The importance of deep mesophotic reefs to fish top predators
(PI: Yannis Papastamatiou (FLMNH), Co-PI's: Carl Meyer (University of Hawaii at Manoa), Randy Kosaki (NOAA, Papahānaumokuākea Marine National Monument), Brian Popp (University of Hawaii at Manoa)
The majority of work on coral reefs has focused on the top 40 m of the water column. This is largely because of the fact that 40 m is considered the maximum depth for divers to work underwater, and hence scientists have been limited to this depth range. However, the recent expansion in the use of technical diving techniques, as well as refinements in equipment and procedures, has enabled scientists to start venturing below this 40 m limit. Technical diving is simply diving beyond 'recreational limits'.In this case mixed gas technology (where divers breath gas mixes containing helium) and decompression techniques, allow scientists to explore and study the marine environment in the 40-100 meter range. These deeper reefs (40-150 m) tend to be called 'mesophotic reefs', due to the lower light levels encountered at these greater depths. Studies on mesophotic reefs have revealed new species of fish and corals, and have started to show us how mesophotic reefs may in fact be a critical link with shallow reef systems. We are only just starting to understand the importance of these little-studied habitats, to the marine ecosystem. The Papahānaumokuākea Marine National Monument, North West Hawaiian Islands (PMNM), is a federally protected refuge, known for its marine life and high abundance of apex predators. During previous exploration dives on the mesophotic reefs of the PMNM, we noticed large numbers of top predators (sharks and jacks).
Currently, the importance of deep reefs to top predators is unknown. Do these predators spend time on the deep reefs and do they feed there? Do they move between deep and shallow reefs? Were we simply seeing predators because they were attracted to the divers and not the reefs themselves? To answer these questions we are using a combination of mixed gas diving technology, acoustic telemetry, and stable isotopes to understand the ecological importance of deep reefs to top predators (Galapagos sharks, Carcharhinus galapagensis, and the giant trevally, Caranx ignobilis) in the North Western Hawaiian Islands.Deep Diving video
Funding provided by National Geographic Committee for Research & Exploration and the Papahānaumokuākea Marine National Monument.
For more information on the Papahānaumokuākea Marine National Monument, please visit their website Papahanaumokuakea.gov