Lake Tanganyika: Difference between revisions

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Coordinates: 6°30′S 29°50′E / 6.500°S 29.833°E / -6.500; 29.833
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==Water characteristics==
==Water characteristics==
The lake's water is [[Hard water|alkaline]] with a [[pH]] of around 9 at the surface to a depth of {{convert|100|m|ft|abbr=on}}.<ref name=Wever2005>De Wever; Muylaert; Van der Gucht; Pirlot; Cocquyt; Descy; Plisnier; and Vyverman (2005). Bacterial Community Composition in Lake Tanganyika: Vertical and Horizontal Heterogeneity. Appl Environ Microbiol. 71(9): 5029–5037. [[doi: 10.1128/AEM.71.9.5029-5037.2005]]</ref> Below this it is around 8.7, gradually decreasing to 8.3—8.5 in the deepest parts of Tanganyika.<ref name=Wever2005/> A similar pattern can be seen in the [[electric conductivity]], ranging from about 670 μS/cm in the upper part to 690 μS/cm in the deepest.<ref name=Wever2005/>
The lake's water is [[Hard water|alkaline]] with a [[pH]] of around 9 at the surface to a depth of {{convert|100|m|ft|abbr=on}}.<ref name=Wever2005>{{cite journal | last1 = De | first1 = Wever | last2 = Muylaert | first2 = | last3 = der Gucht | first3 = Van | last4 = Pirlot | first4 = | last5 = Cocquyt | first5 = | last6 = Descy | first6 = | last7 = Plisnier | first7 = | last8 = Vyverman | first8 = | year = 2005 | title = Bacterial Community Composition in Lake Tanganyika: Vertical and Horizontal Heterogeneity | url = | journal = Appl Environ Microbiol | volume = 71 | issue = 9| pages = 5029–5037 | doi = 10.1128/AEM.71.9.5029-5037.2005 }}</ref> Below this it is around 8.7, gradually decreasing to 8.3—8.5 in the deepest parts of Tanganyika.<ref name=Wever2005/> A similar pattern can be seen in the [[electric conductivity]], ranging from about 670 μS/cm in the upper part to 690 μS/cm in the deepest.<ref name=Wever2005/>


Surface temperatures generally range from about {{convert|24|C|F|abbr=on}} in the southern part of the lake in early August to {{convert|28|-|29|C|F|abbr=on}} in the late rainy season in March—April.<ref name=Edmond1993>Edmond; Stallard; Craigh; Weiss; and Coulter (1993). Nutrient chemistry of the water column of Lake Tanganyika. Limnol. Oceanogr. 38(4): 725-138.</ref> At depths greater than {{convert|400|m|ft|abbr=on}} the temperature is very stabile at {{convert|23.1|-|23.4|C|F|abbr=on}}.<ref name=Reilly2003>{{Cite journal|last1=O'Reilly|first1=Catherine M.|last2=Alin|first2=Simone R.|last3=Plisnier|first3=Pierre-Denis|last4=Cohen|first4=Andrew S.|last5=Mckee|first5=Brent A.|date=August 14, 2003|title=Climate change decreases aquatic ecosystem productivity of Lake Tanganyika, Africa|url=http://www.nature.com/nature/journal/v424/n6950/abs/nature01833.html|doi=10.1038/nature01833|pmid=|access-date=April 27, 2016|journal= Nature|volume=424|pages=766–768}}</ref>
Surface temperatures generally range from about {{convert|24|C|F|abbr=on}} in the southern part of the lake in early August to {{convert|28|-|29|C|F|abbr=on}} in the late rainy season in March—April.<ref name=Edmond1993>{{cite journal | last1 = Edmond | first1 = | last2 = Stallard | first2 = | last3 = Craigh | first3 = | last4 = Weiss | first4 = | last5 = Coulter | first5 = | year = 1993 | title = Nutrient chemistry of the water column of Lake Tanganyika | url = | journal = Limnol. Oceanogr | volume = 38 | issue = 4| pages = 725–138 }}</ref> At depths greater than {{convert|400|m|ft|abbr=on}} the temperature is very stabile at {{convert|23.1|-|23.4|C|F|abbr=on}}.<ref name=Reilly2003>{{Cite journal|last1=O'Reilly|first1=Catherine M.|last2=Alin|first2=Simone R.|last3=Plisnier|first3=Pierre-Denis|last4=Cohen|first4=Andrew S.|last5=Mckee|first5=Brent A.|date=August 14, 2003|title=Climate change decreases aquatic ecosystem productivity of Lake Tanganyika, Africa|url=http://www.nature.com/nature/journal/v424/n6950/abs/nature01833.html|doi=10.1038/nature01833|pmid=12917682|access-date=April 27, 2016|journal= Nature|volume=424|pages=766–768}}</ref>


