Harmful algal blooms (HABs) are overgrowths of algae that can produce toxins or otherwise be harmful to people, animals, and ecosystems. They occur in freshwater, brackish, and marine environments. Factors that contribute to HABs include increased salinity, carbon dioxide, nutrients from eutrophication, temperature, and coastal upwelling. Blooms are caused by various algal species and can have red, green, or brown discoloration. Toxins produced can harm humans and wildlife. Mitigation methods include physical removal, chemicals, and biological controls but each has limitations for large-scale application.

1. HARMFUL ALGAL BLOOMS
(HABs)
& Threat
Ashish sahu

2. What is algae?
Algae are generally microscopic organisms, thought of as
simple aquatic plants which do not have roots, stems or leaves
& have primitive methods of reproduction.
 They are the basic food source for small aquatic animals.
 Algae are simple plants that range in size from microscopic
to large kelp.

3. Definition Of HAB
 A harmful algal bloom (HAB) is a bloom of certain types of
algal species that produce toxins as it blooms or dies.
 According to international council for the exploration of seas
(1984), exceptional blooms have been defined as 'those which
are noticeable, particularly to the general public, directly or
indirectly through their effects such as visible discolouration
of the water, foam production, fish or invertebrate mortality or
toxicity to humans'

4.  Blooms are simply high concentrations of algal cells .
 A bloom is formed by a rapid increase or accumulation in the
population of algae in a water system.
 Algal blooms may occur in freshwater, brackish water as well
as marine environments.
 Algal blooms often accumulate on the surface of water bodies,
giving the water a green, brown, or red appearance.
 Dense blooms near the surface may resemble a layer of green
paint.

5. bloom species can be classified into three
different groups:
1) Produce harmless water discolorations, but the dense bloom on
decomposition can cause anoxia and lead to indiscriminate
mortality of marine life.
2) Species which produce potent toxins causing a variety of
gastrointestinal and neurological illness to humans and
animals.
3) Species which are not toxic to humans but harmful to fish and
invertebrates by damaging or clogging their fish gills.

6. TYPES OF ALGAL BLOOM
1. Freshwater Algal Bloom
BLUE GREEN ALGAE (cyanobacteria)
 Harmful toxic, surface-dwelling, scum-forming genera
Ex: (Anabaena, Nodularia,Microcystis)
 subsurface bloom-formers
Ex: (Cylindrospermopsis, Oscillatoria)

7. The most noxious cyanobacterial bloom genera are
capable of fixing atmospheric nitrogen (N2).
Ex: Anabaena, Aphanizomenon, Cylindrospermopsis, nodularia
Green algal bloom - Euglena bloom, Microcystis bloom,
Anabaena bloom,
Filamentous algal bloom – Spirogyra, Oscillatoria; chlorella,
Nostoc, Odogonium, Chara also cause algal bloom.

8. Microcystis bloom Anabaena bloom
Odogonium bloom Spirogyra bloom

9. 2. Marine algal blooms
•BACILLARIOPHYCEAE (Diatoms)
•DINOPHYCEAE (Dinoflagellates)
•PRYMNESIOPHYCEAE (Golden–brown flagellates)
•CHRYSOPHYCEAE (golden–brown algae)
•RAPHIDOPHYCEAE (Chloromonads)
•DICTOCHOPYCEAE (Silicoflagellates)
•CYANOPHYCEAE (marine blue–green algae)
Marine algal blooms can appear as red water
discolorations commonly referred to as ‘red tides’ or a range of
other discoloured water, from green, yellow and brownish to
an oily or milky appearance.

10. What Types of Algal Blooms Can Phytoplankton
Cause?
1.RED TIDES:
Red tides are caused by phytoplankton that have a
reddish pigment called peridinin. Most dinoflagellates, such
as Alexandrium catenella, have this pigment. As a result,
when there is a bloom of dinoflagellates, the ocean will
generally turn red. This type of tide is very common on both
the east and west coasts as well as Florida and the Gulf of
Mexico.

