Biogenic and taphonomic processes affecting the development of shell assemblages: an actuopaleontological case study from mussel banks on North Sea tidal flats |
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Authors: | Achim Wehrmann |
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Institution: | (1) Dept. of Marine Research, Senckenberg Institute, Schleusenstrasse 39a, D-26382 Wilhelmshaven |
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Abstract: | Summary From spring 1997 to winter 2000, the composition and structure of epibenthic bivalve clusters and patches on a backbarrier
tidal flat of the East Frisian Wadden Sea were continoously analyzed. The studied bivalve aggregates developed from intense
and approximately simultaneous spatfalls of Mytilus edulis and Cerastoderma edule in 1996, after a severe winter (1995/96) with 64 days of driftice coverage. Spatfall occurred on a bare sandy tidal flat,
whereas adjacent shell layers situated at the southern margin of the spatfall site were not colonized. Usually, such shell
layers are the most common secondary hard substrates in the backbarrier area favorable for initial settlement of Mytilus larvae. The shell layers predominantly originate from erosion of former Mya arenaria and C. edule populations.
So far, the studied bivalve aggregates are composed of approximately equal proportions of living specimens of both species,
M. edulis and C. edule. The incorporated cockles were prevented from burrowing into the rediment by the coherent byssal mesh. In contrast to the
results of previous studies, the great bulk of epibenthic living C. edule did survive for several years within the clusters. Therefore, the common terms ‘Mytilus banks’, ‘Mytilus patches’ or ‘Mytilus clumps’ may be too general and may erroneously imply a dominance of (or mono-specific composition by) M. edulis. In the fossil record, i.e. in diagenetically consolidated shell layers, the enforced epibenthic life-mode of C. edule and the remarkable species composition as well as the temporal development of the aggregates would not be recognizable. |
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Keywords: | Bivalve Aggregates Mussel-Bank Composition Biogenic Buildup Epibenthic life-mode Larval Settlement Tidal flats Taphonomy Paleoecology Actuopaleontology North Sea Recent |
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