The lake is [[Stratification (water)|stratified]] and seasonal mixing generally does not extend beyond depths of {{convert|150|m|ft|abbr=on}}.<ref name=Edmond1993/> As a consequence, the deep sections contain "[[fossil water]]".<ref>Hutter; Yongqi; and Chubarenko (2011). Physics of Lakes, volume 1: Foundation of the Mathematical and Physical Background. P. 11. ISBN 978-3-642-15178-1.</ref> This also means that there is no [[oxygen]] (it is [[Anoxic waters|anoxic]]) in the deeper parts, essentially limiting fish and other [[Obligate aerobe|aerobic organism]] to the upper part. There are some geographical variations in this limit, but it is typically at depths of around {{convert|100|m|ft|abbr=on}} in the northern part of the lake and {{convert|240-250|m|ft|abbr=on}} in the south.<ref name=Wright2006>Wright, J.J.; and L.M. Page (2006). Taxonomic revision of Lake Tanganyikan Synodontis (Siluriformes: Mochokidae). Florida Mus. Nat. Hist. Bull. 46(4): 99–154.</ref><ref name=McConnell1987>Lowe-McConnell, R.H. (1987). Ecological Studies in Tropical Fish Communities. ISBN 0-521-28064-8.</ref> The oxygen-devoid deepest sections contain high levels of toxic [[hydrogen sulphide]] and are essentially lifeless,<ref name=zambiatour/> except for [[bacteria]].<ref name=Wever2005/>
The lake is [[Stratification (water)|stratified]] and seasonal mixing generally does not extend beyond depths of {{convert|150|m|ft|abbr=on}}.<ref name=Edmond1993/> As a consequence, the deep sections contain "[[fossil water]]".<ref>Hutter; Yongqi; and Chubarenko (2011). Physics of Lakes, volume 1: Foundation of the Mathematical and Physical Background. P. 11. ISBN 978-3-642-15178-1.</ref> This also means that there is no [[oxygen]] (it is [[Anoxic waters|anoxic]]) in the deeper parts, essentially limiting fish and other [[Obligate aerobe|aerobic organism]] to the upper part. There are some geographical variations in this limit, but it is typically at depths of around {{convert|100|m|ft|abbr=on}} in the northern part of the lake and {{convert|240-250|m|ft|abbr=on}} in the south.<ref name=Wright2006>Wright, J.J.; and L.M. Page (2006). Taxonomic revision of Lake Tanganyikan Synodontis (Siluriformes: Mochokidae). Florida Mus. Nat. Hist. Bull. 46(4): 99–154.</ref><ref name=McConnell1987>Lowe-McConnell, R.H. (1987). Ecological Studies in Tropical Fish Communities. ISBN 0-521-28064-8.</ref> The oxygen-devoid deepest sections contain high levels of toxic [[hydrogen sulphide]] and are essentially lifeless,<ref name=zambiatour/> except for [[bacteria]].<ref name=Wever2005/>
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==Biology==
==Biology==
===Cichlid fish===
===Cichlid fish===
[[Image:Neolamprologus brichardi Magara.jpg|thumb|One of the many Tanganyika cichlids is ''[[Neolamprologus brichardi]]''. The complex behaviors of this species and ''[[Neolamprologus pulcher|N. pulcher]]'' have been studied in detail<ref>Dierkesa; Taborskya; and Kohler (1999). Reproductive parasitism of broodcare helpers in a cooperatively breeding fish Behavioral Ecology 10: 510-515.</ref><ref>Balshine-Earn; and Lotem (1998). Individual recognition in a cooperatively breeding cichlid : Evidence from video playback experiments Behaviour 135: 369-386.</ref><ref>Wernera; Balshineb; Leachc; and Lotem (2003). Helping opportunities and space segregation in cooperatively breeding cichlids Behavioral Ecology 6: 749-756.</ref>]]
[[Image:Neolamprologus brichardi Magara.jpg|thumb|One of the many Tanganyika cichlids is ''[[Neolamprologus brichardi]]''. The complex behaviors of this species and ''[[Neolamprologus pulcher|N. pulcher]]'' have been studied in detail<ref>{{cite journal | last1 = Dierkesa | first1 = | last2 = Taborskya | first2 = | last3 = Kohler | first3 = | year = 1999 | title = Reproductive parasitism of broodcare helpers in a cooperatively breeding fish | url = | journal = Behavioral Ecology | volume = 10 | issue = | pages = 510–515 }}</ref><ref>Balshine-Earn; and Lotem (1998). Individual recognition in a cooperatively breeding cichlid : Evidence from video playback experiments Behaviour 135: 369-386.</ref><ref>{{cite journal | last1 = Wernera | first1 = | last2 = Balshineb | first2 = | last3 = Leachc | first3 = | last4 = Lotem | first4 = | year = 2003 | title = Helping opportunities and space segregation in cooperatively breeding cichlids | url = | journal = Behavioral Ecology | volume = 6 | issue = | pages = 749–756 }}</ref>]]
The lake holds at least 250 species of [[cichlid]] fish<ref name=LTBP>West, K. (prepared by) (2001). ''[http://iwlearn.net/iw-projects/398/reports/lake-tanganyika-biodiversity-final-summary-report-results-and-experiences-of-the-undp-gef-conservation-initiative-raf-92-g32-in-burundi-d-r-congo-tanzania-and-zambia-138p-2-5mb.pdf Lake Tanganyika: Results and Experiences of the UNDP/GEF Conservation Initiative (RAF/92/G32) in Burundi, D.R. Congo, Tanzania, and Zambia.]'' Lake Tanganyika Biodiversity Project.</ref> and [[undescribed species]] remain.<ref name=MortiffTangDiv>Mortiff, C: [http://www.cichlid-forum.com/articles/lake_tanganyika_diverse.php Lake Tanganyika and its Diverse Cichlids.] Cichlid-Forum. Retrieved 1 March 2017.</ref> Almost all (98%) of the Tanganyika cichlids are [[Endemism|endemic]] to the lake and it is thus an important biological resource for the study of [[speciation]] in evolution.<ref name=zambiatour/><ref>Kornfield, Ivy & Smith, Peter A. ''[http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.ecolsys.31.1.163 African Cichlid Fishes: Model Systems for Evolutionary Biology, Annual Review of Ecology and Systematics]'', Vol. 31: 163-196, Nov. 2000</ref> The cichlids of the [[African Great Lakes]], including Tanganyika, represent the most diverse extent of [[adaptive radiation]] in vertebrates.<ref name=":0" />
The lake holds at least 250 species of [[cichlid]] fish<ref name=LTBP>West, K. (prepared by) (2001). ''[http://iwlearn.net/iw-projects/398/reports/lake-tanganyika-biodiversity-final-summary-report-results-and-experiences-of-the-undp-gef-conservation-initiative-raf-92-g32-in-burundi-d-r-congo-tanzania-and-zambia-138p-2-5mb.pdf Lake Tanganyika: Results and Experiences of the UNDP/GEF Conservation Initiative (RAF/92/G32) in Burundi, D.R. Congo, Tanzania, and Zambia.]'' Lake Tanganyika Biodiversity Project.</ref> and [[undescribed species]] remain.<ref name=MortiffTangDiv>Mortiff, C: [http://www.cichlid-forum.com/articles/lake_tanganyika_diverse.php Lake Tanganyika and its Diverse Cichlids.] Cichlid-Forum. Retrieved 1 March 2017.</ref> Almost all (98%) of the Tanganyika cichlids are [[Endemism|endemic]] to the lake and it is thus an important biological resource for the study of [[speciation]] in evolution.<ref name=zambiatour/><ref>Kornfield, Ivy & Smith, Peter A. ''[http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.ecolsys.31.1.163 African Cichlid Fishes: Model Systems for Evolutionary Biology, Annual Review of Ecology and Systematics]'', Vol. 31: 163-196, Nov. 2000</ref> The cichlids of the [[African Great Lakes]], including Tanganyika, represent the most diverse extent of [[adaptive radiation]] in vertebrates.<ref name=":0" />


