THRAUSTOCHYTRID AND FUNGAL COMPONENT OF MARINE DETRITUS .1. FIELD STUDIES ON DECOMPOSITION OF THE BROWN ALGA SARGASSUM-CINEREUM J AG

Thraustochytrid protists and fungi were isolated and enumerated in cul ture from detritus of the brown alga Sargassum cinereum. Both groups o ccurred epi and endobiontically in the detritus. The thraustochytrid L abyrinthuloides minuta occurred in healthy as well as decomposing alga l tissues, whereas Ulkenia visurgensis was found only in the latter. U p to 2.9 X 10(7) of the two thraustochytrids, 5.2 X 10(4) of fungi and 5.5 X 10(11) of bacteria (per g dry wt. detritus) were found, using i mmunofluorescence, culture techniques and direct counts respectively. Populations of all 3 groups (thraustochytrids, fungi and bacteria were lowest in healthy algae containing higher amounts of phenolics than i n detritus. Concentrations of total carbohydrates (TCH), total phenols , proteins, alginate and mannitol, as well as C/N ratios declined as d ecomposition progressed, concomitant with an increase in microbial bio mass. Both thraustochytrids and bacteria attained peak biomass values in 21 d detritus. Maximum observed biomass of thraustochytrids corresp onded to 0.07 % C and that of bacteria to 1.1 % C of detrital dry weig ht. The constant association of thraustochytrids with the brown algal detritus and their endobiontic habitat suggest a definite role for the se protists in detrital dynamics.