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Aquatic Microbial Ecology

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AME 23:55-61 (2000)  -  doi:10.3354/ame023055

Abundance of thraustochytrids and ciliated protozoans in a Mediterranean sandy shore determined by an improved, direct method

Giovanni Santangelo*, Lucia Bongiorni, Lucrezia Pignataro

Dipartimento Etologia, Ecologia, Evoluzione, Università di Pisa, Via Volta 6, 56126 Pisa, Italy

ABSTRACT: Thraustochytrids (fungoid protoctists) and ciliated protozoans are major components of marine sandy shore microcommunities. However they are rarely enumerated together. This report describes the results obtained through application of an improved method for directly enumerating both of these microorganisms from sandy sediments. Thraustochytrids and ciliates were extracted by repeated washing with glutaraldehyde-seawater solution. To separate both microorganisms from non-living material the supernatant was centrifuged in a non-linear silica gel gradient, and then stained with 3 different fluorochromes. Sampling was carried out on a sheltered, medium-grain-sized sandy shore in the Ligurian Sea (NW Mediterranean). Ninety-six 1 ml replicated sand samples were collected. They were arranged following a nested ANOVA design in which factors were 3 successively smaller spatial scales (sampling units of different size, ranging between meters and centimeters). Sampling was repeated 3 times during the autumn-winter period. Average ciliate abundance was 44 ± 26 ml-1, showing a significant decrease with time (from autumn to winter). The average abundance of thraustochytrids was 42.4 ± 35.2 ml-1, with no significant decrease over time. Neither group of protists showed a spatial structure at the scales explored. Variability among replicated 1 ml samples was the main variance source for both microorganisms. The findings presented here are the first to address the distribution of thraustochytrids in marine sediments as determined by direct enumeration.

KEY WORDS: Thraustochytrids · Ciliates · Epifluorescence · Spatial distribution · Sandy shores · Mediterranean Sea

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