Chapter 6 The status and distribution of freshwater decapods
6.4 Major threats to freshwater decapods
6.4.4 Residential and commercial development
Residential & commercial development is listed as a threat in 16 (30%) of the freshwater decapod Red List assessments.
6.4.5 Other threats
Other threats include Energy production & mining (3%), Natural system modifications (3%), Invasive and other problematic species, genes & diseases (3%) and Human intrusions & disturbance (2%).
6.5 Recommended research and conservation actions
6.5.1 Research recommended
As with the other freshwater taxonomic groups assessed, very little is known about the distribution of many of the freshwater decapod species in western Africa. Without this basic information, it is difficult to make informed judgements as to their current conservation status. Testament to this is the fact that 25% of the known species in the region are assessed as Data Deficient (Table 6.1). Furthermore, without
recent distribution data, it is difficult to monitor any changes in the species’ conservation status. The most frequently cited research topics recommended for freshwater decapods were population size and trends, and distribution (24% of all recommended research), life history and ecology (23%), and threats (22%) (Figure 6.9).
Recent surveys have rediscovered several ‘lost’ species of freshwater crabs such as Afrithelphusa afzelii (CR), A.
leonensis (CR), Liberonautes rubigimanus (VU) and L. nimba (VU), and there is still potential for new species discovery, e.g. Euryrhynchina puteola (DD) collected in 2012, described in 2017. However, several species have not been observed for half a century; Potamonautes triangulus (VU), 1950;
Potamonautes senegalensis (DD), 1960; Sudanonautes nigeria (DD), 1973. Even for those species recently re-discovered, we do not sufficiently understand their population sizes, distributions and trends, and they remain highly threatened. Further research in these areas will be vital to ensure their continued survival.
6.5.2 Conservation actions recommended
Some 63% of the conservation actions recommended by assessors were gene-banking of these species (Figure 5.9). This would help to ensure the preservation of genetic material as an insurance policy against extinction, but also by sequencing these species’ genomes and adding them to a genomic library would allow for them to be identified more readily using eDNA surveys.
Site management was identified as another recommended conservation action. Several potential Key Biodiversity Areas (KBAs) were identified for decapod species (see Chapter 9) but are not able to be confirmed until recent confirmation of the species’ presence at these sites comes to light.
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0
Figure 6.10. Conservation actions recommended for freshwater decapods of western Africa. Source: Compiled by the report authors using data from the IUCN Red List (2021).
0
Figure 6.9. Research recommended for freshwater decapods of western Africa. Source: Compiled by the report authors using data from the IUCN Red List (2021).
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Chapter 7
The status and distribution of aquatic plants in western Africa
Diop, F.N. 1, Diop, M.1, Starnes, T. 2
Contents
7.1 Overview of the western Africa aquatic flora ...76 7.2 Conservation status ...77 7.2.1 Critically Endangered species ...78 7.2.2 Endangered species ...79 7.2.3 Vulnerable species ... 80 7.2.4 Extinct species ...81 7.3 Species richness patterns ...82 7.3.1 Overall species richness ...82 7.3.2 Threatened species richness ...82 7.3.3 Regionally endemic species richness ...82 7.3.4 Data Deficient species richness ...82 7.4 Threats to species ...82 7.5 Conservation actions and recommended research ... 85 References ... 86
1 Institute of Environmental Sciences, Faculty of Sciences and Techniques, University Cheikh Anta Diop, Senegal
2 Freshwater Biodiversity Unit, Global Species Programme, IUCN (International Union for Conservation of Nature), David Attenborough Building, Pembroke Street, Cambridge, CB2 3QZ, UK
7.1 Overview of the western Africa aquatic flora
The varied habitat types and high levels of precipitation in parts of the western Africa give rise to a high diversity of aquatic and semi-aquatic flora in the region. The Upper and Lower Guinea ecoregions contain some of the highest levels of plant diversity and endemism in Africa (Linder, 2001).
There are various definitions of aquatic plants or hydrophytes, as they are sometimes termed, but they all include those plants that are adapted to grow in waterlogged habitats. These range from deep water to bogs and marshes, and include seasonally and perennially flooded areas. Both physiological and morphological modifications enable these plants to flourish in places where others would die.
Although morphologically diverse with adaptations to aquatic habitats in many different plant groups, some basic growth forms are prevalent and can be classified under two broad habitat types. The first of these, the helophytes, are rooted underwater but produce emergent stems that bear leaves and reproductive parts above water and the second are the hydrophytes, adapted for living submerged in water
or at the water surface. The latter are divided into species that have roots fixed in the underlying substrate, are free-floating, have leaves and/or reproductive parts immersed underwater or at the water surface, or have leaves and/or reproductive parts above water (Ranarijaona, 1999). Plants adapted to survive saline conditions such as salt marshes, referred to as halophytes, are excluded from this study.
The occurrence of aquatic plants is largely dependent on the depth and speed of water flow, and water quality.
