Jj. Beukema et Gc. Cadee, CONSEQUENCES OF THE SUDDEN REMOVAL OF NEARLY ALL MUSSELS AND COCKLES FROM THE DUTCH WADDEN SEA, Marine ecology, 17(1-3), 1996, pp. 279-289
Three successive years of recruitment failure, intensive fishery, and
high rates of natural mortality eliminated all intertidal mussel beds
and nearly all cockle beds from the Dutch Wadden Sea in the course of
1990. In late 1990 and early 1991, zoobenthic biomass and particularly
bivalve stocks were unprecedentedly low. The following unusual events
were noted: 1) Relatively high diatom and chlorophyll concentrations
in the autumn of 1990 and an exceptionally early and dense spring bloo
m of diatoms in March 1991; 2) Exceptionally early onset of rapid grow
th in the bivalve Macoma balthica in March 1991; 3) Above-average weig
hts of the soft parts of bivalves in the 1990/91 winter; 4) Elevated m
ortality rates in bivalves that could serve as alternative prey for bi
rds specialised on big bivalves (oystercatchers and eiders); 5) Signs
of food shortage in such birds: high mortality rates and emigration to
other feeding areas; 6) A rapid recovery of the benthos started in th
e summer of 1991, accelerated by an exceptionally high recruitment in
some of the affected species. It is concluded that the Wadden Sea ecos
ystem responded in an elastic way to the removal of two of its key spe
cies. The events are not seen as merely coincidental but are regarded
as a chain of causes and effects.