Abundance of thraustochytrids on fallen decaying leaves of Kandelia candel and mangrove sediments in Futian National Nature Reserve, China

Thraustochytrids are important mangrove decomposers on decaying cellulose-rich materials such as macroalgae and mangrove leaves, yet their distribution patterns on decaying mangrove leaves and in surface sediments have never been analyzed systematically. The current study investigates the possible correlation between thraustochytrid abundance on fallen decaying leaves and sediments in mangroves, and seasonal factors, i.e., air temperature and seawater salinity. Fallen decaying leaves of Kandelia candel and surface sediments were collected in April, July, October 2004, and February 2005. Homogenates of both leaves and sediments were plated onto yeast extract peptone agar for the enumeration of thraustochytrid colonies. Both the abundance and frequency of occurrence of thraustochytrids on decaying leaves were consistently higher than that of the sediments. However, thraustochytrid abundance on decaying leaves and in sediments were not correlated, and their abundance was not influenced by changes of air temperature or seawater salinity. The very high abundance of thraustochytrids found in mangrove plant detritus ( 4.8 x 10(3) - 5.6 x 10(5) CFU g(-1)) and sediment (1.0 x 10(2) - 1.6 x 10(3) CFU g(-1)) support the notion that they are an important mangrove decomposer and possibly a vital food source for filter-/detritus-feeders in mangrove food webs.