| Summary: | Corophium volutator (Pallas) fit the criteria of ‘ecosystem engineers’ as defined by Jones and colleagues (1994, 1997): they are widely distributed within and across North Atlantic estuaries, are often present in intertidal soft sediment in vast numbers, and build semi-permanent burrows in the sediment matrix, which they irrigate continuously. Previous studies have demonstrated that C. volutator burrowing and feeding not only modifies the sediment biogeochemistry but can also modify the overlying water biogeochemistry (during immersion). C. volutator activities have also been shown to be detrimental to microphytobenthic (MPB) biofilms in the immediate vicinity of the burrows. As MPB are the stabilizing force in the estuary, the decimation of biofilm destabilizes the habitat for all the organisms colonising it. However, several aspects of C. volutator ecology remain unclear. First, previous studies on the effect of C. volutator on local (within burrow proximity) MPB diversity have not presented a clear signal as to whether they increase or decrease biodiversity or established whether there is preferential survival amongst MPB taxa with certain cell shapes and sizes or lifestyles. Second, as it has been established that C. volutator have the potential to change the water column, it is possible for them to effect MPB populations remotely (outwith burrow proximity). It is therefore of interest to determine the effects they have, whether such an effect can be achieved within a tidal period, and whether these effects can change MPB biomass, behaviour or diversity over time. A series of controlled mesocosm experiments were carried out to quantify those effects of C. volutator on the water column which were likely to impact MPB survival, to determine whether those effects were specific to C. volutator or common to deposit‐feeding bioturbators, to determine to what degree they could be achieved within a single immersion period, and to separate the effects of C. volutator on MPB bulk (chlorophyll-a in top 5 mm) and ...
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