COMPARATIVE ANALYSIS OF CULTURABLE MICROFLORA IN HEALTHY AND BLEACHED RED SEAWEED Kappaphycus alvarezii

Farming of the red seaweed, Kappaphycus alvarezii has emerged as an economically important enterprise and promises to be a profitable livelihood avenue for the low-income coastal communities of India. However, alike other aquatic farming systems, the farming of this commodity is also risked by diseases like ice-ice which causes thallus bleaching. An event of bleaching was noticed in early January 2019 in the farmed Kappaphycus alvarezii at the marine farm of Karwar Research Centre of ICAR-CMFRI.

Samples of healthy, infected and bleached thalli were collected and subjected to microbial analysis. Water samples from the area of bleaching as well as from the area with healthy seaweed were also collected for the analysis of associated bacterial communities. Bacteria were isolated from seaweeds and water using different media such as Zobell Marine Agar, Thiosulfate citrate bile salt agar and Brain Heart infusion agar. Biochemical tests such as gram staining, spore staining, motility, oxidase, catalase, citrate utilization, indole and MR-VP were carried for preliminary identification. The results indicated ten times higher total aerobic count of bacteria in the infected and bleached samples when compared to the healthy sample. Also presumptive vibrios were not detected in healthy samples whereas in case of unhealthy ones it was significantly higher (Table 1). Similar results were also observed in the water samples. It was noteworthy that only gram positive bacteria were found from healthy samples whereas gram-negative bacteria dominated the infected and bleached samples. The bacteria isolated from healthy K.alvarezii was dominated by Bacillus sp. whereas Vibrio group was predominant both in the infected as well as bleached individuals. Important environmental parameters such as temperature, pH and salinity were also recorded and compared with the data corresponding to period prior to the event of bleaching in seaweed .This preliminary study indicates a possible interplay of environment and microbes as a cause of bleaching in red seaweed, K.alvarezii. Further studies are underway for a deeper insight into the occurrence of this damaging event.