THRAUSTOCHYTRID AND FUNGAL COMPONENT OF MARINE DETRITUS .4. LABORATORY STUDIES ON DECOMPOSITION OF LEAVES OF THE MANGROVE RHIZOPHORA-APICULATA BLUME

The role of thraustochytrid protists and fungi in detrital dynamics of leaves of the mangrove Rhizophora apiculata was investigated in the l aboratory. Field detritus of different ages (0, 4, 7, 14, 21, 28, 46, 53 and 60 days) obtained from litter-bag experiments were inoculated i ndividually with five fungi, Cladosporium herbarum, Fusarium monilifor me, Cirrenalia basiminuta, ''Hyphomycete XVII'' and Halophytophthora v esicula and one thraustochytrid, Schizochytrium mangrovei. Biochemical changes occurring after 1 wk in 8 ages of detritus were examined. The results suggested two phases of fungal dynamics, the first correspond ing to decompositional stages of 0-21 and the second to 28-60 days. De trital material of the first phase supported better growth of the fung i Cladosporium herbarum, Fusarium moniliforme, Cirrenalia basiminuta a nd Halophytophthora vesicula. Cellulase production by all the test spe cies, in general, was greatest on such detritus. Detritus of the secon d phase proved to be better for the growth of the fungus ''Hyphomycete XVII'' and production of xylanase by all test species. Pectic enzymes , amylase and protease were produced more or less uniformly in all age s of detritus. The thraustochytrid Schizochytrium mangrovei grew well on both phases of detritus. The test species utilised a wide variety o f substrates as sole carbon sources but differed significantly in thei r capabilities to elaborate the various degradative enzymes in detritu s. Fusarium moniliforme and Halophytophthora vesicula caused marked in creases in detrital protein, while all the test species enhanced amino acid levels. Schizochytrium mangrovei enhanced carbohydrate and reduc ing sugar contents, while Fusarium moniliforme and Halophytophthora ve sicula substantially decreased the levels of the former. Growth of Hal ophytophthora vesicula in detritus caused a decline of total phenolics . The net biochemical status of detritus seems to depend upon interact ions between the biochemical state of detritus, the colonising species and their biomass, and the enzymatic activities of the concerned micr oorganisms.