Some species prefer stagnant or at least calm waters (lentic conditions) – lakes, ponds, marshes and bogs. These lentic species, such as the water lilies (Nymphaea spp.), are rooted in the bed of the water body. Floating species include the duckweeds (Lemna and Wolffia spp.) and the water hyacinth (Eichhornia crassipes). Other species proliferate in running waters (lotic conditions) – rivers, streams, torrents and waterfalls, where floating species are generally absent. Finally, some species are attached to submerged rocks and are able to withstand exceptionally high rates of water flow, notably members of the Hydrostachyaceae and Podostemaceae.
Figure 7.1 Nymphaea micrantha, a water lily native to western Africa. © Fatima Niang-Diop
IUCN Red List Category Number of native species
Number of regionally endemic species
Extinct (EX) 3 (0)
Extinct in the Wild (EW) 0 (0)
Critically Endangered (CR) 9 (2) 3 (2)
Endangered (EN) 5 (0) 2 (0)
Vulnerable (VU) 3 (5) 3 (2)
Near Threatened (NT) 2 (5) 0 (2)
Least Concern (LC) 449 (356) 169 (11) Data Deficient (DD) 15 (104) 9 (25)
TOTAL 486 (472) 186 (42)
Table 7.1 Number of native and endemic aquatic plant species per Red List category in western Africa. Numbers in parentheses refer to the previous assessment (Smith et al., 2009) and include regional assessments. Source: Compiled by the report authors using data from the IUCN Red List (2021) and Smith et al. (2009)
Figure 7.2 Percentage of freshwater plant species assessed according to the IUCN Red List categories in western Africa.
Source: Compiled by the report authors using data from the IUCN Red List (2021).
7.2 Conservation status
This summary refers to the assessment of freshwater species in the western African region based on the IUCN Red List categories and criteria (International Union for Conservation of Nature (IUCN), 2012). Some 486 plant species growing in freshwater areas and wetlands are included in this analysis (Table 7.1). Red List assessments were conducted for 382 species. The remaining 104 species were already recently assessed in 2015. A further 43 species of aquatic plants, 13 Lentibulariaceae and 30 Podostemaceae were ultimately not assessed in this work.
Of the 486 assessed species, 17 species are within one of the threatened categories: nine species are assessed as Critically Endangered (CR), five species are Endangered (EN) and three species are Vulnerable (VU) (Table 7.1).
Three species have been assessed as Extinct (EX). These are Scleria chevalieri (extended from Burkina faso to Senegal), Eriocaulon inundatum (distributed from Senegal to Mali to Senegal) and Eriocaulon jordanii (distributed from Benin to Togo) (Table 7.1).
In total 449 species or 92% of all aquatic plants native to the region are assessed globally as Least Concern (LC) (Table 7.1, Figure 7.2). This majority of species is higher in comparison to species in this category assessed in freshwater ecosystems in North Africa where only 266 taxa are identified as LC. On the one hand, this finding reveals a
0% 20% 40% 60% 80% 100%
Native species
EX EW CR EN VU NT LC DD
Endemic species
positive aspect in relation to the current state of freshwater plant biodiversity, especially as the threats present continue to intensify as they multiply. On the other hand, the efforts that will be made in the protection of this flora will be less directed in their entirety, towards this majority.
There is good documentation on the state of the extinction risk of freshwater plants assessed so far in this region.
However, few of them (15 species or 2%) were classified in the Data Deficient (DD) category. In the Western African region, an evolution in the availability of plant data was indicated in that the species classified as DD was at the time of the last assessment about seven times higher than those obtained in this study. It should be mentioned, however, that the absence of information on these taxa in no way excludes the existence of a threat, the degree of which remains to be determined. The insufficiency of data on this DD category constitutes a limit on the knowledge of West African aquatic flora.
7.2.1 Critically Endangered species
Wahlenbergia tibestica (Campanulaceae)
Wahlenbergia tibestica is an annual or hydrophyte found in seasonal or intermittent freshwater lakes, marshes and pools. This species has been collected only once, in Tibesti (Chad). Its ecology is not clear, but the plant is considered endemic to the region. It has an Area of Occupancy (AOO) of 4 km2. In view of the severe climate in the north of Chad,
particularly for an aquatic plant, we project a continuing decline of the area, extent and/or quality of habitat.
Bolboschoenus grandispicus (Cyperaceae)
Bolboschoenus grandispicus has only been reported from Senegal, Guinea-Bissau and Cabo Verde. However, it is now considered restricted to Senegal. This species is found at the edge of swamps in freshwater depressions behind the coastal dunes. The species is assessed as Critically Endangered based on a restricted AOO of 4 km2 and occurrence at one location, based on the threat of habitat degradation, which is resulting in a continuing decline in habitat. The only recently confirmed and currently extant subpopulation is near Dakar (Rufisque), which was found in 2014 (A. Mesterházy pers. obs. 2014).
Elatine fauquei (Elatinaceae)
The plant is known only from the type locality, the Ravin Balassogo (Balasoko) in Mali, in or around a fountain (spring) in a stony valley. Its AOO is very low at 4 km2 and it occurs in one location based on the threat from recreational activities.
Because this type of habitat is very fragile, we infer a continuing decline in the area of occupancy and area, extent and/or quality of habitat.
