Bacterial biofilms as a trophic resource for certain benthic foraminifera
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Benthic foraminifera from temperate tidal flats and shallow Antarctic waters were challenged with bacterial biofilms to assess possible foraminiferal impact on attached bacterial populations. Two tectinous species (Allogromia sp. and A. laticollaris) used pseudopodial networks to rend and ingest biofilm parcels, an activity we term harvesting. The numerical density of bacteria in harvested biofilm areas was maximally depleted by ca 80 % for Allogromia sp. and 50 % for A. laticollaris. In contrast, the calcareous (Cyclogyra antarctica, Elphidium incertum, Glandulina antarctica, Pyrgo williamsoni) and agglutinated (Astrammina rara, Astrorhiza sp., Crithionina-like mudball) foraminifera studied did not exhibit harvesting behavior. Time-lapse microscopy revealed that biofilm parcels were transported extracellularly toward the cell body by pseudopodia, an observation which further defines pseudopodial function in foraminiferal trophic mechanisms. Our observations indicate that allogromiid foraminifera may play a previously unrecognized role in bacterial population dynamics and nutrient cycling, particularly in intertidal environments and certain deep-sea habitats where they may constitute a major meiofaunal component.