Transcript Tropical Lakes Biodiversity Crisis

The Tropical Lakes Biodiversity
Crisis
Paul Hacker, Ryan Haines & Alex Swan
http://www.go2africa.com/location/6482/why-go
Outline
 Case Study Introduction: Lake Victoria (Witte et al.
2007)
 Analysis of Witte et al. (2007)
 Conclusions from Witte et al.
 Supporting literature
 Conclusion
 Discussion
Case Study: Lake Victoria
(Witte et al. 2007)
http://www.theasc.com/blog/wpcontent/uploads/2011/08/09.-africa_map.jpeg
 Location: Africa - Uganda /
Kenya / Tanzania.
 Size: 68,800km2
 Elevation: 1,134m
 Age: ~ 1 million years
 Dry until 14,000 years ago.
 Fish Species: Several 100
species of haplochromine
cichlids and Nile Perch.
http://www.worldatlas.com/aatlas/infopage/lakevictoria.
gif
Case Study: Lake Victoria
(Witte et al. 2007)
Astatotilapia nubila
 Haplochromine cichlids (>500 sp.)
 Difficult to distinguish
 Evolved in last 14,000 years (Kitchell et al. 1997).
 Monophyletic assemblage
 Phenotypically similar
 Males brightly coloured
 Females choose males based on
colouration (Witte et al. 2007).
http://www.african-cichlid.com/Nubila8116.jpg
Astatoreochromis alluaudi
 Historic food to local peoples &
important part of economy (Kaufman et al. 1997 &
Kitchell et al. 1997).
 Past studies grouped them together.
http://www.african-cichlid.com/Alluaudi4623.jpg
Case Study: Lake Victoria
(Witte et al. 2007)
 Hypothesis: “The identification of this speciose group
to the species level is helpful in unraveling what
happened in Lake Victoria and crucial for the proper
management of its fishery and biodiversity”
Species Distinction: Problem
 Haplochromine cichlids are particularly difficult to
distinguish between species - need specialists
 Intraspecific variation
 Phenotypic plasticity
 Sexual dimorphism
 Colour polymorphism
 Management implications
 Managing for 5oo+ species as 1 causes some problems.
 Signals may not paint the correct picture.
Case Study: Lake Victoria
(Witte et al. 2007)
 A quick history lesson about human involvement in
Lake Victoria before we dive into the data collection
by Witte et al.
Case Study: Lake Victoria
(Witte et al. 2007)
The Human Problem!
 Critically threatened due to humans!
 Collapsing fisheries! (Kaufman et al. 1997 & Witte et al.
2007).
 Lake wide environmental
degradation! (Kaufman et al. 1997 & Witte et al. 2007).
 “Whole sale loss of fish species”! (Kaufman
et al. 1997).
https://global3.memecdn.com/grumpy-catstrikes-again-human-race_o_1112508.jpg
Case Study: Lake Victoria
Causes?
 INTRODUCED SPECIES!
 EUTROPHICATION!
 OVERFISHING!
(Witte et al. 2007)
http://images1.fanpop.com/images/photos/2200000/home
-alone-home-alone-2258019-1024-768.jpg
Case Study: Lake Victoria
(Witte et al. 2007)
INTRODUCING SPECIES!!
 Nile Perch (Lates niloticus)
 Introduced in 1950s to support
fisheries (Witte et al. 2007).
 “The Saviour” (Greboval 1990).
 Yields 4x greater than native sp.
(Kitchell et al. 1997).
 25,000 tons  175,000 tons between
1978-1990.
 150,000 jobs created (Greboval 1990).
 Successful predator
 Grows 1kg in first year (Kitchell et al. 1997).
 Can reach 100kg (220lbs) (Kitchell et al. 1997).
http://www.busiweek.com/img2/nile-perch-colour.jpg
Case Study: Lake Victoria
(Witte et al. 2007)
EUTROPHICATION!!
 Human population pressure!
(Odada et al. 2003)
 Human untreated waste
 30million people live in the rift valley
 Water transparency reduction




(Odada et al. 2003)
5m in 1930  1m in 1990s
Phosphorous loading in deep water
Nitrogen loading in shallow waters
Periods of anoxic conditions in
shallow water
https://sp.yimg.com/ib/th?id=HN.608029410971356475&pid=15.1
&P=0
Case Study: Lake Victoria
(Witte et al. 2007)
OVERFISHING!!
 Historical problem not
improving
 1950s overfishing – Outboard
motors & Nylon nets
 84,000 fisherman in 1990/91 (Odada et
(Kaufman et al. 1997)
al. 2004).
 122,000 fishermen in 2000 (Odada et al.
