MICROBIAL-FLORA ASSOCIATED WITH THE DIGESTIVE-SYSTEM OF UPOGEBIA-STELLATA (CRUSTACEA, DECAPODA, THALASSINIDEA)

The digestive system of the thalassinidean mud-shrimp Upogebia stellat a was investigated using scanning electron microscopy (SEM). Within th e lumen of the midgut both filamentous and rod-shaped bacteria were ob served. The hindgut microbial populations were dominated by dense mats of epimural rod-shaped bacteria. The gut contents were often dominate d by diatoms but also contained bacteria, dinoflagellates, plant and a lgal fragments. Direct bacterial counts by epifluorescence microscopy along the length of the gut revealed a slight decrease in numbers with in the midgut moving from the anterior to the posterior regions, and t hen a dramatic rise in numbers within the hindgut. Numbers deceased ag ain in the posterior regions of the hindgut. Common in the transient/r esident samples (bacterial population when gut contents were present) were enterobacteria and an unidentified fermenter conforming to an iso late named X-ferm. However, nearly 30% of the bacterial isolates remai ned unidentified. The resident-only bacterial isolates from the gut (d etermined when the gut was empty) were dominated by the X-ferm bacteri a and to a lesser extent by the genera Vibrio and Aeromonas. With resp ect to the enzyme capabilities of the gut bacteria, the resident-only collection of bacterial isolates showed much higher levels of amylase, cellulase, chitinase, protease and lipase activity than the transient /resident bacterial isolate collections, suggesting that the indigenou s bacteria are likely to play a significant role in the digestion of t he gut contents. Thalassinidean shrimps are likely to play an importan t role in the breakdown of plant and detrital material, and the recycl ing of nutrients in marine benthic systems.