The spatial distribution of planktonic naked amoebae in the waters of a mangrove and estuarine habitat was investigated. Amoebae were grouped either as 'attached' (when on suspended flocs) or 'free' (when floating in the open water). Consistent with previous studies, amoebae were numerically important in the water column. For example, in mangrove water from south Florida, they averaged 94 640 cells l(-1). In the mangrove, 91.6% of planktonic amoebae were attached to suspended floes. Likewise, the majority of amoebae in Hudson waters were floc associated (86.7%). The results using a novel capture protocol, employing suspended capillary tubes to catch floating amoebae, suggested that free amoebae readily colonized available surfaces. Transmission electron microscopy demonstrated that amoebae were capable of penetrating deep into the cracks and crevices of floc particles. The implications of these results are far reaching. For example, in the mangrove waters where the floc fraction in a liter of water accounted for similar to 0.5 ml volume, the absolute density of amoebae at these loci was 173 380 amoebae per milliliter of floc material. Such high local abundance may have important trophic implications, particularly if amoebae, because of their close association with surfaces, graze attached bacteria unavailable to other micrograzers. The results presented here clearly show that future studies on the microecology of flocs need to include amoebae as well as the more widely investigated ciliates and heterotrophic flagellates.
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