Few areas of the world ocean are as diverse, poorly known, environmentally variable, threatened, and relevant at this time of global change as the waters around the Arabian Peninsula. Reefs survive or thrive here across environmental gradient that include some of the lowest to highest (11-36oC) temperatures, highest salinities (42‰), and lowest pH (7.9), and experience enormous temperature and dissolved oxygen fluctuations in some areas. Habitats range from hyper-oligotrophic reefs to murky, macroalgal dominated systems, across a productivity gradient unparalleled in other reef areas. Recent field efforts showed high novelty among marine organisms of this area and pointed to the coast of Oman, bordering the Arabian Sea and Gulf of Oman, as among the least known and most interesting areas of the tropical Indo-Pacific. The objectives of this project were to (1) document the marine biodiversity of Oman using modern methods that integrate knowledge from live observations, imaging, study of preserved specimens, and genomics, and (2) test hypotheses about the distribution and diversification of tropical marine life. Marine invertebrates were sampled by diving and shore-based sampling by 28 taxonomic experts in a series of field expeditions, and processed using high-throughput, integrative methods.

Over 19,000 specimen lots (a lot represents one or more specimens from a single location), 13,000 corresponding tissue samples, and 42,000 images were taken. Especially thorough collections were made of sponges, octocorals, stony corals, crustaceans, segmented and ribbon worms, mollusks, echinoderms, and sea squirts among 22 phyla sampled, with special attention paid to symbiotic associations. Samples are available for further study through the Florida Museum of Natural History, National Museum of Natural History, and University of Alabama Museums, and information about the organisms, including images and DNA barcodes are available online through a series of portals. The collection includes over 4,000 species, at least one third of which are new to science. Taxonomic work is ongoing with new species being described, and their biology and relationships studied. With less than 250,000 species described from the ocean, this single effort has covered ~1.5% of known marine biodiversity. The DNA barcode library generated from specimens is providing a foundation for biodiversity assessments through environmental DNA methods. Diversity was further documented through metabarcoding of samples taken from Autonomous Reef Monitoring Structures (ARMS) and associated environmental samples that revealed over 100,000 sequence variants. 

Study of the collections revealed high diversity, novelty, and endemism. In well-studied taxa like crabs, shrimp, corals and echinoderms, 10-20% of the species sampled appear to be undescribed, while in less-studied groups like ribbon worms, segmented worms, or sponges, commonly 80-90% are new. Endemism (restriction in distribution) to Arabia is high, 20-30+% for well-sampled groups. Many species show differentiation on a fine spatial scale. The fauna of the Gulf of Oman and Arabian Sea are especially divergent, with only ~50% overlap in many groups. The latter has an especially unusual, endemic fauna, reflecting its unique environment. Here, an intense monsoonal regime drives seasonal upwelling that leads to massive macroalgal growth that coexist with reef corals. Many species recorded from both regions show genetic differentiation between them. Comparison of environmental factors (ecological modeling) and transport (circulation modeling) shows both important in creating this transition. Many of the endemic species appear to be young, attesting to active diversification in the area. Others are old, suggesting they may be relict, Tethyan lineages.

Numerous undergraduate and graduate students and postdoctoral scholars were involved and trained in field, lab, and analytical techniques. Further training was provided through immersion courses on biodiversity and molecular methods at two marine labs, and a workshop carried out in Oman on marine biodiversity. This project has also led to major improvements in high-throughput biodiversity methods that will help accelerate documentation of marine life moving forward.

Last Modified: 01/28/2025
Modified by: Gustav Paulay