Desperate Larva or Death Before Dishonor: can old coral larvae replenish degraded reefs?

Abstract 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 Hypothesis) or become increasingly less discriminatory (Desperate Larva Hypothesis). To examine which of these hypothesized strategies corals follow, we used larvae from three broadcast spawning reef-building corals, Diploria labyrinthiformis, Pseudodiploria clivosa , and Orbicella faveolata , and one brooding, weedy 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 suitable (crustose coralline algae) and unsuitable ( Dictyota sp .) settlement cues. Potential latent effects of delayed metamorphosis on post-settlement survival and growth were also assessed. As larvae got older, broadcast spawning species decreased selectivity (‘Desperate Larva Hypothesis’), whereas the brooding species’ larvae never did (‘Death Before Dishonor Hypothesis’). Delayed settlement of the brooder A. agaricites produced latent effects on post-settlement survival and growth, while O. faveolata displayed latent effects of delayed settlement on post-settlement growth. The other broadcast spawners exhibited no latent effects of delayed settlement on post-settlement. This suggests “old” coral larvae from broadcast spawners have the potential to disperse widely to replenish degraded reefs. The brooding, weedy coral A. agaricites seems to have evolved to disfavor dispersal and maximize local retention, evidenced by the fast acquisition of competency and latent effects of delayed settlement combined with an early loss of competency.