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2011 "Freshwater of : biodiversity, distribution, and conservation." Neil Cumberlidge Northern Michigan University

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Recommended Citation Cumberlidge, N. 2011. Chapter 6. Freshwater crabs of Africa: diversity, distribution, and conservation. [in] W.R.T Darwall, K.G. Smith, D.J. Allen, R.A. Holland, I.J. Harrison & E.G.E. Brooks (eds.). The Diversity of Life in African Freshwaters: Under Water, Under Threat. An Analysis of the Status and Distribution of Freshwater Throughout Mainland Africa. IUCN, Cambridge, UK and Gland, Switzerland. pp. 178-199.

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Cumberlidge, N.¹

¹ department of Biology, Northern Michigan University, Marquette, Michigan 49855, USa

The Purple March afrithelphusa monodosa (Endangered) which lives in swamps and year-round wetland habitats in north-western Guinea where it is known from only a few specimens from two localities. This species is clearly a competent air-breather and has a pair of well-developed pseudolungs. It is mainly threatened by habitat loss and degradation. © PIoTr NaSKreKI

An unidentifi ed species within the family . This specimen was collected in central Africa, a region noted for its limited fi eld sampling. © deNIS TweddLe

IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 178 4/3/11 18:59:15 The Purple March Crab Afrithelphusa monodosa (Endangered) which lives in swamps and year-round wetland habitats in north-western Guinea. © PIoTr NaSKreKI

Potamonautes lirrangensis (Least Concern), a relatively abundant and widespread species found in large slow fl owing rivers in across central and eastern Africa. © deNIS TweddLe

CONTENTS 6.1 Overview of the African freshwater crab fauna 180 6.1.1 Biogeographic patterns 182 6.2 Conservation status 183 6.3 Patterns of species richness 184 6.3.1 All freshwater crab species: interpretation of distribution patterns 186 6.3.2 Threatened species 187 6.3.3 Restricted range species 188 6.3.4 Data Defi cient species 190 6.4 Major threats 191 6.4.1 Habitat destruction 191 6.4.2 Pollution 192 6.4.3 Natural predators and competition with introduced species 192 6.4.4 Taxonomic issues 193 6.5 Research actions required 193 6.6 Conservation recommendations 195 Species in the spotlight – A unique species fl ock of freshwater crabs in : a model for studies in evolution and extinction 196 Species in the spotlight – The East African tree hole crab – spectacular 198

IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 179 4/3/11 18:59:21 IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 180 180 CHAPTER 6 | freSHwaTer CraBS 2006; Cumberlidge 2006; the daniels to2009a,b; 1999, (Cumberlidge belongPotamonautidae all that genera 10 in crabs freshwater of species includes africa 119 afrotropical of part This zone. (Socotra, the Seychelles, and ) that also lie in the desert, but excludes Sahara the islands of the western Indian the ocean of south countries african 43 all includes here with dealt afrotropical zone the of part The 2009). al. et ortmann, (yeo and 1896 1970, Bott, and (Potamonautes two in genera crabs freshwater of species three are there where egypt, and Tunisia, algeria, Morocco, are crabs freshwater the in afrotropical lies zone. that Thecountries continent ofnorthern africa african that host the of rest the and zone, includesnorthernPalaearctictheafrica in zoogeographical which africa, continental of crabs freshwater the on focuses yeo1999; Cumberlidge 1955; al .et 2008). The present work Bott 1936; Balss 1921; (rathbun bodies water smaller and rivers lowland large to streams mountain from habitats, and large these conspicuous are present andin almost all freshwater waters, inland african inhabiting freshwater crabs are among the most important invertebrates 6.1 Overview oftheAfricanfreshwater crab insmallstreams throughouttherainforestand savannazonesofwesternAfrica. The CommonCreekCrabLiberonautes latidactylus(LeastConcern)isthemostcommon andmostfrequentlycaughtfreshwater . 2009). and Ng2009;Cumberlidgeetal.2009). crab fauna . 2008; Cumberlidge2008;2009a,b; al.Cumberlidge et . 2008; yeo2008; al. et ad w families, two and Potamon) et al.et 2008; Cumberlidge et al. et et al. 2009) Tavares Cumberlidge 2008; dobson and Cumberlidge 2006; and Cumberlidge 2006; 2004, reed and Cumberlidge 2004; et al. 2001; Cumberlidge 1998, 1999, 2009a,b; Cumberlidge 1997, Cumberlidge and Boyko 1955; 2000; (Bott Corace fauna regional diverse less a have each genera) two species, (four africa northern and ) one species, (20 africa southern while genera), six species,(33three genera),western andafrica species,(24 easternareafricaspecies,(44 three genera), central africa more than one region. for example, the most diverse regions composition, faunal with crab freshwater only distinct a few a species has(14 out these of 120) offound in each and purposes of this project, subdivided into the Cumberlidge fi ve main regions, 1999; Cumberlidge 1955; (Bott Potamonautidae the family, and species levels with 100% endemicity for the freshwaterpredominant crab fauna is highly endemic (yeo Cumberlidge at the family, regions 2008; genus, families) al. two species, 849 genera, (154 species,families)genera,oriental/Palaearctic298twoand Neotropical (50 the of faunas freshwater crab the in seen 120species, two families) (Table 6.1) is markedly lower than The total taxonomic diversity of continental africa (11 genera, 20) Te fia cniet s fr the for continent african is, The 2009). al. et © PIoTrNaSKreKI et al. 2002; Cumberlidge and Vanini 20) Cnietl africa’s Continental 2009). al. et et et 4/3/11 18:59:24 CHAPTER 6 | freSHwaTer CraBS 181 4/3/11 18:59:26 Potamonautidae, Hydrothelphusinae Potamonautidae, Hydrothelphusinae Potamonautidae, Hydrothelphusinae Potamonautidae, Hydrothelphusinae Potamonautidae, Hydrothelphusinae Potamonautidae, Hydrothelphusinae Potamonautidae, Potamonautinae EE Potamonautidae, Potamonautinae E Potamonautidae, Potamonautinae E Potamonautidae, Potamonautinae E Potamonautidae, Potamonautinae E Potamonautidae, Potamonautinae E Potamonautidae, Potamonautinae E Potamonautidae, Potamonautinae E Potamonautidae, Potamonautinae Potamonautidae, Potamonautinae SS Potamonautidae, Potamonautinae S Potamonautidae, Potamonautinae S Potamonautidae, Potamonautinae S Potamonautidae, Potamonautinae S Potamonautidae, Potamonautinae S Potamonautidae, Potamonautinae S Potamonautidae, Potamonautinae S Potamonautidae, Potamonautinae Potamonautidae, Potamonautinae NN Potaminae Potamidae, N Potamidae, Potaminae N Potaminae Potamidae, Potamidae, Potaminae CC Potamonautidae, Potamonautinae C Potamonautidae, Potamonautinae C Potamonautidae, Potamonautinae C Potamonautidae, Potamonautinae C Potamonautidae, Potamonautinae C Potamonautidae, Potamonautinae Potamonautidae, Potamonautinae W Potamonautidae, Potamonautinae W Potamonautinae Potamonautidae, WW Potamonautidae, Potamonautinae W Potamonautidae, Potamonautinae W Potamonautidae, Potamonautinae Potamonautidae, Potamonautinae WW Potamonautidae, Potamonautinae W Potamonautidae, Potamonautinae W Potamonautidae, Potamonautinae W Potamonautidae, Potamonautinae W Potamonautidae, Potamonautinae Potamonautidae, Potamonautinae W Potamonautidae, Potamonautinae 1 1 1 1 1 1 1 2 1 3 3 2 2 1 2 1 2 1 1 1 3 2 2 1 1 2 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 2 1 3 4 3 No. Genera Region subfamily Family, 1 1 1 1 2 8 1 5 2 6 6 4 2 1 2 2 2 2 1 1 8 4 3 1 3 1 1 6 2 4 1 1 4 5 2 1 3 4 1 3 3 24 13 12 24 14 10 13 11 No. Species Country 1 Morocco 7 Guinea 89 Côte d’Ivoire 10 Ghana 11 Togo Sierra Leone 1213 Benin 14 Chad 15 Mali 16 Mauritania 17 Burkina Faso 18 Niger D. R. Congo 26 Somalia 2728 Ethiopia Kenya 2930 Uganda 31 Rwanda 32 3334 Malawi 35 Angola 36 Botswana 37 Lesotho 38 Mozambique 39 Namibia 40 South Africa 41 Swaziland 42 Zimbabwe 23 Algeria 4 Tunisia Egypt 56 Nigeria Liberia 1920 Cameroon 21 Congo 22 Gabon 23 Central African Republic 24 Equatorial Guinea/Bioko 25 Angola (Cabinda) Sudan Table 6.1. Numbers of species, genera, families and subfamilies, and their regions of occurrence, for each of for each of occurrence, regions and their and subfamilies, families genera, of species, Numbers 6.1. Table e africa, central = C africa, western = w africa, northern = crabs. N has freshwater in Africa that the 43 countries = easternsouthern africa, S = africa.” IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 181 IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 182 182 CHAPTER 6 | freSHwaTer CraBS africa, e = eastern africa, N = northern africa. africa,N=northern africa, e=eastern occurrence, andasummary oftheirconservationstatus. C = central africa, w = western africa, S = southern Table 6.2.Thethreatened speciesoffreshwater crabsfoundincontinentalAfrica,withtheirregions of patterns and freshwater ecoregion boundaries found in the distribution crab freshwaterbetween correlation close no exceptions,isthere fewHowever, 2008). a al. only withet Southern Temperate and freshwater Zambezi,ecoregions) (Thieme Cuanza, Coastal, and eastern Upper Guinea, west Coast equatorial, Congo, Great continent’s Lakes, the of freshwater ecoregions most (e.g., the North african, Nilo-Sudan, in represented also are crabs freshwaterecosystems, africa’saquatic inrepresentation and drain forested highlands. Because of their widespread africa, especially those that fl ow through lowland highest in the rivers and streams of the major is river basins diversity of Species ground. above resources freshwater are there where dry systems xeric rapids, even and rivers, river savanna large lakes, large systems, mountain and highland systems, Mediterranean rivers, forest moist lakes, fl swamps, including oodplains, africa, continental in types habitat major all in found are crabs freshwater 6.1.1 Biogeographicpatterns 7 6 5 4 3 2 1 8 9 10 11 14 13 12 18 17 16 15 19 20 21 22 23 24 26 25 Species Louisea balssi Liberonautes rubigimanus Liberonautes nanoides Globonautes macropus Afrithelphusa monodosa Liberonautes lugbe Liberonautes grandbassa Louisea edeaensis Potamonautes gonocristatus Potamonautes idjiwiensis Potamonautes mutandensis Potamonautes choloensis Liberonautes nimba Potamonautes platycentron Potamonautes lividus Potamonautes infravallatus Potamonautes ignestii Potamonautes gerdalensis Potamonautes montivagus Potamonautes pilosus Potamonautes raybouldi Potamonautes reidi Potamonautes triangulus Potamonautes unisulcatus Potamonemus sachsi Potamonautes xiphoidus et al. 2005; abell itiuinRdLs aeoyRedListCriteria RedListCategory Distribution Regional W/C C/E C/E W W W W W W W W W C C C S E E E E E E E E E E species that have a restricted distribution. distribution coincides with ecoregion boundaries are those africanregion.instancesonlywhereThe freshwater crabs least twofreshwatercrabsspecies. The White Volta River as an example of suitable habitat for at CR CR EN EN EN EN EN EN EN EN EN EN VU VU VU VU VU VU VU VU VU VU VU VU VU VU B1ab(iii,v)+2ab(iii,v); C1+2a(ii) B1ab(iii)+2ab(iii); C2a(i) B1ab(iii)+2ab(iii); C2a(i) B1ab(iii)+2ab(iii); D2 B1ab(iii)+2ab(iii); D2 B1ab(i,iii)+2ab(i,iii) © KLaaS-doUwedIJKSTra B1ab(iii)+2ab(iii) B1ab(iii)+2ab(iii) B1ab(iii)+2ab(iii) B1ab(iii)+2ab(iii) B1ab(iii)+2ab(iii) B1ab(iii)+2ab(iii) B1ab(iii)+2ab(iii) B1ab(i,ii,iii); D2 B1ab(i,ii,iii,iv,v) B1ab(i,ii,iii,iv,v) B1ab(i,iii); D2 B1ab(i,ii,iii,v) B1ab(i); D2 B1ab(i); D2 B1ab(i); D2 B2ab(iii) B1ab(iii) B2ab(iii) B1ab(i) B2ab(i) 4/3/11 18:59:28 CHAPTER 6 | freSHwaTer CraBS

The Purple March Crab afrithelphusa monodosa (Endangered) which lives in swamps and year-round wetland habitats in north- western Guinea where it is known from only a few specimens from two localities. This species is clearly a competent air-breather and has a pair of well-developed pseudolungs. It is mainly threatened by habitat loss and degradation. © PIoTr NaSKreKI

6.2 Conservation status with 26 (21%) of the 120 species assessed as globally Threatened (Table 6.2 and 6.3, and figure 6.1a). There is The conservation status of africa’s freshwater crab fauna insuffi cient information to assess the status of 27 species was assessed by Cumberlidge et al. (2009) using the which were categorised as data defi cient (dd) due to a lack IUCN red List Categories and Criteria at the global scale specimens, and locality and population data (Cumberlidge (IUCN 2003), and individual species assessments are et al. 2009; Table 6.3, and figure 6.1a). If all data defi cient freely available through the IUCN red List website (www. (dd) species also proved to be Threatened, the level of iucnredlist.org). results reveal current high levels of threat threat could be as high as 44%.

Figure 6.1. The proportion (%) of freshwater crab species in each regional IUCN Red List Category in mainland continental Africa (Cumberlidge et al. 2009, Appendix 1): a) all 120 species from the region; and b) following removal of the 27 DD species.

