Is there any critical value of biomass or other indicator for this definition?
Limnology, Environmental sciences, Phycology
A definition of bloom is always controversial. Typically, values higher than 50 ug Chl a L-1 or >20,000 cells L-1 are proposed as definition of bloom (see e.g. Oliver and Ganf, 2000).
As per the causes behind bloom development, cyanobacteria show generally lower growth rates than other algal groups, so I would not attribute it to rapid growth. Instead, cyanos display a number of ecophysiological adaptations to outcompete other algae, despitetheir lower growth rates. Some of them are buoyancy regulation by intracellullar gas vesicles, accessory photosynthetic pigments (increased exploitable light spectrum), N2 fixation, P accumulation. There are some reviews and textbooks describing these (see e.g. Carey et al. 2011)
water bloom, also called algal bloom is a rapid growth of microscopic algae or cyanobacteria in water, often resulting in a colored scum on the surface
Algal blooms can grow in freshwater as well as marine waters. This may occur not only due to human activities, but also due to natural reasons.
According to the American Heritage Dictionary of the English Language (5th edi.); water bloom (usually termed as algal bloom) is defined as growth of algae, especially cyanobacteria, on the surface of a body of water. In other words, water bloom is the production of a murky aquatic population of microscopic photosynthetic organisms combined with abundant nutrient salts in surface water and adequate sunlight for photosynthesis. So, combination of environmental conditions such as nutrients, temperature, light, turbidity are found to be responsible for harmful algal blooms. The indicator parameters of nutrient enrichment (eutrophication) are- total nitrogen, total phosphorus, chlorophyll a, secchi depth, dissolved oxygen.
I find the question very interesting, though do doubt the usefulness of defining a bloom according to concentration of cells/a metabolite alone because microbial diversity is also key. A bloom usually occurs when, out of the background diversity, a population of one (or a small number of) strain(s) explodes. The bloom is therefore charactertised/defined by both increased biomass and reduced dversity...we discussed the environmental factors and cellular traits that give rise to such phenomena for both freshwater and marine blooms in a 2013 paper; The biology of habitat dominance; can microbes act as weeds?
With regards, John
Agual blooms are often seasonal processes triggered by an environmental factor or a combinaison of factors (i.e Spring blooms starting with a combined increased temperature and light availability)..Many systems have several blooms occuring regularly every year. Sometimes, a first bloom will be dominated by a specific phytoplanton group and then followed by another because of switch in nutrient ratio for example. With that in mind, the question of defining a lower threshold to characterize a bloom remains tricky because a bloom is rapid planktonic growth and the concentration in chrorophyll reached should be compared to the "normal" level. In very productive waters, the background chlorophyll level might be quite high through the year while, in oligotrophique waters, the phytoplankton biomass might increase 10 fold in a few days but remains quite low...
Most researchers believe that water blooms was caused by the rapid growth of algae under a complicated condition. However, only for Microcystis, our recent investigation denied this viewpoint.
i) in situ growth rate of Microcystis always below 1 /day;
ii) the vertical and horizontal accumulation is the immediate cause.
A definition of bloom is always controversial. Typically, values higher than 50 ug Chl a L-1 or >20,000 cells L-1 are proposed as definition of bloom (see e.g. Oliver and Ganf, 2000).
As per the causes behind bloom development, cyanobacteria show generally lower growth rates than other algal groups, so I would not attribute it to rapid growth. Instead, cyanos display a number of ecophysiological adaptations to outcompete other algae, despitetheir lower growth rates. Some of them are buoyancy regulation by intracellullar gas vesicles, accessory photosynthetic pigments (increased exploitable light spectrum), N2 fixation, P accumulation. There are some reviews and textbooks describing these (see e.g. Carey et al. 2011)
Hi Ramsy, yes I agree with your points though there are also additional factors: for example ability to resist of avoid predators, grazers and/or viral infection can be key too. We reviewed this topic Microb Biotechnol 6:453-492 (2013). with regards John
Water bloom or plankton bloom. You can take eutrophication or species diversity index as indicator.
Indeed, John. In addition to the factors you mentioned the effect of parasites has been traditionally ignored and it seems it might play a critical role in diatoms and cyanos bloom dynamics.
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