11. 2. GREEN TIDES
Green tides can be caused by Phaeocystis, which is a
unicellular, photosynthetic algae found throughout the
world. Green tides can also be caused by macro algae such as
Enteromorpha spp. and Codium isthmocladum, which have
caused serious damage to many coastal regions When in
bloom, macro algae often outcompete sea grass and coral
reefs. This results in habitat loss for marine fish, less oxygen
and sunlight for other organisms, and an ecosystem that is
more vulnerable to extinction and invasions.

12. 3. BROWN TIDES
Brown tides are caused by the pelagophytes (another type of
microalgae) such as Aureococcus anophagefferens.
Aureococcusis a spherical, non-motile species that has
caused noticeable damage to the coastal ecosystems in which it
occurs. Brown tides are commonly seen in the northeast and
mid-Atlantic US estuaries.

13. Effects of algal blooms
 Effects on Water - tiny, microscopic algae (also called
phytoplankton) multiply rapidly when algal bloom occurs
 Effects on Aquatic Organisms - negative effect on aquatic
species – die offs many creatures because of depletion of
oxygen when bloom decay
 Effects on Human Health - negative effect on humans
health due to consumption of seafood infected with toxins

14.  Effects on commerce and other human activities-
the fishing industry is a victim of harmful algal blooms causes
a rapid die-off of fish so fishermen either cannot fish or bring in a
much smaller catch that reduces their income.
 Poor aesthetics spoil recreation and tourism.
 Nitrogen fixing- positive effect in aquatic ecosystem

15. Types of Algae Causing Blooms
1.Green algae/ Chlorophyta
• Green algae are found in both freshwater and marine environment.
• They are not involved in toxin production.
• Cause localized hypoxia(create stress for fish ).
• Nuisance species of the green algae, include both macro- and
microalgae.
• For Example, the macro algal Chlorophyte ,Cladophora .
 Cladophora forms foul-smelling nuisance blooms that are deposited
on beaches, can clog water intakes, and potentially harbor
pathogens, such as E.Coli.

16. 2. Bacillariophyceae ( Diatoms)
• Diatoms are unicellular and cell wall composed of silica
(frustule).
• ASP is caused by diatom Pseudo nitzschia .
• This diatom is widely distributed in both the northern and
southern hemispheres .

17. 3. Euglenids
• Euglenophytes can be found in
fresh, estuarine, and marine waters.
• Euglena species produce an Ichthyotoxin in freshwater
aquaculture (fish kills).
• Blooms are most likely to occur during summer in freshwater
ponds.
• Most common in slow moving or still waters with high
nutrient concentrations.
• Indicators of organic water pollution .
• Euglenophyte blooms may color the water green, reddish
brown, or red .

18. 4. Prymnesiophyte / GOLDEN-BROWN ALGAE
• It is a small (~10 μm), generally halophilic organism.
• Prymnesium parvum is commonly called the “golden” alga (yellow-brown
accessory pigments) .
• Blooms of golden algae produces an Ichthyotoxin.
• Aquatic insects, birds and mammals are not affected by P. parvum toxins.
• Blooms of p. Parvum have been responsible for fish kills in brackish waters
and inland waters (with relatively high mineral content) .

19. • This results significant economic losses in Europe, North America and
other continents.
• It was first suspected of fish kills in Texas in 1982 and confirmed in 1985.
• Golden algae has killed millions of fish in Texas & has been hit with
recurrent blooms in several reservoirs and rivers.

20. 4. DINOFLAGELLATES
• Most Dinoflagellates are marine plankton but they are common in
freshwater habitats, as well.
• The blooms turn the ocean various shades of red. - red tides.
• They can produce toxins capable of killing fish and accumulating in filter
feeders such as shellfish.

