The exceptional concentration of marine biodiversity in the Coral Triangle is among the best-known biogeographic patterns in the ocean. Marine biodiversity peaks in the islands of Eastern part of Indonesia and the Philippines, the heart of the Coral Triangle, and significantly decreases moving away from this global biodiversity hotspot. However, data supporting this pattern largely come from fishes, corals and larger metazoans, and exclude smaller organisms that comprise the majority of marine biodiversity. This study utilized Autonomous Reef Monitoring Structure (ARMS) and DNA metabarcoding to examine biodiversity patterns of marine communities across Indonesia, the largest and most biologically diverse region of the Coral Triangle. In Chapter 1, I examine eukaryote biodiversity patterns of marine communities across Indonesia. Results demonstrate that smaller cryptofauna display similar biodiversity patterns to larger metazoans; the most diverse parts of Indonesia had more diversity per unit area, and greater heterogeneity and beta diversity across all spatial scales, individual ARMS, reefs, or regions. The results show that processes shaping biodiversity hotspots appear consistent in marine and terrestrial ecosystems, and across size and spatial scales. In Chapter 2, I examine patterns marine bacterial diversity across Indonesia, comparing microbial diversity to eukaryotic and metazoan diversity from ARMS. Results showed strong regional differentiation in microbial communities. Microbial diversity tracked eukaryote and metazoan diversity, and displayed a significant pattern of isolation by distance, strongly indicating that associations with larger eukaryotes and physical limitations to dispersal differentiate microbial communities in the Coral Triangle. These results are counter to the hypothesis that “everything is everywhere, but the environment selects”, and provide novel insights into the processes shaping marine microbial diversity in the world’s most diverse marine ecosystem. In Chapter 3, I re-examine data from Chapter 1 to determine how strategies for marine ecosystem monitoring in Indonesia could be developed to yield the best results for the least cost, allowing resource managers to harness the power of metabarcoding to better monitor this region’s biodiversity. Comparisons of cytochrome oxidase 1 (COI) and 18S rRNA metabarcoding data across three separate organismal size classes recovered from ARMS indicate that metabarcoding the 100 �m size fraction with COI captures the largest amount of diversity at the highest resolution. Results indicate that metabarcoding the 100 �m size fraction with COI provides the most accurate and economical approach to monitoring diversity in megadiverse regions where limited research investment precludes sequencing multiple size fractions with multiple metabarcoding markers. Combined, the results of this thesis demonstrate the power of ARMS and metabarcoding for the study and monitoring of marine biodiversity, providing new tools for the study and management of the exceptional marine biodiversity of the Coral Triangle