Most Tanganyika cichlids live along the shoreline down to a depth of {{convert|100|m|ft|abbr=on|-1}}, but some deep-water species regularly decend to {{convert|200|m|ft|abbr=on|-1}}.<ref name=Kirchberger2012>Kirchberger; Sefc; Sturmbauer; and Koblmuller (2012). Evolutionary History of Lake Tanganyika’s Predatory Deepwater Cichlids. International Journal of Evolutionary Biology, Volume 2012, Article ID 716209.</ref> ''[[Trematocara]]'' species have exceptionally been found at more than {{convert|300|m|ft|abbr=on|-1}}, which is deeper than any other cichlid in the world.<ref>Loiselle, Paul (1994). The Cichlid Aquarium, p. 304. Tetra Press, Germany. ISBN 978-1564651464.</ref> Some of the deeper-water cichlids (e.g., ''[[Bathybates]]'', ''[[Gnathochromis]]'', ''[[Hemibates]]'' and ''[[Xenochromis]]'') have been caught at places virtually devoid of oxygen, but how they are able to survive there is unclear.<ref name=McConnell1987/> Tanganyika cichlids are generally [[benthic]] (found at or near the bottom) and/or coastal.<ref name=Lindqvist1999>Lindqvist, O.V.; H. Mölsä; K. Solonen; J. Sarvala, editors (1999). From Limnology to Fisheries: Lake Tanganyika and Other Large Lakes. Pp. 213—214. Springer. ISBN 978-0792360179</ref> No Tanganyika cichlids are truly [[pelagic]] ''and'' offshore, except for some of the [[Planktivore|zooplanktivorous]] and [[piscivorous]] ''Bathybates''.<ref name=Kirchberger2012/> Two of these, ''[[Bathybates fasciatus|B. fasciatus]]'' and ''[[Bathybates leo|B. leo]]'', mainly feed on [[Tanganyika sardine]]s.<ref name=Kirchberger2012/><ref name=McConnell1987/> Although Tanganyika has far fewer cichlid species than [[Lake Malawi]] and [[Lake Victoria|Victoria]] which both have experienced relatively recent explosive species [[Adaptive radiation|radiations]] (resulting in many closely related species),<ref name=Turner2001>Turner, Seehausen, Knight, Allender, and Robinson (2001). How many species of cichlid fishes are there in African lakes? Molecular Ecology 10: 793–806.</ref> its cichlids are the most [[Morphology (biology)|morphologically]] and [[Genetics|genetically]] diverse.<ref name=":0">{{Cite journal|last=Meyer, Matchiner, Salburger|first=Britta, Michael, Walter|date=25 November 2013|title=A tribal level phylogeny of Lake Tanganyika cichlid fishes based on a genomic multi-marker approach|url=|journal=Molecular Phylogenetics and Evolution|doi=|pmid=|access-date=}}</ref> This is linked to the high age of Tanganyika, as it is far older than the other lakes.<ref>Nishida, M. (1991). Lake Tanganyika as an evolutionary reservoir of old lineages of East African cichlid fishes: Inferences from allozyme data. Experientia 47(9): 974–979.</ref> Tanganyika has the largest number of [[Endemism|endemic]] cichlid [[genera]] of all African lakes.<ref name=":0"/> All Tanganyika cichlids are in the subfamily [[Pseudocrenilabrinae]]. Of the 10 [[Tribe (biology)|tribes]] in this subfamily, half are largely or entirely restricted to the lake ([[Cyprichromini]], [[Ectodini]], [[Lamprologini]], [[Limnochromini]] and [[Tropheini]]) and another three have species in the lake ([[Haplochromine]], [[Tilapiini]] and [[Tylochromini]]).<ref>Sparks & Smith (2004). ''Phylogeny and biogeography of cichlid fishes (Teleostei: Perciformes: Cichlidae).'' Cladistics 20(6): 501–517</ref> Others have proposed splitting the Tanganyika cichlids into as many as 12—16 tribes (in addition to previous mentioned, [[Bathybatini]], [[Benthochromini]], [[Boulengerochromini]], [[Cyphotilapiini]], [[Eretmodini]], [[Greenwoodochromini]], [[Limnochromini]] and [[Perissodini]]).<ref name=":0"/>
Most Tanganyika cichlids live along the shoreline down to a depth of {{convert|100|m|ft|abbr=on|-1}}, but some deep-water species regularly decend to {{convert|200|m|ft|abbr=on|-1}}.<ref name=Kirchberger2012>Kirchberger; Sefc; Sturmbauer; and Koblmuller (2012). Evolutionary History of Lake Tanganyika’s Predatory Deepwater Cichlids" ''International Journal of Evolutionary Biology'', Volume 2012, Article ID 716209.</ref> ''[[Trematocara]]'' species have exceptionally been found at more than {{convert|300|m|ft|abbr=on|-1}}, which is deeper than any other cichlid in the world.<ref>Loiselle, Paul (1994). The Cichlid Aquarium, p. 304. Tetra Press, Germany. ISBN 978-1564651464.</ref> Some of the deeper-water cichlids (e.g., ''[[Bathybates]]'', ''[[Gnathochromis]]'', ''[[Hemibates]]'' and ''[[Xenochromis]]'') have been caught at places virtually devoid of oxygen, but how they are able to survive there is unclear.<ref name=McConnell1987/> Tanganyika cichlids are generally [[benthic]] (found at or near the bottom) and/or coastal.<ref name=Lindqvist1999>Lindqvist, O.V.; H. Mölsä; K. Solonen; J. Sarvala, editors (1999). From Limnology to Fisheries: Lake Tanganyika and Other Large Lakes. Pp. 213—214. Springer. ISBN 978-0792360179</ref> No Tanganyika cichlids are truly [[pelagic]] ''and'' offshore, except for some of the [[Planktivore|zooplanktivorous]] and [[piscivorous]] ''Bathybates''.<ref name=Kirchberger2012/> Two of these, ''[[Bathybates fasciatus|B. fasciatus]]'' and ''[[Bathybates leo|B. leo]]'', mainly feed on [[Tanganyika sardine]]s.<ref name=Kirchberger2012/><ref name=McConnell1987/> Although Tanganyika has far fewer cichlid species than [[Lake Malawi]] and [[Lake Victoria|Victoria]] which both have experienced relatively recent explosive species [[Adaptive radiation|radiations]] (resulting in many closely related species),<ref name=Turner2001>{{cite journal | last1 = Turner | first1 = Seehausen | last2 = Knight | first2 = Allender | last3 = Robinson | first3 = | year = 2001 | title = How many species of cichlid fishes are there in African lakes? | url = | journal = Molecular Ecology | volume = 10 | issue = | pages = 793–806 }}</ref> its cichlids are the most [[Morphology (biology)|morphologically]] and [[Genetics|genetically]] diverse.<ref name=":0">{{Cite journal|last=Meyer, Matchiner, Salburger|first=Britta, Michael, Walter|date=25 November 2013|title=A tribal level phylogeny of Lake Tanganyika cichlid fishes based on a genomic multi-marker approach|url=|journal=Molecular Phylogenetics and Evolution|doi=|pmid=|access-date=}}</ref> This is linked to the high age of Tanganyika, as it is far older than the other lakes.<ref>{{cite journal | last1 = Nishida | first1 = M | year = 1991 | title = Lake Tanganyika as an evolutionary reservoir of old lineages of East African cichlid fishes: Inferences from allozyme data | url = | journal = Experientia | volume = 47 | issue = 9| pages = 974–979 }}</ref> Tanganyika has the largest number of [[Endemism|endemic]] cichlid [[genera]] of all African lakes.<ref name=":0"/> All Tanganyika cichlids are in the subfamily [[Pseudocrenilabrinae]]. Of the 10 [[Tribe (biology)|tribes]] in this subfamily, half are largely or entirely restricted to the lake ([[Cyprichromini]], [[Ectodini]], [[Lamprologini]], [[Limnochromini]] and [[Tropheini]]) and another three have species in the lake ([[Haplochromine]], [[Tilapiini]] and [[Tylochromini]]).<ref>{{cite journal | last1 = Sparks | first1 = | last2 = Smith | first2 = | year = 2004 | title = Phylogeny and biogeography of cichlid fishes (Teleostei: Perciformes: Cichlidae) | url = | journal = Cladistics | volume = 20 | issue = 6| pages = 501–517 }}</ref> Others have proposed splitting the Tanganyika cichlids into as many as 12—16 tribes (in addition to previous mentioned, [[Bathybatini]], [[Benthochromini]], [[Boulengerochromini]], [[Cyphotilapiini]], [[Eretmodini]], [[Greenwoodochromini]], [[Limnochromini]] and [[Perissodini]]).<ref name=":0"/>


[[Image:Cyphotilapia frontosa2.jpg|thumb|''[[Cyphotilapia frontosa]]'' is one of the larger Tanganyika cichlids, reaching up to {{convert|33|cm|ft|abbr=on|1}} in length<ref>{{FishBase species | genus = Cyphotilapia | species = frontosa | month = March| year = 2017}}</ref>]]
[[Image:Cyphotilapia frontosa2.jpg|thumb|''[[Cyphotilapia frontosa]]'' is one of the larger Tanganyika cichlids, reaching up to {{convert|33|cm|ft|abbr=on|1}} in length<ref>{{FishBase species | genus = Cyphotilapia | species = frontosa | month = March| year = 2017}}</ref>]]
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===Other fish===
===Other fish===
[[Image:Lamprichthys tanganicanus.JPG|thumb|The [[Tanganyika killifish]] (''Lamprichthys tanganicanus'') is the only member of its genus<ref>{{FishBase genus | genus = Lamprichthys | month = March| year = 2017}}</ref>]]
[[Image:Lamprichthys tanganicanus.JPG|thumb|The [[Tanganyika killifish]] (''Lamprichthys tanganicanus'') is the only member of its genus<ref>{{FishBase genus | genus = Lamprichthys | month = March| year = 2017}}</ref>]]
Lake Tanganyika is home to more than 80 species of non-cichlid fish and about 60% of these are endemic.<ref name=Wright2006/><ref name=LTBP/><ref name=Brown2011>Brown; Britz; Bills; Rüber; and Day (2011). Pectoral fin loss in the Mastacembelidae: a new species from Lake Tanganyika. Journal of Zoology 284(4): 286–293. [[doi: 10.1111/j.1469-7998.2011.00804.x]]</ref><ref>Wright, J.J.; and Bailey, R.M. (2012). Systematic revision of the formerly monotypic genus Tanganikallabes (Siluriformes: Clariidae). Zoological Journal of the Linnean Society 165 (1): 121–142.</ref>
Lake Tanganyika is home to more than 80 species of non-cichlid fish and about 60% of these are endemic.<ref name=Wright2006/><ref name=LTBP/><ref name=Brown2011>{{cite journal | last1 = Brown | first1 = | last2 = Britz | first2 = | last3 = Bills | first3 = | last4 = Rüber | first4 = | last5 = Day | first5 = | year = 2011 | title = Pectoral fin loss in the Mastacembelidae: a new species from Lake Tanganyika | url = | journal = Journal of Zoology | volume = 284 | issue = 4| pages = 286–293 | doi = 10.1111/j.1469-7998.2011.00804.x }}</ref><ref>{{cite journal | last1 = Wright | first1 = J.J. | last2 = Bailey | first2 = R.M. | year = 2012 | title = Systematic revision of the formerly monotypic genus Tanganikallabes (Siluriformes: Clariidae) | url = | journal = Zoological Journal of the Linnean Society | volume = 165 | issue = 1| pages = 121–142 }}</ref>


