Lack of coral recruitment in the Northern Caribbean: Suggestions from a “corals and cues around the world” approach

Background/Question/Methods

The majority of reef-building corals are broadcast-spawning species, and reef recovery post disturbance is critically dependent on successful recruitment of their pelagic larvae. In recent years, recruitment rates of broadcast-spawning corals and reef recovery rates in the Northern Caribbean have been consistently low. The most northerly reef, the Flower Garden Banks in the Gulf of Mexico, has experienced extremely low recruitment of broadcast-spawning species in the recent past and no recruitment has been observed in the past three years. Recruitment in the Pacific, in contrast, is strong and rapid recoveries of devastated reefs are not uncommon. In this study, we investigate whether these differences between the two biogeographic regions might be explained by the scarcity of the settlement cue in the Northern Caribbean, or divergent mechanisms of cue perception by the larvae of resident Caribbean corals.

We assembled a collection of crustose coralline algae (CCA, a well-documented settlement cue) from a number of locations in the Caribbean and Pacific, including the Florida Keys, Flower Garden Banks, Bonaire, Great Barrier Reef, Pohnpei, and Guam. We tested these cues on coral larvae from several species; four from the Great Barrier Reef (Acropora millepora, Acropora tenuis, Favia lizardensis, and Ctenactis echinata) and one from the Flower Garden Banks (Montastrea franksi).

Results/Conclusions

Larvae of M. franksi were not the least responsive of the coral species tested, suggesting that the lack of local recruitment of this species is not due to poor ability of its larvae to perceive the cue. Also, CCA from Flower Garden Banks and Florida Keys were successful in inducing settlement of both M. franksi and the Pacific corals, indicating that the proper cue is available on Caribbean reefs. Interestingly, the statistically significant rankings of the CCA samples by settlement response were not unanimous across coral species, indicating divergent species-specific cue preferences. However, no correlation relating the respective origin of the coral and CCA exists, disproving the most straightforward hypothesis of region-wide co-adaptation of corals and CCA. A meta-barcoding genetic study of our CCA panel involving red algae and bacterial markers is currently underway, aiming to elucidate the more subtle correlations that may help explain the observed coral-specific preferences.

Overall, our results indicate that the lack of coral recruitment in the Northern Caribbean is due to some other factor(s) than the lack of CCA-derived settlement cue, or poor response to that cue by the local larvae.