Importance of Including Chemically Mediated Behavior in Creating Effective Marine Management
Coral reefs are in dramatic global decline, with reefs converting from species-rich and topographically-complex communities dominated by corals to species-poor and topographically-simplified communities dominated by seaweeds. These phase-shifts cause a critical loss of ecosystem function. Since habitat selection is critical to fitness, larvae native to natural coral reefs may have evolved to detect and avoid settling in degraded systems dominated by seaweeds. This behavior would reduce the ability of intact coral-dominated systems to “rescue” degraded, seaweed-dominated reefs via larval export once these communities have diverged beyond some critical point. Juvenile coral and fish species were repelled by chemical cues from seaweed-dominated reefs, but attracted to adjacent, healthy coral-dominated marine protected areas (MPAs). Water borne chemical cues of specific seaweed species from degraded reefs acted as repellants whereas cues from specific coral species typical of healthy reefs attracted juveniles. Fish and coral larvae were present, but behaviorally avoided recruiting or settling onto degraded reef sites. The 6-9x greater attraction to chemical cues form coral dominated MPAs resulted in a similar 6-9x greater density of fish recruits despite 3x more predators. Adult fishes, (fished or unfished species), were also commonly 3-17x more abundant in MPAs, suggesting that recruitment or habitat value could be generating the pattern rather than direct effects of fishing. This chemically-cued behavior can limit larval export to degraded habitats and suppress the open nature of marine populations.