Southern Upper Guinea

Southern Upper Guinea is the wet, forested western end of West Africa's coastal drainage — the short rivers that drop off the Wologisi and Nimba highlands and run straight to the Atlantic across Liberia, southern Guinea and western Côte d'Ivoire. The St Paul, St John, Cestos, Cavally, Mano and Lofa are the names that matter here; none is long, most are rocky and broken by cataracts, and together they carry one of the more distinctive freshwater faunas in Africa. About a fifth of the region's 151 fish species live nowhere else, the legacy of a forest block that stayed wet while the savanna dried, and that biologists read as a refuge. That same forest is now among the most fragmented on Earth.

Geography & hydrology

The Southern Upper Guinea ecoregion (FEOW Ecoregion 512) is defined by the basins of the Mano, Lofa, St Paul, St John, Cestos and Cavally rivers, covering nearly all of Liberia along with a slice of southern Guinea and the western edge of Côte d'Ivoire. It belongs to the larger Upper Guinea bioregion, the West-African forest block that runs from Guinea's Fouta Djallon down to the Bandama, and it is the southern, wetter, more heavily forested half of that block (FEOW Ecoregion 512; Hugueny & Lévêque, 1994).

These are short rivers in a hurry. Most rise in the Wologisi Range in the north or the Nimba Range along the southern frontier, between roughly 500 and 1,0 ft above sea level, and reach the ocean over a fairly direct course rather than meandering across a great basin the way the Niger or Congo do. The upper reaches are slowly eroding the plateau, so they tend to be rocky and torrential; the relief stays steep toward the coast, and cataracts are common right down the rivers' lengths. The Mano alone drops over more than fifteen waterfalls in its lower course (Lévêque, Paugy & Teugels, 1990; Hughes & Hughes, 1992). Floodplains are scarce here — there is little of the broad seasonally inundated lowland that shapes the big Sudanian rivers — and the main soft-bottomed, low-gradient habitat appears near the river mouths, where swamps and mangrove forest take over as the freshwater meets brackish tidal water.

Because the catchments are small and the rainfall is heavy, discharge is strongly seasonal but the rivers stay comparatively clear and fast over their middle and upper sections. The basins themselves are modest by continental standards: the St Paul drains on the order of 18,0 mi², the St John more than 14,0 mi², the Cestos around 12,0 mi², the Lofa about 13,0 mi² and the Mano roughly 8,0 mi² (Paugy, Lévêque & Teugels, 1990). What the region lacks in size it makes up for in gradient and isolation — each river is, to a fish, something close to an island, walled off from its neighbours by the sea at one end and rough water within.

Water & habitat

The defining habitat of Southern Upper Guinea is the rainforest stream: water shaded by closed canopy, running cool and clear over rock and coarse sand, soft and on the acidic side because it drains leached forest soils and crystalline basement rather than limestone. There is little dissolved mineral load and a steady input of leaf litter and woody debris, which stains backwaters and pools tea-brown and feeds a detritus-based food web. This is the opposite end of the spectrum from the hard, alkaline rift lakes most people picture when they hear 'African cichlid' — the fishes here are blackwater and clearwater forest animals, tuned to low conductivity and a narrow temperature band.

The physical template is a staircase. Rocky, torrential upper courses give way to a long succession of riffles, rapids and cataracts as the rivers cut toward the coast, with deeper, slower pools strung between them. That alternation of fast and slow water over bedrock, boulder, gravel and sand creates a patchwork of microhabitats packed into a small drainage — exactly the kind of structural variety that lets many species partition a short river. The waterfalls do double duty: they are habitat, and they are barriers, isolating stretches of a single basin from one another and helping drive the fine-scale endemism the region is known for (Lévêque, 1997; Hugueny & Lévêque, 1994).

The coastal zone is a different world again. Near the mouths the gradient flattens, the forest stream meets the tide, and swamp and mangrove replace rapids. Salinity, turbidity and substrate all shift, and a set of estuarine and brackish-tolerant fishes lives in that transition rather than in the forest reaches upstream. The result, across one of these rivers, is a chain of contrasting environments — torrent, pool, lowland river, mangrove estuary — over a remarkably short distance, with water that grows warmer, softer-edged and more sediment-laden as it nears the sea. It is a fauna sorted by where in that chain a species can hold on.

The cichlid fauna

West-African forest cichlids are smaller, quieter and less famous than the rift-lake radiations, but Southern Upper Guinea has a tidy, characteristic set of them, and cichlids are one of the families the ecoregion is flagged for in terms of endemism, alongside the killifishes (Cyprinodontidae) and the carps and minnows (Cyprinidae) (FEOW Ecoregion 512).