Eriocaulon adamesii (Eriocaulaceae)
Eriocaulon adamesii (CR (Possibly Extinct)) is a rare endemic in West Africa, known from few collections from Sierra Leone Figure 7.3 Dopatrium senegalense is a widespread species with no known major threats, assessed as Least Concern. This species colonises wet places such as rice paddies. This plant in Senegal is in full flower. © Attila Mesterházy
(Hepper, 2000) and one from Liberia, collected mainly in the 1960s. Recently, none of these collections have been reconfirmed. However, some potential sites need surveying for this species because there are still some remaining natural habitats which can be found near type locality. The most significant threat is habitat degradation as a consequence of increasing human activity, such as the building of houses, farms and plantations, and this has resulted in a continuing decline in habitat extent and quality. If extant, the species is expected to have an AOO of, at most, 8 km2.
Eriocaulon obtriangulare (Eriocaulaceae)
Eriocaulon obtriangulare (CR (Possibly Extinct)) has only been collected once from Côte d’Ivoire in 1967. Although the type locality is in Comoé National Park, where the influence of human activities is low, this species has not been found since the initial collection. The type locality was visited in 2013, but this species was not found (A. Mesterházy pers. obs. 2013).
As the site is in the north forest-savanna region, dry periods might become longer in the future with lower annual rainfall due to climate change, which might cause a negative effect to temporary pools. As this species has not been found since 1967, but suitable habitats remain at Comoé National Park where the species might appear in the future, it is assessed as Critically Endangered (Possibly Extinct). Further surveys are needed to look for this species in Comoé National Park.
The type specimens are all incomplete and so the taxonomic status of this species is not clear, and further research is recommended.
Inversodicraea abbayesii (Podostemaceae)
Inversodicraea abbayesii (CR (Possibly Extinct)) was previously assessed as Ledermaniella abbayesii (DD) in 2008 (Diop, 2010). Since that time, the species has been transferred to the genus Inversodicraea (Cheek et al., 2017), and a targeted survey for Podostemaceae including this species was made in January 2018 resulting in new data allowing a revised assessment (Cheek & Diop, 2018).
Inversodicrea abbayesii is endemic to Guinea, collected by Des Abbayes c. 1950, and known only from the single collection that he made at that time from the Grandess Chute de Kinkon, near Pita in the Fouta Djalon Highlands. Des Abbayes observed that it emerged to flower from the white water of the falls themselves. In January 2018, a team from the National Herbarium of Guinea with RBG Kew (funded by a Darwin Initiative project on Guinea Important Plant Areas), with expertise in Podostemaceae, visited the falls at the best season to rediscover this species (Couch et al., 2019). They found the species to be absent, probably because a hydro-electric dam constructed after the species was collected, has diverted much of the river flow around the falls, and has probably altered the natural hydrological pattern. In addition the river supplying the falls carries large amounts of silt (deposited on the rocks of the bank) and is contaminated
on its journey through the town of Pita where it is used for laundry and other purposes. Although locally extinct at the type locality, the species may yet be found at other sites, since several falls in Guinea have never been sampled for their plants. However, many species of this family are single-site endemics so it cannot be ruled out that this species is globally extinct. The species is therefore assessed as Critically Endangered (Possibly Extinct) (Cheek & Diop, 2018).
Inversodicraea pygmaea (Podostemaceae)
Inversodicraea pygmaea (CR (Possibly Extinct)) is only known from a single locality: the Grandes Chutes de Kindia waterfalls in Guinea. In January 2018, a team of four from the National Herbarium of Guinea with RBG Kew with expertise in Podostemaceae, visited the falls at the best season specifically to rediscover this species (Cheek, 2018). They found this species and all other Podostemaceae species to be absent, including even the most widespread, common and ecologically tolerant, Tristicha trifaria. A hydro-electric dam constructed in 1962 after the species was discovered, has diverted much of the river flow around the falls, and has altered the natural hydrological pattern. In addition, the stream below the dam is contaminated where it is used for laundry and as a latrine, explaining high algal growth, inimical to Podostemaceae, which are associated with clean, nutrient poor water.
Stonesia fascicularis (Podostemaceae)
Stonesia fascicularis (CR (Possibly Extinct)) is known only from the type locality, Grandes Chute de Kinkon, near Pita in the Fouta Djalon Highlands, c. 1950 (Cheek & Ouedraogo, 2018a), as per I. abbayesii (Cheek & Diop, 2018).
Stonesia gracilis (Podostemaceae)
Previously assessed as DD by (Ouedraogo, 2010) on the basis of sparse and erroneous information, the assessment of Stonesia gracilis was updated and revised to CR (Possibly Extinct) in 2018 by Cheek and Ouedraogo (2018b). This species, together with Inversodicraea pygmaea, is only known from the Grandes Chutes, Kindia but was recently found to be absent from the site ( Cheek and Ouedraogo, 2018b). There appears to be no evidence for records of this species in Cameroon and Sierra Leone, although occurrence in the latter is possible.
7.2.2 Endangered species
Commelina ascendens (Commelinaceae)
This plant, known from Nigeria and Ghana, is a herb found in
This plant, known from Nigeria and Ghana, is a herb found in