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Über dieses Buch

In the marine environment, single-celled, microscopic, plant-like organisms naturally occur in the well-lit surface layer of any body of water. These organisms, referred to as phytoplankton or microalgae, form the base of the food web upon which nearly all other marine organisms depend. Algal bloom is a rapid increase in or accumulation of the population of about 300 species of algae due to excess nutrients (eutrophication), and is of major global interest as it causes reduction in species diversity, abrupt changes in water quality, and discoloration of the water (green, yellow, brown or red) depending on the species of algae and the type of pigments they contain. Dying blooms can also be an environmental concern as when the cells sink and decay, bacteria break down the organic material, which in turn strips oxygen from the water. This microbial oxygen demand at times leads to very low oxygen levels in the bottom waters, harming aquatic life. Documentation of this sporadic high abundance of algae, together with the significant species richness of the diatoms, requires comprehensive studies in the Sundarban coastal environment, which is facing severe degradation due to natural & anthropogenic stressors. In addition, a better understanding of the effects of algal blooms on seafood quality, the complex biological, chemical and physical interactions and subsequent effects on trophodynamics is needed to develop strategies for effective coastal zone management.

The book discusses the occurrence of harmful algal blooms (HABs) caused by the dinoflagellates of the genus Alexandrium and Karenia, or diatoms of the genus Pseudo-nitzschia, which have large and varied impacts on marine ecosystems (such as large-scale marine mortality events that have been associated with various types of shellfish poisonings) depending on the species involved, the environment where they are found, and the mechanism by which they exert negative effects. HABs represent a major environmental problem in all regions of the U.S., and their occurrence is on the rise due to increased nutrient pollution.

HABs have severe impacts on human health, aquatic ecosystems, and the economy. Such blooms, known colloquially as red tides due to their red or brown hues, are increasing in frequency and magnitude worldwide as a result of changes in oceanic climate, increased coastal eutrophication and enhanced long-distance dispersal in ballast water. As such, the book offers an in-depth account of the complex biological, chemical and physical interactions of the algal blooms (both innocuous and harmful ones). It also discusses the highly topical issue of the impact of global climate change on the frequency and severity of HABs in the context of alterations in temperature, stratification, light and ocean acidification.

Focusing on both basic and applied limnology, this book is a reliable and up-to-date reference resource for students, teachers and researchers engaged in the field of coastal research/management at regional and global scales.



Chapter 1. Algal Blooms: Basic Concepts

An algal bloom is a rapid and prolific increase in phytoplankton biomass in freshwater, brackish water or marine water systems and is recognized by the discolouration in the water based on the phytopigments in the algal cells (either innocuous or toxic). Algae can be considered to be blooming at widely varied concentrations, reaching millions of cells per millilitre, or tens of thousands of cells per litre. Occurrence of bloom and its persistence are a complex environmental process involving multiple factors such as anthropogenic nutrient (eutrophication), solar radiation, temperature, current patterns and other associated factors. This natural but stochastic event leads to severe ecological health hazards, degradation of water quality and productivity and pelagic community structure. Proliferations of toxic microalgae in aquatic systems can cause massive fish kills, contaminate seafood with toxins and alter ecosystems in ways that humans perceive as harmful. The chapter addresses a comprehensive account regarding basic features related to algal bloom, such as Redfield ratios, eutrophication and hypoxia (deoxygenation). This is followed by detailed account of the major bloom causative agents (diatoms, dinoflagellates and cyanobacteria) and the remote sensors usually in practice for water quality monitoring. Finally a comprehensive account of the analytical instruments has been discussed generally used for microalgal studies for taxonomic and chemical component analyses.
Santosh Kumar Sarkar

Chapter 2. Algal Blooms: Potential Drivers, Occurrences and Impact

The growth of marine phytoplankton (both non-toxic and toxic) is generally limited by the availability of nitrates and phosphates, which can be abundant in coastal upwelling zones as well as in agricultural runoff. The type of nitrates and phosphates available in the system is also a factor, since phytoplankton can grow at different rates depending on the relative abundance of these substances (e.g. ammonia, urea, nitrate ion). A variety of other nutrient sources can also play an important role in affecting algal bloom formation, including iron, silica or carbon. This chapter has given importance to gain insight into the characteristics of algal blooms along with their potential drivers in relation to the marine environment. The chapter has also highlighted the current understanding on the mechanisms of algal bloom and addresses the regional differences in the persistence and causative agents of algal bloom in eutrophic tropical aquatic systems.
Santosh Kumar Sarkar

Chapter 3. Harmful Algal Blooms (HABs)

Harmful algal blooms (HABs) are serious biological nuisances and become a global epidemic. This is primarily flagellate events, causing mass mortality, physiological impairment or other negative in situ effects. HABs are increasing their frequency, persistence, regional coverage/spatial extent and economic impact worldwide in recent decades as a result of changes in enhanced coastal eutrophication and climate change along with invasion of alien species through ballast water exchange. This also happens on account of the world’s increasing trend of unscientific and irrational exploitation on the coastal zone for shelter, food, construction, food, aquaculture, recreation and other commercial uses, which results in increasing eutrophication. Naturally occurring red tides and harmful algal blooms (HABs) are of increasing importance in the eutrophic coastal environment and can have remarkable adverse impacts on coastal benthic and epipelagic communities. Determining the key regulatory factors is somehow problematic since algal blooms are often unpredictable, irregular or of short duration. The chapter has addressed an illustrative account of all the six categories of HABs along with description of the causative agents and their associated clinical symptoms. The recent tools and techniques developed towards operational status for prediction or detection of HABs have described. Finally, climate change impact on the occurrence of algal blooms in a global scale has also been illustrated.
Santosh Kumar Sarkar
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