The most charismatic of the atlas roster is Pelvicachromis humilis, a krib — one of the dwarf 'rainbow cichlids' that hobbyists prize — restricted to the coastal forest streams of this corner of Africa, occurring in Guinea, Sierra Leone and Liberia. Like its better-known relative P. pulcher, it is a cave-spawning soft-water fish of small, shaded watercourses, the kind of cichlid that wants exactly the low-pH, low-conductivity conditions these rivers supply. Sharing the forest streams is the jewel cichlid Hemichromis bimaculatus, the original 'jewelfish,' a hardy, brilliantly red substrate-spawner of marginal vegetation and slower water that ranges widely across West-African forest drainages and is at home here.

The larger end of the roster runs toward tilapiines and the Tylochromis genus. Heterotilapia buettikoferi — the zebra tilapia, formerly Tilapia buettikoferi — is a big, boldly barred substrate-brooder of the larger rivers from Guinea-Bissau down into western Liberia, a fish that favours main channels with rocky bottoms rather than small creeks, and a herbivore-leaning omnivore that grows large for the group. Then there are the Tylochromis, deep-bodied sand-sifters with thick lips and small mouths that work the lower, slower, often brackish reaches. Three sit on the roster: Tylochromis leonensis, described from the Taia River in Sierra Leone and endemic to the region; Tylochromis jentinki, a coastal-river and lagoon species ranging from the Gambia east to Ghana's Tano that turns up in the brackish lower courses and estuaries; and Tylochromis intermedius, named for a scale count midway between its congeners. As a group the Tylochromis sit downstream of the krib-and-jewel forest fauna, in the transitional water near the coast — so the cichlids alone trace the river's whole gradient, from shaded headwater stream to mangrove mouth. Endemism across the region is the real story: roughly a fifth of 151 fish species are found only here, a figure that owes to long isolation behind the Guinean highlands, to waterfalls splitting individual basins, and to the forest having stayed wet as a refuge while the surrounding savanna dried (Hugueny & Lévêque, 1994; Lévêque, 1997).

Conservation

The forest that makes this fauna possible is disappearing fast. The Upper Guinean forest once covered something like 360,0 mi² of West Africa; by 2013 only around 70,0 mi² of dense forest remained, of which roughly 32,0 mi² lay inside reserves, and the rest survives as fragments. Most of that loss is old — about 84% of the original extent was gone before 1975 — but the bleeding continued, with another 28% of what stood in 1975 cleared by 2013, driven by unregulated logging and slash-and-burn farming as the population grew. Liberia is the pivotal country: roughly half of all remaining intact Upper Guinean forest is inside its borders, which makes the fate of these rivers and the fate of Liberian forest policy essentially the same question (USGS EROS; CEPF Guinean Forests profile). When the canopy goes, the streams lose their shade, warm up, silt in from eroding slopes and shift away from the cool, clear, soft water the forest cichlids and killifishes need.

Mining sharpens the threat in the highlands where these rivers are born. The Nimba Range, the transboundary massif shared by Guinea, Côte d'Ivoire and Liberia and protected in part as the Mount Nimba Strict Nature Reserve, holds some of the richest iron-ore deposits in West Africa, and large-scale extraction of iron and bauxite in mountain headwaters is a recognised concern for the streams draining them — through direct habitat loss and through the sediment and pollution that mining sends downriver (CEPF Guinean Forests profile; Fauna & Flora International). Because the endemic fishes are split among small, separate basins, a single mine or a single fouled headwater can hit a disproportionate share of a species' total range.

Dams are the third pressure, concentrated on the largest river. The Mount Coffee hydropower scheme on the St Paul, originally built in the 1960s and breached and abandoned during Liberia's civil war in the early 1990s, was rebuilt and brought back online in the 2010s; the river around the site supports on the order of a hundred fish species, and the rebuild prompted work on a naturalised bypass channel and even a dedicated pass for the migratory river prawns whose runs the dam blocks (Fishtek; Mount Coffee ESIA). Those civil conflicts — Liberia's and Sierra Leone's wars through the 1990s and into the 2000s — left their own legacy on the rivers, stalling conservation and surveys for years and leaving the fauna 'fairly' explored at best (FEOW Ecoregion 512). The basics still hold: short forest rivers, high endemism, each basin its own small world — and a forest being pulled out from under them faster than the fishes are being catalogued.

Where these cichlids live

Geography & hydrology

Water & habitat

The cichlid fauna

Conservation

Sources

Cichlids recorded here

Anomalochromis · 1

Heterotilapia · 1

Pelvicachromis · 1

Rubricatochromis · 1

Tylochromis · 3

Wallaceochromis · 1