This study was undertaken to investigate the effect of sea-cucumber (Holothuria atra) population density on sediment
microbial community structure. Feeding effects were investigated over six months in protected aquaculture ponds at National
Institute of Oceanography and Fisheries (NIOF). Four treatments of high population density (108 individuals/30m2
), Medium
population density (54 individuals/30m2
), low population density (18 individuals/30m2
) and Reference (pond without H.
atra). Intestinal (Foregut and hindgut), skin of H. atra and ambient sediment samples were used to investigate its effect on
sediment's pH, Total phosphorus (TP), grain size and culturable bacterial groups represented in; Total Viable bacteria (TVB),
Total coliform (TC), Vibrio sp (V), Fecal coliform (FC) and Salmonella and Shigella (SS). The data showed that water
temperature ranged from 20.8 o
C to 33.1o
C during February and May 2009 respectively. The pH decreased in ponds of H.
atra by 0.64 (7.8 to 7.16); 0.46 (7.81 to 7.35); 0.28 (7.84 to 7.56) in HPDP, MPDP and LPDP respectively, while in sediment
of reference pond increased by 0.11 (7.93 up to 8.04). Dilution plating of samples indicated that numbers of culturable
bacteria (TVB, V, TC and SS) in hindgut contents were higher than in foregut content samples, skin, and ambient sediment,
While FC count exhibited highest count in foregut than hindgut contents, ambient sediment and skin respectively. Data
analysis showed no significant effect of H. atra density on TP, fine sediment (Ø4 + Ø5) and Vibrio sp while a significant
effect recorded on pH, coarse sediment (Ø-1+ Ø0+ Ø1), medium sediment (Ø2 + Ø3), TVB, FC, TC and SS. Observing
reduction in Total coliforms, Fecal coliforms, Vibrio sp, salmonella and shigella in addition to its role as a pH controller, it
can be concluded that Holothuria atra can be used successfully for the improvement of coastal regions with its associated
fauna and flora. This study emphasizes the feeding selectivity and ecological role of the most dominant holothurians speciesH. atra in the red sea