Award: OCE-0745606

Intellectual Merit Since 1997, the Shark Bay Ecosystem Research Project of Florida International University has investigated the ecological importance of marine top predators. During this award, we were able to use a combination of ecosystem-scale surveys, manipulative experiments, and long-term behavioral observations across a range of environmental conditions to show that tiger sharks play a critical role in structuring Shark BayÆs relatively pristine seagrass ecosystem. Interestingly, tiger sharks play this role not by consuming large numbers of prey, but instead by modifying the behavior of key prey species – especially large plant-eaters like sea turtles and sea cows (dugongs) and fish-eating dolphins and cormorants. When large tiger sharks are abundant (most of the year and in most years) their prey avoid dangerous shallow seagrass habitats and spend more time in safer deeper habitats. This results in high herbivory on seagrasses, including destructive removal of seagrass stems by dugongs, in deeper waters. In contrast, in shallower waters that are preferred by tiger sharks, destructive grazing by large plant-eaters is limited. Fish-eating dolphins and comorants also avoid tiger sharks, and since many of the fish that they eat in turn consume seagrasses, fish grazing of their preferred seagrass species is higher in the habitats that dolphins and comorants avoid because of tiger sharks. The net result of these "behavioral cascades" is that the presence of tiger sharks promotes the existence of dense, valuable seagrass meadows in dangerous shallow habitats and heavily grazed low-biomass seagrass beds in safer habitats. By extension, the loss of tiger sharks would likely result in substantial losses of ecosystem services due to unrestricted grazing by herbivores no longer constrained by predation risk. In the final year of our work, Shark Bay experienced a æmarine heatwaveÆ that resulted in massive (>80%) declines in the foundational seagrass species. Based on our past work and opportunistic field experiments, we are determining whether tiger sharks, through their influence on the behavior of their prey, help determine the way that Shark BayÆs seagrasses recover from the heatwave. Overall, our NSF-funded work in Shark Bay has provided the most in-depth empirical investigation of the ecological role and importance of large sharks in coastal ecosystems and suggests that ongoing declines in these species may trigger trophic cascades with detrimental impacts to ecosystem structure and function, including the ability of ecosystems to sequester carbon ("blue carbon"). Importantly, these impacts may operate largely through anti-predator behavior of prey rather than death rates inflicted by predators- suggesting that traditional ecological models may underestimate the effects of top predator declines in the oceans and on land. When viewed in light of changes in other ecosystems, where sharks have declined and their prey (sea turtles) have been protected, it is now apparent that restoration of large shark populations should be a management priority. Broader Impacts This project has produced substantial broader impacts. We developed a comprehensive project website (sberp.org) that provides details on our research methods, projects, and results, species fact sheets, image and video galleries, and teacher resources. Video vignettes and clips are disseminated through the website, a YouTube Channel, and Heithaus lab blog (heithauslab.blogspot.com). Perhaps most importantly, we developed a new style for using high production-quality video and science-based activities for use in K-12 classrooms. These "video-based projects" present a compelling scientific question, challenge students to develop hypotheses, and then take students through a scientific investigation where they observe videos of researchers at work and then do data-analysis activities to test the hypotheses and predictions they had made...