The open waters of the pelagic zone are dominated by four non-cichlid species: Two species of "Tanganyika sardine" (''[[Limnothrissa miodon]]'' and ''[[Stolothrissa tanganicae]] '') form the largest [[biomass]] of fish in this zone, and they are important prey for the [[forktail lates]] (''Lates microlepis'') and [[sleek lates]] (''L. stappersii'').<ref name=Lindqvist1999/> Two additional lates are found in the lake, the [[Tanganyika lates]] (''L. angustifrons'') and [[bigeye lates]] (''L. mariae''), but both these are primarily benthic hunters, although they also may move into open waters.<ref name=Lindqvist1999/> The four lates, all endemic to Tanganyika, have been overfished and larger individuals are rare today.<ref name=Lindqvist1999/>
The open waters of the pelagic zone are dominated by four non-cichlid species: Two species of "Tanganyika sardine" (''[[Limnothrissa miodon]]'' and ''[[Stolothrissa tanganicae]] '') form the largest [[biomass]] of fish in this zone, and they are important prey for the [[forktail lates]] (''Lates microlepis'') and [[sleek lates]] (''L. stappersii'').<ref name=Lindqvist1999/> Two additional lates are found in the lake, the [[Tanganyika lates]] (''L. angustifrons'') and [[bigeye lates]] (''L. mariae''), but both these are primarily benthic hunters, although they also may move into open waters.<ref name=Lindqvist1999/> The four lates, all endemic to Tanganyika, have been overfished and larger individuals are rare today.<ref name=Lindqvist1999/>


[[Image:Synodontis polli white1.jpg|thumb|There are 11 species of ''[[Synodontis]]'' catfish in the lake and 10 of these, including ''[[Synodontis polli|S. polli]]'' (pictured), are endemic<ref name=Wright2006/>]]
[[Image:Synodontis polli white1.jpg|thumb|There are 11 species of ''[[Synodontis]]'' catfish in the lake and 10 of these, including ''[[Synodontis polli|S. polli]]'' (pictured), are endemic<ref name=Wright2006/>]]
Among the more unusual fish in the lake are the endemic, [[Facultative parasite|facultatively]] [[brood parasitic]] "cuckoo catfish", including at least ''[[Synodontis grandiops]]''<ref>PlanetCatfish: [https://www.planetcatfish.com/common/species.php?species_id=710 Synodontis grandiops.] Retrieved 1 April 2017.</ref> and ''[[Synodontis multipunctatus|S. multipunctatus]]''.<ref name=Wright2006/><ref name=Schliewen1992/> A number of others are very similar (e.g., ''[[Synodontis lucipinnis|S. lucipinnis]]'' and ''[[Synodontis petricola|S. petricola]]'') and have often been confused; it is unclear if they have a similar behavior.<ref name=Wright2006/><ref>PlanetCatfish: [https://www.planetcatfish.com/common/species.php?task=&species_id=103 Synodontis lucipinnis.] Retrieved 1 April 2017.</ref><ref>PlanetCatfish: [https://www.planetcatfish.com/common/species.php?task=&species_id=857 Synodontis petricola.] Retrieved 1 April 2017.</ref> The facultative brood parasites often lay their eggs synchronously with mouthbroding cichlids. The cichlid pick up the eggs in their mouth as if they were their own. Once the catfish eggs hatch the young eat the cichlid eggs.<ref name=Wright2006/><ref name=Schliewen1992/> Five catfish genera are entirely restricted to the lake basin: ''[[Bathybagrus]]'', ''[[Dinotopterus]]'', ''[[Lophiobagrus]]'', ''[[Phyllonemus]]'' and ''[[Tanganikallabes]]''.<ref name=FishbaseList>FishBase: [http://www.fishbase.se/TrophicEco/FishEcoList.php?ve_code=4 Species in Tanganyika.] Retrieved 3 April 2017.</ref> Although not endemic on a genus level, six species of ''[[Chrysichthys]]'' catfish are only found in the Tanganyika basin where they live both in shallow and relatively deep waters;<ref name=FishbaseList/> in the latter habitat they are the primary predators and scavangers.<ref name=McConnell1987/> A unique [[evolutionary radiation]] in the lake is the 15 species of ''[[Mastacembelus]]'' spiny eels, all but one endemic to its basin.<ref name=LTBP/><ref name=Brown2011/><ref name=Brown2010>Brown; Rüber; Bills; and Day (2010). Mastacembelid eels support Lake Tanganyika as an evolutionary hotspot of diversification. BMC Evolutionary Biology 10: 188 [[doi: 10.1186/1471-2148-10-188]]</ref> Although other African Great Lakes have ''Synodontis'' catfish and ''Mastacembelus'' spiny eels, the relatively high diversity is unique to Tanganyika, which likely is related to its old age.<ref name=Brown2010/>
Among the more unusual fish in the lake are the endemic, [[Facultative parasite|facultatively]] [[brood parasitic]] "cuckoo catfish", including at least ''[[Synodontis grandiops]]''<ref>PlanetCatfish: [https://www.planetcatfish.com/common/species.php?species_id=710 Synodontis grandiops.] Retrieved 1 April 2017.</ref> and ''[[Synodontis multipunctatus|S. multipunctatus]]''.<ref name=Wright2006/><ref name=Schliewen1992/> A number of others are very similar (e.g., ''[[Synodontis lucipinnis|S. lucipinnis]]'' and ''[[Synodontis petricola|S. petricola]]'') and have often been confused; it is unclear if they have a similar behavior.<ref name=Wright2006/><ref>PlanetCatfish: [https://www.planetcatfish.com/common/species.php?task=&species_id=103 Synodontis lucipinnis.] Retrieved 1 April 2017.</ref><ref>PlanetCatfish: [https://www.planetcatfish.com/common/species.php?task=&species_id=857 Synodontis petricola.] Retrieved 1 April 2017.</ref> The facultative brood parasites often lay their eggs synchronously with mouthbroding cichlids. The cichlid pick up the eggs in their mouth as if they were their own. Once the catfish eggs hatch the young eat the cichlid eggs.<ref name=Wright2006/><ref name=Schliewen1992/> Five catfish genera are entirely restricted to the lake basin: ''[[Bathybagrus]]'', ''[[Dinotopterus]]'', ''[[Lophiobagrus]]'', ''[[Phyllonemus]]'' and ''[[Tanganikallabes]]''.<ref name=FishbaseList>FishBase: [http://www.fishbase.se/TrophicEco/FishEcoList.php?ve_code=4 Species in Tanganyika.] Retrieved 3 April 2017.</ref> Although not endemic on a genus level, six species of ''[[Chrysichthys]]'' catfish are only found in the Tanganyika basin where they live both in shallow and relatively deep waters;<ref name=FishbaseList/> in the latter habitat they are the primary predators and scavangers.<ref name=McConnell1987/> A unique [[evolutionary radiation]] in the lake is the 15 species of ''[[Mastacembelus]]'' spiny eels, all but one endemic to its basin.<ref name=LTBP/><ref name=Brown2011/><ref name=Brown2010>{{cite journal | last1 = Brown | first1 = | last2 = Rüber | first2 = | last3 = Bills | first3 = | last4 = Day | first4 = | year = 2010 | title = Mastacembelid eels support Lake Tanganyika as an evolutionary hotspot of diversification | url = | journal = BMC Evolutionary Biology | volume = 10 | issue = | page = 188 | doi = 10.1186/1471-2148-10-188 }}</ref> Although other African Great Lakes have ''Synodontis'' catfish and ''Mastacembelus'' spiny eels, the relatively high diversity is unique to Tanganyika, which likely is related to its old age.<ref name=Brown2010/>


