mangrove resilience and fiddler crabs in south africa...•fiddler crabs are largely...
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Renzo Perissinotto, Janine B Adams, Ricky H Taylor, Anusha Rajkaran, Nelson AF Miranda, Nasreen Peer, Jacqueline L Raw.
Mangrove resilience and fiddler crabs in South Africa
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Ecosystem stability and resilience
…a greater biodiversity promotes ecosystem stability and resilience through the assured maintenance of ecosystem processes and reduced susceptibility to
species invasion. …a greater biodiversity insures the delivery of
ecosystem goods and services which are economically valuable.
Macarthur 1955, Goodman 1975, Loreau 2000, Chapin et al. 2000
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Ecosystem stability and resilience
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“Systems need to be managed for flexibility rather than stability”“managing for resilience requires directing a system in a way that provides flexibility during times of disturbance and that allows a way to take advantage of the latent diversity within the system and the range of opportunities following release.”
Ecosystem stability and resilience
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Stress events are not always negative
“Thus, with continued degradation caused by local stressors, altered communities become composed of disturbance‐tolerant species…making the ecosystem more resilient to climate disturbance”
Ecosystem stability and resilience
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South African mangrovesIn sheltered bays or estuaries
Subtropical and temperate
Thrive at latitudinal limits
Macnae 1963
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South African mangroves
NORT
HER
N
GRO
UP
SOUTH
ERN
GRO
UP
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What has changed….
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What has changed….
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What has changed….
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2015/2016 dedicated survey
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2015/2016 dedicated survey• Physico‐chemical data• Microphytobenthic biomass• Tree density, diversity, and age structure
• Meiofauna density and dominant groups
• Macrobenthos – mollusc and arthropod diversity and density
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The cosmopolitan distribution of fiddler crabs
www.fidd
lercrab.info/uca_ran
ges.html
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a. Uca annulipes
b. Uca chlorophthalmus
c. Uca hesperiae
d. Uca urvillei
e. Uca inversa(Photo courtesy of Branch et al. 2010)
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Uca inversa
XX
Uca hesperiae
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Uca urvilleiUca chlorophthalmus
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Uca annulipes
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Complications – continuous climate and land use changes
Resilience and
adaptable nature
Global changeBo
th
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Uca annulipes
The St Lucia fiddler crab community as a case study…
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The St Lucia fiddler crab community as a case study…
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Fiddler crab resilience
Influenced by:
physico‐chemical variables
• Eurythermal (Edney 1961)
• Euryhaline (Khanyile 2012)
• Soil moisture (Macnae 1963)
environmental cycles
• Diel
• Tidal
• Seasonal
?
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Feeding dynamics of the fiddler crab Uca annulipes in a non‐tidal mangrove forest
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• Fiddler crabs are largely herbivores feeding on microphytobenthos (MPB)
• Feeding behaviour is affected by tidal rhythms, temperature, time of day, sexual dimorphism
Feeding dynamics of the fiddler crab Uca annulipes in a non‐tidal mangrove forest
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Seasonal and diel variation
Summer Winter
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Seasonal and diel variation
Summer Winter
summer winter
4.0 – 10.7 3.4 – 6.4
% of available MPB consumed per day in each season
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Requires an open connection to the ocean
LIFE CYC
LE
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Suspended silt and salinity tolerances of the first zoeal stage of the fiddlercrab Uca annulipes (Decapoda: Brachyura)
• First stage larvae were maintained under various salinities and silt levels in the laboratory
• They were well cared for• Mortality was measured at 2, 4, 8, 16, 24, 48, 72, 96, and 120 hours
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RESPONSE TO SILT LOADINGNo significant difference in survival but a lower turbidity level appears to be optimal
Between 40 – 60 % survival rate overall
Turbidity in the Narrows ‐> 50 – 100 NTU
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RESPONSE TO SALINITY FLUCTUATIONS
20 – 35 is the ideal salinity for development (~ 60 % survival rate)
At salinities < 20 and > 35 survival is 0%
Salinity in the Narrows ‐> 5 ‐ 10
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Conclusion• Adaptable• Maintain ecological role in the absence of important environmental rhythms
• Potentially resilient species
BUTrequire a connection to the marine environment
Not all life stages display the same level of resilience
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Conclusion• Adaptable• Maintain ecological role in the absence of important environmental rhythms
• Potentially resilient species
BUTrequire a connection to the marine environment
Only sustainable due to refuge populations
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IMPLICATIONS FOR CONSERVATION?
• Consider what the most resilient ecosystem components require to survive
• This knowledge gives us a direction and priority for conservation efforts
…In this case…marine connectivity is key
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THANK YOU