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ECOLOGY OF CRABS & MOLLUSCS
 

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My laboratory’s primary research thrusts are in the study of the ecology of crabs and molluscs in wetland and coastal regions.  Extensive field studies on ocypodid crabs and littorinid snails have been carried out by my research students at two off-shore islands (e.g., Pulau Ubin, Tanjung Chek Jawa’s rocky shore and on the sandy-muddy lagoon on Pulau Hantu), as well as at other coastal sites on mainland Singapore (e.g., Pasir Ris mangroves, Changi beach and the East Coast sandy shores).

Ocypodid crab biology & ecology

Some of my research students are currently conducting research on the ecology of ocypodid crabs (fiddler crabs, ghost crabs and soldier crabs), the most prominent wetland and coastal macrofauna. These bioenergetically significant crustaceans play an important role in the nutrient cycling and energy flow in coastal ecosystems, and may be used as indicators of eco-system disturbances. A comparative study of mouthpart adaptations of ocypodid crabs to habitat characteristics sampled from many parts of the world (e.g., Singapore, Malaysia, Australia, Taiwan, China and Panama) is also ongoing.

Foraging ecology of fiddler crabs

Sexual dimorphism is distinct in fiddler crabs as the male has an enlarged cheliped that is used as a mate attractant and for combat with other males.  Only the minor cheliped can be used for foraging! 
 

What are the foraging strategies used by the male fiddler crab to compensate for this apparent ‘disadvantage’? Do males feed faster to compensate?

When do males & females leave a foraging patch?

Sequential patch depletion is studied by comparing the chlorophyll concentration in the surface sediment sampled from each patch.

 

Conclusion:   Male U. annulipes have higher critical threshold of [Chl a] in both PneuH & BareH

⇒     Males compensate by leaving a patch at a higher threshold of food density

[Chl a] depletion in Uca annulipes’ first five feeding patches in bare & pneumatophore mangrove microhabitats

Mean scoop rate vs carapace width of Uca annulipes

Conclusion:   For any given carapace width, female U. annulipes have a faster mean scoop rate than males

⇒     Males, with only one cheliped with which to feed, do not compensate for handicap by feeding faster

Relationship between (a) dactyl length and (b) dactyl-pollex width, with carapace width in Uca annulipes

Conclusion:  For any given carapace width, although slopes and intercepts are not significantly different between the two sexes, males tend to have larger DL & DPW

⇒     Males collect more sediment per scoop than females

Overall Conclusion:  Male U. annulipes compensates for the apparent ‘handicap’ of having only one cheliped with which to feed by: (1) leaving a patch at a higher threshold of food density, (2) larger scoops of sediment per lift, (3) traveling shorter distances in between patches

⇒     Male U. annulipes does not compensate by feeding at a faster rate than females

 

Sexual selection in fiddler crabs

     

 

 Are females attracted to larger males?

 

 

Female fiddler crabs' attraction to males that are magnified to different sizes is studied in the field. 

Conclusion: Size of male is an important criterion in mate choice.

 

Burrow fidelity study

On Pulau Hantu, two species of fiddler crabs, Uca annulipes and U. vocans are found in abundance on the lagoonal shore, with pure populations of U. vocans patchy in distribution and U. annulipes, the more abundant species.

Is there a difference in the burrow residency period between Uca vocans (a droving species) & U. annulipes (a non-droving species)?

Uca vocans (seen here in these photographs) and U. annulipes were tracked for a few consecutive days in many low tide periods in the field in order to answer the above question.

Repeated re-emergence is indicated by the number of sticks next to the burrow.

 

Ghost crab as a bioindicator

Density and spatial distribution of the burrows of the ghost crab, Ocypode ceratophthalmus, on the wave beaches at Pulau Hantu and East Coast Park were studied, in order to determine the potential of using the abundance of the crab as an indicator of human disturbance on Singapore beaches.

Can the ghost crab be used as a potential bioindicator for human disturbance on sandy shores in Singapore?

Burrows of juvenile Ocypode ceratophthalmus in southern Thailand are typically catapult-shaped. 

Is there a functional significance in this form of burrow architecture?

 

Mouthpart adaptations of ocypodids

Do the mouthparts of Australian fiddler crabs from different habitats differ in their setation?

