The Nekton Maldives Mission, which included researchers from the University of Oxford, discovered evidence of a previously unknown ecosystem known as "The Trapping Zone," which is creating an oasis of life 500 meters below the surface of the Indian Ocean. The Maldives government has hailed the discovery as extremely significant.
|Bramble shark. Credit: Nekton Maldives Mission
Video evidence from Nekton science cameras aboard the Omega Seamaster II submersible, combined with biological samples collected and extensive sonar mapping, indicate that predators such as sharks and other large fish feed on swarms of small organisms known as micro-nekton in this zone.
These are marine organisms that can swim against the current and typically migrate from the deep sea to the surface at night and back again at dawn (known as Vertical Migration). However, at 500m, the micro-nekton becomes trapped against the subsea landscape.
The Maldivian atolls' volcanic subsea strata and fossilized carbonate reefs combine steep vertical cliffs and shelving terraces. These appear to be the reasons why these species are unable to dive deeper as the sun rises.
Large pelagic predators, such as schools of tuna and sharks, as well as well-known, large deep-water fish such as the spiky oreo (named after the biscuit) and alfonsino, attack the trapped animals. The mission documented tiger sharks, gill sharks, sand tiger sharks, dogfish, gulper sharks, scalloped hammerhead sharks, silky sharks, and the extremely rare bramble shark.
Both topography and ocean life define marine ecosystems. "This has all the hallmarks of a distinct new ecosystem," said University of Oxford Professor Alex Rogers, who spent over 30 hours underwater in the mission's submersibles observing The Trapping Zone during the expedition. "The Trapping Zone is creating a life oasis in the Maldives, and it is very likely that it will exist in other oceanic islands as well as on the slopes of continents."
According to Lucy Woodall, Associate Professor of Marine Biology at Oxford and Principal Scientist at Nekton, "We're particularly intrigued by this level of detail—going what's on? Is this something unique to 500 meters, or does this life go even deeper? What is this transition, what is there, and why is it there? That is the critical question we must address next. Why are we noticing the patterns we have on this expedition? This will greatly improve our understanding of the deep ocean."
While a trapping effect has been linked to biodiversity hotspots on subsea mountains or seamounts, it has not previously been linked to the various geomorphology and biological parameters of oceanic islands such as the Maldives.
- Ancient beach lines: Terracing and wave erosion at depths of 122 m, 101 m, 94 m, 84 m, and 55 m revealed evidence of different beach lines caused by sea level rise over the last 20,000 years since the last glacial maximum.
- Coral reefs: To inform the Maldives Government's conservation and management policies, the mission systematically mapped, surveyed, and determined the location, health, and resilience of coral reefs in six major locations. The reefs are vital to life in the Maldives, helping to mitigate the effects of rising sea levels and increasing frequency and intensity of storms caused by climate change.