THRAUSTOCHYTRID AND FUNGAL COMPONENT OF MARINE DETRITUS .3. FIELD STUDIES ON DECOMPOSITION OF LEAVES OF THE MANGROVE RHIZOPHORA-APICULATA

The sequence of colonisation, densities and biomass of fungi, thrausto chytrid protists and bacteria during decomposition of leaves of the ma ngrove Rhizophora apiculata Blume, as well as the accompanying biochem ical changes of the detritus, were studied in 2 litterbag experiments at Goa, India. Three phases were observed. (1) Thraustochytrids and th e fungi Cladosporium herbarum and Halophytophthora vesicula colonised detritus during the first week, characterised by a rapid loss of detri tal dry weight and a reduction in proteins, carbohydrates, reducing su gars, phenolics and cellulose. (2) Decline of most of the organic cons tituents in detritus to almost the lowest observed levels within 21 d was accompanied by an increase in fungal and bacterial biomass. Fungi and bacteria together contributed maxima of 0.052 and 0.065% to dry we ight of 21 and 35 d detritus respectively. Protein values never increa sed with decomposition and microbial biomass buildup, although C:N val ues declined. (3) Total fungal and bacterial biomass decreased after 3 and 5 wk, respectively. However, thraustochytrids and marine fungal s pecies such as Cirrenalia basiminuta and 'Hyphomycete XVII' attained h igh densities by 56 to 60 d. Most of the species present initially in the detritus were observed even in the last stages of decomposition ex amined (56 to 60 d). Thraustochytrids and fungi were isolated both fro m surface-sterilized and untreated detritus, suggesting epi- and endob iontic modes of life. Distinct sequences of fungal and thraustochytrid colonisation, presence of high fungal biomass relative to bacterial b iomass, the high densities of thraustochytrids and accompanying bioche mical changes indicate the importance of these organisms in the mangro ve detrital processes.