:16
:1 Stuuy Arca
3.5
Biofacies in the Spiekeroog Backbarrier Tidal Flats
Carmen-Pia Gunther
Abstract: Swinnplate and Grcininger Plate are typical sandy tidal flats of the backbarrier area of the island of Spiekeroog. Their biofacies differ mainly in the occurrence, rsp. lack of beds of Mytilus edulis. Due to the fact that this species is a biogenic mud collector, sediments of both flats also differ in their mud content
(Chap. 3.4). The ice winter 1995/96 resulted in a lack of Mytilus beds on both
sandtlats and of Lanice conchi/ega in large parts of the Swinnplate and nearly
entirely on the Grijninger Plate. On the Swinnplate a loss not only of the ecosystem
engineer Mytilus edulis but also of the bioaccumulated sediment fraction <63 11m
was recorded. Directly after the ice winter, Heteromastusfiliformis was observed
in areas where sediment of the fraction <63 11m was newly deposited.
On a large temporal and spatial scale, biofacies provide information on patterns
(vertically) and variability (horizontally) of sediment structure and associated
macrofauna. The interpretation of sequences of macrofauna associations at one
locality as cyclic changes in the sense of the mosaic-cycle theory may be misleading. Vertical sequences ot'facies may not only result from a temporal succession of
macrobenthic associations, but also from a horizontal transport of sediment layers.
The vertical sequence of facies may also be affected by erosion due to storms or
ice cover leading to a removal of once existing facies. New methods in determining the absolute age of facies, e.g. age determination via the amino acid content in
bivalve shells, may provide more precise results in the future.
3.5.1
Introduction
In geology, a facies is defined as a specific character of a sediment with a differentiation between anorganic (lithofacies) and biogenic characteristics (biofacies).
The latter may be presented by bodies or skeletons of fossil lifeforms or their
traces (Lebensspuren). Actuopaleontology uses recent organisms to interpret biofacies assuming that the same processes lead to the same results independent from
the point of time in the earth's history.
Generally, the sediment bodies of the Wadden Sea underlie continuous changes
in their morphology and composition (e.g. sediments, biota). Climate, hydrodynamics as well as biological processes interact and produce characteristic facies.
Changes of facies indicate changes in sediment composition and associations of
biota in vertical and horizontal direction. By estimating the time span in which
changes occur. it can be described which macrofauna association characterizes an
area, how long an association persisted at one place rsp. whether temporal sequences of associations occurred. Using this biotope history, long-term effects of
events in the sediments may be evaluated allowing the consideration of stability
properties on a larger temporal scale than the time span of most scientific projects.
In the frame of ELA W A T, the evidence based on biofacies in relation to the mosaic-cycle theory was of special importance (compare Chap. 2).
:1 Stuuy Arca
3.5
Biofacies in the Spiekeroog Backbarrier Tidal Flats
Carmen-Pia Gunther
Abstract: Swinnplate and Grcininger Plate are typical sandy tidal flats of the backbarrier area of the island of Spiekeroog. Their biofacies differ mainly in the occurrence, rsp. lack of beds of Mytilus edulis. Due to the fact that this species is a biogenic mud collector, sediments of both flats also differ in their mud content
(Chap. 3.4). The ice winter 1995/96 resulted in a lack of Mytilus beds on both
sandtlats and of Lanice conchi/ega in large parts of the Swinnplate and nearly
entirely on the Grijninger Plate. On the Swinnplate a loss not only of the ecosystem
engineer Mytilus edulis but also of the bioaccumulated sediment fraction <63 11m
was recorded. Directly after the ice winter, Heteromastusfiliformis was observed
in areas where sediment of the fraction <63 11m was newly deposited.
On a large temporal and spatial scale, biofacies provide information on patterns
(vertically) and variability (horizontally) of sediment structure and associated
macrofauna. The interpretation of sequences of macrofauna associations at one
locality as cyclic changes in the sense of the mosaic-cycle theory may be misleading. Vertical sequences ot'facies may not only result from a temporal succession of
macrobenthic associations, but also from a horizontal transport of sediment layers.
The vertical sequence of facies may also be affected by erosion due to storms or
ice cover leading to a removal of once existing facies. New methods in determining the absolute age of facies, e.g. age determination via the amino acid content in
bivalve shells, may provide more precise results in the future.
3.5.1
Introduction
In geology, a facies is defined as a specific character of a sediment with a differentiation between anorganic (lithofacies) and biogenic characteristics (biofacies).
The latter may be presented by bodies or skeletons of fossil lifeforms or their
traces (Lebensspuren). Actuopaleontology uses recent organisms to interpret biofacies assuming that the same processes lead to the same results independent from
the point of time in the earth's history.
Generally, the sediment bodies of the Wadden Sea underlie continuous changes
in their morphology and composition (e.g. sediments, biota). Climate, hydrodynamics as well as biological processes interact and produce characteristic facies.
Changes of facies indicate changes in sediment composition and associations of
biota in vertical and horizontal direction. By estimating the time span in which
changes occur. it can be described which macrofauna association characterizes an
area, how long an association persisted at one place rsp. whether temporal sequences of associations occurred. Using this biotope history, long-term effects of
events in the sediments may be evaluated allowing the consideration of stability
properties on a larger temporal scale than the time span of most scientific projects.
In the frame of ELA W A T, the evidence based on biofacies in relation to the mosaic-cycle theory was of special importance (compare Chap. 2).