Growth and physiological responses of the Singapore strain of Heterosigma to various nitrogen sources and light conditions

Nutrient pollution of coastal environments particularly by nitrogen (N) sources can lead to harmful algal blooms. Ameliorating the incidence of such events requires an understanding of how harmful taxa respond to different N sources. In particular, the blooms of toxic Heterosigma have been known to cause costly and highly detrimental effects to surrounding ecosystem function. The threat is especially dire in the case of Singapore where growth dynamics of Heterosigma species under tropical environmental conditions are poorly understood. The present study examined how the growth rates of Heterosigma species isolated from the Johor Straits of Singapore differ under various N sources as well as varying light intensity. Heterosigma was found to grow well under both nitrogen sources, but grew at a faster rate when exposed to nitrate compared to ammonium. In addition, the study also observed tolerance for high- and low-light conditions. These results indicate that present modifications to the coastal environment through high sedimentation and nutrient pollution rates might be creating conditions conducive to the growth of Heterosigma.