What factors are attractive for coral settlers on substrates?

Coral settlers are particularly attracted to biofilms and crustose coralline algae on substrates for several reasons. Biofilms serve as a critical source of nutrients and microorganisms that can be beneficial to the early life stages of corals. They provide a safe environment that enhances the survival and successful attachment of coral larvae.

Crustose coralline algae, in particular, play a significant role in promoting coral settlement. This type of algae releases chemical signals that can stimulate coral larvae to settle and metamorphose into polyps. These algal structures also contribute to the overall health of the reef ecosystem, supporting biodiversity and providing a stable substrate for coral growth.

The other factors, while they might influence the marine environment, do not provide the same kind of specific ecological benefits that biofilms and crustose coralline algae offer. For example, the presence of predators would deter coral settlers rather than attract them, while attributes like bright colors and large openings might not have any biological significance for settlement. Similarly, movements of water currents can play a role in larval distribution but aren't direct attractants for coral settlers in the way that biofilms and crustose coralline algae are.