Namib Desert ecosystem

• Category: Desert Biomes.
• Geographic Location: Africa.
• Summary: This Atlantic coastal desert has the second-largest dunes in the world and an ecosystem uniquely adapted to its fog belt.

The Namib Desert (the term Namib means vast place in the language of the Nama people), one of the oldest deserts in the world, stretches for 1,200 miles (1,931 kilometers) along the South Atlantic Ocean coasts of Angola, Namibia, and South Africa. It is a neighbor to the Kalahari Desert in the south, which is semiarid compared to the Namib, a traditional arid desert. In the north, from the Angola-Namibia border, the Namib is known as the Mocamedes Desert and includes the Kunene River, which flows from the Angola highlands to the border—one of the few perennial rivers in the Namib.

As a coastal desert, the Namib enjoys a unique climate and ecosystem. While the Namib’s climate is arid, it is close enough to an ocean to receive moisture from advective fog, which forms above the ocean and drifts over the land. The ocean is thus a partial remedy for the desert’s aridity—but also one of its causes. The Atlantic currents desiccated the coast over time by being too cold to contribute much atmospheric moisture; the biome receives extremely limited coastal precipitation of less than 1 inch (25 millimeters) per year.

The Namib has some unique features, including grand spreads of high dunes; the 700-million-year-old granite peaks of Spitzkoppe; the Sperrgebiet diamond mine in the southwest; and Swakopmund, one of the nearest cities to the desert.

There are only a few small settlements in the Namib, and most of the human population belongs to indigenous pastoral groups like the Himba, who raise cattle and goats, moving their herds from place to place through the desert and protecting them from predation by lions. The Himba follow rainfall patterns to bring their herds to the places most likely to have food, and they use herbs from the omuzumba shrub mixed with butter to protect themselves from the sun.

Heat, Fog, and Rain

Though the South Atlantic is cold here, its presence is a moderating influence on the Namib’s temperature, and the diurnal range—the difference between the cold night and the hot afternoon—is considerably foreshortened in the Namib compared with other deserts. This is less true in the Namib’s furthest inland regions, where summer nights can drop to 32 degrees F (0 degrees C), while afternoons reach a high of 113 degrees F (45 degrees C).

The northern stretch of coastline is known alternately as Skeleton Coast and Gates of Hell, names that speak to the difficulty of safe navigation. Until the advent of motor-powered boats, it was impossible to launch boats from the shore, and the ones that did successfully navigate the surf to land on the coasts were forced to cross both marsh and desert to leave again.

The skeleton part comes from the whale and seal bones left behind on the beaches when the whaling industry was an ongoing concern. The wooden and metal skeletons remaining from numerous shipwrecks justify the name equally well. Today, a portion of the coast is a designated wilderness area and part of Skeleton Coast National Park. The inland riverbeds are home to baboons, giraffes, lions, springboks, and rhinoceroses. The coast’s bird populations have been the subject of numerous research studies and documentaries.

The Namib’s coast is foggy even by the standards of other coastal deserts, with thick mist hanging over the area approximately 180 days a year. The fog occurs when the cold Benguela Current meets the warm air from the Hadley Cell. Much of the coast receives twice as much fog precipitation every year as rain. Long known as a hazard for sailing, the fog is vital to the life of the sand seas along the coast—broad, flat areas with little to no plant cover, where the sand has been formed by the wind.

The Namib’s soil is fine-textured and porous, with little organic material. Plants like salt bush, buckwheat bush, and rice grass have adapted to the environment, with strong root systems to take advantage of the rains that do occur, as well as fleshy leaves and stems that store water. In the north, rain typically falls in the summer, and in the south, it falls in the winter. At the transition belt between the two, there is no seasonal pattern; rains are even more erratic and less predictable than in most desert areas.

Most rivers in the Namib are underground or ephemeral streams: waterways that follow consistent paths, but flow only immediately after precipitation. One of the best-established of these rivers is the Tsauchab, which flows from the Naukluft Mountains when it rains—because the rock and soil of the mountain cannot accommodate seeping precipitation—resulting in flash floods. Within hours of rainfall, the Tsauchab emerges from the dust as a fast-running river with a strong flow through the Sesriem Canyon until reaching the Sossusvlei salt pan.

Vegetation

Lichens and succulents comprise most of the plant life near the coast, and grasses and shrubs predominate along the escarpment. Because of the dearth of plants, there is little to hold the soil in place and less microbial activity. When rain does occur, it can have a much greater erosive effect than it would elsewhere.

A thin layer of organisms forms on the surface of rocks and in their pore spaces, including bacteria, funguses, and cryptogams—organisms that reproduce by spores, in this case mainly lichens such as wreath lichen (Phaeophyscia orbicularis) and golden hair lichen (Teleoschistes flavicans). This biofilm excretes acids that contribute to the breakdown of rocks and the further desertification of the soil. Microbes and cryptogams also thrive in the fog zones, and the minerals they pick up from the fog help form “desert varnish,” a paper-thin coating of mineral clay and iron on exposed rocks.