Relationship between number of spoon-tipped setae and carapace width in Uca perplexa & U. vomeris

Conclusion: Uca perplexa (a sandy habitat fiddler crab) has significantly more spoon-tipped setae than U. vomeris (a muddy habitat inhabitant)

 

Foraging ecology of other ocypodids

I am also interested in getting students to study the feeding ecology of other ocypodids, such as Dotilla sp. and Scopimera sp.

 

Littorinid snail biology & ecology

Littorinid ecology and behaviour also fascinate my students and me.  We have investigated the strange ‘head standing’ behaviour of periwinkles, compared the enzyme stability in various species of periwinkles when subjected to heat stress and looked at the effects of temperature and density on the aggregation behaviour of periwinkles. In addition, we are also interested in using these gastropods as bioindicators of coastal habitats; studies involving the use of gastropod mucus and radula as non-invasive methods with which to assess environmental pollution have recently started.

Amazing! These Australian littorinids can withstand temperatures of more than 40ºC! Does the ‘head stand’ behaviour help to alleviate heat stress?

Two local littorinids also exhibit this peculiar ‘standing’ behaviour at Tanjung Chek Jawa, Pulau Ubin. Is there a ‘cooling-off’ effect seen in ‘standing’ Echinolittorina malaccana? Why are there more ‘standing’ Echinolittorina vidua than E. malaccana?

 

  
 

Selected recent publications from the Ecology Lab:

  1. Lim, S.S.L. & J.A.C. Wong.  In press.  Burrow residency and re-emergence rate in a droving species, Uca vocans (Linnaeus, 1758) and its sympatric associate, U. annulipes (H. Milne Edwards, 1837) (Brachyura, Ocypodidae).  Crustaceana.
  2. Yong, A.Y.P. & S.S.L. Lim.  2009.  The potential of Ocypode ceratophthalmus (Pallas, 1772) as a bioindicator of human disturbance on Singapore beaches.  Crustaceana.  82(12): 1579-1597.
  3. Lee, S.L. & S.S.L. Lim.  2009.  Zonation and heat tolerance of three littorinid gastropods on the rocky shore of Tanjung Chek Jawa, Singapore.  The Raffles Bulletin of Zoology.  57(2): 551-560.
  4. Lim, S.S.L. & C.K Lim.  2008.  Running speed of Uca annulipes (H. Milne Edwards, 1837) and Uca vocans (L., 1758).  Crustaceana 81(11): 1367-1380.
  5. Lim, S.S.L., R. Yeo, P.K.L. Ng & S.K. Tan.  2008.  Front lines: 91-114. [In] Ng, P.K.L., L.K. Wang & K.K.P. Lim (eds). Private lives: An éxpose of Singapore’s mangroves.  National University of Singapore.  249 pp
  6. Lim, S.S.L.  2008.  Body posturing in Nodilittorina pyramidalis and Austrolittorina unifasciata (Mollusca: Gastropoda: Littorinidae): a behavioural response to reduce heat stress.  [In] Davie, P.F. & J.A. Phillips (eds.), Proceedings of The Thirteenth International Marine Biological Workshop, The marine fauna and flora of Moreton Bay, Queensland.  Memoirs of The Queensland Museum – Nature  54(1): 339-347.
  7. Lim, S.S.L. & T.L. Tan.  2008.  The use of infrared spectroscopy as a test for species-specific pedal mucus in gastropod molluscs – a comparative study in Moreton Bay and Singapore.  [In] Davie, P.F. & J.A. Phillips (eds.), Proceedings of The Thirteenth International Marine Biological Workshop, The marine fauna and flora of Moreton Bay, Queensland.  Memoirs of The Queensland Museum – Nature  54(1): 349-354.
  8. Lim, S.S.L. & Rosiah A.  2007.  Influence of pneumatophores on the burrow morphology of Uca annulipes (H. Milne Edwards, 1837) in the field and in simulated mangrove micro-habitats.  Crustaceana  80(11): 1327-1338.
  9. Ng, P.K.L., S.S.L. Lim, L.K. Wang & L.W.H. Tan.  2007.  Private lives: An exposé of Singapore’s shores.  National University of Singapore.  212 pp.
  10. Lim, S.S.L. & M.M.S. Heng.  2007.  Mangrove micro-habitat influence on bioturbative activities and burrow morphology of the fiddler crab, Uca annulipes (H. Milne Edwards, 1837).  Crustaceana  80(1): 31-45.
  11. Lim, S.S.L.  2006.  Fiddler crab burrow morphology: How do burrow dimensions and bioturbative activities compare in sympatric populations of Uca vocans (Linnaeus, 1758) and U. annulipes (H. Milne Edwards, 1837).  Crustaceana  79(5): 525-540.
  12. Lim, S.S.L., Lee, P.S. & C.H. Diong.  2005.  Influence of biotope characteristics on the distribution of Uca annulipes (H. Milne Edwards, 1837) and U. vocans (Linnaeus, 1758) (Crustacea: Brachyura: Ocypodidae) on Pulau Hantu Besar, Singapore.  The Raffles Bulletin of Zoology  53(1): 111-114.
  13. Lim, S.S.L.  2004.  A comparative study of some mouthpart adaptations of Uca annulipes (H. Milne Edwards, 1837) and U. vocans (Linnaeus, 1758)(Brachyura, Ocypodidae) in relation to their habitats.  Crustaceana  77(10): 1245-1251.
  14. Lee, S.L. & S.S.L. Lim.  2004.  Do diameters of burrows and food pellets provide estimates of the size structure of a population of Dotilla myctiroides on the sand-flats of Ao Tung Khen, Phuket, Thailand?  Phuket Marine Biological Center Research Bulletin  65: 55-60.
  15. Lee, P.S. & S. S.L. Lim.  2003.  Distributional patterns and species density of a fiddler crab community (Uca annulipes and U. vocans) at Telok Assam, Bako National Park, Sarawak.  Sarawak Museum Journal Malaysia.  LVIII (79) New Series: 183-198.
  16. Lim, S.S.L. & C.H. Diong.  2003.  Burrow-morphological characters of the fiddler crab, Uca annulipes (H. Milne Edwards, 1837) and ecological correlates in a lagoonal beach on Pulau Hantu, Singapore.  Crustaceana.  76(9): 1055-1069.

