Meeting Abstract
Flowing water carries nutrients, oxygen, and prey to the organisms living in coral reefs, carries away wastes and sediments, disperses chemical cues, and transports released larvae from and settling larvae into reefs. Many coral reefs are being overgrown by algae. We studied how algae with different morphologies (branching vs. mat-forming) affected the flow of water into and out of the spaces within Hawaiian reefs dominated by branching coral. Transects across reefs since 2003 showed dominance in different years by living or dead coral, mat-forming bubble algae, or branching algae. Measurements of vertical water velocities into and out of reefs revealed that there was net flow into reefs in concave areas and net flow up out of reefs at convex areas when coral or branching algae dominated, but that flow was stopped when the cover of bubble algae was >60%. Field releases of larval mimics showed that fewer mimics contacted surfaces within reefs (where hydrodynamic forces on larvae are low enough that they can recruit) when there was algal cover, and that bubble algae stopped more mimics from entering the reef than did branching algae. Thus, algae not only compete with coral, but also can interfere with the recruitment of larvae and the transport of materials to and from the organisms living in the reef.