Among the non-endemic fish, some are widespread African species but several are only shared with the Malagarasi and Congo River basins, such as the [[Congo bichir]] (''Polypterus congicus''), [[goliath tigerfish]] (''Hydrocynus goliath''), ''[[Citharinus]] citharus'', [[six-banded distichodus]] (''Distichodus sexfasciatus'') and [[mbu puffer]] (''Tetraodon mbu'').<ref name=FishbaseList/>
Among the non-endemic fish, some are widespread African species but several are only shared with the Malagarasi and Congo River basins, such as the [[Congo bichir]] (''Polypterus congicus''), [[goliath tigerfish]] (''Hydrocynus goliath''), ''[[Citharinus]] citharus'', [[six-banded distichodus]] (''Distichodus sexfasciatus'') and [[mbu puffer]] (''Tetraodon mbu'').<ref name=FishbaseList/>
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===Molluscs and crustaceans===
===Molluscs and crustaceans===
[[Image:Tiphobia horei 01.JPG|thumb|The shell of the endemic thallasoid freshwater snail ''[[Tiphobia horei]]'' with its elaborate shape and spines.]]
[[Image:Tiphobia horei 01.JPG|thumb|The shell of the endemic thallasoid freshwater snail ''[[Tiphobia horei]]'' with its elaborate shape and spines.]]
A total of 68 [[freshwater snail]] species (45 endemic) and 15 [[bivalve]] species (8 endemic) are known from the lake.<ref name=Mollusc>Segers, H.; and Martens, K; editors (2005). ''The Diversity of Aquatic Ecosystems.'' p. 46. Developments in Hydrobiology. Aquatic Biodiversity. ISBN 1-4020-3745-7</ref> Many of the snails are unusual for species living in freshwater in having noticeably thickened shells and/or distinct [[Sculpture (mollusc)|sculpture]], features more commonly seen in marine snails. They are referred to as thallasoids, which can be translated to "marine-like".<ref name=Snail>Brown, D. (1994). ''Freshwater Snails Of Africa And Their Medical Importance.'' 2nd edition. ISBN 0-7484-0026-5</ref> All the Tanganyika thallasoids, which are part of [[Prosobranchia]], are endemic to the lake.<ref name=Snail/> Initially they were believed to be related to similar marine snails, but they are now known to be unrelated. Their appearance is now believed to be the result of the highly diverse habitats in Lake Tanganyika and [[evolutionary pressure]] from snail-eating fish and, in particular, ''[[Platythelphusa]]'' crabs.<ref name=LTBP/><ref name=Snail/><ref>West, K.; and Cohen, A. (1996). ''Shell microstructure of gastropods from Lake Tanganyika, Africa: adaptation, convergent evolution, and escalation.'' Evolution 50: 672–682.</ref> A total of 17 freshwater snail genera are endemic to the lake, such as ''[[Lavigeria]]'', ''[[Reymondia]]'', ''[[Spekia]]'', ''[[Tanganyicia]]'' and ''[[Tiphobia]]''.<ref name=Snail/> There are about 30 species of non-thallasoid snails in the lake, but only five of these are endemic, including ''[[Ferrissia tanganyicensis]]'' and ''[[Neothauma tanganyicense]]''.<ref name=Snail/> The latter is the largest Tanganyika snail and its shell is often used by small [[Shell dwellers|shell-dwelling cichlids]].<ref>Koblmüller; Duftner; Sefc; Aibara; Stipacek; Blanc; Egger; and Sturmbauer (2007). ''Reticulate phylogeny of gastropod-shell-breeding cichlids from Lake Tanganyika — the result of repeated introgressive hybridization.'' BMC Evolutionary Biology 7: 7.</ref>
A total of 68 [[freshwater snail]] species (45 endemic) and 15 [[bivalve]] species (8 endemic) are known from the lake.<ref name=Mollusc>Segers, H.; and Martens, K; editors (2005). ''The Diversity of Aquatic Ecosystems.'' p. 46. Developments in Hydrobiology. Aquatic Biodiversity. ISBN 1-4020-3745-7</ref> Many of the snails are unusual for species living in freshwater in having noticeably thickened shells and/or distinct [[Sculpture (mollusc)|sculpture]], features more commonly seen in marine snails. They are referred to as thallasoids, which can be translated to "marine-like".<ref name=Snail>Brown, D. (1994). ''Freshwater Snails Of Africa And Their Medical Importance.'' 2nd edition. ISBN 0-7484-0026-5</ref> All the Tanganyika thallasoids, which are part of [[Prosobranchia]], are endemic to the lake.<ref name=Snail/> Initially they were believed to be related to similar marine snails, but they are now known to be unrelated. Their appearance is now believed to be the result of the highly diverse habitats in Lake Tanganyika and [[evolutionary pressure]] from snail-eating fish and, in particular, ''[[Platythelphusa]]'' crabs.<ref name=LTBP/><ref name=Snail/><ref>{{cite journal | last1 = West | first1 = K. | last2 = Cohen | first2 = A. | year = 1996 | title = Shell microstructure of gastropods from Lake Tanganyika, Africa: adaptation, convergent evolution, and escalation. | url = | journal = Evolution | volume = 50 | issue = | pages = 672–682 }}</ref> A total of 17 freshwater snail genera are endemic to the lake, such as ''[[Lavigeria]]'', ''[[Reymondia]]'', ''[[Spekia]]'', ''[[Tanganyicia]]'' and ''[[Tiphobia]]''.<ref name=Snail/> There are about 30 species of non-thallasoid snails in the lake, but only five of these are endemic, including ''[[Ferrissia tanganyicensis]]'' and ''[[Neothauma tanganyicense]]''.<ref name=Snail/> The latter is the largest Tanganyika snail and its shell is often used by small [[Shell dwellers|shell-dwelling cichlids]].<ref>{{cite journal | last1 = Koblmüller | first1 = | last2 = Duftner | first2 = | last3 = Sefc | first3 = | last4 = Aibara | first4 = | last5 = Stipacek | first5 = | last6 = Blanc | first6 = | last7 = Egger | first7 = | last8 = Sturmbauer | first8 = | year = 2007 | title = Reticulate phylogeny of gastropod-shell-breeding cichlids from Lake Tanganyika — the result of repeated introgressive hybridization. | url = | journal = BMC Evolutionary Biology | volume = 7 | issue = | page = 7 }}</ref>