Selected recent conference presentations from the Ecology Lab:

  1. Lim, S.S.L., C.H. Diong & S.N.O. Khatijah.  2009.  Influence of magnified reflections of male chelipeds on female choice in Uca annulipes.  Presented at The Crustacean Society Summer Meeting 2009 (20-24 September 2009), Tokyo, Japan.
  2. Lim, S.S.L., A.Y.P. Yong & P. Tantichodok.  2009.  Ocypode ceratophthalmus: Precision engineers of sandy beaches.  Presented at The Crustacean Society Summer Meeting 2009 (20-24 September 2009), Tokyo, Japan.
  3. Kalpana, S. & S.S.L. Lim.  2009.  Maxilliped setation in Uca perplexa and U. vomeris – evidence of habitat adaptation.  Presented at The Crustacean Society Summer Meeting 2009 (20-24 September 2009), Tokyo, Japan.
  4. Lim, S.S.L. and Fahmy M.S.  2008.  Is ‘standing’ posture an effective behavioural adaptation to reduce heat stress in Echinolittorina malaccana?  Presented at the IX International Symposium on Littorinid Biology and Evolution 2008, (2-7 September 2008), Oia, Spain.
  5. Lim, S.S.L., X.T. Tan and C.H. Diong.  2008.  Foraging ecology of Uca annulipes in two mangrove microhabitats in Singapore.  Presented at The Crustacean Society Summer Meeting 2008, (9-13 June 2008), Galveston, USA.
  6. Wong, J.A.C. and S.S.L. Lim.  2008.  Comparison of re-emergence rate and burrow residency duration in a droving species, Uca vocans and its sympatric associate, U. annulipes.  Presented at The Crustacean Society Summer Meeting 2008, (9-13 June 2008), Galveston, USA.
  7. Yong, A.Y.P. and S.S.L. Lim.  2007.  Distribution and abundance of ghost crabs, Ocypode ceratophthalmus in relation to abiotic factors and human disturbance on Singapore beaches.  Presented at the 21st Pacific Science Congress, (June 12-18 2007), Okinawa, Japan.