21. • Some dinoflagellate blooms are not dangerous.
• Bluish flickers visible in ocean water at night often come from
blooms of bioluminescent dinoflagellates, which emit short
flashes of light when disturbed.

22. 5. Blue green algal bloom
• Cyanobacteria are the major harmful algal group in freshwater
environments.
• These are recognized as a rapidly expanding global problem that threatens
human and ecosystem health .
• In the marine environment, only few species of blue-green algae cause
problems.
• Cyanobacteria form blooms in different colours.

23. The most common species of
cyanobacteria
• Anabaena, Oscillatoria, Nostoc and microcystis– fresh water
• Trichodesmium and Nodularia, are marine species but these have not been
associated with human syndroms so far.
• Nodularia is also found in brackish water.
Microcystis sp Anabaena flos-aquae Anabaena circinalis

24. Aphanizomenon
Cylindrospermopsis
oscillatoria

25. Factors that contribute algal blooms;
1. Salinity:
 Climate change leads to increase evaporation rate
 Increased salinity favor the growth of algal bloom
2. Carbon-di-oxide:
 Increased carbon-di-oxide levels in aquatic environment triggers algal bloom
3. Eutrophication:
 Sudden enrichment of nutrients
 Chattonella antiqua, Heterosigma akashiwo and Cochlodinium polykrikoides can form
bloom even small amounts of nutrients.

26. 4. Temperature
 Increased thermal stratification
 Decreased viscosity of water
 Increase temperature by absorbing sunlight
5. Monsoon
 Summer monsoon leads seasonal oscillations in the form of active
and weak rainfall
 It causes sudden changes in salinity and water temperature
6.Coastal upwelling
 Leads to high nutrient conditions – high primary production – cause
oxygen depletion

27. Favorable conditions for HABs
Conditions which promote HABs include:
 Sunlight
 Increases in nutrients
 Low flow conditions
 Still water
 Release of nutrients from sediments
 Reduced grazing by predators
 High temperature
 Low salinity

28. TOXINS
• Only a few HAB species actually produce toxins.
• poisonous to people and marine animals.
• The most well known HAB toxins are generically referred to
as,
1. Ciguatera fish poisoning (CFP) – Gambierdiscus,
Prorocentrum - Ciguatoxin, Maitotoxin
2. Neurotoxic shellfish poisoning (NSP)-Gymnodinium breve
and Karenia brevis - Brevetoxins

29. 3.Paralytic shellfish poisoning (PSP) - Alexandrium,
Pyrodinium & Gymnodinium – Saxitoxins
4.Diarrheic shellfish poisoning (DSP) - Dinophysis,
Prorocentrum - Okadoic Acid and Dinophysistoxin
5.Amnesic shellfish poisoning(ASP)-Pseudonitzschia
australis and Pseudonitzschia pungens - Domoic acid

30. GENUS TOXINS PRODUCED
Anabaena circinalis Saxitoxins
Anabaena flos-aquae Anatoxins, Microcystins
Anabaenopsis Microcystins
Aphanizomenon Saxitoxins, Cylindrospermopsins
Cylindrospermopsis Cylindrospermopsins, Saxitoxins
Hapalosiphon Microcystins
Lyngbya Aplysiatoxins, Lyngbyatoxin a
Microcystis (M.aeruginosa, M.viridis) Microcystins
Nocularia Nodularin
Nostoc Microcystins
Phormidium (Oscillatoria) Anatoxin
Planktothrix (Oscillatoria) Anatoxins, Aplysiatoxins, Microcystins, Saxitoxins
Schizothrix Aplysiatoxins
Trichodesmium Not yet identified
Umezakia Cylindrospermopsin

