Desperate larva or death before dishonor: Can old coral larvae replenish degraded reefs?

The recovery of coral populations depends largely on larval recruitment. Coral larvae settle in response to environmental cues that indicate habitat quality. In the absence of suitable cues, lecithotrophic larvae may delay settlement until they die (Death Before Dishonor strategy) or become increasingly less discriminatory (Desperate Larva strategy). To examine which of these strategies corals follow, we used larvae from three broadcast-spawning reef-building corals, Diploria labyrinthiformis, Pseudodiploria clivosa, and Orbicella faveolata, and one brooding coral, Agaricia agaricites. Settlement behaviors of larvae of different ages, specifically 0, 7, 14, or 21 days after becoming competent, were examined in response to inducing (crustose coralline algae) and inhibitory (Dictyota sp.) settlement cues. Potential latent effects of delaying metamorphosis on post-settlement survival and growth were also assessed. As larvae got older, broadcast-spawning species decreased selectivity, doubling to quadrupling their settlement in tiles with Dictyota sp. (i.e., followed the ‘Desperate Larva strategy’), whereas the brooding species’ larvae never did (i.e., followed the ‘Death Before Dishonor strategy’). Delayed settlement of A. agaricites produced latent effects on post-settlement survival (up to 50% reduction) and growth (sixfold decrease), while O. faveolata displayed latent effects to growth only (reduced by 50% or more). No latent effects of delayed settlement were observed in the other species. Our results suggest that brooding corals may have evolved to disfavor dispersal and maximize local retention. In contrast, “old” coral larvae from broadcast spawners have the potential to disperse widely and replenish degraded reefs. Hence, albeit at a lower rate, disturbed reefs can recover through larval replenishment.