132
G.c. Cadee
6.3 Types of Bioturbation
6.3.1 Crawling and Dwelling Traces
Birds that walk over a tidal flat, or meiofauna that moves between the sand
grains, rework surface sediments. Schafer (1956) carried out some excellent
experiments to study animals moving on the sediment or resting in the
surface layer (see some examples in Fig. 6.3). He provided a layered sediment
in aquariums and studied disturbance of the layering, either by adding new
layered sediment during the experiment, studying how the animals worked
upwards (escape traces), or introducing the animals on top of the layered
sediment. These experiments were very nicely illustrated. The study of the
traces formed is now a separate science: ichnology. Trace fossils are keys to
paleo-environmental studies of sediments where traces may be the only
fossils found. Unlike body fossils, they preserve fossil behaviour (Seilacher
1967).
Organisms may only find shelter in the sediment (dwelling traces in
Seilacher's 1964 terminology). This may vary from shrimps and flatfish hiding
themselves temporarily in surface sediments to large permanent burrows
formed by tilefish: large specimens of 1 m length produced crater-like holes of
4-5 m in diameter and at least 2-3 m deep on the shelf off Long Island (Able et
al. 1982, 1987). Even deeper burrows (5-9 m, diameter 0.5 cm) were described
by Bromley et al. (1975), from the Upper Cretaceous and Danian of NW, the
dwelling place of an unknown organism. Temperate areas lack the speciesrich communities of crustaceans (ghost crabs Ocypode, fiddler crabs Uca) so
abundant in (sub)tropical intertidal areas (Verwey 1930; Krejci-Graf 1935;
Frey and Mayou 1971). Katz (1980) was the first to estimate the sedimentreworking activity of fiddler crabs related to digging of their dwelling
burrows; they leave their burrows to feed on algae which they scrape from the
sediment surface.
The burrowing callianassid crustaceans belong to the most important
sediment reworkers with regards to the amount reworked as well as to the
depth to which they can burrow, in coastal areas as well as subtidal. Their deep
burrows have a good fossilisation potential (Frey et al. 1978). Bromley (1990)
reviews both recent and fossil examples. Callianassa major lives in the
intertidal of the Atlantic coast of southeast USA, in a communal burrow
system formed in a horizontal plane 3-5 m below the surface. With long
vertical shafts the animals remain in contact with the overlying water from
which they filter their food. Some species are gardeners, bringing seagrass
leaves into their burrows and feeding on the bacteria cultures, such as
Callianassa longiventris and C. acanthochirus (Suchanek 1983). Other
callianassids are deposit feeders, e. g. Callianassa japonica on intertidal sand-
G.c. Cadee
6.3 Types of Bioturbation
6.3.1 Crawling and Dwelling Traces
Birds that walk over a tidal flat, or meiofauna that moves between the sand
grains, rework surface sediments. Schafer (1956) carried out some excellent
experiments to study animals moving on the sediment or resting in the
surface layer (see some examples in Fig. 6.3). He provided a layered sediment
in aquariums and studied disturbance of the layering, either by adding new
layered sediment during the experiment, studying how the animals worked
upwards (escape traces), or introducing the animals on top of the layered
sediment. These experiments were very nicely illustrated. The study of the
traces formed is now a separate science: ichnology. Trace fossils are keys to
paleo-environmental studies of sediments where traces may be the only
fossils found. Unlike body fossils, they preserve fossil behaviour (Seilacher
1967).
Organisms may only find shelter in the sediment (dwelling traces in
Seilacher's 1964 terminology). This may vary from shrimps and flatfish hiding
themselves temporarily in surface sediments to large permanent burrows
formed by tilefish: large specimens of 1 m length produced crater-like holes of
4-5 m in diameter and at least 2-3 m deep on the shelf off Long Island (Able et
al. 1982, 1987). Even deeper burrows (5-9 m, diameter 0.5 cm) were described
by Bromley et al. (1975), from the Upper Cretaceous and Danian of NW, the
dwelling place of an unknown organism. Temperate areas lack the speciesrich communities of crustaceans (ghost crabs Ocypode, fiddler crabs Uca) so
abundant in (sub)tropical intertidal areas (Verwey 1930; Krejci-Graf 1935;
Frey and Mayou 1971). Katz (1980) was the first to estimate the sedimentreworking activity of fiddler crabs related to digging of their dwelling
burrows; they leave their burrows to feed on algae which they scrape from the
sediment surface.
The burrowing callianassid crustaceans belong to the most important
sediment reworkers with regards to the amount reworked as well as to the
depth to which they can burrow, in coastal areas as well as subtidal. Their deep
burrows have a good fossilisation potential (Frey et al. 1978). Bromley (1990)
reviews both recent and fossil examples. Callianassa major lives in the
intertidal of the Atlantic coast of southeast USA, in a communal burrow
system formed in a horizontal plane 3-5 m below the surface. With long
vertical shafts the animals remain in contact with the overlying water from
which they filter their food. Some species are gardeners, bringing seagrass
leaves into their burrows and feeding on the bacteria cultures, such as
Callianassa longiventris and C. acanthochirus (Suchanek 1983). Other
callianassids are deposit feeders, e. g. Callianassa japonica on intertidal sand-