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Bivalve traits and distributions to explore species diversity at tropical and temperate tidal flats

24 October 2008

PhD ceremony: mw. T.J. Compton, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Bivalve traits and distributions to explore species diversity at tropical and temperate tidal flats

Promotor(s): prof.dr. W.J. Wolff, prof.dr. T. Piersma

Faculty: Mathematics and Natural Sciences


Greater diversity in the tropics might suggest that species have specialized adaptations that enable them to coexist. In this thesis, bivalve species are used as a model organism to examine whether there are greater physiological, morphological and habitat specializations in tropical than temperate tidal flat systems. We show that tropical bivalves have adapted to the relatively constant climate of the tropics by having narrow thermal tolerance ranges. Unlike temperate species that deal with fluctuating temperatures, tropical species might instead invest their energy into other adaptive specializations that increase their competitive advantage. But surprisingly, bivalve feeding organs showed greater morphological overlap in tropical Roebuck Bay relative to the temperate Wadden Sea. Morphological overlap appears to be synonymous with diet overlap, as a direct correlation between bivalve feeding organs and diet stable isotope signatures was observed. These results suggest that competition for food is not a driver of resource specialization in Roebuck Bay. Based on the observation that juvenile bivalve species can actively select their habitat, we expected that habitat differentiation should be important for species coexistence. However, a comparison across nine tropical and temperate tidal flats showed that bivalve species do not use the full range of sediments available within a system, but instead prefer the same sediment type. Results from this thesis suggest that habitat and diet specializations are not important for bivalve species coexistence in diverse tidal flat systems. This leads us to wonder how coexistence is possible in diverse tidal flats like Roebuck Bay.


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