Sunlit coral reefs are perhaps the most famous marine habitat and many people have dived or dived into one at some point. Home to a quarter of all known ocean organisms, these “ocean rainforests” have been at the forefront of marine research for decades and featured in documentaries such as The Blue Planet and animations such as Finding Nemo.
However, reefs and corals do not end where there is no sunlight. Largely hidden from the masses lie great expanses of deep reefs that collectively have a greater geographic footprint than their shallower counterparts.
Sandwiched between shallow reefs and the deep sea, reefs between 30 and 300 meters deep receive relatively little scientific attention to this day, considered too deep for shallow reef biologists and too shallow for deep-sea researchers. Combined with the cost and difficult logistics of studying them, and because of the common perception that they are simply deep, these reefs are of low risk, despite evidence to the contrary, deep reefs remain significantly understudied.
Fortunately, recent advances have allowed us to learn more about these unique ecosystems. Specialized diving equipment, known as technical diving, can go as deep as 150 meters, and remotely operated or autonomous vehicles and even crewed small submarines can go even deeper.
As we go deeper and less light penetrates the water, the hard corals and other light-dependent organisms that dominate the shallows become less numerous. They are replaced by other photosynthesizing groups such as fleshy algae until these too are replaced by sponges, soft corals and sea fans.
More than a dozen times I had the honor of being in a submarine, where the acrylic hull gives an almost 360-degree view of underwater life. The feeling is unique when you visit the depths of our ocean and observe its creatures – things you usually only see in documentaries – first hand. The huge sea fans are a particularly amazing sight, often exceeding 2 meters in diameter:
I’ve had a few encounters with reef sharks, floating tube-like pyrosomes, and bioluminescent jellies, but my favorites are the interactions with the ever-curious potato groupers, which will follow and hover around the sub and even pose for photos:
Fish are more mobile than corals or sponges, so the species of fish on the highest deep reefs are still mostly known. However, as you go deeper, the fish gradually become more unique and adapted to the low light and food-poor conditions of deep reefs.
It’s worth noting that it’s only been a few years since scientists first described and classified a new zone of the reef – a zone of rare or rare light with a depth of about 150 to 300 meters. The unique collection of benthic organisms and fish helped define this depth range as an entirely new reef ecosystem. As we are just beginning to scratch the surface of the deep reefs, many more exciting discoveries will follow in the coming years.
Deep reefs require targeted protection
Deep reefs provide a host of essential services for people and the planet. They help protect coasts from waves and storms, provide breeding grounds and protection for fish, and shelter some of the organisms that live on highly threatened shallow reefs. Natural medicinal products have also been discovered in species that live in deep reefs, including anti-cancer and anti-fungal compounds found in sponges collected from 125 meters deep in the Pacific island nation of Palau.
The logistical and financial challenges of studying deep reefs mean that less data is available than for shallow reefs, and deep reefs are rarely used to inform management and conservation efforts. While their unique biological communities warrant targeted conservation efforts, most deep and offshore reef habitats remain unprotected. The few that are protected are often included haphazardly due to geopolitical boundaries and are rarely explicitly included in management plans and designation objectives.
How can we save the deep reefs
I am part of a team of 18 scientists from various organizations around the world who recently developed a framework for the protection of deep reefs in the western Indian Ocean, home to some of the least known deep reefs in the world. Our framework includes practical recommendations that we hope will improve deep reef management across the region and may eventually be adopted globally.
Below are our top five recommendations:
Protect: Ensure 30% of ecosystems are highly protected by 2030 (“30 out of 30”) and include deep reefs for this purpose.
Protect: Protect deep reef ecosystems and their resources by specifically integrating them into fisheries legislation, marine protected areas and marine spatial planning.
Management: Extend current shallow reef management efforts to include deep reefs as these ecosystems are often connected.
Invest: Invest in basic, fundamental and applied research into deep reef biodiversity, ecosystem function and services provided.
Cooperate: Develop national and international collaborations to explore and protect deep reefs in national and international waters (high seas).
This article has been republished from The Conversation under a Creative Commons license. Read the original article.
Paris Stefanoudis is affiliated with and receives funding from the Nekton Foundation.