Award: OCE-1638296

The goal of this project was to investigate the symbiosis between marine sponges and their microbiome, and understand how those relationships drive the evolution and ecology of sponge diversity on coral reefs across the Caribbean basin. Coral reefs, the tropical rain forests of the marine environment, are under significant threat from a variety of stressors such as pollution, overfishing, coastal development and climate change. Because of continuing reef degradation, the phylogenetic, genetic, and functional diversity of coral reefs will increasingly be found in taxa other than scleractinian corals, such as sponges. Sponges are a very old group of organisms essential to reef health because of their roles in nutrient cycling, providing food and homes for many other reef organisms, and their ability to synthesize diverse chemical compounds of ecological and biomedical importance. Many of these important functions would not be possible without the sponge's symbiotic microbes (e.g., bacteria) known as the microbiome. In this project, we examined important questions about the relationship between the sponge host and its microbiome as the key to understanding their ecology and biodiversity. To do this we studied the phylogenetic, genetic, and functional biodiversity of coral reef sponges across the Caribbean basin. Marine sponges host a diverse assemblage of symbiotic microorganisms that appear in two different types depending on the number of symbionts in their tissues: commonly known as low microbial abundance (LMA), and high microbial abundance (HMA) sponges. Our work has shown that the LMA state is ancestral, and HMA sponges have evolved from the HMA state several times. We also described the different physiological capacities of LMA and HMA sponges related to two key categories: their trophic ecology (i.e., what they eat), and their chemistry (i.e., what they use to defend themselves). To do this we used a combination of ecological approaches combined with biochemical and molecular analyses to unravel the role of the microbiome in the ecology and evolution of sponges. Through this integrative approach important insights were obtained by identifying the drivers of sponge biodiversity on coral reefs. The results of these studies will enhance our understanding of the ecology and evolution of this understudied group of marine organisms, and how the co-evolution of the sponge host and its microbiome leads to emergent functional properties that result in increased sponge biodiversity. These functions were also analyzed in the context of the degradation of coral reefs and whether sponges will be "winners" in a future coral reef. At both the University of New Hampshire and the University of Mississippi, we provided training opportunities for undergraduate and graduate students as well as post-doctoral researchers, especially from underrepresented groups. Additionally, we developed unique outreach programs to provide public education on the importance of coral reef ecosystems. Last Modified: 08/25/2022 Submitted by: Michael P Lesser