183

IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 183 4/3/11 18:59:32 IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 184 184 CHAPTER 6 | freSHwaTer CraBS species of freshwater crabs from africa could be confi rmed ThreatenedNearNo (NT).were assessedas(3%) species three Just 6.3). Table and 6.1b (figure species) (14 (VU) Vulnerableorspecies) species),endangered(10(two (eN) three of threatened one categories, either as Critically in endangered (Cr) listed were species assessed 94 the of pce of species of species eight of species nine the of eight of species 11 the of eight Potamonemus, of Cumberlidge mountain or lowlands, marshy streamsforestedthein partsafricaof(Cumberlidge 1999; rivers, in live most these and (LC), of Concern Least be to judged were and genera seven to belong 6.1b) figure 69%, species, (65 majority the assessed, be could that species 94 the of found in both C + S). C = central africa, w = western africa, S = , e = eastern africa, N = northern africa. africa,N=northern africa,e=eastern africa,S=southern found inbothC+S).=centralafrica,wwestern both e+ C, e + S, and S + C + e); eN includes two species that are found infi both C + e); vedd speciesincludes that one arespecies found that in isboth w + C, two species that arewith found an * in= totalboth especies + N, and per one region species including each that those is foundspecies in that are foundAppendix 1).The in total more number than oneof speciesregion. per for Category example, does LC includesnot include species found in Tablemore 6.3. than one region. Numbers of breathingair. during rainstormsitisoftenfound onlandbecauseitiscapable and ponds,digsburrowsnear waterways;atnightand Equatorial Guinea.Thislargespecies inhabitsstreams,rivers, border of the Campo Maan National Park on the border to Central Africa. This specimen was collected on the western widespread speciesfoundthroughoutmuchofwesternand Aubry’s CrabSudanonautesaubryi(LeastConcern)isa IUCN RedListCategory Least Concern Near Threatened Vulnerable Endangered Critically Endangered Total speciesperregion* Data Defi cient Potamonautes are LC, as are one of the three species of . 2009, The numberofAfricancrabspeciesineachIUCNRedListcategorybyregion (Cumberlidgeetal.2009, and Erimetopus et al. 2009). © JeNSKIPPING ad n ec o te two the of each one and Liberonautes, forty-three out of the 76 species Tet-i (28%) Twenty-six Potamon. tre f the of three , *2*3*4*20* 44* 31* 24* 2* S E C W N 01 415 0 1 24 0 2 0 9 16 4 0 0 1 10 2 0 0 3 2 4 0 2 0 0 0 51 4 5 12 5 0 Sudanonautes, REGION central africa(Brooks etal . 2011). africa (Smith western 2008), daniels and (Cumberlidge africa (darwall africa eastern for available also are statusregional species’ of assessmentsdetailed extinct untilexhaustivesurveyshavebeencarriedout. as assessed formally be cannot species a that noted be (ew).However,wildtheextinct extinctin or(eX) shouldit dnia frs aes ht ae gain o declining thereexample, of for (Cumberlidge 1999).numbersspecies gradient a have that areas forest apparentlyidentical by surrounded diversity biotic high of areas is forests african in species of distribution the by shown pattern interesting one ecosystems. savanna in fewest the and areas, highland in especially ecosystems,rainforest in occurring species of number highest the with water, of appearstodepend onvegetation cover and the availability diversity Species 1999). (Cumberlidge regions highland in rainforest,especiallythe in abundantmorenoticeably are found in all of the major ecosystems are in crabs freshwater continental example, for cover. africa, vegetation andbut region, and varies with ecosystem, aquatic drainage basins, crabfaunaafricain notuniform, is changes from region to available data indicate that The the distributions. actual composition their ascertainof the to necessaryfreshwater are collectionsfurther cases these in andrecords, few from a just or locality the either from only known are that somestill studied,arethere well quite arespecies african the of majority a although incomplete. be to likely still are but records specimen available all from derived been have (Cumberlidge1999;Table 6.1).distribution hereuseddata species all with endemic to the continent, fauna, and distributed over 43 countries crab freshwater recognisable distinctly and diverse, highly rich, a has africa Continental ofspeciesrichness 6.3 Patterns . 2009), northern et africa al. (Garcia2009), northern Red ListCategory Total speciesper . 2005), southern 2005), al. et 117 14 10 64 25 2 2 et al. 2010), and 4/3/11 18:59:35 CHAPTER 6 | freSHwaTer CraBS 185 4/3/11 18:59:38 et al. 2000), Erimetopus are has a number of number a has is found REGION Potamon 2 6 6 4 1 Louisea and © deNIS TweddLe 9 0 0 9 9 0 8 0 7 0 0 0 4 0 4 0 0 0 3 0 1 2 0 0 2 0 0 0 2 0 2 0 0 2 0 0 2 0 0 2 0 0 1 1 0 0 0 0 1 0 1 0 0 0 76 2 4 23 33 19 11 0 5 5 1 0 Potamonautes Genus # Species N W C E S Sudanonautes Platythelphusa Liberonautes* Afrithelphusa* Potamonemus Deckenia* Erimetopus* Louisea* Potamon Globonautes* Genera /region endemic to western africa, both found only in central africa, and easternin only although africa. wide distributional ranges in the Mediterranean and Middle and Mediterranean the in ranges distributional wide east as far east as the Himalayas (Brandis within africa this genus is found only in the Palaearctic zone of northern africa. Table 6.4. Number of species and genera found in in found genera and species of Number 6.4. Table western = w africa, northern = N in Africa. each region southern = S africa, eastern = e africa, central = C africa, endemic. regional africa. * =

