PMB (P)- 01

Bacteriological Indicators of marine environmental health: Case studies from Mandovi and Zuari estuaries
Shama Kakti, Jaysankar De, X. N. Verlecar and N. Ramaiah*
National Institute of Oceanography Dona Paula, Goa 403 004
*e-mail: ramaiah@darya.nio.org

Marine environmental contamination is an inevitable consequence of anthropogenic activities, and bacterial communities are the quickest to respond to such alterations. Major developmental activities have taken place along the banks of rivers and estuaries. The wastewaters discharged from cities and a variety of industries are discharged with minimal treatment into these water bodies (Anon., 1993). Moreover, occasional pollution by sewage effluents containing human pathogens may result in the prohibition of sale of shellfish causing economic loss (Liv et al 1994). However, these discharges have a negative impact on the coastal environments making them vulnerable to deterioration. Marine ecosystem surveillance is a complex process involving accessibility, weather conditions, sea-worthiness of analysts among other factors (Kinne 1980). Despite such intimidating situations, a lot of efforts have been made world wide to document the status of marine environment health. Marine microbial communities play a fundamental role in the biogeochemical processes occurring in the oceans. An understanding of their abundance, type and distribution in the coastal zone are of importance in quantifying the state of environmental health.

The project Coastal Ocean Monitoring and Prediction system (COMAPS) was implemented to assess the health of our coastal waters on long-term basis and to facilitate pollution control. In the light of the above programme the following study was carried out at the National Institute of Oceanography. The main objective of this study was to discern trends in bacterial distribution and behavior by examining the retrievability of indicator bacteria from water samples collected from a sensitive area prone to contamination at the river mouths of Mandovi and Zuari, the two major rivers in Goa.

A variety of human pathogenic and indicator bacterial groups were enumerated by following standard microbiological methods. The results reported here are for four years from 2000 to 2003. Bacterial media were prepared in 50% seawater to yield the best results for estuarine samples. Samples were plated for total viable counts (TVC) on Nutrient agar; total coliforms (TC) on Macconkeys agar; Vibrio parahaemolyticus like organisms(VPLO) and Vibrio cholerae like organisms(VCLO) on thiosulphate citrate bile sucrose agar; Salmonella, Shigella, Proteus , and Klebsiella like organisms(SALO, SHLO, PKLO) on xylose lysine deoxycholate agar. Counts of all these groups were obtained after incubating the samples on the respective selective media at 35 + 2° C. Results of these groups are presented in Fig 1 and Tables 1 and 2.

Briefly, the TVC were ranging from 86.7 to 16,712 cells ml^-1 in the Zuari mouth, showing highest density in the year 2001. There was a steady decrease in the number of TVC from year 2001 to 2003 in the Mandovi region. The bacterial abundance reflects the properties particularly the organic load of the study area. Increasing incidence of total coliforms both in Mandovi and Zuari river mouths suggest increased sewage outfall and these sites have become “contamination hot-spots”. There was a decline in ECLO density from year 2001 to 2003 in the Zuari mouth. Whereas, both ECLO and total vibrios were found in high concentrations in Mandovi. Vibrios are an important group of autochthonous microflora in the marine environment. Their presence implies that there is an active biodegradable process by the native microflora (Anon 1996 and Ramaiah et al 1996). Although the current work discusses the abundance of pollution indicators, it is restricted to those that are retrieved on media prepared with 50% seawater. Sewage pollution indicators that survive include the ones that get acclimated to marine environment.

Highest bacterial density of ECLO, SHLO, PKLO, VPLO were found in the year 2003 (Table 1). The frequency of occurrence also was comparatively high during that year. VCLO were present in all the samples analysed in year 2001 and 2003, but their density was the highest during 2001. During the four years study period, the average ECLO counts were ranging from 0.2 to 2.3 cells ml^-1 and they were present in less than 17% of the total samples (n = 30) analysed. Average densities of SHLO, PKLO and VPLO were 1.8 to 20 cells ml^-1, 0.7 to 23.1 cells ml^-1 and 0.06 to 1.66 ml^-1 cells respectively.

The average ECLO densities were ranging from 0.03 to 0.75 cells ml^-1 (Table 2). They were always present in up to 10% of the total samples (n = 10) analyzed. SHLO and PKLO were found during all the four years of study in varying densities and frequencies as shown in Table 2. VPLO and SALO occurred rarely in 2002 and 2003; otherwise they were absent. High recovery of the above indicator groups probably suggests higher allochthonous inputs as well as their abilities to survive in the estuarine environments.

Balakrish Nair et al (1980), Lokabharathi et al (1986), Mohandas et al (1999 and 2003) reported higher frequency of occurrence of these forms in coastal waters. There could be many factors governing the survival and mortality of bacteria including physical (such as depth), chemical (dissolved oxygen, salinity, right types of nutrients, pH, dissolved organics, and toxicants) and biological (competition, phages etc).

Typically only a small fraction (often less than 1%) of the prokaryotes from an aquatic or soil environment grow on agar plates (Staley and Konopka 1985) . This has hampered the study of assessing total prokaryotic abundance in a sample. It has even been argued that viral lysis might be one of the reasons for low plating efficiency of bacteria (Rehnstam et al 1993) . Heldal and Brakbak (1991) estimated that phages lyse 2 to 24% of the bacterial population in an aquatic environment. Limited knowledge of the rate of bacterial mortality in the marine environment is a great source of uncertainty in predictive calculation of bacterial levels (Gameson, 1984)

In conclusion, the long-term observation we have carried out gives an indication of the extent of microbial pollution in terms of total coliforms, V. parahaemolyticus , V. cholerae, Salmonella, Shigella , Proteus and Klebsiella like organisms could be isolated from the sampling locations despite the lack of definite point sources of pollution. Therefore, continued monitoring for these indicator and human pathogenic bacteria covering a wider area would enable researchers to locate the definite point sources of pollution, understand the environmental health and perhaps suggest remedial measures. Concerted efforts to understand molecular, physiological and other biological changes these communities experience are required to evolve newer guidelines to monitor and conserve the coastal ecosystems.

References

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Table 1- Bacterial density and frequency of occurrence of different populations of bacteria in Mandovi estuarine station

*Annual average counts; ** Occurrence in percentage derived from total number of samples positive by total number analyzed

Table 2- Bacterial density and frequency of occurrence of different populations of bacteria in Zuari estuarine station

*Annual average counts; ** Occurrence in percentage derived from total number of samples positive by total number analyzed.