2004).
 Unrestricted access and lack of
enforcement of existing
legislation (Odada et al. 2004)
https://c2.staticflickr.com/4/3087/2331808854_31e2549c7b_z.jp
g?zz=1
Case Study: Lake Victoria
(Witte et al. 2007)
Timeline: The decline of cichlids and the rise of the Nile Perch.
 1920s: Eutrophication began (Hecky 1993).
 1950s: Introduction of Nile perch (Witte et al. 2007).
 Needed to support fishery due to overfishing of cichlids.
 1980s: Nile Perch Boom & Blue-green algal bloom! (Witte et al. 2007).
 Haplochromines vanished from sublittoral and offshore areas.
 1990s: Overfishing = Decline in Nile Perch (Witte et al. 2007 & Kitchell et al.
1997).
 Slow recovery in some cichlids
 1998 Nile Perch harvest half of 1990 catch.
 Eutrophication still a problem.
 IMPORTANT: Most studies categorize cichlids as one.
Methods
(Witte et al. 2007)
What was caught?
Haplochromine cichlids
 Eleven Stations
monitored for 26
years (1979-2005)
 Transect 5km wide,
depth ranges from 215m
Witte et al. (2007)
Methods
(Witte et al. 2007)
 Trawling samples
 Small
 Bottom (headrope: 4.6m, cod-end mesh: 5mm)
 Surface (beam: 4.5m, cod-end mesh: 5mm)
 Large
 The gulfs (headrope: 18-25m, cod-end mesh: 20mm)
http://anw.inl.nl/article/trawler#s=0&l=&lp=
Witte et al. (2007)
Methods
(Witte et al. 2007)
 Rocky shores fished
 Gill nets
 Local traps
 Angler rods baited with worms
https://photosundari.wordpress.com/2012/01/17/960/
 Adults and Sub-adults
 Approx >4cm long
http://www.oldeastafricapostcards.com/?page_id=2338
Methods
(Witte et al. 2007)
 Total number of haplochromine species in Lake
Victoria is still debated…
http://etims.net/?p=6052
... So Witte et al. (2007) must consider all data!
Results
(Witte et al. 2007)
Species Discovery/ Distribution
Species Discovery and Description
 3 periods of study
1. 1888-1938

61 species: little to no ecological data
2. 1956-1969
 104 species: littoral studies and species descriptions
3. 1975- present
 Estimated 500+ species
Results
(Witte et al. 2007)
Species Discovery/Description
Witte et al. (2007)
Results
(Witte et al. 2007)
Trophic Groups
 15 groups have been identified
 Number of species per group different
 Highest number of individuals = piscivores
 Highest biomass = detritivores
 Habitat type determined distribution
 Multiple habitat types means many sampling stations
Results
(Witte et al. 2007)
Haplochromine Communities
 Many different communities
 Communities differ vastly based on substrate
 Bottom: Sand (75) > Mud (49)
 Causes of differences
 Food availability
 Abiotic conditions:
 light effects feeding efficiency
 Dissolved oxygen
Results
(Witte et al. 2007)
Is the biodiversity Crisis in Lake Victoria Real?
Witte et al. (2007) analyze the data
http://register.eau.ac.th/
Results
(Witte et al. 2007)
Is the biodiversity Crisis in Lake Victoria Real?
There has been an overall decline in haplochromines!!!
 80 species disappeared from 1972-1990…
 BUT scientists disagree
 Can we determine extinction based on extirpation?
 NO, disagreements over causes or severity
Luckily, Witte et al. (2007) attempt to analyze the full
picture coupling their findings with the historical
Results
(Witte et al. 2007)
Impacts on Communities
 1987 reported decreases (Barel et al. 1985, Coulter et al. 1986)
 >90% sublittoral
 70% littoral
 40% rock dwelling
NOT NECESSARILY CORRECT!
What does the data ACTUALLY indicate?
 Nile perch have inverse distribution
 Abiotic factors can not be ruled out
Results
(Witte et al. 2007)
Impacts on Trophic Groups
1.
Large size species declined faster than small
 Piscivores, molluscivores, insectivores
2. Interspecific differences
 Number of individuals = same, species composition is
different
 Zooplanktivores: H. pyrrhocephalus better adapted to lowlight than H. heusinkveldi
 Spawning and diet effected
 Gills surface area increased 70% in H. pyrrhocephalus between
1970-1990.
Results
(Witte et al. 2007)
Adaptive Responses in Recovering Species
Morphological selection and creation of “new species” has
occurred
Why?
