Agriculture, Aquatic, and Natural Resources

Occurrence and Spatial Distribution of Cyanobacteria in Recreational Waters of Honda Bay, Palawan: Environmental Conditions and Public Health Implications

Ben Jan E. Hisona, Edgar P. Paalan, Jhonamie A. Mabuhay-Omar

Abstract

The increasing occurrence of cyanobacteria in coastal waters poses ecological and human safety concerns. However, baseline information for recreational areas in Honda Bay, Palawan remains limited. This study assessed cyanobacteria occurrence and spatial distribution, determined associated environmental conditions, and evaluated public health risks. Water samples were collected at five stations (Wharf, Cowrie Island, Pandan Island, Starfish Island, and Luli Island) using the vertical tow method. Cyanobacteria were identified microscopically and expressed as cells/L; potentially toxin–producing genera were identified for public health risk assessment. Physicochemical parameters measured on–site included temperature, pH, salinity, dissolved oxygen, conductivity, oxidation–reduction potential, total dissolved solids, total suspended solids, water transparency, and depth. Cyanobacteria were present at all stations, ranging from 168 to 3,032 cells/L with marked spatial variation. Dominant and potentially harmful genera included Planktothrix sp., Nodularia sp., Trichodesmium sp., Synechococcus sp., and Merismopedia sp., which are associated with skin irritation, allergic reactions, and poisoning posing risks to tourism and recreation. Analysis showed that water transparency influenced cyanobacterial density; clearer waters with increased light penetration enhanced photosynthetic efficiency, supporting cyanobacterial growth. These findings provide baseline data for Honda Bay and highlight the need for regular monitoring to support local coastal water management and risk reduction strategies.