and for example, for Sudanonautes Potamonautes, Platythelphusa Liberonautes are all and include some widespread widespread some include Liberonautes (Least Concern) is a relatively abundant and widespread species found in large slow fl owing rivers in in rivers owing fl slow large in found species widespread and abundant relatively a is Concern) (Least Potamonautes lirrangensis shery in Malawi. rainforests across central and eastern Africa. It is subject to a small commercial fi Afrithelphusa, Globonautes species, and some species that are endemic to a particular a to endemic are that species some and species, region. In contrast, six genera have a relatively restricted region. particular a to endemic are and range is found in three Potamonemus regions, occur while in and Sudanonautes, two regions. are three relatively small areas of the african rainforest that that rainforest african the of areas small relatively three are stand out as having an unusually high number of species the and of a species: number than endemic normal higher Upper Guinea forest in western africa, the Lower Guinea of eastern and the forests and Cameroon, in Nigeria forest 1999). (Cumberlidge Congo r. d. at the genus level the taxonomic diversity is highest western in and central africa (six genera), lower in eastern africa (four genera), and lowest in northern genera) africa (two and (with region rich southern species most the is africa africa eastern although (one genus) (Table 6.4). 44 species in three genera and two subfamilies), western africa stands out as the most diverse (with 24 six species, genera and two subfamilies) (Table 6.4). distribution patterns considered at the genus level indicate that each of ve the african fi regions has genera with have that species species other many and that distribution, wide a have a restricted distribution. five out of eleven genera have a wide distribution in more than one region. for example, Potamonautes is found in ve all regions, fi IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 185 IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 186 186 CHAPTER 6 | freSHwaTer CraBS 19; ubrig 19, 98 19, 2009a,b; 1999, 1998, Corace 1997; Stewart 1997, Cumberlidge 1995; al. et of Stewart number 1970; 1969, 1959, largest 1955, (Bott, africa the in species far by includes Potamonautes 6.3.1 All freshwater crabspecies:interpretation of western africa; the western limit of the genus is Senegal, is genus the of limit western the africa; western Liberonautes of species eight The 1999; CumberlidgeandBoyko 2000). (Cumberlidge africa central in distribution restricted a have species, two other the are widespread throughout western and centralof species africa, 11 whilethe of eight savanna. Sudan monodi is the only species found in both Guinea and in dry savanna in Nigeria, while the semi-terrestrial air-breathing savanna. woodland andrainforest both flin found S. are while and oweri habitats, rainforest in exclusively occur chavanesii S. orthostylis, S. granulatus, land. on and rivers) (standingwater,majorhabitatsaquatic andstreamsmost in found are and savanna), Sudan and Guinearainforest, (tropical africa central and western of ecosystems major of island of the Species Bioko. on and Cameroon, south-west Nigeria, species africa 6.2) (figure eastern1999) in Sudan 1995,a,b,c,d, 1994b, and 1993b,c, 1991, 1989, Uganda (Cumberlidge as east far as fl reaching (S. oweri) species one with africa, central and western in distributed species 11 includes Sudanonautes Niger riverfl ows through Timbuktu(Cumberlidge1999). is even found in the Sahara desert in Mali, but only where ecorssei) (Potamonautes species one river). Nile the thealong found widespreadspecies (both africa northern in two and of species (33, 24, and 20 species respectively), and there are only four Potamonautes forested Congo river basin. The vast majority of species of species of are endemic to a very restricted area. The largest numbers of air-breathing habit, semi-terrestrial while others have a a narrow distribution adopted and have some continent, the throughout basins river major the with associated are and of species Some region. Palaearcticzoogeographicalthe in lies Maghreb)that (the coastalthedoesoccurinnotis fringe north-west of africa Potamonautes where region only The 6.2). (figure africa of Horn the to Senegalfrom andCairo, to Cape the from africa sub-Saharan throughout distributed are and africa, fiall in foundare regionsofgenus large thisve ofspecies and Tavares 2006; Cumberlidge and dobson 2008). The 76 Cumberlidge 2000; Boyko and Cumberlidge Cumberlidge 2006; 2004, and reed 2004; Vanini and Cumberlidge distribution patterns r fud n h frse rgo o south-east of region forested the in found are Sudanonautes kagoroensis occurs only in Guinea occur in eastern africa and in the africa and in the Potamonautes occur in eastern in western africa (all endemic), endemic), (all africa western in Potamonautes occur in eastern, central, and southern africa Te ags nmes of numbers largest The . Sudanonautes africanus, S. nigeria, S. S. nigeria, S. africanus, Sudanonautes cu i ms o the of most in occur Sudanonautes . 2001; Cumberlidge 2001; al. et and orthostylis S. Potamonautes r al etitd to restricted all are and , each sangha, S. r widespread are Sudanonautes Sudanonautes S. faradjensis S. . 2002; 2002; al. et . aubryi S. S.

© JeaN-PIerreBoUdoT population growthandindustrialagrariandevelopment. threats such as habitat loss and degradation linked to Tunisia. ItisLeastConcernandaffectedbyhumaninduced endemic tothestreamsandriversofMorocco,Algeria The freshwatercrabPotamonalgeriense(Least Concern) is africa. western of forest Guinea Upper the of part western the in 1996a,b; 1999). The four species of 1991, Cumberlidge 1991; Sachs and (Cumberlidge forest canopy closed in holes tree in reservoirs water small in of the Upper Guinea forest in Liberia and Guinea, and lives the Liberian Tree Hole Crab, occurs only in the western part 1992; Cumberlidge 1993a; 1999). Globonautes macropus, Clark and (Cumberlidge feed to night at water the leave probably and streams small in occur species These 6.2). Togo western (figure and Cameroon, south-west Nigeria, south-east of highlands forested the in africa central and The three species of Potamonemus occur in only in western nanoides are foundexclusivelyinthe majorrivers. and altitudes, high at found are nimba L. paludicolisismore terrestrial andL.rubigimanus are found in aquatic habitats (streams or major rivers) while species Most zones. savanna Sudan and Guinea both in although rainforest, in mostly of Species d’Ivoire. Côte and seven remaining the while species each have a limited distribution in Liberia, Guinea, genus, the of range entire the over widespread is latidactylus) (L. species one 6.2). (Cumberlidge 1999; Cumberlidge Mali and is Huguet 2003) limit figure( northern the and Ghana, is limit eastern the other species, other is relatively widespread in the lower Congo river, while the of species two the of one 1999). 1994a, (Cumberlidge rainforests lowland moist the and highlands forested the in Cameroon south-west in only of species two The 1999). 1996a,b; 1991; 1987, (Cumberlidge Leone Sierra from known only while Guinea, in only found al. 2009). all nine species of distribution (Cumberlidge and reed 2004; Cumberlidge Afrithelphusa gerhildae and E. vandenbrandeni, E. Platythelphusa A. afzelii A. is also found also is latidactylus L. r found are Liberonautes Erimetopus ( Afrithelphusa is more restricted in its in restrictedmore is A. monodosa are both and r found are Louisea and chaperi L. are leonensis A. are endemic to E. brazzae) E. occur only et L. 4/3/11 18:59:40 CHAPTER 6 | freSHwaTer CraBS 187 4/3/11 18:59:46 ), ). L. balssi). P. xiphoidus), four and P. and P. ) gonocristatus P. lividus (P. southernafrica from one nimba), L. and P. idjwiensis, (P. africa eastern from four rubigimanus), L. central africa (the most speciose region) and in southern just africa one (figure 6.3). There are no threatened species in the northern africa region. of the threatened species, 10 were assessed as eN, of which four are from western africa (A. monodosa, G. macropus, L. nanoides, and P. mutandensis, P. platycentron, and two from central africa (L. edeaensis and None of the species from southern africa was assessed as eN. a further fourteen species were assessed as VU, of which nine are from eastern africa (P. gerdalensis, choloensis, P. ignestii, P. P. infravallatus, P. montivagus, P. unisulcatus, raybouldi, P. pilosus, P. from western africa reidi, triangulus, (P. P. Potamonemus sachsi, et