Crustaceans are also highly diverse in Tanganyika with more than 200 species, of which more than half are endemic.<ref name=LTBP/> They include 10 species of [[freshwater crab]]s (9 ''Platythelphusa'' and ''[[Potamonautes platynotus]]''; all endemic),<ref name=crabs>Marijnissen; Michel; Daniels; Erpenbeck; Menken; Schram (2006). ''Molecular evidence for recent divergence of Lake Tanganyika endemic crabs (Decapoda: Platythelphusidae).'' Molecular Phylogenetics and Evolution 40(2): 628–634.</ref> at least 11 species of small [[Atyidae|atyid]] shrimp (''[[Atyella]]'', ''[[Caridella]]'' and ''[[Limnocaridina]]''),<ref name=Atyid>Fryer, G. (2006). ''Evolution in ancient lakes: radiation of Tanganyikan atyid prawns and speciation of pelagic cichlid fishes in Lake Malawi.'' Hydrobiologia 568(1): 131–142.</ref> an endemic [[Palaemonidae|palaemonid]] shrimp (''[[Macrobrachium]] moorei''),<ref>{{IUCN|id=196882|taxon=''Macrobrachium moorei''| assessors=De Grave, S.| assessment_year=2013| version=2017.1| accessdate=3 April 2017}}</ref> at least 23 endemic [[ostracod]]s<ref>Gitter, F.; M. Gross; and W.E. Piller (2015). Sub-Decadal Resolution in Sediments of Late Miocene Lake Pannon Reveals Speciation of Cyprideis (Crustacea, Ostracoda). [[doi: 10.1371/journal.pone.0109360]].</ref><ref>Schön, I.; K. Martens (2012). Molecular analyses of ostracod flocks from Lake Baikal and Lake Tanganyika. Hydrobiologia 682(1): 91–110.[[doi: 10.1007/s10750-011-0935-6]].</ref> and several [[copepod]]s.<ref>Cirhuza, D.M.; and P.-D. Plisnier (2016). Composition and seasonal variations in abundance of Copepod (Crustacea) populations from the northern part of Lake Tanganyika. Aquatic Ecosystem Health & Management 19(4): 401–410.</ref>
Crustaceans are also highly diverse in Tanganyika with more than 200 species, of which more than half are endemic.<ref name=LTBP/> They include 10 species of [[freshwater crab]]s (9 ''Platythelphusa'' and ''[[Potamonautes platynotus]]''; all endemic),<ref name=crabs>{{cite journal | last1 = Marijnissen | first1 = | last2 = Michel | first2 = | last3 = Daniels | first3 = | last4 = Erpenbeck | first4 = | last5 = Menken | first5 = | last6 = Schram | first6 = | year = 2006 | title = Molecular evidence for recent divergence of Lake Tanganyika endemic crabs (Decapoda: Platythelphusidae) | url = | journal = Molecular Phylogenetics and Evolution | volume = 40 | issue = 2| pages = 628–634 }}</ref> at least 11 species of small [[Atyidae|atyid]] shrimp (''[[Atyella]]'', ''[[Caridella]]'' and ''[[Limnocaridina]]''),<ref name=Atyid>{{cite journal | last1 = Fryer | first1 = G | year = 2006 | title = Evolution in ancient lakes: radiation of Tanganyikan atyid prawns and speciation of pelagic cichlid fishes in Lake Malawi. | url = | journal = Hydrobiologia | volume = 568 | issue = 1| pages = 131–142 }}</ref> an endemic [[Palaemonidae|palaemonid]] shrimp (''[[Macrobrachium]] moorei''),<ref>{{IUCN|id=196882|taxon=''Macrobrachium moorei''| assessors=De Grave, S.| assessment_year=2013| version=2017.1| accessdate=3 April 2017}}</ref> at least 23 endemic [[ostracod]]s<ref>Gitter, F.; M. Gross; and W.E. Piller (2015). Sub-Decadal Resolution in Sediments of Late Miocene Lake Pannon Reveals Speciation of Cyprideis (Crustacea, Ostracoda). {{doi| 10.1371/journal.pone.0109360}}.</ref><ref>{{cite journal | last1 = Schön | first1 = I. | last2 = Martens | first2 = K. | year = 2012 | title = Molecular analyses of ostracod flocks from Lake Baikal and Lake Tanganyika | url = | journal = Hydrobiologia | volume = 682 | issue = 1| pages = 91–110 | doi = 10.1007/s10750-011-0935-6 }}</ref> and several [[copepod]]s.<ref>{{cite journal | last1 = Cirhuza | first1 = D.M. | last2 = Plisnier | first2 = P.-D. | year = 2016 | title = Composition and seasonal variations in abundance of Copepod (Crustacea) populations from the northern part of Lake Tanganyika | url = | journal = Aquatic Ecosystem Health & Management | volume = 19 | issue = 4| pages = 401–410 }}</ref>


Among [[Rift Valley lakes]], Lake Tanganyika far surpasses all others in terms of crustacean and freshwater snail richness (both in total number of species and number of endemics).<ref name=Mollusc/> For example, the only other Rift Valley lake with endemic freshwater crabs is Lake Kivu with two species.<ref>Cumberlidge, N.; and Meyer, K. S. (2011). ''[http://commons.nmu.edu/cgi/viewcontent.cgi?article=1029&context=facwork_journalarticles A revision of the freshwater crabs of Lake Kivu, East Africa.]'' Journal Articles. Paper 30.</ref>
Among [[Rift Valley lakes]], Lake Tanganyika far surpasses all others in terms of crustacean and freshwater snail richness (both in total number of species and number of endemics).<ref name=Mollusc/> For example, the only other Rift Valley lake with endemic freshwater crabs is Lake Kivu with two species.<ref>Cumberlidge, N.; and Meyer, K. S. (2011). ''[http://commons.nmu.edu/cgi/viewcontent.cgi?article=1029&context=facwork_journalarticles A revision of the freshwater crabs of Lake Kivu, East Africa.]'' Journal Articles. Paper 30.</ref>

Revision as of 08:30, 4 April 2017

Lake Tanganyika
Lake Tanganyika from space, June 1985
Lake Tanganyika map
Coordinates6°30′S 29°50′E / 6.500°S 29.833°E / -6.500; 29.833
Lake typeRift Valley Lake
Primary inflowsRuzizi River
Malagarasi River
Kalambo River
Primary outflowsLukuga River
Catchment area231,000 km2 (89,000 sq mi)
Basin countriesBurundi
DR Congo
Tanzania
Zambia
Max. length673 km (418 mi)
Max. width72 km (45 mi)
Surface area32,900 km2 (12,700 sq mi)
Average depth570 m (1,870 ft)
Max. depth1,470 m (4,820 ft)
Water volume18,900 km3 (4,500 cu mi)
Residence time5500 years[1]
Shore length11,828 km (1,136 mi)
Surface elevation773 m (2,536 ft)[2]
SettlementsKigoma, Tanzania
Kalemie, DRC
Bujumbura, Burundi
References[2]
1 Shore length is not a well-defined measure.

Lake Tanganyika is an African Great Lake. It is the second oldest freshwater lake in the world, second largest by volume, and the second deepest, in all cases after Lake Baikal in Siberia;[3][4] it is also the world's longest freshwater lake. The lake is divided among four countries – Tanzania, Democratic Republic of the Congo (DRC), Burundi, and Zambia, with Tanzania (46%) and DRC (40%) possessing the majority of the lake. The water flows into the Congo River system and ultimately into the Atlantic Ocean.

The name apparently refers to "Tanganika, 'the great lake spreading out like a plain', or 'plain-like lake'."[5]: Vol.Two, 16 

Geography

Lake Tanganyika is situated within the Albertine Rift, the western branch of the East African Rift, and is confined by the mountainous walls of the valley. It is the largest rift lake in Africa and the second largest lake by volume in the world. It is the deepest lake in Africa and holds the greatest volume of fresh water, accounting for 18% of the world's available fresh water. It extends for 676 km (420 mi) in a general north-south direction and averages 50 km (31 mi) in width. The lake covers 32,900 km2 (12,700 sq mi), with a shoreline of 1,828 km (1,136 mi), a mean depth of 570 m (1,870 ft) and a maximum depth of 1,470 m (4,820 ft) (in the northern basin). It holds an estimated 18,900 cubic kilometres (4,500 cu mi).[6] This is equivalent to about 16% of all fresh water on Earth.

The catchment area of the lake is 231,000 km2 (89,000 sq mi). Two main rivers flow into the lake, as well as numerous smaller rivers and streams (whose lengths are limited by the steep mountains around the lake). There is one major outflow, the Lukuga River, which empties into the Congo River drainage.

The major river flowing into the lake is the Ruzizi River, formed about 10,000 years ago, which enters the north of the lake from Lake Kivu. The Malagarasi River, which is Tanzania's second largest river, enters the east side of Lake Tanganyika. The Malagarasi is older than Lake Tanganyika and, before the lake was formed, directly drained into the Congo River.

The lake has a complex history of changing flow patterns, due to its high altitude, great depth, slow rate of refill and mountainous location in a turbulently volcanic area that has undergone climate changes. Apparently it has rarely in the past had an outflow to the sea. It has been described as 'practically endorheic' for this reason. The lake's connection to the sea is dependent on a high water level allowing water to overflow out of the lake through the Lukunga into the Congo.

