Hierarchical settlement behaviours of coral larvae to common coralline algae

Abstract

Natural regeneration of degraded reefs relies on the recruitment of larvae to restore populations. Intervention strategies are being developed to enhance this process through aquaculture production of coral larvae and their deployment as spat. Larval settlement relies on cues associated with crustose coralline algae (CCA) that are known to induce attachment and metamorphosis. To understand processes underpinning recruitment, we tested larval settlement responses of 15 coral species, to 15 species of CCA from the Great Barrier Reef (GBR). CCA in the family Lithophyllaceae were overall the best inducer across most coral species, with Titanoderma cf. tessellatum being the most effective species that induced at least 50% settlement in 14 of the coral species (mean 81%). Taxonomic level associations were found, with species of Porolithon inducing high settlement in the genus Acropora; while a previously understudied CCA, Sporolithon sp., was a strong inducer for the Lobophyllidae. Habitat-specific associations were detected, with CCA collected from similar light environment as the coral inducing higher levels of settlement. This study revealed the intimate relationships between coral larvae and CCA and provides optimal coral-algal species pairings that could be utilized to increase the success of larval settlement to generate healthy spat for reef restoration.

Larval precompetency and settlement behaviour in 25 Indo-Pacific coral species

“…This result was somewhat surprising because CCA is known to be a strong settlement inducers in Acropora 28 , 31 – 34 , 86 , 89 . However, Abdul Wahab et al 33 recently demonstrated species-specific preferences amongst a broad taxonomic cross-section of coral/CCA pairings, and Porolithon was not the most universal CCA cue, corroborating previous findings 28 , 30 , 90 , 91 . Therefore, other CCAs may be as effective as rubble at inducing settlement across Acropora spp.…”

“…It is also likely that biofilm discs supported early successional species (+4 weeks conditioned) 83 that were less mature and inductive than those on rubble fragments. Thirdly, while rubble was visually searched for CCA, it is likely that at least some fragments harboured cryptic and/or recruit CCA communities, which would be more diverse than the single CCA treatment tested and could be highly inductive 31 – 33 , 86 . As in Turnlund et al 84 , sequencing the cryptic taxa on more and less inductive fragments may provide further insights into key inductive and inhibitory communities.…”

“…Our data also indicated that while all but one species ( P. speciosa ) achieved 100% settlement in at least one replicate at some point during experimentation, the average peak competency wasn’t at or near 100% for all taxa. The reasons for not reaching 100% competency could be related to many factors including species- or genotype-specific differences in maximum competence, sub-optimal larval health, or that none of the cues selected was optimal for that species 33 . More work is needed to understand this phenomenon.…”

Shifts in dominance of benthic communities along a gradient of water temperature and turbidity in tropical coastal ecosystems

“…High temperatures, suspended particulate matter, and dissolved inorganic nutrients can inhibit fertilization, fecundity, and larval settlement of coral ( Fabricius, 2005 ; Haas et al, 2016 ). CCA, which contribute to building and solidifying the reef structure ( Lewis, Kennedy & Diaz-Pulido, 2017 ; Weiss & Martindale, 2017 ; Chen et al, 2020 ) and offer settlement cues for coral larvae ( Whitman et al, 2020 ; Deinhart, Mills & Schils, 2022 ; Abdul Wahab et al, 2023 ), have been found to be sensitive to thermal stress ( Webster et al, 2011 ; Vásquez-Elizondo & Enríquez, 2016 ). A positive correlation was observed between increased CCA fragments and an increase in species, type, and coverage of hard corals ( Weiss & Martindale, 2017 ; Whitman et al, 2020 ; Abdul Wahab et al, 2023 ).…”

“…CCA, which contribute to building and solidifying the reef structure ( Lewis, Kennedy & Diaz-Pulido, 2017 ; Weiss & Martindale, 2017 ; Chen et al, 2020 ) and offer settlement cues for coral larvae ( Whitman et al, 2020 ; Deinhart, Mills & Schils, 2022 ; Abdul Wahab et al, 2023 ), have been found to be sensitive to thermal stress ( Webster et al, 2011 ; Vásquez-Elizondo & Enríquez, 2016 ). A positive correlation was observed between increased CCA fragments and an increase in species, type, and coverage of hard corals ( Weiss & Martindale, 2017 ; Whitman et al, 2020 ; Abdul Wahab et al, 2023 ). This suggests that an increased availability of CCA in the ecosystem likely increases the diversity and coverage of hard corals.…”