Growth and size-dependent loss of newly settled bivalves in two distant regions of the Wadden Sea

Individual growth and the timing of life history events determine the course of individual body sizes. Hence, these factors can influence size-dependent species interactions, such as predation. In the Wadden Sea, predation by crustaceans plays an important role in the survival of pre-recruit bivalves. To investigate growth rates and size-dependent loss in 2 distant regions of the Wadden Sea, in situ marking with the fluorochrome calcein was combined with cage experiments. Through marking, we obtained, for the first time, size-increment data for the fragile newly settled juveniles of the species Macoma balthica and Cerastoderma edule in the field. Growth and size-selective mortality were analysed separately, whereas hitherto both have usually been inferred from size distributions at this life stage. Fluorescent marking also revealed that growth rates were very variable among individuals. Growth was temporarily higher at Texel than at Sylt in both species. In combination with the exclosure experiments and the sampling of predators and migrating bivalves, selective loss of smaller individuals was detected in both regions and was related to predation pressure. Climate influences on phenology have potentially strong effects on species interactions, altering survival and thus recruitment and population dynamics