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Palaeoenvironments of vertebrates on the southern shore of Tethys: the nonmarine Early Cretaceous of Tunisia

Palaeoenvironments of vertebrates on the southern shore of Tethys: the nonmarine Early Cretaceous of Tunisia
Palaeoenvironments of vertebrates on the southern shore of Tethys: the nonmarine Early Cretaceous of Tunisia
In the early 1990’s a conspicuous shift took place in the density of two key macrofauna species at the Frisian Front (SE North Sea). The density of the formerly dominant brittlestar Amphiura filiformis showed tenfold reduction and remained low throughout the observation period (1986–2000). In the same period, the burrowing mud shrimp Callianassa subterranea showed a fourfold increase in density. Since the Frisian Front is a transition area where tidal currents fall just below the erosion threshold of silt and bioturbating mud shrimps can potentially affect the sediment erosion threshold, we examined the effects of the species on sediment erodibility. Two experiments were conducted in laboratory annular flumes. In the first experiment we compared the effects of pre-shift and post-shift combinations of the two species on the erodibility of Frisian Front sediment. The results indicated that the erosion was facilitated by a combination of high densities of C. subterranea and low densities of A. filiformis, representing the situation in the late 1990s. The difference in erodibility was already apparent at velocities equal to the critical near-bed current speed measured at the Frisian Front. In the second experiment the effects of pre- and post-shift densities of A. filiformis on sediment erodibility were compared. This showed that low A. filiformis densities as found in the late 1990’s facilitate erosion, but the effect is only significant at velocities above the critical near-bed velocity in the field. At the latter velocity, no significant difference in erodibility was found between the two A. filiformis densities. This implies that the difference in turbidity in the first experiment was mainly due to the activity of C. subterranea. The experimental results indicate that resuspension at the Frisian Front may occur more frequently as a result of the shift towards a Callianassa dominated community. More frequent resuspension of bottom sediment, most likely amplified by the climate induced increase of wind strength in the North Sea, may hamper the recovery of the A. filiformis adult population.
Resuspension, Sediment erosion, Callianassa subterranea, Amphiura filiformis, Suspension feeders, Frisian Front
0031-0182
118-131
Anderson, P.E.
6f0705b0-887f-4734-a9ae-2f67b4a1ebc8
Benton, M.J.
fda7373b-9d94-4180-a24f-d6a2fd9ad053
Trueman, C.N.
d00d3bd6-a47b-4d47-89ae-841c3d506205
Paterson, B.A.
b08c2777-40d4-4341-9d87-31a2331eeb65
Curly, G.
57c1f0fc-acc5-4fff-a2a1-0baf59c2f102
Anderson, P.E.
6f0705b0-887f-4734-a9ae-2f67b4a1ebc8
Benton, M.J.
fda7373b-9d94-4180-a24f-d6a2fd9ad053
Trueman, C.N.
d00d3bd6-a47b-4d47-89ae-841c3d506205
Paterson, B.A.
b08c2777-40d4-4341-9d87-31a2331eeb65
Curly, G.
57c1f0fc-acc5-4fff-a2a1-0baf59c2f102

Anderson, P.E., Benton, M.J., Trueman, C.N., Paterson, B.A. and Curly, G. (2007) Palaeoenvironments of vertebrates on the southern shore of Tethys: the nonmarine Early Cretaceous of Tunisia. Palaeogeography, Palaeoclimatology, Palaeoecology, 243 (1-2), 118-131. (doi:10.1016/j.palaeo.2006.07.015).

Record type: Article

Abstract

In the early 1990’s a conspicuous shift took place in the density of two key macrofauna species at the Frisian Front (SE North Sea). The density of the formerly dominant brittlestar Amphiura filiformis showed tenfold reduction and remained low throughout the observation period (1986–2000). In the same period, the burrowing mud shrimp Callianassa subterranea showed a fourfold increase in density. Since the Frisian Front is a transition area where tidal currents fall just below the erosion threshold of silt and bioturbating mud shrimps can potentially affect the sediment erosion threshold, we examined the effects of the species on sediment erodibility. Two experiments were conducted in laboratory annular flumes. In the first experiment we compared the effects of pre-shift and post-shift combinations of the two species on the erodibility of Frisian Front sediment. The results indicated that the erosion was facilitated by a combination of high densities of C. subterranea and low densities of A. filiformis, representing the situation in the late 1990s. The difference in erodibility was already apparent at velocities equal to the critical near-bed current speed measured at the Frisian Front. In the second experiment the effects of pre- and post-shift densities of A. filiformis on sediment erodibility were compared. This showed that low A. filiformis densities as found in the late 1990’s facilitate erosion, but the effect is only significant at velocities above the critical near-bed velocity in the field. At the latter velocity, no significant difference in erodibility was found between the two A. filiformis densities. This implies that the difference in turbidity in the first experiment was mainly due to the activity of C. subterranea. The experimental results indicate that resuspension at the Frisian Front may occur more frequently as a result of the shift towards a Callianassa dominated community. More frequent resuspension of bottom sediment, most likely amplified by the climate induced increase of wind strength in the North Sea, may hamper the recovery of the A. filiformis adult population.

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More information

Published date: September 2007
Keywords: Resuspension, Sediment erosion, Callianassa subterranea, Amphiura filiformis, Suspension feeders, Frisian Front

Identifiers

Local EPrints ID: 49657
URI: https://eprints.soton.ac.uk/id/eprint/49657
ISSN: 0031-0182
PURE UUID: cec1ccb7-b18e-411f-b1ab-92cca68e6b5a

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Date deposited: 20 Nov 2007
Last modified: 13 Mar 2019 20:53

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Contributors

Author: P.E. Anderson
Author: M.J. Benton
Author: C.N. Trueman
Author: B.A. Paterson
Author: G. Curly

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