Calcium Calling: Guiding Caribbean Coral Larvae Home

Upon release into the water column, coral larvae employ physical and chemical cues to navigate toward a suitable habitat and establish their settlement. To engineer substrates that induce settlement, it is crucial to have quantitative data about the types and concentrations of chemicals eliciting behavioral responses in these larvae. Here, we conducted chemotaxis experiments with Caribbean coral larvae (C. natans and O. faveolata) within microfluidic chambers to investigate their responses to various soluble inorganic (magnesium, calcium, strontium) and organic cues (crustose coralline algae). The positions, trajectories, and swimming speeds of the larvae were quantified in relation to the chemical gradients. The outcomes of our experiments reveal that the larvae exhibit attraction to high concentrations of calcium while being repelled by high concentrations of magnesium and strontium. Furthermore, the larval response to calcium mirrors that of crustose coralline algal exudates, commonly used for inducing settlement. The larvae exhibit their response to cues by modulating their swimming speed. 2D agent-based simulations were conducted, incorporating larval speed changes, to determine the approximate calcium concentration that triggered a response. The insights from our research facilitate the development of substrates that augment larval settlement through chemical cues, thereby enhancing the efficacy of reef restoration endeavors.