IMPACT OF WATER AND SEDIMENT QUALITY ON BACTERIAL DENSITIES AND DIVERSITIES IN MARINE POND CULTURE SYSTEM IN MTWAPA CREEK, KENYA

Abstract

The purpose of the present study was to analyze the impact of water quality and sediment quality on temporal variations of bacterial densities and diversities in marine pond culture system in Mtwapa Creek. The work was based on sediment and water samples collected from grow-out and nurseries ponds from November 2011 to April 2012. The objectives of the study were to; isolate and identify bacterial genera, determine bacterial densities, determine temporal variations of bacterial densities and diversities and determine the influence of variations in water and sediment quality parameters on the densities and diversities of bacteria in marine pond culture system in Mtwapa creek. Cultural methods were used for the identification of bacterial types and the total colony plate counts were used to estimate the bacterial densities. One way ANOVA (Analysis of variance) was used to compare the difference in bacterial densities between water and sediment samples. The RELATE routine technique was then applied to total bacterial count (TBC) data to determine the presence of change in TBCs between sites and among months for the two types of samples; sediment and water samples. For sample types where change occurred, the BIO-ENV routine was used to determine which subset of physico- chemical parameters best described sample-specific changes in TBCs among sites and months. A total of 4 bacterial groups belonging to 22 bacterial families and 30 genera were isolated from the 10 study sites. There was significant difference in bacterial counts between sediment and water samples with the sediment recording higher bacterial counts compared to the water samples. The most dominant bacterial types in the sediments were Actinomyces, Vibrio, Clostridium, and Listonella while Vibrio and Listonella, Clostridium and Norcadia were dominant in water samples. Temporal change in bacterial types was observed at 5 of the 10 sites evaluated. At four of these sites, changes in physico-chemical parameters were significantly correlated with the concurrent temporal change identified in bacterial types. Continuous and constant monitoring is recommended in order to establish and reveal the changes that are likely to take place in the system with mariculture intensification which is likely to change bacteria, chemical and physical conditions in the pond culture system and communities in nearby waters and sediments.