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Aquatic Microbial Ecology

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AME 74:187-204 (2015)  -  DOI:

Seasonal dynamics of culturable thraustochytrids (Labyrinthulomycetes, Stramenopiles) in estuarine and coastal waters

Mayumi Ueda1,2, Yuka Nomura3, Kosaku Doi1,2, Masaki Nakajima4, Daiske Honda2,3,*

1Graduate School of Natural Science, 2Institute for Integrative Neurobiology, and 3Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Higashinada, Kobe, Hyogo 658-8501, Japan
4Research Institute of Environment, Agriculture and Fisheries, Osaka Prefecture, 442 Shakudo, Habikino, Osaka 583-0862, Japan
*Corresponding author:

ABSTRACT: Regular monitoring of estuarine and coastal areas at fixed points was carried out to investigate changes in biomass and species composition of thraustochytrids, which are colorless heterotrophs in the class Labyrinthulomycetes, Stramenopiles. Cell number counts using the most probable number (MPN) method with pine pollen baiting showed that 1 or 2 conspicuous peaks in abundance (termed ‘thraustochytrid spikes’) occurred between spring and late summer in most sampling years. Changes in thraustochytrid biomass had no correlation with phytoplankton abundance, although spikes seemed to occur after reductions in salinity and associated rapid rises of water temperature. The average cell density at the estuary site, excluding values during spike periods, was 4670 cells l–1. Although thraustochytrid biomass was only 1.59% that of bacterial biomass, the fixed energy (as biomass) transferred directly from thraustochytrids to zooplankton was estimated to be 15.9% of that transferred from bacterioplankton via phagotrophic protists. This is because, per the theory of energy efficiency, energy transfer between trophic levels only creates 10% of the net production in the next trophic level relative to the first. The phylogenetic identification of established strains revealed an unexpectedly high diversity of thraustochytrids, including 10 unidentified lineages. A similar seasonal succession of phylogenetic groups was observed in each year of sampling. The differences in thraustochytrids isolated at each monitoring site and date suggest that habitat segregation may occur as a result of differences in environmental factors such as water temperature, salinity, and nutrient sources.

KEY WORDS: Thraustochytrids · Biomass · Seasonal succession · Phylogeny · Habitat segregation · Estuary · Microbial loop · Osmotrophs

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Cite this article as: Ueda M, Nomura Y, Doi K, Nakajima M, Honda D (2015) Seasonal dynamics of culturable thraustochytrids (Labyrinthulomycetes, Stramenopiles) in estuarine and coastal waters. Aquat Microb Ecol 74:187-204.

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