130
G.c. Cadee
6.2 History of Bioturbation Research
The word bioturbation was first used by Richter (1952), but studies in
sediment reworking by organisms had started much earlier. Darwin was the
first. He showed a lifelong interest in bioturbation by earthworms. His first
paper on this subject (Darwin 1837) was inspired by his uncle and future
father-in-law, Josiah Wedgwood, who suggested that the fact that fragments of
burnt marl and cinders strewed over the surface of several meadows were
found after 10 years as a layer sunken to a depth of 2-3 inches below the turf,
was due to the large quantities of fine earth continually brought to the surface
by worms in the form of castings. In December 1842, just after settling in
Down House, Darwin spread a quantity of broken chalk over part of a field
near his house "for the sake of observing at some future period at what depth
it would become buried". This future period arrived in 1871 after 29 years (!)
and the chalk was observed at a depth of 7 inches, resulting in an average
sediment reworking rate of 0.22 inches per year. The last book Darwin wrote
(1881) is devoted to the activity of worms. It was a best-seller in his time and
still inspiring to read (see e.g. Pemberton and Frey 1990). Keith (1942),
restudying the same fields in Downe, was able to recognise some of the material Darwin had used. Darwin also collected data on the worm castings
brought to the surface within a given time and area. What is so interesting in
Darwin's experiments in my opinion is that the same methods to estimate
bioturbation are still in use. Castings are collected to estimate deposit-feeder
activities, and the rate at which particles sink below the surface is also used
nowadays to estimate bioturbation rates. Glass beads, fluorescent sand grains,
or radioactive materials have long since replaced the cinders and burnt marl;
and one other difference is that we want our results within days or weeks, not
years.
Davison (1891), inspired by Darwin's book, carried out some measurements on the castings of the polychaete Arenicola marina on a tidal flat off
Northumberland in August 1891. He assumed the same number and weight of
castings to be produced every tide and so calculated the annual production of
castings. In earlier work (Cadee 1976), I compared annual estimates of
sediment reworking by Arenicola marina of Davison and later authors. They
usually based their estimates on short-term observations and were unable to
deal adequately with the seasonal trend in Arenicola activity. They estimated
Arenicola to be able to rework an amount of sediment equalling a sediment
layer of 10-60 cm per year depending on the density of animals. Somewhat
lower values were obtained in measurements over the whole year (Cadee
1976; Riisgard and Banta 1998).
A few early quantitative studies dealt with deposit feeders outside Europe,
e.g. Crozier (1918) collected data on a holothurian (Stichopus) in Bermuda
G.c. Cadee
6.2 History of Bioturbation Research
The word bioturbation was first used by Richter (1952), but studies in
sediment reworking by organisms had started much earlier. Darwin was the
first. He showed a lifelong interest in bioturbation by earthworms. His first
paper on this subject (Darwin 1837) was inspired by his uncle and future
father-in-law, Josiah Wedgwood, who suggested that the fact that fragments of
burnt marl and cinders strewed over the surface of several meadows were
found after 10 years as a layer sunken to a depth of 2-3 inches below the turf,
was due to the large quantities of fine earth continually brought to the surface
by worms in the form of castings. In December 1842, just after settling in
Down House, Darwin spread a quantity of broken chalk over part of a field
near his house "for the sake of observing at some future period at what depth
it would become buried". This future period arrived in 1871 after 29 years (!)
and the chalk was observed at a depth of 7 inches, resulting in an average
sediment reworking rate of 0.22 inches per year. The last book Darwin wrote
(1881) is devoted to the activity of worms. It was a best-seller in his time and
still inspiring to read (see e.g. Pemberton and Frey 1990). Keith (1942),
restudying the same fields in Downe, was able to recognise some of the material Darwin had used. Darwin also collected data on the worm castings
brought to the surface within a given time and area. What is so interesting in
Darwin's experiments in my opinion is that the same methods to estimate
bioturbation are still in use. Castings are collected to estimate deposit-feeder
activities, and the rate at which particles sink below the surface is also used
nowadays to estimate bioturbation rates. Glass beads, fluorescent sand grains,
or radioactive materials have long since replaced the cinders and burnt marl;
and one other difference is that we want our results within days or weeks, not
years.
Davison (1891), inspired by Darwin's book, carried out some measurements on the castings of the polychaete Arenicola marina on a tidal flat off
Northumberland in August 1891. He assumed the same number and weight of
castings to be produced every tide and so calculated the annual production of
castings. In earlier work (Cadee 1976), I compared annual estimates of
sediment reworking by Arenicola marina of Davison and later authors. They
usually based their estimates on short-term observations and were unable to
deal adequately with the seasonal trend in Arenicola activity. They estimated
Arenicola to be able to rework an amount of sediment equalling a sediment
layer of 10-60 cm per year depending on the density of animals. Somewhat
lower values were obtained in measurements over the whole year (Cadee
1976; Riisgard and Banta 1998).
A few early quantitative studies dealt with deposit feeders outside Europe,
e.g. Crozier (1918) collected data on a holothurian (Stichopus) in Bermuda