em
o
2
4
6
8
10
12
14
16
@
,
Fig. 38. Cores from the 28-m-deep sandy area in the German Bight which later became the waste
disposal area for the wastes from the titanium pigment industry. Cores were sampled after a
heavy gale struck the area in February 1967 and eroded the sediment even at that water depth.
There is a 3 -1 0 cm thick layer of freshly deposited sand (white) above the older, grayish sediment (dotted). In a schematic way the position of some macrofauna representatives is indicated
(Hickel 1969)
It cannot be expected that the bottom fauna of a 28-m-deep area in the North Sea
will remain unchanged over a period of decades, and reflect in an ideal way unchanged
pollution stress. According to the season, the spectrum of species changes in correspondence with the reproductive rhythm of the various species. Over a relatively
long period of time, increases and decreases result from stocks that do not successfully reproduce in the same numbers every year. In the winter of 1962-63, 5 years
before the beginning of the bottom research in the dumping area, very low water temperatures had a devastating effect on the bottom animals. In particular, certain
species of molluscs had practically disappeared in wide areas of the Bay of Helgoland.
Thus, ecological niches were freed which were at first partly filled by various worms
until species of molluscs were gradually able to repossess the area. In February of
1967, that is, just before the beginning of the bottom fauna research, a strong gale
stirred the bay up so strongly that the sea bottom was eroded. After the weather had
settled down, a IO-<:m layer of sediment was deposited (Fig. 38). It can be calculated
that the strength of waves 100 m in length and 6 m in height is enough to produce
an orbital current of 2 mls at a depth of 20 m which is enough to stir up the sediment (Gienapp 1973). Since 1967, the number of small, easily injured worms has
increased in the dumping area. To associate this increase with the effect of the acids
which have been dumped would, however, be wrong. Presumably, the next strong
gale will destroy this fauna again and leave behind just the robust, heavy animals and
those which are able to retreat into the farily deep layers of sand.
The erosion of the bottom during storms probably also causes especially large
amounts of nutrient elements to enter the sea water and cause a more luxuriant
growth of algae than usual. This could have a favorable effect on the bottom animals
that secure their food from seawater as filter feeders. Chance, too, can also playa
large role in bottom animal communities. Most bristle worms (Polychaeta), echinoderms, and bivalves produce pelagic larva for propagation. These larvae are not able
to settle directly on the sea floor but must drift around in the water for a few days
61
o
2
4
6
8
10
12
14
16
@
,
Fig. 38. Cores from the 28-m-deep sandy area in the German Bight which later became the waste
disposal area for the wastes from the titanium pigment industry. Cores were sampled after a
heavy gale struck the area in February 1967 and eroded the sediment even at that water depth.
There is a 3 -1 0 cm thick layer of freshly deposited sand (white) above the older, grayish sediment (dotted). In a schematic way the position of some macrofauna representatives is indicated
(Hickel 1969)
It cannot be expected that the bottom fauna of a 28-m-deep area in the North Sea
will remain unchanged over a period of decades, and reflect in an ideal way unchanged
pollution stress. According to the season, the spectrum of species changes in correspondence with the reproductive rhythm of the various species. Over a relatively
long period of time, increases and decreases result from stocks that do not successfully reproduce in the same numbers every year. In the winter of 1962-63, 5 years
before the beginning of the bottom research in the dumping area, very low water temperatures had a devastating effect on the bottom animals. In particular, certain
species of molluscs had practically disappeared in wide areas of the Bay of Helgoland.
Thus, ecological niches were freed which were at first partly filled by various worms
until species of molluscs were gradually able to repossess the area. In February of
1967, that is, just before the beginning of the bottom fauna research, a strong gale
stirred the bay up so strongly that the sea bottom was eroded. After the weather had
settled down, a IO-<:m layer of sediment was deposited (Fig. 38). It can be calculated
that the strength of waves 100 m in length and 6 m in height is enough to produce
an orbital current of 2 mls at a depth of 20 m which is enough to stir up the sediment (Gienapp 1973). Since 1967, the number of small, easily injured worms has
increased in the dumping area. To associate this increase with the effect of the acids
which have been dumped would, however, be wrong. Presumably, the next strong
gale will destroy this fauna again and leave behind just the robust, heavy animals and
those which are able to retreat into the farily deep layers of sand.
The erosion of the bottom during storms probably also causes especially large
amounts of nutrient elements to enter the sea water and cause a more luxuriant
growth of algae than usual. This could have a favorable effect on the bottom animals
that secure their food from seawater as filter feeders. Chance, too, can also playa
large role in bottom animal communities. Most bristle worms (Polychaeta), echinoderms, and bivalves produce pelagic larva for propagation. These larvae are not able
to settle directly on the sea floor but must drift around in the water for a few days
61