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The distribution of molluscan assemblages and their postmortem fate on coral reefs in the Gulf of Aqaba (northern Red Sea)
Zuschin, M.; Stachowitsch, M. (2007). The distribution of molluscan assemblages and their postmortem fate on coral reefs in the Gulf of Aqaba (northern Red Sea). Mar. Biol. (Berl.) 151(6): 2217-2230.
In: Marine Biology. Springer: Heidelberg; Berlin. ISSN 0025-3162, more
Peer reviewed article  

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  • Zuschin, M.
  • Stachowitsch, M.

    Molluscan assemblages were studied on fringing reefs (reef flats, Millepora-fringing reefs, fringing reefs with massive corals) and fore-reef hard substrata (coral patches, coral carpets and small patch reefs) in the Gulf of Aqaba at water depths ranging from the intertidal to 26 m. A total of 1,665 molluscan individuals from 51 taxa was counted on 44 transects, which covered 220 m² at eight diving sites. The most important molluscs in the assemblage were the parasitic gastropod Coralliophila neritoidea, the encrusting gastropod Dendropoma maxima and the coral-associated bivalve Pedum spondyloideum. The dead assemblage, in contrast, was dominated by encrusting bivalves (Ostreoidea, Chamoidea, Spondylidae) and the coral-predating gastropod Drupella cornus. Distinct molluscan assemblages inhabit each of the three fringing reef-habitats and most of the important depth-related community changes occurred within the uppermost 5 m. In contrast, the three deeper fore-reef habitats are characterized by a more uniform molluscan composition. Molluscan assemblages were more dependent on substrata and their coral associations than on water depth. Comparisons with other published studies indicate that reefoidal hard substrata in the northern Red Sea are largely characterized by similar species-abundance patterns. The minor differences to other Red Sea studies probably reflect the northern, isolated position of the Gulf of Aqaba, the lack of certain molluscan habitats, and the differential impact of anthropogenic influences. Strong differences between living and dead assemblages in Aqaba are similar to those observed in other regions and are due to distinct biases in the dead assemblage. Molluscs closely associated with living corals (mostly bivalves and Dendropoma) can easily be overgrown after death and are thus undetectable in visual censuses. Some gastropod taxa are preferentially transported into surrounding soft-substrata postmortem or redistributed by hermit crabs. Such complex relationships between ecology and taphonomy are crucial in evaluating the quality of the molluscan fossil record in coral reef environments. The comparison of our results with literature data documents an increase in coral predators during the last two decades in the northern Red Sea. Due to the greater mollusc biodiversity in the shallower Aqaba reef habitats, damage to this coral reef zone would have the greatest impact on the overall mollusc community.

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