2005). one 2005). al. et et al. 2009; figure Deckenia are endemic to P. algeriensis) is found in continental P. . 1995; Marijnissen 1995; al. et Potamon ( species of africa and is endemic to the Mahgreb in northern africa (Brandis et al. 2000; Cumberlidge 2009a). species 6.3.2 Threatened Some 28% threatened (26 three out the of of 94 one in species) being of as african assessed freshwater were crabs categories (Cr, eN, VU) (Cumberlidge 6.1a; Table 6.5). Most of these (20 species) are found in either eastern africa (11 species) or western africa (nine species), and there are only three threatened species in al. 2004), while both species of (Ng africa eastern Lake Tanganyika (Cumberlidge Lake et Tanganyika al . 1999; Marijnissen Figure 6.2. The distribution of freshwater crab species across mainland continental Africa. Species richness = richness Africa. Species continental mainland across crab species of freshwater distribution 6.2. The Figure sub-catchment. river/lake per species of number IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 187 IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 188 188 CHAPTER 6 | freSHwaTer CraBS IUCN RedListCategory. Table 6.5. Number of species from each genus in each richness = number of species per river/lake sub-catchment. Figure 6.3. oa pce 431 0227 2 10 14 3 64 Total species Globonautes Potamon Louisea Erimetopus Deckenia Potamonemus Afrithelphusa Liberonautes Platythelphusa Sudanonautes Potamonautes Genus The distribution of Threatened freshwater crab species across mainland continental Africa. Species CN UE RDD CR EN VU NT LC 301 18 0 4 12 0 43 0 0 0 0 0 1 1 0 0 0 0 0 1 2 0 0 3 0 0 0 0 0 0 1 0 0 0 1 0 0 2 0 0 3 1 0 0 1 0 2 2 0 0 1 0 0 1 0 0 0 0 1 0 0 0 0 3 0 8 8 IUCN REDLISTCATEGORY

a lackaknowledgeof under-collection.or These species are from stemming errors omission of product a simply not are species these of distributions (figurelimited africa The 6.4). restricted range species are irregularly distributed throughout L. grandbassa (L. species Two africa). western and one from central africa (P. sachsi, which is also found in have a restricted range (<20,000km range restricted a have to found were species 29 some species, dd excluding 6.3.3 Restrictedrangespecies habitat degradationandpollution. aquatic associated the and development agricultural and threatsto these species were identifi edas urban, industrial, easternafrica)fromNT.(bothassessedweremainasThe species, two Just western fromafrica. are which of both Cr, as assessed were

and imitatrix Deckenia 2 ) (Table 6.6), and these these (Tableand ) 6.6), and L. lugbe) L. . mitis D.

4/3/11 18:59:53 CHAPTER 6 | freSHwaTer CraBS 189 4/3/11 18:59:55 E E E E E E E E E E E E E S C C C C C C W W W W W W W W W W Region © wINKS eMMerSoN Y Y Y Y N N N N N N N N N N N N N N N N N N N N N N N N N N PA 2 5 1 3 2 1 1 3 8 6 4 7 <5 <5 <5 <5 <5 <5 <5 <5 <5 <10 <10 <10 <10 <10 <10 <10 <10 <10 < 5,000 < 20,000 < 5,000 < 5,000 < 5,000 < 20,000 < 5,000 ~ 100 ~ 100 < 5,000 < 500 < 500 < 500 < 20,000 < 800 < 20,000 < 20,000 < 20,000 < 2,000 < 20,000 < 20,000 < 20,000 < 2,000 < 20,000 < 20,000 < 20,000 < 20,000 < 20,000 < 20,000 < 5,000 (Vulnerable) is a The Blue River Crab Potamonautes lividus (Vulnerable) relatively restricted range species endemic to swamp forests in north-eastern Kwa-Zulu Natal, South Africa. (and 2 or less). or 2 LC LC LC LC VU VU VU VU VU VU VU VU VU VU VU VU VU VU EN EN EN EN EN EN EN EN EN EN CR CR RL Category (km2) Range # Loc Liberonautes lugbe Afrithelphusa monodosa Globonautes macropus Liberonautes nanoides Liberonautes rubigimanus Louisea edeaensis Liberonautes grandbassa Species Louisea balssi Potamonautes gonocristatus Potamonautes idjiwiensis Potamonautes mutandensis Potamonautes platycentron Erimetopus brazzae Potamonautes margaritarius Potamonemus mambilorum Potamonemus sachsi Potamonautes montivagus Potamonautes pilosus Potamonautes raybouldi Potamonautes reidi Potamonautes triangulus Potamonautes unisulcatus Potamonautes xiphoidus Liberonautes nimba Potamonautes choloensis Potamonautes gerdalensis Potamonautes ignestii Potamonautes infravallatus Potamonautes lividus Sudanonautes kagoroensis despite despite the dangers of population current fragmentation, population levels of stenotopic species assessed as LC or NT were estimated to be stable because they have been Table 6.6. Table Species of freshwater crabs of Africa restricted to single river basins, excluding cient. rL those = IUCN red considered be List Data status; toDefi LC = Least Concern; VU = Vulnerable; eN = endangered; Cr = Critically range = endangered; an of estimation range the based on species distribution all #Loc known = specimens; Number of y of= yes, N = no; area; regions = found in a protected which the species was discontinuous collected; localities Pa from N = northern noted as africa, w = westernafrica are = eastern C = central africa, e africa, africa, S = southern africa. specifi cally specifi recorded, through many surveys conducted over the years, as being absent in localities they maywhere habitats the to disruption any occur. to expected been have of that these given species consequences, (either serious from have development, pollution, could or unrest) political as assessed been have species range restricted these of 24 is range restricted a with species any 6.6). (Table Threatened to fragmentation vulnerable population extreme potentially and could a suffer and rapid in decline, even a extinction, concern immediate of relatively short therefore time is should It dramatic habitat. changes in its land-use affect suddenly that 24 of the 94 crab species that could be assessed are distribution ranges known of from less than 20,000km some of these have an estimated range of 5,000km of range estimated an have these of some IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 189 IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 190 190 CHAPTER 6 | freSHwaTer CraBS . adnrnei P acristatus, P. vandenbrandeni, (E. africa central from are species(Tabledddd figurethe6.1a).Thirteenbe6.3, of to judged were assessed (28%) species 94 the of 27 Some 6.3.4 DataDeficient species al. 2009). et Cumberlidge 2008; (Cumberlidge decline in now species theirbeing the remnant populations of formerly widespread (marginal)habitat or through island colonization, rather than specialised a isolation in response to relatively recently in speciatedhave they thatlikelythought is it butunknown, largelystenotopicarespeciesthe restricted ofranges the for reasons The existence. long-term streams their those endanger and of health the impact would that threats identifi immediate no able are there and recently collected mainland continentalAfrica.Speciesrichness=numberofspeciesperriver/lakesub-catchment. Figure 6.4.Thedistributionoffreshwater crabspecies withseverely restricted distributionalrangesacross in view of the absence of recent information on their extent extent their on information recent of absence the of view in found in recent years. These species have been listed as dd concern that in many cases these dd species have not been Cumberlidge 1999; Cumberlidge 1955; (Bott species little-known these of distributionthe specimens of lackavailable, a scarcity generalthat continues to fuel refluncertainty the about species ects dd of relativelyproportionThehigh dd. be tofound wereafrica macrobrachii) (figure 6.5). None of the species from northern three are fromafrica(P. southern kensleyi,P. dubius,and P. bipartitus, P. didieri, P. rodolphianus, (P. praelongata, P. amalerensis, P. africa eastern from are gerhildae, A. leonensis, P.senegalensis, leonensis, A. gerhildae, A. afzelii, A. ( africa western from fi are sangha), ve S. and P. schubotzi, punctatus, P. P. semilunaris, Potamonemus lueboensis, asylos, S. P.orthostylis adentatus, P. adeleae, P. . 2009). It is of greatof is It2009). al. et and P. rothschildsi), and S. nigeria), S. and

