Kenyan Mangrove Crabs
The Kenyan Experience
Before summarizing what my graduate biology thesis was about I would like to thank the people with whom I spent almost all of my time there living together. From the Università degli Studi di Firenze Stefano Cannicci and Silvia Ritossa, from the University of Gent Jan Schrijvers, from a bit all over the world Bruno Bautil, from the K.M.F.R.I. Diane Anyona and last but not least from my home university, home town, home high school and home primary school Marc Verneirt. Remember all the great times we had together guys.
Kenyan Mangrove Crabs : feeding ecology and behavioural ecology of some selected species.
This thesis, which was defended with high honours, is concentrating on two aspects of Kenyan mangrove crabs. Starting from several crab species (Cardisoma carnifex, Epixanthus dentatus, Eurycarcinus natalensis, Metopograpsus oceanicus, Metopograpsus thukukhar, Selatium elongatum, Sesarma guttatum, Sesarma leptosoma, Sesarma ortmanni, Neosarmatium meinerti and Thalamita crenata) it tries to understand which species are eating which food items. One species is investigated in particular, namely Thalamita crenata and in a second part of this thesis its orientational capacities are investigated.
The investigation of the natural diets was done through stomach content analysis using the percentage occurence method. For the initial crab species a significant correlation was found between the stomach fullness and the herbivority (and hence also carnivority), when they were classified in four groups : 100% herbivore (C. carnifex, S. elongatum, S. guttatum, S. ortmanni and N. meinerti), 75% herbivore (M. oceanicus, M. thukukhar and S. Leptosoma), 25% herbivore (E. dentatus and T. crenata) and 0% herbivore (E. natalensis). The diet of T. crenata in particular revealed that this species ingests a variety of food items (Algae, Anomura, Brachyura and other Crustacea, Bivalvia, Foraminifera, Gastropoda, Pisces, Polychaeta, Polyplacofora, mangrove detritus and sand). Also significant differences were found when confronting stomach fullness and herbivority at low/high tide, spring/neap tide and day/night time. Its diet contains more in quantity and more animal matter at spring tide, low tide and during daytime.
For the orientational capacities of T. crenata a series of homing experiments were designed based on removal of the crab from its home hole using different distances, transporting means, terrain alternations, and so forth, while variables such as homing performance, walking behaviour, straightness index of the walk and homeward component were investigated. It was found that vision of the terrain closeby was a major help in going back to its home range.
Keywords : mangrove, crab, diet, Thalamita crenata, Kenya.
Honours degree : magna cum laude, met grote onderscheiding, with high honours
Scientific publications with respect to this study can be found in :
Cannicci, S., F. Dahdouh-Guebas, D. Anyona & M. Vannini, 1995. Homing in the mangrove swimming crab Thalamita crenata (Decapoda, Portunidae). Ethology 100: 242-252.
Cannicci, S., F. Dahdouh-Guebas, D. Anyona & M. Vannini, 1996. Natural diet and feeding habits of Thalamita crenata (Decapoda : Portunidae). Journal of Crustacean Biology 16(4): 678-683.
Dahdouh-Guebas, F., M. Verneirt, J.F. Tack, D. Van Speybroeck & N. Koedam, 1997. Food preferences in Neosarmatium meinerti de Man (Decapoda : Sesarminae), and its possible effects on mangrove regeneration. Hydrobiologia 347: 83-89.
Dahdouh-Guebas, F., M. Verneirt, J.F Tack, D. Van Speybroeck & N. Koedam, 1998. Propagules predators in Kenyan mangrove forests and their possible effect on the regeneration. Marine and Freshwater Biology 49: 345-350.
Dahdouh-Guebas, F., M. Giuggioli, A. Oluoch, M. Vannini & S. Cannicci, 1999. Feeding habits of non-ocypodid crabs from two mangrove forests in Kenya. Bulletin of Marine Science 64(2): 291-297.
As you can see, this is an extremely short summary for many months and years of research. If some of your questions remain unanswered of if you just want to get some more detailed information do not hesitate to mail me. I'll try to answer or to help you get in touch with some of the greater specialists in this field.
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This page is maintained by Farid Dahdouh-Guebas, fdahdouh@vub.ac.be