Adaptive value of migrations and nursery use for an intertidal bivalve
Hiddink, J.G. (2002). Adaptive value of migrations and nursery use for an intertidal bivalve, in: Hiddink, J.G. The adaptive value of migrations for the bivalve Macoma balthica. pp. 123-133
In: Hiddink, J.G. (2002). The adaptive value of migrations for the bivalve Macoma balthica. PhD Thesis. Rijksuniversiteit Groningen: Groningen. ISBN 90-9016102-3. 172 pp., more
Ontogenetic niche changes (migrations) are worthwhile when there exist spatial differences that are age or size-selective. In the Wadden Sea, juveniles of the bivalve Macoma balthica use nurseries in the high intertidal, while adults are more abundant in the low intertidal. Therefore, a M. balthica individual has to migrate twice, from the primary settlement locations (low) to the high-level nursery (spring migration) and back to the low intertidal at an age of 9 months (winter migration). This study evaluates by means of a model based on empirical data, under what conditions the costs of migration (increased mortality) are traded-off against an increased reproductive output (RO). Density was modelled as a function of predation and migration mortality. From density the RO over a period of 5 years was calculated, assuming that parasitised animals do not reproduce. RO was maximised for M. balthica that settle in the high intertidal and migrate to low tidal flats at an age of approximately 9 months. Shrimp predation makes living on the low tidal flats unfavourable for small M. balthica. Parasitation by the trematode Parvatrema affinis makes it beneficial for M. balthica to leave the high tidal flats around the age of 1 year. Of other examined predators (crabs, birds and polychaetes), some did affect the RO, but none of them had an effect on the migration moment that maximises RO, because spatial differences in predation pressure were not large enough to trade off migration costs. In conclusion, migrations of M. balthica to and from nurseries on high tidal flats of the Wadden Sea may be seen as an adaptation to avoid shrimp predation on the juveniles and parasite infection of the adults. Although the costs of the migration are large, fitness is increased due to the migration because it is traded off by an increased RO.
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