HABs: causes and possible strategies to control them

In 2003 the USA EPA sponsored a roundtable discussion in order to develop a consensus on the relationship between HABs and eutrophication. Although the committee focused on cases study along the US coasts, the statements can be adopted also by other countries. Briefly, it has been unanimously established that :

• both cronic and episodic nutrient pollution promote the development and persistence of many HABs
• the composition -not just the quality-of nutrient pool impacts HABs
• high biomass blooms must have exogenous nutrients to be sustained
• further experimental studies are necessary to better understand the role of nutrients in HABs: the reduction in nutrient input decreases HABs, although this strategy is challenge (for many species these relationships can be complex) and extremely costly, hence developing other bloom control strategies would be better.

Many studies focusing on bloom control strategies development occurred after this meeting, and at the present day chinese institutions are strongly contributing in increasing the knowledge of this matter.

Tang and Gobler in 2011 demonstrated that the green macroalga Ulva lactuca can have a strong growth-inhibiting effects on multiple HAB species. In this experiment both fresh talli and extracts of the dried powder of macroalga were capable of lysing or strongly inhibiting the growth of 7 common HAB species through the release of heat-stable allelochemicals. Furthermore a field-based experiment proved that U. lactuca can reduce the densities of field population of A. anophagefferens.

In late 2011 a research team of Xiamen University pusblished a study showing the algicidal activity of two marine bacteria. Molecular characterization classified them to the gamma-proteobacteria subclass and the genus Vibrio and Pseudoalteromonas. These strains have been isolated and used to purify a protein (P7) that showed algicidal activity against the toxic dinoflagellate A. tamarense. P7 algicidal activity was well evident as the algal cells were lysed and cellular substances were released under visual fields of microscope.

All of these studies contribute in increasing the knowledge of toxic microalgae ecology, biology and interaction with other organisms. Two possible strategies in controlling HABs blooms were provided although more investigations are necessary in order to state their real application and possibility to be used in field: methods were very complicated and should be improved.

References:

Heisler, J., P. M. Glibert, et al. (2008). "Eutrophication and harmful algal blooms: A scientific consensus." Harmful Algae 8(1): 3-13.

Tang, Y. Z. and C. J. Gobler (2011). "The green macroalga, Ulva lactuca, inhibits the growth of seven common harmful algal bloom species via allelopathy." Harmful Algae 10(5): 480-488.

Wang, B., X. Yang, et al. (2012). "A marine bacterium producing protein with algicidal activity against Alexandrium tamarense." Harmful Algae 13(0): 83-88.