After years of underwater expeditions in the southern Caribbean Sea, a team of researchers from the Smithsonian National Museum of Natural History has provided the first detailed snapshot of a surprisingly diverse ecosystem , so unique that it has been defined as a new oceanic zone with numerous new species. . Welcome to the rare.
It has always been there, but this layer of the ocean is so different from the upper and lower waters that it needed its own category.
Scientists have defined an ocean layer between depths of 130 and 300 meters , an area with little light or “penumbra” in deeper reef regions, as rarephotic.
The raropotic is found just below the mesophotic zone, between 40 and 150 meters, where medium light penetrates – the optimal waters for tropical coral reefs. And this area is teeming with unknown fish – a whole new ecosystem uncovered.
These fish are closely related to reef fish, which the researchers did not believe could live below the mesophytic. This has led to the hypothesis that the new area may be a haven for shallow reef fish seeking respite from the warming waters and corals increasingly damaged by climate change.
There are many things that we do not know about this ocean, basically because it is very difficult to access. But thanks to advances in submersible technology (Curasub), it has been possible for marine scientists to explore under the reef off the coast of Curaçao at a depth of 309 meters for 8 consecutive hours at a time.
Numerous species of fish discovered
So far, the researchers have made observations of around 4,500 rariphotic fish, representing 71 different species. Most of them are closely related to the fish that swim on top of the reef. However, by exploring a deep reef area of just 0.2 square kilometers, the researchers discovered six new genera and about 30 new species of fish and invertebrates.
“ About one in five fish that we find in the Caribbean rariphotic is a new species ,” said Ross Robertson, a co-author of the work.
Many of the new findings are still awaiting official analysis and description, but the study published in Scientific Reports is not just about these new inhabitants. It challenges the previous belief that, after the mesophotic zone, ecosystems move immediately to those of the deep sea.
The rarophytic is a kind of “missing link” between the reef zones of medium light and the ocean without light , known as the aphotic zone. And researchers have also come up with a new name for shallower waters more than 40 meters, where a lot of light penetrates: the altipotic.
“It is estimated that 95% of the habitable space on our planet is in the ocean, yet only a fraction of that space has been explored,” says Carole Baldwin, leader of the study.
“That’s understandable for areas that are thousands of miles offshore and deep. But deep tropical reefs are just below shallow, well-studied reefs – essentially our own backyards. And deep tropical reefs are not landscapes. Barren at the bottom of the ocean: they are very diverse ecosystems that deserve further study. We hope that by naming this area of deep reefs, we will draw attention to the need to continue exploring deep reefs. “
Reference: Baldwin, CC, Tornabene, L. and Robertson, DR 2018. Below the Mesophotic. Scientific Reports, 2018. DOI: doi: 10.1038 / s41598-018-23067-1
Images credit: Carole Baldwin, Smithsonian
