Cyanobacteria can form intense and sometimes toxic blooms in all kinds of aquatic ecosystems, typified as cyanobacterial bloom. Cyanobacterial blooms can create a range of harmful toxins, which may disturb water sources, successively posing serious health threat to living organisms, and at this stage they are termed as cyanobacterial harmful algal blooms (CyanoHABs). The occurrence of cyanobacterial blooms and cyanobacterial toxins are globally reported, so is the evident in Bangladesh, mainly trigged by increased anthropogenic eutrophication and global climate change.Cyanobacterial blooms and the accumulation of several toxins in human's drinking water, recreational water and aquatic biota such as zooplankton, fish larvae and juveniles interrupt aquaculture, aquatic ecosystem and public health in Bangladesh. As the management measures of toxic cyanobacteria and cyanotoxin are insufficient in Bangladesh, and the proper management for mitigating the worldwide occurrence of toxic cyanobacterial blooms is crucial for maintenance and sustainable development of functional ecosystems, some recommendations are illustrated. Further appropriate research on biology and ecology of cyanobacteria, cyanobacterial toxins and their relationship with environmental factors as well as nutrient management in fish ponds to manage noxious and harmful algae is essential to minimize their adverse impacts on aquaculture and public health for the country.

A winter bloom event of Trichodesmium erythraeum was monitored for the first time in the southeastern coastal parts of Bangladesh along the Bay of Bengal. This study presents the brownish to light pinkish bloom that appeared in mid-winter and disappeared abruptly during spring. Heavy blooms of T. erythraeum revealed the highest concentration of 91.47 ± 52.94 × 103 colonies/L in the Bakkhali River Estuary, and 66.93 ± 12.95 × 103 colonies/L in the Maheshkhali Channel of the Bay of Bengal. Three distinct morphological shapes, namely puffs, tufts and asymmetrical colonies, were depicted as major types. Several environmental factors, such as water temperature, salinity, pH, dissolved oxygen, NO3–N and PO4–P, were analyzed to determine their relationship with the occurrence, abundance and bloom formation of T. erythraeum. The abundance of the species showed a positive correlation with salinity and pH while exhibiting a negative correlation with temperature and DO. A cluster analysis revealed a clear indication of T. erythraeum bloom during winter. Thus, the prevalence of the highest density of the bloom in the present study area strongly suggests increased monitoring and research efforts in order to effectively manage or impede harmful algal blooms.

Harmful algal blooms (HABs) constitute a global problem, affecting aquatic ecosystems, human health, fisheries and local economies. The Bay of Bengal, along the Bangladesh coast, is exceedingly suffering from pollution or anthropogenic nutrification that influences frequently occurring HAB species. The progression of climate change and eutrophication invigorate HAB trends and responses that in turn affect the respective coastal livelihood and economic growth. Tripos spp., Dinophysis spp., Protoperidinium spp., Chaetoceros spp., and Pseudo-nitzschia spp. are the common bloom-forming HAB species in the coastal waters of Bangladesh. Despite having huge potentiality for regional and global perspectives, the coastal region of Bangladesh remains relatively unexplored compared to other regions in the context of HABs and their pernicious effects. As a result, harmful algal blooms and the accumulation of algal toxins may interrupt fisheries, aquaculture, aquatic ecosystems and public health in the country. Therefore, proper research on the biology and ecology of harmful algae, biotoxins and their relationship with environmental factors need to be adequately understood to minimize their adverse effects on the noted marine resources of the Bay. This review focused on an overview of the HAB related issues – causes of HABs, their occurrences and abundances, associated environmental factors and adverse effects in the coastal zone of Bangladesh.

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