The Uddevalla Shellbanks - a unique phenomenon

Land uplift

After the Ice Age, land uplift in the Bohuslän region was initially as rapid as 10 metres or so per century. The landscape was essentially coastal and fringed by rocks and islands of all sizes and shapes. Between the larger areas of land, deep, wide sounds or straits were formed - these are the so called Bohus straits and include the Idefors strait, the Munkedal strait and the Uddevalla strait.

Origin of the shellbanks

For approximately 1000 year, fresh, food-rich water from the Vänern basin mixed with the salt water coming from the sea, thereby creating the perfect conditions for a rich and varied local fauna. The shellbanks were formed by agglomerations of shell deposited in the mud on what was once the bottom of the sea. As the land rose, the action of waves, wind and tide washed away the mud, which was deposited in calmer waters some distance away, while gravel, sand and shell sand were moved to lower levels of the terrain. Shellbanks are normally encountered just below hills and where the straits are at their narrowest.

Wide variety of species

The faunal composition of the shellbanks is unique; it is found nowhere else in the world. Not all species were contemporaneous, however. Which species were present at any one time depended on such factors as the amount of meltwater, the rate of isostatic uplift, etc. Of the marine invertebrates, over 100 have been identified. Many of these are today found only in Arctic or northern waters, while others have long since been extinct. Skeletal parts of the following vertebrates have been found: cod, ling, halibut, Swedenborg´s whale, white whale, whitebeaked dolphin, common porpoise, bearded seal, ringed seal, Atlantic seal, polar bear, reindeer and eider.

Exploitation of the shellbanks

The shellbanks have been heavily exploited since the beginning of the 18th century. The shell-rich earth was chiefly used as poultry-feed, for lime-burning and as a fertilizer, although large quantities also went as fill for roads and railways.

Lime-loving flora

As might be expected, the local flora is dominated by lime-loving species such as small alison, hairy rockcress, Satureja acinos, blue fleabane, bloody cranesbill, Fragaria viridis, cowslip, Irish fleabane (left picture), and hepatica, while among the rarer species we find Ranunculus polyanthemos, rock cinquefoil and red hemp-nettle. In July and August, the flowers of greater knapweed (right picture), yellow chamomile, viper´s bugloss and great mullein dominate the local flora. The center picture is Mountain everlasting. Scattered groves of elm, ash, aspen, beech and pussy willow grow on the Kuröd and Bräcke banks, while the Samneröd bank is more generally wooded. Here, the predominant is aspen.

Drawings made by Boel Larsson

Photos made by Thomas Mårtensson

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