Collaborative Research: Can Larvae Utilize Dissolved Settlement Cues in the Wave-Driven Flow on Coral Reefs?

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Koehl 9907120The objective of this project is to determine whether water-borne chemical cues can affect the settlement of larvae of benthic marine invertebrates in habitats subjected to the wave-driven water flow that characterizes many coastal habitats. This question will be addressed by studying the nudibranch Phestilla sibogae, whose larvae metamorphose in response to a species-specific metabolite of its prey, Porites compressa, an abundant coral that forms reefs in shallow, wave--dominated habitats in Hawaii. The well-studied coral-eating nudibranch P. sibogae will serve as a model for benthic invertebrates that live on coral reefs and rely on recruitment of larvae from the plankton to found and replenish populations and maintain genetic continuity across small and large distances. The expertise of Hadfield in larval biology will be combined with that of Koehl in biomechanics and Koseff in environmental hydrodynamics to address the following questions: (1) How does ambient water flow disperse dissolved cues in nature? (2) Do P. sibogae larvae recruit in the field in microhabitats where advection and mixing of dissolved cues is low? (3) Do larvae of P. sibogae respond to water-borne cues in ways that affect their retention and settlement on a reef in wave-driven water flow? This mechanistic study of the role of dissolved cues in larval settlement at sites exposed to wave--driven flow goes beyond earlier studies of such processes in unidirectional flow. This investigation of the effects of rigid canopy-forming organisms on small-scale flow and mass transport in coastal habitats complements similar studies in flexible macrophyte canopies, and also complements larger--scale flow studies of coral reefs. The project has a potential impact on both larval ecology (larval recruitment processes can have profound effects on the dynamics and genetic structure of populations, and on community structure in coastal benthic habitats), and on coral reef ecology (reef structure can alter the small-scale flow and transport of water-born nutrients, food, wastes, and propagules to the community of organisms living in these important tropical ecosystems).***