Microphytobenthic diversity and function in estuarine soft sediment

Estuarine sediments;Estuarine ecology;Corophiidae--Ecology;Corophiidae--Environmental enrichment;Benthos--Ecology;Benthos--Effects of turbidity on

Weinmann, Birgit Ellen ; Laland, Kevin N. ; Laland, Kevin N.

University:University of St Andrews

Department:Biology (School of)

关键词: Estuarine sediments;    Estuarine ecology;    Corophiidae--Ecology;    Corophiidae--Environmental enrichment;    Benthos--Ecology;    Benthos--Effects of turbidity on;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/3664/BirgitWeinmannPhDThesis.pdf?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

Corophium volutator(Pallas)fitthecriteriaof‘ecosystemengineers’asdefinedby 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 activitieshavealsobeenshowntobedetrimentaltomicrophytobenthic(MPB)biofilmsin 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 remainunclear.First, previousstudiesontheeffectofC. volutatoronlocal(withinburrowproximity) 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 cellshapes and sizes or lifestyles.Second, as it has been established that C. volutator have the potential tochange 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. Aseriesofcontrolledmesocosmexperimentswerecarriedout to quantify those effects of C. volutator on the water column which were likely to impact MPBsurvival, 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 immersionperiod, and to separate the effects of C. volutator on MPB bulk (chlorophyll-a in top 5 mm) and photosynthesizing (fluorescing) biomass and diversity both ‘locally’ and ‘remotely’.The results of the first 3 experiments consistently showed that C. volutator substantially increased the resuspension of sediment to the overlying water column and that the resulting turbidity could reduce lightpenetration to the sediment by as much as 50% within one immersion period.Results of nutrient fluxes were less consistent and clear within and between experiments but there was some suggestion thatincreased bioirrigation increased inorganicnitrogenfluxtotheoverlyingwatercolumnin accordancewithprevious studies.The effects of C. volutator on local and remote MPB biomass (bulk and surface)anddiversityvariedbetweenexperimentsbut,broadlyspeaking:(1)bulk biomasswasunaffected,reducedlocally,orincreasedremotely;(2)surfacebiomass was reduced both locally and remotely; and (3) community diversity (Simpson’s diversity index) was consistently unaffected, both locally and remotely.BecauseincreasedwatercolumnturbidityisthemostdistinctivecallingcardofC. volutator but is only likely to affect the photosynthetically active (surface) MPB biomass during immersion, a controlled laboratory experiment was designed to examine the extent to which turbidity could influence MPB migratory behaviour and photosyntheticactivity.MPBbulkmigrationwasshowntobedrivenbysitespecific, entrained rhythms of light availability and spatial variation in light availability only drove micro‐cycling in the photic zone during the immersion period.So, in the absence ofC. volutator, or any other turbidity producing phenomenon (deep water columns, high flow rates, physical disturbance, etc.), MPB will remain atthesurfacetophotosynthesizeduringimmersionandtheproductivityduring thisperiodisdeterminedbytotallightintensityandexposurehours(or‘light dose’).Therefore, the proximity and size of C. volutator populations to a site is likely to be influential in determining local productivity patterns of MPB.In addition, differencesinMPBassemblagecompositionwereshowntoinfluencethebiofilm productivity but what drives changes in MPB assemblage composition is still unclear and requires further investigation.