Quantifying coral larval behavior response to chemical cues in a microfluidic channel

Coral reef restoration often utilizes artificial substrates designed to induce settlement of coral larvae. These larvae use physical and chemical cues to navigate to a suitable habitat. However, the lack of quantitative data regarding the type and concentration of chemicals needed to trigger a behavioral response makes it difficult to engineer substrates that aid settlement. Here, we conduct chemotaxis experiments with Caribbean coral larvae in microfluidic chambers to study their response to different soluble inorganic (Magnesium, Strontium, and Calcium) and organic (Crustose coralline algae) chemical cues. Using particle tracking velocimetry, we quantify the positions, trajectories, and swimming speeds of larvae with respect to the chemical gradients. We augment this study by performing 2D simulations modeled after the experiments to characterize the chemical concentrations at which the larvae show behavioral changes. Our results enable the design of substrates that enhance larval settlement using chemical cues, improving their effectiveness in reef restoration.