A cross-ocean comparison of responses to settlement cues in reef-building corals

Abstract

Caribbean coral reefs have deteriorated substantially over the past 30 years, which is broadly attributable to the effects of global climate change. In the same time, Indo-Pacific reefs maintain higher coral cover and typically recover rapidly after disturbances. This difference in reef resilience is largely due to much higher coral recruitment rates in the Pacific. We hypothesized that the lack of Caribbean recruitment might be explained by diminishing quality of settlement cues and/or impaired sensitivity of Caribbean coral larvae to those cues, relative to the Pacific. To evaluate this hypothesis, we assembled a collection of bulk samples of reef encrusting communities, mostly consisting of crustose coralline algae (CCA), from various reefs around the world and tested them as settlement cues for several coral species originating from different ocean provinces. Cue samples were meta-barcoded to evaluate their taxonomic diversity. We observed no systematic differences either in cue potency or in strength of larval responses depending on the ocean province, and no preference of coral larvae towards cues from the same ocean. Instead, we detected significant differences in cue preferences among coral species, even for corals originating from the same reef. We conclude that the region-wide disruption of the settlement process is unlikely to be the major cause of Caribbean reef loss. However, due to their high sensitivity to the effects of climate change, shifts in the composition of CCA-associated communities, combined with pronounced differences in cue preferences among coral species, could substantially influence future coral community structure.

Estimating Trait Heritability in Highly Fecund Species

“…On August 14, 2012, 6-d-old, precompetent larvae from the three replicate bins for a single dam were divided across three settlement assays. Four hundred healthy larvae per culture replicate were added to a sterile 800-mL container with five conditioned glass slides and finely ground, locally collected crustose coralline algae, a known settlement inducer for this coral genus ( Davies et al 2014 ). Cultures were maintained for 3 d, after which each slide was removed and recruits were individually preserved in 96% ethanol, representing larvae exhibiting “early” responsiveness to settlement cue.…”

“…Sire genotyping was completed with the use of nine loci from Davies et al (2014) and four loci from Severance et al (2004) following published protocols. Amplicons were resolved on agarose gel to verify amplification and molecular weights were analyzed using the ABI 3130XL capillary sequencer.…”

The Effects of Anthropogenic Stressors on Reproduction and Recruitment of Corals and Reef Organisms

“…Since persistence of populations, and ultimately species, depends on producing better adapted genotypes, the larval stages play a key role in coral population dynamics, connectivity, and survival. The fitness of existing individuals depends on their acclimatization potential, and many larval behaviors likely contribute to increasing their fitness; examples include selecting an optimal environment to settle (e.g., Davies et al, 2014;Dixson et al, 2014;Doropoulos et al, 2016), using reverse metamorphosis to escape from adverse conditions (Richmond, 1985;Negri et al, 2005), and potentially benefitting from increased size by forming a chimeric aggregate (Amar et al, 2008). When selective pressures exceed the acclimatization capacity of an individual, the individual will be eliminated from the population (i.e., selection).…”

Coral larvae for restoration and research: a large-scale method for rearing Acropora millepora larvae, inducing settlement, and establishing symbiosis

“…Certain species of CCA are known to induce settlement and metamorphosis in coral larvae, but not all species and/or strains elicit equal settlement success ( Morse et al, 1996 ; Heyward & Negri, 1999 ; Harrington et al, 2004 ; Davies et al, 2014 ). Here we demonstrate that while several CCA assemblages failed to stimulate larval settlement, the presence of these non-settlement-inducing assemblages did not inhibit settlement if other suitable assemblages were present.…”

“…Taxonomic compositions of assemblages associated with each CCA fragment were determined via deep metabarcoding amplicon sequencing with modifications for 454-rapid technology (as per Davies et al, 2013 ; Davies et al, 2014 ; see Supplemental Information 1 ). Sequences were trimmed and analyzed as described previously ( Davies et al, 2014 ). In brief, raw reads were split by barcode ( Table S1 ), adaptors were trimmed, and bases of low quality and reads <250 bp were discarded.…”