World Oceans Day 2021

How Mount Kilimanjaro and We Can Save Corals

By Tim McClanahan | June 8, 2021

Dr. Tim McClanahan underwater surveying coral reefs in coastal Tanzania. Photo credit: ©Michael Markovina

verything is connected” is a truism frequently expressed by ecologists. It’s an adage that practicing ecologists like myself keep in mind. While practically speaking this aphorism rarely commands my daily attention, which is more frequently focused on more specific intricacies of nature, there are times when I look up and, once again, recognize its simple truth.

This aha moment recently resurfaced during my ongoing investigations into the drama of marine life in East Africa. I realized that Kilimanjaro and corals were connected, and to the benefit of corals. The meandering path of scientific empiricism only slowly unveils these hidden ecological secrets, connections, and the rare epiphanies.

Two questions loomed over my work: Were there sanctuaries from increasing climate oscillations? And could better management reduce climate impacts on coral reefs? Nature replied with a qualified “yes.”

Since the early 1980s, I have been trying to discover ways to better manage coral reefs through protected areas and fishing regulations. Through my dive mask, I have watched strong oceanic oscillations of cool and warm water increasingly stress and kill corals — a consequence of climate change. Thus, my original and singular focus on managing fishing has become increasingly inadequate.

A spear fisherman goes after an octopus on a reef in southern Kenya. Above, two boys watch from under a cliffside of fossilized reef. Photo credit: © Erika Pineros

Two questions loomed over my work. First, were there sanctuaries from these increasing climate oscillations? And, secondly, could better management reduce climate impacts on critical ecosystems like coral reefs? After a long search, nature slowly replied with a qualified yes — a nuance so common to the attentive listeners of her story.

Nature can often be hostile and therefore the persistence of life is tenuous. The marine species we see today have persisted through glacial cycles and extremes that have dominated the Earth for the past 3 million years, oscillations taking between 40 to 120 thousand years.

Consequently, sea level has risen and fallen by up to 120 meters along with changes in tropical monsoons, rainfall, and the size and extent of the glaciers on East Africa’s high-altitude volcanic mountains. Only 15,000 years ago, ancient estuaries were 120 meters below the present tranquil and palm-fringed coastlines.

The marine species we see today have persisted through glacial cycles and extremes that have dominated the Earth for the past 3 million years

Corals create calcium carbonate skeletons that cement and expand the fringes of reefs to form the coral islands of Wasini, Pemba, and Zanzibar. These are among the many reefs below current sea level that harbor the region’s rich coral and fish fauna. Historically, these reefs have been dissected by the freshwater rivers and ocean currents and many of these ancient estuaries are now buried beneath the sea.

One of these estuaries sits 100 meters below the sea, separating Pemba Island from the mainland. It also connects to deeper water via the channel that separates Pemba and Zanzibar islands. This channel, in turn, connects to offshore waters plunging to 1500 meters east of the Zanzibar shoreline — a highly unusual depth so close to the African continent.

Graphic by Sarah Markes/WCS

The consequence is an area of cool, deep water and islands that act together to dissipate the deadly warm-water travelling to the African coastline from the warmer Pacific and Indian Oceans. A stable climate sanctuary for corals and marine life is therefore created by this convergence of volcanic mountains, sea level changes, and reefs.

Climatic and oceanic processes oscillate between benign and severe conditions. When climate becomes severe, as is the current situation under climate change, diversity contracts. While this is bad for many species, their smaller populations are maintained in sanctuaries. When climate is benign, as before human climate-change began, species expand and populations are found far from these sanctuaries. This process of pulsing in space and time has shaped the region’s unique patterns of diversity.

A stable climate sanctuary for corals and marine life was created by a convergence of volcanic mountains, sea level changes, and reefs.

So, we have been given an underwater climate sanctuary for the moment, but it has to balance the increasing dependence of people on fish resources. Practically speaking, many species have contracting ranges at the same time that their populations are declining as a result of fishing. Climate sanctuaries reduce one of these effects (the global impact of climate change) and leave the other (local human needs). For the moment, improving the management of sanctuaries makes sense until the global climate crisis can be resolved.

[Take a 360-degree tour of East Africa’s Coral Refuge]

So, has Kilimanjaro created the only coral sanctuary? Are all our biodiversity eggs in a single, or multiple baskets? Encouragingly, patterns of species diversity in the seascape suggest similar sanctuaries also occur in southern Tanzania, northern Mozambique, and northwestern Madagascar–Mayotte.

Fishers living and working in the marine climate refuge drop a traditional basket trap onto the reef. Photo credit: © Erika Pineros

Three locations in this large faunal province is less than a basketful. Common sense, therefore, suggests the need for care. Past efforts to instill care have been variable. Much has been learned about managing the ocean since the first modern efforts in the 1970s, but a more successful management needs to emerge from this early trial-and-often-error-prone process. Many efforts were not realistic about the costs, sustainable finances, and social resistance to adoption. Thus, overcoming these limits needs to be the core focus of our new era of management.

Calls for expansion of nationally protected areas, combined with community and private involvement, have increased on-the-sea conservation efforts. Ambitious projects, such as the French government’s 2010 creation of a protected area that includes all national waters of the island of Mayotte and the proposed trans-boundary conservation areas between Kenya, Tanzania, and Mozambique, suggest a serious intention and commitment.

A number of scientific collaborations have discovered key ecological benchmarks for reef fish and corals that ensure both the protection of nature and food security for African people.

Legal status is, however, not ecological status, and the latter is what matters to nature. Fortunately, a number of scientific collaborations have discovered key ecological benchmarks for reef fish and corals that ensure both the protection of nature and food security for African people. It is now easier to know the status of people and resources and develop the most appropriate conservation goals for both.

So while sanctuaries are the core that must be protected, there are broader regional goals that can allow nature to flourish and provide human resources across harsh climate cycles if we better protect them now.

Tim McClanahan is Senior Coral Reef Scientist with WCS (Wildlife Conservation Society).

Our Ocean, Our Future

Conserving and managing the marine biodiversity of our…

Our Ocean, Our Future

Conserving and managing the marine biodiversity of our oceans is a monumental task that few countries have the capacity to do on their own. WCS is responding by investing in ocean protection, sustainable fisheries, and marine species conservation where the need is greatest

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WCS saves wildlife and wild places worldwide through science, conservation action, education, and inspiring people to value nature.

Our Ocean, Our Future

Conserving and managing the marine biodiversity of our oceans is a monumental task that few countries have the capacity to do on their own. WCS is responding by investing in ocean protection, sustainable fisheries, and marine species conservation where the need is greatest