Creation of temperate-climate intertidal mudflats: Factors affecting colonization and use by benthic invertebrates and their bird predators

Colonization of a recreated area of intertidal land by marine invertebrates and their bird predators was studied from April 1993 to August 1997, The m ost important food of large shorebirds, the ragworm Nereis diversicolor, di d not reappear until late summer 1995 and did not become abundant until the following autumn. Annual attempts at colonization by the crustacean Coroph ium volutator, the main food of several small shorebird species, failed unt il summer 1996 when animals survived through the subsequent winter for the first time. Colonization by the mud-snail Hydrobia ulvae took place a year after flooding of the site, but densities in 1997,were still well below tho se found elsewhere on the adjacent estuary. The delay in successful colonization by Nereis and Corophium may be attribu table in part to the compaction of the intertidal muds caused by the earthm oving equipment used to contour the site. The slow increase in Hydrobia den sity may be a consequence of low organic content of the mud. Bird use is co ncentrated chiefly during the hours when the adjacent estuarine mudflats (w ith unrestricted tidal flow) are covered by the tide, since the new site th en provides a supplementary feeding area, Peak daytime usage occurs during the migratory passage periods when birds need to feed for longer periods th an usual, in order to refuel for their migrations; high usage is also antic ipated in cold winters, On this evidence, creation of intertidal areas in mitigation for any lost n earby to industrial or other development should take place at least three y ears before the losses, in order to make the new areas profitable for feedi ng waterfowl. (C) 1999 Elsevier Science Ltd, All rights reserved.