Reef waters stimulate substratum exploration in planulae from brooding Caribbean corals

This study tested the hypothesis that waters surrounding reefs with healthy coral populations are more likely than degraded sites to induce planulae to navigate downward and begin benthic probing. In the laboratory, larvae from two brooding Caribbean coral species, Agaricia tenuifolia and Porites astreoides, were introduced to seawater collected at (1) 1 m above shallow, healthy reef with high-coral cover, (2) 1 m above shallow, degraded reef with high-macroalgal cover, and (3) ~400 m ocean-ward of the reef in deep, blue water. Counter to the hypothesis, water from both the healthy and degraded reef caused the larvae to swim downward and begin benthic probing. These results suggest that substances carried in reef waters may contribute to macro-scale habitat selection by planulae and that understanding how these waterborne cues mesh with other stimuli used by planulae to select a settlement site may be valuable for deciphering a site’s recruitment potential for corals.