1. Populations in all areas understudied
2. Anatomy of coloration changes due to environmental
changes
3. Creation of hybrids
4. Genetic changes have taken place in small surviving
populations
5. Combination of the above
Conclusion
(Witte et al. 2007)
What do we already know?
 Haplochromines can not be considered as a
homogeneous unit
 Adaptive responses to water conditions have played a
role in population dynamics
 Low- light adaptations advantageous
 Zooplanktivourous diet advantageous
Conclusion
(Witte et al. 2007)
What do we already know?
 Need a credible list on extinction to be able to
implement rigorous regulations and criteria
 Currently the number of unknown extinctions is likely
high
 Causes of haplochromine populaiton changes
 Nile Perch
 Eutrophication
 Fishing
Conclusion
(Witte et al. 2007)
Why do we need to know more?
 Knowledge of haplochromine cichlids is important for
management
 Biodiversity
 Fish production
 The studies in the 70s and 80s were integral in
identifying crisis
 the extent of the crisis is still unknown
Conclusion
(Witte et al. 2007)
What’s next?
 Future Management
 Focus on Nile perch important, but not comprehensive
 Eutrophication needs to be halted and reversed if
possible
 Areas of refuge need to be created
 Each habitat type needs to be represented
 Key issue in managing the lake:
KNOWLEDGE OF CICHLIDS
Case Study #1: Witte et al 2013
 Compared the densities and diversity of cichlids over
different substrate types before and after
environmental damage of Lake Victoria
 Anthropogenic Environmental Damage
 Nile Perch—disruption of the food web
 Algal blooms
 Eutrophication
 Decreased water transparency and Dissolved Oxygen (DO)
Case Study #1: Cont’d
 Eutrophication and introduction of Nile Perch to the
lake coincided with the disappearance of cichlid
species.
 Debate on what the cause of cichlids declining is.
Eutrophication or Nile Perch?
 This study looks at the effects of eutrophication as a
possible cause for the decline of cichlids.
Case Study #1: Cont’d
 Significantly more DO and
light at the bottom of
sand sites.
 Significantly higher mean
number of species in the
sand sites.
 Mud sites had
significantly more
detritivores but
significantly less
insectivores and mollusc
shellers.
Case Study #1: Cont’d
 Mud sites saw a
significant decline in
haplochromine catch and
diversity.
Case Study #1: Cont’d
 Mud substrate sites had
lower frequency of
brooding females overall
and in months with
predicted high turbidity
levels.
 Months with low DO (FebApril) affected the
frequency of brooding
females regardless of
substrate type.
Case Study #1: Cont’d
 Human impacts have caused about 70% decline in the
loss of species in Lake Victoria.
 Nile Perch strongly affected haplochromine densities
and forced them into different, less ideal habitats.
 However, results of their study suggest that water
transparency affects species diversity the most.
Case Study #2: Getahun & Stiassny 1998
 Ethiopia is currently facing fish biodiversity crisis.
 Diversity of ichthyofauna is unknown, like Lake
Victoria.
 Environmental degradation at accelerated levels.
Case Study #2: Cont’d
 Threats to freshwater fauna:
 River/Stream alterations (dams and irrigation)
 Deforestation
 Introduction of invasive species
 Interestingly, fish as a food source is not a major
threat in Ethiopia.
Case Study #2: Cont’d
 81% from Cyprinidae.
 Most diverse family.
 Cichlids comprise largest
part of inland commercial
fishery.
Case Study #2: Cont’d
 Vulnerable freshwater ecosystems are not well
protected
 Diversity of fish is underestimated
 Fish faced with considerable threats
 HIPPO
 Need more studies to establish baseline of fish
diversity knowledge
 Need to alleviate environmental degradation
Case Study #3: Kaufman et al 1997
 Case study of rapid speciation and adaptive radiation
of haplochromines in Lake Victoria is unprecedented
 However, Lake Victoria is a case study in
anthropogenic mass extinction
 >50% of endemic fishes disappeared 1980-1986
 Examine the dynamics of haplochromine volatility
 Find ways to manage and conserve
Case Study #3: Kaufman et al 1997
 East Africa has greatest
concentration of freshwater fish
species on earth.
 Around 2000 species
 8% of global fish species
 Haplochromines very diverse
group.
 Traditionally lumped together as
one unit
 Increased taxonomic distinction
has provided a clearer picture of
cichlidae family
Case Study #3: Kaufman et al 1997
 Haplochromines are relatively young
 12,000 years old
 Where does 600+ species of fish with broad trophic
variation come from in such a short amount of time?