six

4/3/11 19:00:02 CHAPTER 6 | freSHwaTer CraBS 191 4/3/11 19:00:09 6.4 Major threats 6.4 Major threats water include crabs freshwater african to threats main The pollution, urban, industrial, and agricultural development, and habitat loss and deforestation resulting from human population and urban and agricultural expansion (figure 6.6). 6.4.1 Habitat destruction destruction habitat include species endemic the to Threats in the form of deforestation driven by timber extraction, mining, increasing agriculture, the demands of increasing industrial development, the alteration rivers of for the fast creation owing of fl hydroelectric drainage power, of wetlands and for farming the and other uses (figure E. S. S. and or where they are known from either only , vandenbrandeni) of occurrence, habitat, ecological requirements, population population requirements, ecological habitat, occurrence, of (Cumberlidge threats long-term and trends, population size, et al. 2009). It is also of concern that many of these species years many collected individuals few a from only known are recently. found been have specimens new no that and ago, The dd status is also assigned where cient there is insuffi information either on their taxonomic distinction (e.g. P. schubotzi, S. orthostylis S. schubotzi, (P. localities few a only or one ) and the full range extent is uncertain. It is possible It is possible is uncertain. extent range sangha) full the and that in some cases the dd status may be sampling due but, as to mentioned above, this is under- not thought to is research further species. dd the of many for case the be may they at least, because, species of on these all needed habitat to vulnerable endemics range restricted be to prove loss. Figure 6.5. The distribution of Data Defi cient freshwater crab species across mainland continental Africa. Species Species Africa. continental mainland across species crab freshwater cient Defi of Data distribution 6.5. The Figure per river/lake sub-catchment. = number species richness IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 191 IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 192 192 CHAPTER 6 | freSHwaTer CraBS towns in africa include pollution by sewage and industrial and sewage by pollution include africa in towns to and cities with associated threats rivers in communities future aquatic Potential ecosystems. freshwater to damage environmental contributes that erosion soil and movements, refugee which are often and accompanied unrest bydeforestation political include destruction habitat and deforestation in result that threats of other forest. parts the undisturbed provide previously and that remote roads to access logging by exacerbated africa further of is parts many in forests the of destruction 6.6). Figure 6.6.Majorthreats tofreshwater crabspeciesinmainland continentalAfrica. region oftheUpper GuineanRainforest. Deforestation nearthevillageSimpa inwesternGhana,the © JoHaNNeSfÖrSTer ges hrn, in knfises mntr lizards, monitor kingfi shers, giant herons, kites, egrets, civets, african mongooses, water otters, necked yellow- including – predators african of number large a 6.4.3 Natural predators andcompetition with health of people that may eat them. the increasingforproblem an pose couldcrabs in metals bioaccumulation of the because least not areas, these in quality water the of improvement the to given be should attention Immediate contaminants. of levels high contain benthic feeders arethat ingest other invertebrates and detritus theythat may because populations crab freshwater rivers and other freshwater bodies. These pollutants impact sewage systems in urban areas in africa can accumulate in ironore,andcoltan, andfromorganic wastes fromleaking Pollutants from mining activities for diamonds, gold, bauxite, 6.4.2 Pollution survival. long-term their on impact biggest the have will future the in resources water careful and forests the africa’s of and management species, endemic threat range-restricted of level to overall the increase to combine factors above the of all out. carried be to needs research more but crabs, freshwater to lethal be to prove may farmers by used pesticides agricultural Some waste. general and introduced species 4/3/11 19:00:13 CHAPTER 6 | freSHwaTer CraBS 193 4/3/11 19:00:15 et S. P. P. lirrangensis and that are all currently assessed as LC primarily 6.5 Research actions required 6.5 Research cant Signifi areas of ciently this insuffi explored, vast and new continent species of still crabs freshwater are remain sure to be discovered if remote collection areas efforts in are ed intensifi and cation taxonomic identifi of form the in available readily more become advances keys. although taxonomic knowledge considerably has recently, advanced and freshwater crabs have museum improved, a great collections deal still needs to be done. There of is a need for further surveys work of al. 2002). recently, some recently, taxa currently assumed to be widespread and common may prove to distinct be cryptic complexes taxa, of each several c with ecologies specifi distributions and requiring direct conservation action. Three such possibilities are P. perlatus, granulatus on account of their wide distributional ranges. However, the distribution patterns of these species consist of many relatively isolated subpopulations that show a great deal of morphological variation, and further investigations may show these species to be species complexes (daniels Platythelphusa Procambarus clarkii is rapidly et al. 2009). The ecological importance of (Howard, pers. comm.). (Howard, issues 6.4.4 Taxonomic The evolving of freshwater crabs may to prove be a challenge for conservation planning in the future because, although a lot of progress has been made spreading elsewhere in eastern africa and may even reach reach even may and africa eastern in elsewhere spreading Lake Tanganyika, where it could threaten populations of freshwater crabs in the endemic genus freshwater freshwater crabs in food webs in africa is underlined by (Procambarus sh crayfi american North alien of impact the out-competed which Kenya, western of rivers the in clarkii) crab freshwater in drop The crabs. native the replaced and populations in these systems led to a subsequent decline in clawless otter populations that fed likely due on to increased competition crabs, with other most predators Harper and (foster sh crayfi of abundance the by attracted 2006, 2007; ogada 2006). recent reports indicate that the highly competitive and crocodiles – depend on crabs freshwater because is This freshwater diet. their of components crabs as vital are the largest macro-invertebrates in ecosystems and african form an aquatic integral part of the food chain (Cumberlidge Pollution from urban and domestic sources is a major threat to threatened freshwater crab species. © raNdaLL BrUMMeTT Pollution from urban and domestic sources IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 193 The Louisiana Crayfish Procambarus clarkia has become seriously invasive throughout inland waters in Africa. It is omnivorous and will hunt and compete with the native freshwater crab species. © Geoffrey Howard

IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 194 4/3/11 19:00:19 CHAPTER 6 | freSHwaTer CraBS 195 4/3/11 19:00:20 et al. 2009) represents rst a step fi and streams. The increasing loss of natural vegetation and vegetation natural of loss increasing The streams. and pollution as a result of land development and agriculture are, however, likely to affect the long lowland term, and rivers many of in the the wholly aquatic species that live there could eventually be vulnerable. even species assessed as declines LC should catastrophic could suffer there be abrupt changes in land development, hydrology, highland the how known not is It regimes. pesticide-use or taxa will cope with habitat disturbance and pollution but, considering their specialised habitat as readily as requirements, adapt not will it species these of most is that likely the more widespread lowland species. In many countries with a rapid pace of development, often ne only line a fi separates a species assessed as LC from one assessed as VU, or a VU species from one that is assessed as eN. development projects could have a dramatic impact restricted a on and requirements habitat c specifi with species distribution. Conservation activities should therefore be aimed primarily at preserving the integrity of habitats sites while and at the same time closely monitoring crab populations. freshwater key The 27 species of african freshwater crabs judged to be of result the as primarily category this to assigned were dd specimens available of scarcity The survey. eld fi cient insuffi is in some parts of the continent due poor to security situation, the and long-term as a result little is known of the habitat needs, population trends, or threats to these species. when more information has been gathered, it is expected that almost all dd species will have a relatively restricted distribution and be endemic to the river basin found. are they where The conservation assessment of africa freshwater (Cumberlidge crabs in cation of threatened toward species the within identifi the region and toward the development of strategy a for conservation endemic species. The human-induced on-going the with together species, many restricted range of loss of habitat in many parts of the region, are causes of concern survival of this fauna. for the long-term primary endemism, of degree high a have crabs freshwater africa’s with many species living in specialised habitats such as river rapids, lowland marshes, forested determine to highlands, recommended is research additional islands. and the minimum effective size and design of protected areas species such as crabs. for freshwater et et al. 2008; Cumberlidge 6.6. Conservation recommendations 6.6. Conservation crabs freshwater the of patterns distribution and biology The of africa are becoming better known, as are the potential threats to their long-term survival. with 27 species (28%) of the 94 non-dd species of freshwater crabs from africa currently assessed as being at risk of global extinction, the long-term survival of the continent’s largely endemic freshwater crab fauna is a concern. Nevertheless, hoped it that is conservation recovery plans for threatened species will be developed for ed those to species identifi be in need of conservation action through this red List assessment process (Collen to discover new c species, habitat ne requirements, describe ne population specifi refi defi species distributions, levels and c trends, threats and to identify africa’s specifi the to vital is It fauna. crab freshwater unique and important consider managers shery fi that ecosystems these of health measures cally that include specifi the conservation and populations of river crabs. sustainable use of local al. 2009). The conservation of many species of freshwater depends crabs primarily on preservation of although it enough to habitat maintain large water quality. areas of natural is not yet known exactly how sensitive african freshwater crabs are to polluted or silted waters, there is evidence from that similar crabs when are exposed not to likely these to development, survive factors (Ng agriculture and and yeo economies, developing in realities necessary are products exploitation 2007). of natural crab freshwater if made be to have may compromises but species are not to be extirpated in the future. Judicious and careful use of resources is unlikely to cause species extinctions as long as water drainages are polluted not heavily or redirected, cover is some maintained, and protected forest areas are respected and (Cumberlidge et al. 2009). vegetation distribution wide a have LC as assessed species Common region the of streams mountain and wetlands, rivers, the in changes of tolerant relatively be to proved have far, so and, encouraging is It ecosystems. aquatic affecting land-use in already the in persist can species adaptable more these that disturbed and visibly polluted parts of the lowland rivers IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 195 IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 196 196 CHAPTER 6 | SPeCIeS IN THe SPoTLIGHT L evolution andextinction in Lake Tanganyika: amodelforstudiesin A unique species flock of freshwater crabs UNDP/GEF ProjectonLakeTanganyika, Regional CoordinationUnit, c/oSecretariatoftheLakeTanganyika Authority, RoutePrincipale, KigobeNord, ¹ Platythelphusa maculata, crevices underneathrocksandstones. that enables it to hide inside narrow has evolved an extremely flat body shells. Platythelphusa conculcata claw that they use to crush snail with onesignifi cantly enlarged of Platythelphusaarmataare armed instance, bothmalesandfemales al. 1999;Marijnissenet 2004). For adaptive evolution(Cumberlidgeet them idealsubjectsforstudiesin and ecological features making a strikingvarietyofmorphological Africa. Platythelphusid crabs have species fl ock offreshwatercrabsin form theonlyknownlacustrine the genusPlatythelphusawhich platynotus and nine species in crabs, includingPotamonautes derived from freshwater ancestors. derived fromfreshwaterancestors. that all Lake Tanganyika crabs are However, genetic evidenceindicates millions ofyears(Moore1903). sea and remained unchanged over in the lake after a recession of the of marine crabs that got trapped platythelphusids were a relict group Initially, it was thought that the Glor 2010,andreferencestherein). processes ofadaptiveevolution(e.g. famed natural laboratory for studying diverse lake,LakeTanganyika isa million years)andmostspecies tanganyicensis. large endemicsnailNeothauma refuge within empty shells of the species, whichisoftenfoundtaking other hand, is a tiny round-bodied As Africa’s oldest (estimated 9-12 As Africa’soldest(estimated9-12 Bujumura, Burundi endemic species of freshwater Lakes inharbouring10 among theAfricanGreat ake Tanganyika isunique Species inthespotlight

on the 2000). Research on the crabs shows 2000). Researchonthecrabsshows niche diversifi cation (Schluter result ofcompetitionandecological in the African Great Lakes are the the high levels of species diversity longstanding hypothesisisthat relatively shortperiodoftime.A seem tohaveevolvedwithina between theplatythelphusidcrabs million years ago. during thesameperiod,about3.3-2.5 (Day and Wilkinson 2006), diverged the Synodontiscatfish species fl ock et al.2004,2005,2007),aswell (Duftner etal.2005;Koblmüller including severalcichlidgroups Marijnissen etal.2006).Othertaxa, basins (CaneandMolnar2001; Tanganyika was split into separate dropped substantiallyandLake and drought,whenthelakelevels with a period of climate change the platythelpusidscoincides The evolutionarydivergenceof Potamonautes platynotus out ofthewatertofeedamongstrocksalonglakeshore. The morphological differences The morphologicaldifferences (LC) is primarily aquatic but has been observed toclimb (LC)isprimarilyaquaticbuthasbeenobserved and C. stappersi), and catfish catfish ( endemic fish, suchasspinyeels included inthedietofnumerous prey aswellpredators.Theyare components ofthefood-webas areas. The crabs are important the species are found in the rocky these habitats,butthemajorityof of mud.Crabscanbefoundinall shells, sandybeachesanddeeplayers of emptyNeothauma tanganyicensis stromatolite reefs,toextensivebeds cobble beaches,rockyoutcrops,and diversity of habitats, ranging from (Marijnissen etal.2008). that coexist in rocky shore areas among platythelphusidspecies considerable ecologicalversatility However, there is also evidence of niche divergence(Marijnissen2007). could indeedbelinkedtoecological morphological differentiationthat Mastacembelus plagiostomus ), bagrid Lake Tanganyika offers a wide

