Benthic losers and winners in a tidal bay since the 1920s

Abstract

It is in the very nature of coastal ecosystems to respond rapidly to external driving factors from land, sea, and man. Human-induced environmental change from local to global scale, and introduced species in particular, has accelerated ecological transformation at many coasts worldwide. A series of major events has fundamentally changed the macrobenthos in a tidal bay of the Wadden Sea (Königshafen, south-eastern North Sea, Atlantic Europe) since 1924. (1) Overexploitation extirpated native oysters. (2) The once dominating seagrasses declined dramatically in the 1930s due to an introduced pandemic disease. This was followed by a loss of fine mud, and an expansion of bioturbating lugworms on sandy flats. (3) In the 1980s–2000s, seagrasses declined further and massive green algal mats spread due to eutrophication. (4) Mussel beds gradually expanded in spite of recurrent resets caused by severe winters. (5) Since the 2000s, introduced Pacific oysters dominated mussel beds. With the spread of the mixed reefs of native mussels and Pacific oysters, the extent of mud flats increased again. (6) Since the last three decades, many more non-native species, that are well adapted to a warmer climate, have increased benthic diversity. The ecological developments in this small bay may anticipate change on larger scales and could serve as a model site for learning about the role of contingent history for the functioning of a novel benthic ecosystem.