Harmful algal blooms (HABs) are symptomatic of ecosystem imbalance, often caused by the many environmental changes that demonstrate the expanding global human footprint and climate change. HABs are a major issue in marine, brackish, and freshwater systems worldwide. HAB species include representatives from most major algal and cyanobacterial taxonomic groups, but, despite this diversity, many HAB taxa respond to similar broad environmental stimuli (e.g., nutrients, light) and employ similar growth and defense strategies to maximize growth and minimize losses. In inland waters, attention is focused on dense surface HABs caused by planktonic cyanobacteria (cHABs), and the past few decades have seen an apparent increase in cHAB frequency and geographic range. There has also been an apparent rise in blooms of eukaryotic phytoplankton, including invasive marine flagellates, while reports of thick shoreline and benthic mats of chlorophytes, cyanobacteria, and other benthic HABs are likewise increasing. Research has made tremendous advances in our understanding of HAB events, yet they remain poorly understood. This chapter provides an overview of these intriguing and challenging phenomena, which affect ecosystems and human societies. While HABs are as diverse as the water bodies they impact, we focus on some specific examples of known HAB taxa that affect inland waters in North America and highlight some of the important strategies used by these species to enable their excessive growth.

http://scitechconnect.elsevier.com/wp-content/uploads/2016/01/Wehr_Excerpt1.pdf

Harmful Algal Blooms

The monocyclic heptapeptides microcystins (MCs), are a group of hepatotoxins, produced worldwide by some bloom-forming cyanobacterial species/strains both in marine and freshwater ecosystems. MCs are synthesized non-ribosomally by large multi-enzyme complexes consisting of different modules including polyketide synthases and non-ribosomal peptide synthetases, as well as several tailoring enzymes. More than 85 different variants of MCs have been reported to exist in nature. These are chemically stable, but undergo bio-degradation in natural water reservoirs. Direct or indirect intake of MCs through the food web is assumed to be a highly exposed route in risk assessment of cyanotoxins. MCs are the most commonly found cyanobacterial toxins that cause a major challenge for the production of safe drinking water and pose a serious threat to global public health as well as fundamental ecological processes due to their potential carcinogenicity. Here, we emphasize recent updates on different modes of action of their possible carcinogenicity. Besides the harmful effects on human and animals, MC producing cyanobacteria can also present a harmful effect on growth and development of agriculturally important plants. Overall, this review emphasizes the current understanding of MCs with their occurrence, geographical distribution, accumulation in the aquatic as well as terrestrial ecosystems, biosynthesis, climate-driven changes in their synthesis, stability and current aspects on its degradation, analysis, mode of action and their ecotoxicological effects.

Wei Han

Papers

Cyanobacterial population and harmful metabolites dynamics during a bloom in Yanghe Reservoir, North China