Due to the lake's tropical location, it suffers a high rate of evaporation. Thus it depends on a high inflow through the Ruzizi out of Lake Kivu to keep the lake high enough to overflow. This outflow is apparently not more than 12,000 years old, and resulted from lava flows blocking and diverting the Kivu basin's previous outflow into Lake Edward and then the Nile system, and diverting it to Lake Tanganyika. Signs of ancient shorelines indicate that at times Tanganyika may have been up to 300 m lower than its present surface level, with no outlet to the sea. Even its current outlet is intermittent and may not have been operating when first visited by Western explorers in 1858.

The lake may also have at times had different inflows and outflows: inward flows from a higher Lake Rukwa, access to Lake Malawi and an exit route to the Nile have all been proposed to have existed at some point in the lake's history.[7]

Islands

There are several islands in Lake Tanganyika. The most important of them are

  • Kavala Island (The Democratic Republic of the Congo)
  • Mamba-Kayenda Islands (The Democratic Republic of the Congo)
  • Milima Island (The Democratic Republic of the Congo)
  • Kibishie Island (The Democratic Republic of the Congo)
  • Mutonowe Island ( Zambia)
  • Kumbula Island ( Zambia)

Water characteristics

The lake's water is alkaline with a pH of around 9 at the surface to a depth of 100 m (330 ft).[8] Below this it is around 8.7, gradually decreasing to 8.3—8.5 in the deepest parts of Tanganyika.[8] A similar pattern can be seen in the electric conductivity, ranging from about 670 μS/cm in the upper part to 690 μS/cm in the deepest.[8]

Surface temperatures generally range from about 24 °C (75 °F) in the southern part of the lake in early August to 28–29 °C (82–84 °F) in the late rainy season in March—April.[9] At depths greater than 400 m (1,300 ft) the temperature is very stabile at 23.1–23.4 °C (73.6–74.1 °F).[10]

The lake is stratified and seasonal mixing generally does not extend beyond depths of 150 m (490 ft).[9] As a consequence, the deep sections contain "fossil water".[11] This also means that there is no oxygen (it is anoxic) in the deeper parts, essentially limiting fish and other aerobic organism to the upper part. There are some geographical variations in this limit, but it is typically at depths of around 100 m (330 ft) in the northern part of the lake and 240–250 m (790–820 ft) in the south.[12][13] The oxygen-devoid deepest sections contain high levels of toxic hydrogen sulphide and are essentially lifeless,[3] except for bacteria.[8]

Biology

Cichlid fish

File:Neolamprologus brichardi Magara.jpg
One of the many Tanganyika cichlids is Neolamprologus brichardi. The complex behaviors of this species and N. pulcher have been studied in detail[14][15][16]

The lake holds at least 250 species of cichlid fish[17] and undescribed species remain.[18] Almost all (98%) of the Tanganyika cichlids are endemic to the lake and it is thus an important biological resource for the study of speciation in evolution.[3][19] The cichlids of the African Great Lakes, including Tanganyika, represent the most diverse extent of adaptive radiation in vertebrates.[20]

Most Tanganyika cichlids live along the shoreline down to a depth of 100 m (330 ft), but some deep-water species regularly decend to 200 m (660 ft).[21] Trematocara species have exceptionally been found at more than 300 m (980 ft), which is deeper than any other cichlid in the world.[22] Some of the deeper-water cichlids (e.g., Bathybates, Gnathochromis, Hemibates and Xenochromis) have been caught at places virtually devoid of oxygen, but how they are able to survive there is unclear.[13] Tanganyika cichlids are generally benthic (found at or near the bottom) and/or coastal.[23] No Tanganyika cichlids are truly pelagic and offshore, except for some of the zooplanktivorous and piscivorous Bathybates.[21] Two of these, B. fasciatus and B. leo, mainly feed on Tanganyika sardines.[21][13] Although Tanganyika has far fewer cichlid species than Lake Malawi and Victoria which both have experienced relatively recent explosive species radiations (resulting in many closely related species),[24] its cichlids are the most morphologically and genetically diverse.[20] This is linked to the high age of Tanganyika, as it is far older than the other lakes.[25] Tanganyika has the largest number of endemic cichlid genera of all African lakes.[20] All Tanganyika cichlids are in the subfamily Pseudocrenilabrinae. Of the 10 tribes in this subfamily, half are largely or entirely restricted to the lake (Cyprichromini, Ectodini, Lamprologini, Limnochromini and Tropheini) and another three have species in the lake (Haplochromine, Tilapiini and Tylochromini).[26] Others have proposed splitting the Tanganyika cichlids into as many as 12—16 tribes (in addition to previous mentioned, Bathybatini, Benthochromini, Boulengerochromini, Cyphotilapiini, Eretmodini, Greenwoodochromini, Limnochromini and Perissodini).[20]

Cyphotilapia frontosa is one of the larger Tanganyika cichlids, reaching up to 33 cm (1.1 ft) in length[27]

Among the endemic species are two of the world's smallest cichlids, Neolamprologus multifasciatus and N. similis (both shell dwellers) at up to 4–5 cm (1.6–2.0 in),[28][29] and one of the largest, the giant cichlid (Boulengerochromis microlepis) at up to 90 cm (3.0 ft).[18][30] Tanganyika cichlids differ extensively in ecology and include species that are herbivores, detritivores, planktivores, insectivores, molluscivores, scavengers, scale-eaters and piscivores.[18] Their breeding behavior fall into two main groups, the substrate spawners and the mouthbrooders.[31]

Many cichlids from Lake Tanganyika, such as species from the genera Altolamprologus, Cyprichromis, Eretmodus, Julidochromis, Lamprologus, Neolamprologus, Tropheus and Xenotilapia, are popular aquarium fish due to their bright colors and patterns, and interesting behaviors.[31] Recreating a Lake Tanganyika biotope to host those cichlids in a habitat similar to their natural environment is also popular in the aquarium hobby.[31][32]

Other fish

The Tanganyika killifish (Lamprichthys tanganicanus) is the only member of its genus[33]

Lake Tanganyika is home to more than 80 species of non-cichlid fish and about 60% of these are endemic.[12][17][34][35]

The open waters of the pelagic zone are dominated by four non-cichlid species: Two species of "Tanganyika sardine" (Limnothrissa miodon and Stolothrissa tanganicae ) form the largest biomass of fish in this zone, and they are important prey for the forktail lates (Lates microlepis) and sleek lates (L. stappersii).[23] Two additional lates are found in the lake, the Tanganyika lates (L. angustifrons) and bigeye lates (L. mariae), but both these are primarily benthic hunters, although they also may move into open waters.[23] The four lates, all endemic to Tanganyika, have been overfished and larger individuals are rare today.[23]

File:Synodontis polli white1.jpg
There are 11 species of Synodontis catfish in the lake and 10 of these, including S. polli (pictured), are endemic[12]

Among the more unusual fish in the lake are the endemic, facultatively brood parasitic "cuckoo catfish", including at least Synodontis grandiops[36] and S. multipunctatus.[12][31] A number of others are very similar (e.g., S. lucipinnis and S. petricola) and have often been confused; it is unclear if they have a similar behavior.[12][37][38] The facultative brood parasites often lay their eggs synchronously with mouthbroding cichlids. The cichlid pick up the eggs in their mouth as if they were their own. Once the catfish eggs hatch the young eat the cichlid eggs.[12][31] Five catfish genera are entirely restricted to the lake basin: Bathybagrus, Dinotopterus, Lophiobagrus, Phyllonemus and Tanganikallabes.[39] Although not endemic on a genus level, six species of Chrysichthys catfish are only found in the Tanganyika basin where they live both in shallow and relatively deep waters;[39] in the latter habitat they are the primary predators and scavangers.[13] A unique evolutionary radiation in the lake is the 15 species of Mastacembelus spiny eels, all but one endemic to its basin.[17][34][40] Although other African Great Lakes have Synodontis catfish and Mastacembelus spiny eels, the relatively high diversity is unique to Tanganyika, which likely is related to its old age.[40]

Among the non-endemic fish, some are widespread African species but several are only shared with the Malagarasi and Congo River basins, such as the Congo bichir (Polypterus congicus), goliath tigerfish (Hydrocynus goliath), Citharinus citharus, six-banded distichodus (Distichodus sexfasciatus) and mbu puffer (Tetraodon mbu).[39]

Molluscs and crustaceans

The shell of the endemic thallasoid freshwater snail Tiphobia horei with its elaborate shape and spines.

