5 algal bloom

8/9/2019 5 Algal Bloom

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y

Algal bloom concentrations may reachmillions of cells per milliliter.

y Are often green, but they can also be othercolors such as yellow-brown or red,

depending on the species of algae.y Bright green blooms are a result of blue-

green algae, which are actually bacteria(cyanobacteria).

Freshwater algal blooms are the result of an

excess of nutrients, particularly phosphorus.



HARMFUL ALGAL BLOOMS (HABs), arealgal bloom events involving toxic or otherwise

harmful phytoplankton such as dinoflagellates of the genus Alexandrium and Karenia.

y Such blooms often take on a red or brown

hue and are known colloquially as red tides.y Is an algal bloom that causes negative impactsto other organisms via production of naturaltoxins, mechanical damage to other organisms,

or by other means.H

ABs are often associatedwith large-scale marine mortality events andhave been associated with various types of shellfish poisonings.



y The excess of nutrients may originate from fertilizersthat are applied to land for agricultural orrecreational purposes, these nutrients can then enterwatersheds through water runoff.

y Algae tend to grow very quickly under high nutrientavailability, but each alga is short-lived, and the result

is a high concentration of dead organic matter whichstarts to decay.

y Blooms may be observed in freshwater aquariumswhen fish are overfed and excess nutrients are not

absorbed by plants.These are not generally harmfulfor fish, and the situation can be corrected bychanging the water in the tank and then reducing theamount of food given.



Examples of common harmful effectsExamples of common harmful effects

of HABs include:of HABs include: the production of neurotoxins which cause mass

mortalities in fish, seabirds and marine mammals

human illness or death via consumption of seafoodcontaminated by toxic algae

mechanical damage to other organisms, such asdisruption of epithelial gill tissues in fish, resultingin asphyxiation

oxygen depletion of the water column (hypoxia oranoxia) from cellular respiration and bacterialdegradation



Causes of HAB:Causes of HAB:

y It is unclear what causes HABs; their

occurrence in some locations appears to be

entirely natural, while in others they appear

to be a result of human activities.Furthermore, there are many different

species of algae that can form HABs, each

with different environmental requirementsfor optimal growth.



y In other areas,HABs are a predictable

seasonal occurrence resulting from coastalupwelling, a natural result of the movementof certain ocean currents.

y Coastal water pollution produced by

humans and systematic increase in sea watertemperature have also been suggested aspossible contributing factors in HABs.[

y Other factors such as iron-rich dust influx

from large desert areas such as the Saharandesert are thought to play a role in causingHABs.



Water treatmentWater treatment

Algal blooms sometimes occur in

drinking water supplies. In such cases, toxinsfrom the bloom can survive standard water

purifying treatments.



Red tideRed tide

- is a term often used to describe HABs inmarine coastal areas, as the dinoflagellatespecies involved in HABs are often red orbrown, and tint the sea water to a reddish

color.The more correct and preferred term inuse is harmful algal bloom, because:

1. these blooms are not associated with tides

2. not all algal blooms cause reddish discoloration of water

3. not all algal blooms are harmful, even thoseinvolving red discolouration



REDALGAL BLOOM HARMFUL ALGAL BLOOM



Algae (singular alga) are autotrophic organismsthat can carry out photosynthesis. As of now, more

than 30,000 species of algae are identified.Thoughalgae possess chlorophyll similar to green plants, theylack true roots, rhizoids and leaves.Hence, algae arenot categorized as plants, rather they are considered

as a different organism.T

he structure of algae can besimple unicellular (for example, Micromonas) tocomplex multicellular (for example, Kelps) forms.Usually, algae are found in any type of habitat;freshwater, marine water, swampy areas, moist soil and

rocks. Based on the characteristic features, there arefour major types of algae, namely, cyanobacteria, greenalgae, red algae and brown algae.



Reproduction in AlgaeReproduction in Algae

y The reproduction of algae can be discussedunder two types, namely, asexual reproductionand sexual reproduction.The former type

refers to reproduction in which a new organismis generated from a single parent. In case of sexual type, two haploid sex cells are fused toform a diploid zygote that develops into anorganism. Let's discuss in brief about theasexual and sexual reproduction in algae alongwith examples.



Asexual Reproduction in AlgaeAsexual Reproduction in Algae

Asexual reproduction in algae is quite

diverse. Some unicellular forms of algae like

Euglena reproduce by binary fission, in whichthe parent cell divides (longitudinal or

transverse) into two similar parts.These two

cells develop as organisms and are similar to

the parent cell.



Fragmentation is a process of asexual

division in Sargassum and other colonialalgae, whereby the parent cell divides intotwo or more fragments that grow into neworganisms. Another method of asexual

reproduction in algae is by formation of spores; the algal species Chlamydomonas andChlorella reproduce by this method.Depending upon the algal species, the spores

can be produced in normal vegetative cellsor specialized cells.They are either motile ornon motile.



Sexual Reproduction in AlgaeSexual Reproduction in Algae

As already mentioned, sexual reproduction

takes place by the union of male and female

gametes.T

he gametes may be identical inshape and size (isogamy) or different

(heterogamy). Some of the simplest forms of

algae like Spirogyra reproduce by the

conjugation method of sexual reproduction.



In the process of conjugation, twofilamentous strands (or two organisms) of

the same algae species exchange genetic

material through the conjugation tube.

Among two strands, one acts as a donorand another serves as a receiver. After

exchanging the genetic material, two strands

separate from each other.T

he receiver thengive rise to a diploid organism.



In the higher forms of algae, for example,U lva and Laminaria, an alternation of

generation is usually observed. Both asexual

and sexual reproduction occur in such

organisms.Thus, mature forms of haploidorganisms called gametophyte and diploid

organisms called sporophyte are present in

the life cycle.



If gametophyte and sporophyte organismsare similar in appearance, then they are

referred to as isomorphic; whereas algae with

different gametophyte and sporophyte formsare called heteromorphic.



The gametophyte produces haploidgametes by mitosis cell-division, which unite

to form diploid zygote that develops into a

sporophyte.T

he sporophyte then undergoesmeiosis cell-division to give rise to haploid

spores, which grow into gametophytes.This

way, the gametophyte and sporophyte

generations alter with each other.

5 algal bloom

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