The Namib is part of the Succulent Karoo ecoregion, which includes the deserts of Namibia and South Africa, and contains the world’s largest concentration of succulent plants—about one-third of the world’s species, more than 3,000 in total. Like the rest of the Succulent Karoo region, the Namib is home to monkey beetles, masarine wasps, and colletid and melittid bees.

For centuries, people have marveled at the “fairy rings” of the Namib, though they are most striking from the air. The fairy rings are circles on the ground caused by shifts in the soil and sudden changes in the pattern of vegetation. Recent studies have suggested that these rings are the result of termite activity—Hodotermes mossambicus, Psammotermes allocerus, and Baucalioterms hainsei all live in the desert—but this is the most recent of numerous theories and may yet be disproved.

Fauna

Along the coast, brown fur seals and shorebirds feed on the many fish; lions feed on the seals and shorebirds. Away from the coast, much of the fauna obtain water through diet. Small mammals like the rock mouse (Aethomys namaquensis), cape short-eared gerbil (Desmodillus aricularis), dune hairy-footed gerbil (Gerbillurus tytonis), and Grant’s golden mole (Eremitalpa granti) may feed mainly on plants and insects that retain water from the last rainfall. The same is true of reptiles like the dwarf puff adder (Bitis peringueyi), wedge-snouted desert lizard (Meroles cuneirostris), and Koch’s chirping gecko (Ptenopus kochi).

Much of the desert fauna here consists of arthropods. There are 13 species of darkling beetles (Onymacris) in the Namib, which have longer legs than other beetles, along similar proportions to those of many spiders. These extra-long legs allow them to lift their bodies above the hot layer of air clinging to the desert floor—an adaptation known as stilting. Just as interesting is fog basking, a behavior shown by two darklings: O. unguicularis and O. bicolor. These darklings crawl to the tops of the coastal sand seas in large numbers when the fog settles in, letting it condense on their abdomens and drip into their mouths.

While large mammals cannot rely on such methods, ungulates like springboks have adapted by ceasing to sweat, making their water consumption more efficient while also requiring careful use of energy to avoid overheating.

The black widow spider (Latrodectus indistinctus) also thrives in the Namib Desert, feeding primarily on detrital-algae-feeding flies that have flown over the coast from the Atlantic. The presence of the black widow helps protect the dune vegetation, as it poisons and reduces the local herbivore population.

Local Features

Namib-Naukluft National Park is a national game park encompassing part of the desert near the Naukluft Mountains. Located in the fog zone, the park is home to hyenas, jackals, gemsboks, and reptiles, as well as endemic (found nowhere else) insect species. The mountains are home to mountain zebras and leopards. The dunes are among the largest in the world, and are a striking orange color as a result of the oxidation, over millions of years, of the soil’s iron content.

In the southern part of the Namib is the Sossusvlei, a salt and clay pan surrounded by reddish dunes that is a drainage basin without outflows for the Tsauchab River. Like the dunes of the Namib-Naukluft Park, the dunes here are highly oxidized. The marshes are seasonally flooded by underground rivers; they turn nearly white when dry from the high levels of salt.

Rodents, jackals, antelopes, and ostriches live in the area, and migrant birds arrive with the floodwaters. The nearby Deadvlei was an oasis once, but the river that fed it has since changed course, and it is now an empty salt pan filled with long-dead acacia trees. Some of the oasis vegetation has managed to survive without the river—notably clusters of saltwort and the nara melon (Acanthosicyos horridus), endemic to Namibia. The nara melon is a vital foodstuff for the Topnaar tribe, as well as the bush cricket (Acanthoproctus diadematus), which lives in the southern part of the desert, moving ceaselessly from one melon plant to the next.

In the southwest is the Sperrgebiet, a series of diamond mines jointly owned by the Namibian government and the De Beers corporation. Due to the limited human presence in the area in the 100 years since the German government first established a colony here for the purpose of operating the mines, the wildlife remains very diverse and largely unchanged from before the arrival of Europeans.

The Orange River is the only permanent water supply to the area, but there are 800 species of plants in the area, 234 of which are endemic to the Namib, primarily succulents. The Namba padloper, a rare tortoise, is found almost exclusively in this area.

Climate Change

Temperatures are rising globally and in the Namib Desert. In fact, temperatures have been recorded as rising in this desert since the sixteenth century. Scientists have found that the weather is getting hotter and the desert is growing drier. Rainfall seasons are shorter and starting later, which has pushed back the planting season and depleted some water supplies. On the coast rising sea levels and changing ocean temperatures negatively impact marine life. Increases in frequency and intensity of coastal storms create an even more perilous coast. The flora and fauna of this biome are hardened to arid conditions, and it remains to be seen how much the Atlantic fogs may counteract the rainfall drought.

Bibliography

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