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Africa’s Submerged Savannas

For the month of April 2014, National Geographic Pristine Seas expedition leader Paul Rose will lead a group of key scientists and filmmakers, together with National Geographic Emerging Explorer Andrea Marshall and the Marine Megafauna Foundation, to explore, survey, and record what they expect to be some of the healthiest reefs in East Africa, home to ocean giants like manta rays, dugongs, and more.

by Kike Ballesteros

There are many iconic images of Africa, from camels in the Sahara desert to gorillas in the mountain rainforest of Virunga or surfing hippos in Loango beaches, but the African wilderness is probably most identified by the savanna—the open grassland where elephants, giraffes, cheetahs, and lions roam.

Although some scattered trees thrive in the savanna, most of is covered by grass, the major element that feeds wildebeest, zebras, and other herbivores, which are in turn prey of the big cats. Grasses are a kind of plant that prosper better in semiarid climates with short seasonal periods of good environmental conditions, when they grow quickly and abundantly. However their growth is usually limited by the scarcity of water.

Strange as it seems, grasses also develop where water is plentiful: in the ocean. Oceanic grasses or seagrasses have terrestrial ancestors: they have adapted secondarily to water. This is a striking difference with seaweeds, whose evolution has been largely underwater their entire history. Moreover, seagrasses produce flowers, and fruits are their major method of dispersal—a feature that is only explained by their aerial origin.

Estuaries are for sure the habitat of seagrasses’ first ancestors and they still are their preferred place. These last three days, because of the high seas, our expedition has been confined to the estuary of the Matamba river, close to the city of Inhambane. We have dived extensively in the waters of the estuary and several times we dropped onto seagrass. The diversity of grass here is great. I have found up to six species in a seagrass patch of hardly 100 square meters. More species than in the entire Mediterranean Sea! In fact, the Indian Ocean is the world’s hotspot for seagrass biodiversity.

Who Does What

These seagrass meadows are the marine counterpart of the terrestrial savannas. They hold large populations of animals that graze on them, from sea hares and small crustaceans to sea urchins and herbivorous fish. Seagrass meadows are also critical to maintain the dugongs’ populations as they almost exclusively feed on them. Green turtles also depend on seagrass to feed.

These two animals are the biggest herbivores in the seagrass meadows, with a role similar to antelopes and zebras or elephants in the savanna. Most crabs and some snails play the role of scavengers—the function played by hyenas and vultures in the savanna. The carnivores here can be cautious, like sea stars and sea horses, or eager, like jacks and barracudas. The top predators—the lions of seagrass meadows—are sharks.

Dugongs and green turtles are in danger all over the Indian Ocean, threatened by habitat destruction and hunting. So are the bullsharks which were the major estuarine predators until humans began to fish them. Seagrass itself is apparently doing well in the bottoms of Matamba estuary, but big herbivorous fish and dugongs are becoming scarce.

Our First Dugong Sighting

 

Yesterday afternoon Janneman and Andrea, our partners of the Megafauna Foundation, spotted a dugong and her calf close to Linga Linga, in the mouth of the estuary. They called us by radio and we quickly launched a small team to join them and obtain some images.

We tried to get close but dugongs are extremely suspicious animals. Scott Ressler, one of our terrestrial filmmakers, got some two-second shots of dugongs’ backs from above. Manu San Félix tried to shoot them underwater. I followed him. The sun was low in the skyline, the water was murky and visibility was only seven feet. We made two unsuccessful attempts to approach them. We free dived again and again. We found sickle-leaved seagrass, a favourite food for dugongs, everywhere. It is clear that seagrass abundance is not limiting dugong populations. Humans are.

These have been the first sights of dugongs in our expedition. For the days to ahead we will face the waters of Bazaruto National Park, which hold the largest population of dugongs in Africa. Thus, we will surely have better opportunities to record them on film. But few dugongs still graze seagrass in the Matamba estuary, where they are extremely vulnerable. They are the elephants of the underwater savannah and as such they need protection. Our expedition is here to provide a promising future for the calf we saw yesterday. And we will do our best to succeed.

Read All Pristine Seas: Mozambique Blog Posts

The Pristine Seas Mozambique expedition is sponsored by Blancpain and Davidoff Cool Water.

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Comments

  1. Rebejcca
    Atlanta
    April 23, 3:40 pm

    AMAZING!!! I LOVE SEA LIFE. Sometimes you only have one picture for an article. I was SURPRISED AND DELIGHTED that you all had several pictures for this article. I love it.