larvae and crustose coralline red algae (CCA), their preferred settlement substrate. In this study we tested larval settlement preferences of 15 coral species for 15 common species of coralline red algae from the Great Barrier Reef to identify important CCA inducers (and inhibitors) of settlement. To understand potential mechanisms driving these interactions we examined the metabolomic profiles, anatomical and morphological characteristics and phylogenetic relationships of the CCA, in relation to the strength of their settlement cues. All CCA induced some level of coral settlement but the family Lithophyllaceae, was overall the best inducer across most coral families. Characteristic metabolomic composition and the lack (or reduced abundance) of trichocytes (surficial translucent hairs) may explain the preference of coral larvae for Lithophyllaceae. Ongoing studies using Lithophyllaceae species will elucidate chemical pathways involved in the interactions between coral larvae and CCA, such information is critical to optimise methods for coral propagation in aquaculture and for the restoration of degraded coral reefs.