Coral reefs in the Caribbean Sea are undergoing unprecedented declines in coral cover due in large part to climate change, pollution, and reductions in fish biodiversity and abundance. Macroalgae have become abundant on reefs, probably due to decreases in herbivory (e.g., through overfishing) and increases in anthropogenic inputs of nutrients. The spread of macroalgae has negative feedbacks on reef recovery because algae are often superior competitors and suppress growth of both adult and juvenile corals. A majority of reef studies to date have focused on how stressors affect macroorganisms, while relatively few have investigated how these stressors and the resultant algal-dominated states affect microorganisms. Yet, coral reef-associated microbes play significant roles in coral reef ecosystems through biogeochemical cycling and disease. Since microbes are important mutualists of corals as well as potential pathogens, it is important to understand the mechanisms that control their taxonomic and functional diversity.
The goal of this proposal is to quantify how alterations of top-down (removal of herbivorous fish) and bottom-up (inorganic nutrient addition) forces alter macrobial as well as microbial dynamics on coral reefs in order to understand the mechanisms that reinforce coral-depauperate reef systems. This work asks two main questions:
Q1. How do nutrient enrichment and herbivore removal interact to affect benthic algal abundance, coral-algal interactions, and coral survivorship and growth?
Q2. How do nutrient enrichment and herbivore removal affect bacterial abundance, taxonomic diversity, and functional diversity on and within corals?
The proposed research will directly and empirically address many of the current hypotheses about how bottom-up and top-down forces alter reef dynamics. The PIs will investigate: (1) the impact of multiple stressors over several years; (2) impacts on multiple levels of biological organization (from fishes to algae to microbes); and (3) the mechanisms underlying changes in algal-coral microbe interactions. Significantly, the approach will provide the statistical power necessary to distinguish between seasonal- and stress-induced changes in macro- and microbial diversity.
The proposed work is a unique combination of experimental ecology and microbiology that will improve our ability to evaluate global threats to reefs. Training will include a postdoctoral researcher, a graduate student, and two undergraduates in the fields of marine ecology, microbial symbiosis, and molecular biology. The project will also provide research opportunities for undergraduate minority students, since FIU is one of the largest minority and urban-serving institutions in the US, with over 70% of its students from under-represented groups in science (59% Hispanic, 13% Black, 4% Asian; 56% female). The PIs are also committed to strong outreach programs outside their university at both the local and national levels. For example, they have established a monthly science cafÃ© ("Eat, Think, and Be Merry!") at an independent Miami bookstore to provide a casual environment for the public to come together with local scientists to learn about and discuss science and conservation topics that impact Florida waters. They are also collaborating with Symbio Studios to produce videos on coral reef ecosystems for their educational series for Houghton Mifflin Harcourt's Science Fusion programs.