( Chrysichthys brachynema © HeINZBUSCHer Marijnissen, S.A.E.¹

4/3/11 19:00:39 CHAPTER 6 ( dhonti), as well as and breakdown of mate recognition Lake Tanganyika crab species (Boulengerochromis microlepsis systems as water visibility is reduced (Marijnissen et al. 2008). and Lamprolus lemarii). The crabs (Donohue and Molinos 2009). Lake Tanganyika’s crabs are themselves are top invertebrate Research in Lake Tanganyika has also threatened by invasion

predators, and their relative demonstrated negative impacts of of the non-native Louisiana | SPeCIeS IN THe SPoTLIGHT abundance can have important sedimentation on algal productivity Crayfi sh (Procambarus clarkii) and implications for organisms lower as well as on species diversity and the Red Claw Crayfi sh (Cherax in the food web, including algae, densities of ostracods, snails, and quadricarinatus). Both of these insect larvae, ostracods, and snails fi shes (McIntyre et al. 2004, and crayfi sh have been introduced to (Marijnissen et al. 2008, 2009). references therein). As crabs are Africa for aquaculture purposes and Lake Tanganyika is increasingly closely linked, either as predators are spreading rapidly throughout the under pressure from environmental or prey, to many other organisms continent (e.g. Arrignon et al. 1990; problems generated by human that are vulnerable to the impacts G. Howard, IUCN, pers. comm.). populations (reviewed in Lowe- of increased sedimentation, it is Considering their current presence McConnell 2003). The majority likely that they will respond by in catchments adjacent to Lake of species diversity is found shifting their foraging patterns (e.g. Tanganyika, it is likely that these in rocky near-shore areas, McIntyre et al. 2004). However, crayfi sh will move into the lake which are severely impacted by demonstrating and predicting the basin in the near future. Due to their sedimentation resulting from effects that habitat disruptions will resilience to different environmental ongoing deforestation in the lake have on the endemic crabs requires circumstances, high dispersal capacity catchment (Cohen et al. 2005). taking into account the complexity and opportunistic diet, crayfi sh Sedimentation can negatively affect of the ecosystem. Changes in the are capable of causing dramatic aquatic organisms through a range species fl ock may be delayed relative biodiversity shifts (e.g. Smart et al. of factors including deterioration of to those of other species as crabs 2002; Snyder and Evans 2006; Cruz habitat quality and heterogeneity, occupy multiple positions within and Rebelo 2007), and could cause an reduction of food intake, alteration the food web, and a considerable ecological disaster if they establish of competitive relationships, amount of overlap exists among the themselves in Lake Tanganyika. decrease of reproductive success, ecological niches of the different Without conservation effort to address environmental threats in Lake Tanganyika is the Lake Tanganyika basin, this could lead to the loss of a dynamic increasingly under pressure endemic species fl ock that provides from environmental problems unique insight into the evolution and ecological functioning of this generated by human populations unusually diverse lake system.

Platythelphusa armata (LC) is the largest and most distinctive species in the genus. Juveniles are often found sheltering within the empty shells of the gastropod tanganyicense. © SaSKIa MarIJNISSeN 197

IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 197 4/3/11 19:01:01 Species in the spotlight The East African tree hole crab – spectacular adaptation

Bayliss, J¹

otamonautes raybouldi, where a tree branches. When snails. When it fi nd these snails it SPeCIeS IN THe SPoTLIGHT | the East African tree hole branching occurs it often creates a takes pieces of the snail shell back crab, is a bizarre example small hole, or bole, which fi lls with to its water-fi lled tree hole and P of crab evolution. It is water. The East African tree hole masticates them, which releases exceptionally rare for a crab to crab has evolved to occupy this the calcium ions into solution. It live in a tree (an arboreal species), niche, adapting its behaviour and then ingests the calcium in order to CHAPTER 6 and most of those that do depend morphology accordingly. obtain suffi cient quantities to build on an external water supply – What is remarkable about this its own exoskeleton. It also eats its for example, several species of species is its natural history. This old exoskeleton when it moults. mangrove crab reside in trees for species has an apparent lack of As crabs have a hard exoskeleton protection but lay their eggs in dependence on any water body, they need to moult in order to be the sea. except that collected in tree holes able to grow and mature. Below the There are over 1,200 species as water run-off from the host tree. hard exoskeleton is soft tissue that of freshwater crab, out of which What is yet more remarkable is the expands over time. Eventually the only a handful exhibit some kind way in which it obtains the calcium hard exoskeleton will prevent any of arboreal association. The East in order to build its exoskeleton further expansion, at which stage African tree hole crab is unique (Bayliss 2002). It forages at night the process of moulting (or ecdysis) in this case. It lives solely in the or in heavy rain, when it leaves occurs. water fi lled tree holes formed its hole to search for leaf-litter It was fi rst observed and collected by Professor John Raybould in 1966, but it was not until 2004 when it was eventually described under the patronym Potamonautes raybouldi (Cumberlidge and Vannini 2004). It is a forest species found in just a few sites in , such as the East Usambara Mountains in northern Tanzania, and several sites in southern Kenya (e.g. the Shimba Hills). It has primitive lungs that enable it to spend time outside water, and elongated legs that allow it to climb up and down the tree trunks. The males have one claw that is larger than the other, which is presumably used for display and eventual mating. The females have been found protecting their young (parental care), living in the same tree holes with a brood of juvenile crabs that is presumably their own. These tree holes need Juvenile crabs in a communal tree hole. © JULIaN BayLISS cleaning on a regular basis as leaves

198 ¹ Conservation Science Group, Department of Zoology, University of Cambridge

IUCN AFR2011_pp178-199_chapter 6_crabs V2.indd 198 4/3/11 19:01:24 CHAPTER 6 and other debris accumulate. The juvenile crabs are often too small to cope with moving larger leaves and debris, and would be unable

to clean the tree-hole without | SPeCIeS IN THe SPoTLIGHT assistance from the adult female crab. They also need protection from predators, possibly including other crabs. The local people in the East Usambara Mountains use the water that Potamonautes raybouldi lives in as a medicinal potion. They often collect the water, which they call ‘Mazi yangodi’ (the water from holes with crabs), to give to pregnant women. The water contains calcium, which is required by pregnant women to reduce the risk of pregnancy- induced hypertension (PIH), high blood pressure (pre-eclampsia), and kidney failure, all of which can result in miscarriage. Exactly how and when the connection between the ‘crab water’ and calcium defi ciency in pregnant woman was arrived at is a mystery. The East African tree hole crab is a spectacular example of adaptation, essentially of an aquatic species not only to a terrestrial environment but also to an arboreal existence. It has lost its dependency on larger water bodies such a streams and rivers, and via the process of natural selection, through trial and error (otherwise known as evolution), it has managed to exploit a niche that crabs have rarely occupied. The further connection between the local population of the East Usambara Mountains and their use of the Mazi Yangodi further highlights this species scenario as an amazing example of natural history and a connection with a human society. However, this story of natural history is not fi nished. Exactly how the males and females fi nd each other in order to mate in closed canopy, dark forest, when each crab resides in a different tree and they are relatively short- sighted, remains an exciting mystery yet to be solved. Adult crabs defending their tree hole. © JULIaN BayLISS 199

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