 Re-invasion of Lake Victoria from outside the basin
 Intra-lacustrine radiation
 Not mutually exclusive
Case Study #3: Kaufman et al 1997
 Re-invasion of Lake Victoria from other Lakes
 Great Rift Lakes are connected
 Most likely from Edward-George Lake System
 Haplochromines do exist in Lake Kyoga and Edward-George
Lake System
 Rescue effect would have to flow both ways
 From Lake Victoria to Edward-George Lake System and vice
versa
 Could only be possible if flooding was great enough to create
more lacustrine connectivity between these lake systems
Case Study #3: Kaufman et al 1997
 Lacustrine Radiation
 Rapid physical change of the lake could create new
habitat (Volcanic eruptions and fluctuating water levels).
 New habitat allows for species radiation to occur.
 Isolation of sub-lakes and lagoons on a decadal time
scale could allow for species radiation
 Lagoons and isolated lakes are hostile to lacustrine taxa
 Rapid adaptation would be needed to survive
 Haplochromines are volatile and could potentially adapt
that quickly
Case Study #3: Kaufman et al 1997
 Haplochromines have faced previous extinction cycles and
are quite resistant to it
 If the extinction wave in the 80’s has passed, then the
existing flock could be the basis for future lacustrine
radiation
 Find ways to conserve haplochromines via:
 Decreasing habitat degradation
 Increased speciation distinction knowledge
 Increased studies of haplochromine populations now that
Nile Perch has decreased sufficiently to allow for a recovery
effect.
Conclusion
 Tropical lakes are all facing anthropogenic changes.
 Species distinction plays an important role in
identifying biodiversity loss
 Historically not properly studied and understood
 Must know more for correct management
 Actions going forward
 Halt environmental degradation
 Enforce international fishing regulations
Questions?
Discussion
1. Should management strategies target restoring the
original ecosystem or sustaining the current
equilibrium?
2. If you were to manage Lake Victoria, what aspect of
the lake would you focus on first?
3. Will the international aspect of management
preclude success? Or does economic development
of surrounding countries play a more significant role
in management practices?
Discussion
4. How integral are regulations in solving this crisis?
Will they work?
5. Is gathering data on individual species (500+)
realistic? Should energy be better spent elsewhere?
References
Barel C.D. N., R. Dorit, P.H. Greenwood, G. Fryer, N. Hughes, P.B.N. Jackson, H. Kanawabe, R.H. Lowe-McConnell, M. Nagoshi, A.J.
Ribbink, E. Trewavas, F. Witte and K. Yamaoka. 1985. Destruction of fisheries in Africa’s lakes. Nature 315: 19-20.
Coulter, G.W., B.R. Allanson, M.N. Bruton, P.H. Greenwood, R.C. Hart, P.B.N. Jackson and A.J. Ribbink. 1986. Unique qualities and
special problems of the Afican Great Lakes. Environmental Biology of Fishes 17: 117-118.
Getahun, A., and M. L. J. Stiassny. 1998. The freshwater biodiversity crisis: the case of the Ethiopian fish fauna. Ethiopian Journal of
Sience 21: 207-230.
Greboval, D. 1990. Socio-economic issues for planning in support of fisheries management. In CIFA report of the 5 th session of the
Sub-committee for the Development and Management of the Fisheries of Lake Victoria, Mwanze, Tanzania, 12–14 September
1989. FAO Fisheries Report 430: 75–97.
Hecky, R. E. 1993. The eutrophication of Lake Victoria. Verhandlungen der Internationalen Vereinigung fu¨r Theoretische und
Angewandte Limnologie 25: 39–48.
Kaufman, L.S., L.J. Chapman, and C. A. Chapman. 1997. Evolution in fast forward: haplochromine fishes of the Lake Victoria region.
Endeavour 21: 1997.
Kitchell, J.K., D.E. Schindler, R. Ogutu-Ohwayo, and P.N. Reinthal. 1997. The Nile Perch in Lake Victoria: interactions between
predation and fisheries. Ecological applications 7: 653-664.
Odada, E.O., D.O. Olago, K. Kulindwa, M. Ntiba, and S. Wandinga. 2004. Mitigation of environmental problems in Lake Victoria, East
Africa: casual chain and policy options analyses. A Journal of the Human Environment 33: 13-23.
Witte, F., J.H. Wanink and M. Kishe-Machumu. 2007. Species distinction and the biodiversity crisis in Lake Victoria. Transactions of
the American Fisheries Society 136: 1146-1159
Witte, F., O. Seehausen, J.H. Wanink, M.A. Kishe-Machumu, M. Rensing, and T. Goldschmidt. 2013. Cichlid species diversity in
naturally and anthropogenically turbid habitats of Lake Victoria, East Africa. Aquatic Sciences 75: 169-183.