Abstract:
Sharks and rays (elasmobranchs) are key to healthy marine ecosystems, yet their populations have sharply declined worldwide. One major obstacle to their conservation is the lack of historical data showing how abundant they once were.
This thesis combines ecological surveys with molecular tools (environmental DNA, sedimentary ancient DNA, and digital PCR) to reconstruct long-term biodiversity changes and investigate historical populations of elasmobranchs. Research focused on two contrasting regions: the Red Sea, where fishing has been largely unmanaged, and the Bahamas, a nearly 30-year model for shark protection.
In the Red Sea, survey and eDNA evidence revealed previously unknown depth ranges for some species and new information on elasmobranchs habitat use, but also a century-long decline in fish and shark populations linked to anthropogenic pressures. In contrast, the Bahamas showed signs of stability and recovery, reflecting the potential success of early conservation policies such as the 2011 Shark Sanctuary.
By refining eDNA and dPCR methods, this work enhances our ability to detect species and extend biodiversity records into the past. Together, the findings demonstrate that timely management, grounded in historical context, is essential to restore and safeguard ocean ecosystems.

Bio:
Sofia Frappi is a Ph.D. candidate in Marine Science at King Abdullah University of Science and Technology (KAUST) within the Tarek Ahmed Juffali Research Chair Lab led by Prof. Carlos M. Duarte. Drawing on her background in marine ecology and molecular biology, her research focuses on elasmobranch ecology and the use of environmental DNA (eDNA) to investigate marine biodiversity in tropical and deep-sea ecosystems.