L. conchilega reefs are preferred foraging habitats for many species of overwintering migratory birds, however the transience of these assemblages makes them an undependable food source. The macrobenthic community in the Flemish Beach Reserve ‘Bay of Heist’, Belgium was significantly altered after the 2010-2011 winter season as lower than usual temperatures led to the eradication of L. conchilega reefs. Investigation into the sediment and macrobenthic community was coupled with distribution and behavioural data from oystercatchers and grey plovers to investigate the response to this disturbance event. Comparisons with 2010 data revealed a homogenization of the intertidal flat in the absence of the L. conchilega reefs in terms of both sediment composition and macrobenthic abundance. Numerous dominance shifts involving Aphelochaeta marioni and juvenile polychaetes signalled strong changes in macrobenthic community composition. Overall bird abundance decreased by 66% from 2010, 57% for oystercatchers and 80% for grey plovers. Oystercatchers’ preference for more stable mussel bed habitats in the area increased but some continued to forage in the intertidal, although at a higher foraging rate. Gauging change in grey plover distribution and foraging behaviour was not possible do to their low abundance but since they depended almost exclusively on the intertidal for food in 2010 and they have a limited foraging strategy, their absence could be a reflection of this macrobenthic shift. Oystercatchers are much more flexible foragers and could compensate for the change by spending more time in the mussel bed and by increasing foraging rate in the intertidal. Since macrobenthic abundance did not decrease significantly, macrobenthic quality is proposed as an explanation for these behavioural changes and change in biomass should be evaluated. While L. conchilega reefs are a crucial and beneficial component to the Bay of Heist ecosystem, the importance of other ecosystem engineers such as M. edulis as well as overall habitat quality cannot be overlooked as time spent in these areas is often higher.
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