Study Sheds Light on Hidden Biodiversity in Palau’s Reefs

The Palau International Coral Reef Center (PICRC), in collaboration with the University of the Ryukyus (Okinawa) and the Japan International Cooperation Agency (JICA), has completed the first country-wide survey of small animals living in coral rubble, known as rubble cryptofauna. These often-overlooked species play key roles in reef ecosystems, and the findings establish new baseline data to track how Palau’s reefs respond to climate change and coastal development.

Between January and July 2017, scientists surveyed 40 sites across Palau’s archipelago, representing five different habitats: outer reefs, inner reefs, mangroves, channels, and Ngermid (Nikko) Bay. Nearly 5,000 individual organisms were recorded, representing 9 major animal groups, over 170 families, and more than 280 types of organisms. Outer reefs hosted the highest levels of biodiversity, while Nikko Bay’s unique environment supported a smaller but unique community. The study also highlighted the importance of reef channels, which act as ecological links between inner and outer reef environments.

Rubble cryptofauna recycle nutrients, provide food for fish, and contribute to the resilience of reef systems. Despite their importance, they are rarely included in monitoring programs. “Healthy reefs depend on more than corals and fish,” said Dr. Piera Biondi, PICRC Researcher and lead author of the study. “By including rubble cryptofauna in our assessments, we gain a more complete picture of reef ecosystems. This knowledge will support stronger conservation strategies for Micronesia.” 

The study also points to new directions for future monitoring. Since all specimens were photographed as part of the research, similar future surveys release animals back to the reef after documentation to reduce impacts on reef communities while still providing valuable biodiversity data.

Taken together, the findings provide a reference point for future research and management decisions to strengthen the resilience of Palau’s reefs. 

“Our partnership with Professor James Reimer and the University of the Ryukyus exemplifies the power of collaboration to advance science and amplify impact,” said Ms. Geraldine Rengiil, Director of Research at PICRC. “By joining forces, we’re enhancing our research capacity to better understand and guide the management of Palau’s reefs.”The full study, Rubble in paradise: motile infaunal diversity patterns across reef environments in Palau, is published in the journal Coral Reefs. The article is open access and available at: https://doi.org/10.1007/s00338-025-02731-9.