CLIMATIC CATASTROPHES

Periodically, heavy rainfall in the tidal flat environment of the North Sea can bring about the mass mortality of the calamar. This is not invariably the case, however, inasmuch as these cephalopods are migratory, and it is only during their periods in the tidal zone of the North Sea that they run the risk of succumbing to a salinity catastrophe. In June 1969, there was such an episode in the Danish tidal flats at Esbjerg, the effects of which I witnessed in the company of a party of my research students. Thousands of dead calamars were observed stranded along the upper tidal zone after prolonged heavy rain had lowered the salinity level.

Can such an event be identified in fossil material? The answer is yes, at least in the case of broad epicontinental environments. For example, in the region just south of the Damergou of Niger Republic in deposits of the Saharan epicontinental sea of the early Turonian, great numbers of monospecific Nigericeras can be observed strewn over a flat, marly surface, presumably the victims of a sudden drop in salinity due to heavy rain (Schöbel 1975; Courville and Thierry 1993; Reyment 2003). The pictures of "stranded" orthocones in Gnoli (2003) bear a striking resemblance to the stranded individuals of Loligo vulgaris mentioned above.