A total of 68 freshwater snail species (45 endemic) and 15 bivalve species (8 endemic) are known from the lake.[41] Many of the snails are unusual for species living in freshwater in having noticeably thickened shells and/or distinct sculpture, features more commonly seen in marine snails. They are referred to as thallasoids, which can be translated to "marine-like".[42] All the Tanganyika thallasoids, which are part of Prosobranchia, are endemic to the lake.[42] Initially they were believed to be related to similar marine snails, but they are now known to be unrelated. Their appearance is now believed to be the result of the highly diverse habitats in Lake Tanganyika and evolutionary pressure from snail-eating fish and, in particular, Platythelphusa crabs.[17][42][43] A total of 17 freshwater snail genera are endemic to the lake, such as Lavigeria, Reymondia, Spekia, Tanganyicia and Tiphobia.[42] There are about 30 species of non-thallasoid snails in the lake, but only five of these are endemic, including Ferrissia tanganyicensis and Neothauma tanganyicense.[42] The latter is the largest Tanganyika snail and its shell is often used by small shell-dwelling cichlids.[44]

Crustaceans are also highly diverse in Tanganyika with more than 200 species, of which more than half are endemic.[17] They include 10 species of freshwater crabs (9 Platythelphusa and Potamonautes platynotus; all endemic),[45] at least 11 species of small atyid shrimp (Atyella, Caridella and Limnocaridina),[46] an endemic palaemonid shrimp (Macrobrachium moorei),[47] at least 23 endemic ostracods[48][49] and several copepods.[50]

Among Rift Valley lakes, Lake Tanganyika far surpasses all others in terms of crustacean and freshwater snail richness (both in total number of species and number of endemics).[41] For example, the only other Rift Valley lake with endemic freshwater crabs is Lake Kivu with two species.[51]

Other invertebrates

The diversity of other invertebrate groups in Lake Tanganyika is often not well-known, but there are at least 20 described species of leeches (12 endemics),[52] 9 sponges (7 endemic), 6 bryozoa (2 endemic), 11 flatworms (7 endemic), 20 nematodes (7 endemic), 28 annelids (17 endemic)[17] and the small hydrozoan jellyfish Limnocnida tanganyicae.[53]

Industry

Fishermen on Lake Tanganyika

It is estimated that 25–40% of the protein in the diet of the approximately one million people living around the lake comes from lake fish.[54] Currently, there are around 100,000 people directly involved in the fisheries operating from almost 800 sites. The lake is also vital to the estimated 10 million people living in the greater basin.

Lake Tanganyika fish can be found exported throughout East Africa. Commercial fishing began in the mid-1950s and has had an extremely heavy impact on the pelagic fish species; in 1995 the total catch was around 180,000 tonnes. Former industrial fisheries, which boomed in the 1980s, have subsequently collapsed.

Transport

Two ferries carry passengers and cargo along the eastern shore of the lake: MV Liemba between Kigoma and Mpulungu and MV Mwongozo between Kigoma and Bujumbura.

On Dec. 12, 2014, the ferry MV Mutambala capsized on Lake Tanganyika, and more than 120 lives were lost.[56]

History

Lake Tanganyika. The black line indicates Henry Morton Stanley's route.

It is thought that early Homo Sapiens was making an impact on the region already during the stone age. The time period of the Middle Stone Age to Late Stone Age is described as an age of advanced hunter-gatherers. It is believed they would have caused megafaunal extinctions.[57]

There are many methods in which the native people of the area were fishing. Most of them included using a lantern as a lure for fish that are attracted to light. There were three basic forms. One called Lusenga which is a wide net used by one person from a canoe. The second one is using a lift net. This was done by dropping a net deep below the boat using two parallel canoes and then simultaneously pulling it up. The third is called Chiromila which consisted of three canoes. One canoe was stationary with a lantern while another canoe holds one end of the net and the other circles the stationary one to meet up with the net.[58]

The first known Westerners to find the lake were the British explorers Richard Burton and John Speke, in 1858. They located it while searching for the source of the Nile River. Speke continued and found the actual source, Lake Victoria. Later David Livingstone passed by the lake. He noted the name "Liemba" for its southern part, a word probably from the Fipa language, and in 1927 this was chosen as the new name for the conquered German First World War ship Graf von Götzen which is still serving the lake up to the present time.[59]

World War I

Main article: Battle for Lake Tanganyika

The lake was the scene of two celebrated battles during World War I.

With the aid of the Graf Goetzen (named after Count Gustav Adolf Graf von Götzen, the former governor of German East Africa), the Germans had complete control of the lake in the early stages of the war. The ship was used both to ferry cargo and personnel across the lake, and as a base from which to launch surprise attacks on Allied troops.[60]

It therefore became essential for the Allied forces to gain control of the lake themselves. Under the command of Lieutenant Commander Geoffrey Spicer-Simson the British Royal Navy achieved the monumental task of bringing two armed motor boats HMS Mimi and HMS Toutou from England to the lake by rail, road and river to Albertville (since renamed Kalemie in 1971) on the western shore of Lake Tanganyika. The two boats waited until December 1915, and mounted a surprise attack on the Germans, with the capture of the gunboat Kingani. Another German vessel, the Hedwig, was sunk in February 1916, leaving the Götzen as the only German vessel remaining to control the lake.[60]

As a result of their strengthened position on the lake, the Allies started advancing towards Kigoma by land, and the Belgians established an airbase on the western shore at Albertville. It was from there, in June 1916, that they launched a bombing raid on German positions in and around Kigoma. It is unclear whether or not the Götzen was hit (the Belgians claimed to have hit it but the Germans denied this), but German morale suffered and the ship was subsequently stripped of its gun since it was needed elsewhere.[60]

The war on the lake had reached a stalemate by this stage, with both sides refusing to mount attacks. However, the war on land was progressing, largely to the advantage of the Allies, who cut off the railway link in July 1916 and threatened to isolate Kigoma completely. This led the German commander, Gustav Zimmer, to abandon the town and head south. In order to avoid his prize ship falling into Allied hands, Zimmer scuttled the vessel on July 26, 1916. The vessel was later raised in 1924 and renamed MV Liemba (see transport).[60]

Che Guevara

Main article: Che Guevara

In 1965 Argentinian revolutionary Che Guevara used the western shores of Lake Tanganyika as a training camp for guerrilla forces in the Congo. From his camp, Che and his forces attempted to overthrow the government, but ended up pulling out in less than a year since the National Security Agency (NSA) had been monitoring him the entire time and aided government forces in ambushing his guerrillas.[citation needed]

Recent history

In 1992 Lake Tanganyika featured in the British TV documentary series Pole to Pole. The BBC documentarian Michael Palin stayed on board the MV Liemba and travelled across the lake.

Since 2004 the lake has been the focus of a massive Water and Nature Initiative by the IUCN. The project is scheduled to take five years at a total cost of US$27 million. The initiative is attempting to monitor the resources and state of the lake, set common criteria for acceptable level of sediments, pollution, and water quality in general, and design and establish a lake basin management authority.[citation needed]

Effects of global warming

Because of increasing global temperature there is a direct correlation to lower productivity in Lake Tanganyika.[10] Southern winds create upwells of deep nutrient-rich water on the southern end of the lake. This happens during the cooler months (May to September). These nutrients that are in deep water are vital in maintaining the aquatic food web. The southernly winds are slowing down which limits the ability for the mixing of nutrients. This is correlating with less productivity in the lake.

See also

References

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External links

Wikivoyage has a travel guide for Lake Tanganyika.
Wikimedia Commons has media related to Lake Tanganyika.
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