31. Toxin Types Examples Effects
Neurotoxins Anatoxin-a, Anatoxin-a(s),
Saxitoxin, Neosaxitoxin
Affects central nervous system,
causes seizures, paralysis,
respiratory failure, and death
Hepatotoxins Microcystins, Nodularins,
Cylindrospermopsin
Affects liver, causes
hemorrhaging, tissue damage,
tumors, liver cancer, and death
Dermatotoxins and
Gastrointestinal toxins
Aplysiatoxins, Lyngbyatoxin-a,
lipopolysaccharide endotoxins
Affects skin and mucous
membranes, causes rashes,
respiratory illness, headache,
and stomach upset
Cytotoxins Cylindrospermopsin Affects liver and other organs,
causes chromosome loss, DNA
strand breakage, and organ
damage

32. Effects on people and wildlife
HABs can cause illness and death in humans, pets, and wildlife.
Symptoms include:
 Skin rash
 Muscle cramps
 Twitching
 Paralysis
 Nausea and vomiting
 Cardiac or respiratory failure
 Acute liver failure

33. Impacts of HABs
• Humans, wildlife, and domestic animals can be exposed to
algal toxins via contaminated food, water, or aerosols,
depending on the toxin
• Other HAB species are nontoxic to humans and wildlife but
degrade ecosystems by forming such large blooms that they
alter habitat quality through overgrowth, shading, or oxygen
depletion (hypoxia).

34. • Adversely affecting corals, sea grasses, and bottom-dwelling
organisms.
• High biomass blooms of certain nontoxic harmful algae can
also harm fish and invertebrates by,
 damaging gills
 causing starvation
 low reproduction due to poor food quality

35. Water quality parameters during bloom
Parameters Range
Temperature (°C) 29-31
Salinity (ppt) 35-37
pH 7.3 – 7.5
DO (ml/l) 3.4
Phosphate 0.040
Nitrite 0.023
Nitrate 0.003

36. Mitigation and Control of Harmful Algal
Blooms
The principles of controlling HABs are to decrease the
algal cell densities, stop its rapid proliferation, and mitigate its
harmful effects.
Methods can be divided into 3 types based on mechanisms of
actions,
1. Physical methods,
2. Chemical methods,
3. Biological methods

37. 1. PHYSICAL METHODS
 Physical methods are those that rely on physical mechanisms
to directly remove or isolate the cells from water, and these
techniques include skimming, isolation, and disruption .
 Sometimes these methods are coupled with the use of some
coagulants or flocculants. Physical methods are usually simple
and do not cause secondary pollution.
 They have been successful in controlling HABs organisms in
small volume ballast water and cyanobacterial blooms that
form surface scums, especially in the later stages of a bloom in
some field studies.
 However, physical methods usually show little effect on low
density and benthic HABs organisms and are usually
expensive when applied in large volume of water.

38. 2. BIOLOGICAL METHODS
 Biological methods to control HABs usually utilize enzymolysis or
parasitism effects on micro organisms , nutrient competition or allelopathic
effects of macro algae or sea grass, or grazing by marine protozoa,
zooplankton, and filter-feeding shellfish.
 Biological methods usually do not cause secondary pollution and can be
species-specific, without impacts on non-HAB species.
 However, there are possibilities of introducing invasive species into the
ecosystem, resulting in ecosystem disruption. Furthermore, filtration of
toxic algae by shellfish may cause harm to human beings via toxin
bioaccumulation.
 Additionally, there are great difficulties in cultivation, transportation, and
timeliness when these methods are applied in the field, which makes it
difficult to use biological methods to control HABs when rapid response is
necessary.

39.  The feasibility of controlling HABs using zooplankton
(Acartia clausi) and bivalves (clam and oyster) was estimated
and showed that the method was completely infeasible,
considering the cost, space, and facilities .
 Nevertheless, filter-feeding shellfish do contribute to
prevention of HABs occurrence.
 Thus far, biological methods have only studied in the
laboratory, and few field applications have been reported.
 Biological control in many regions also requires extensive
permits, again limiting the timeliness of such approaches.

40. 3. CHEMICAL METHODS
 Chemical methods employ either chemicals toxic to HAB
organisms (killing them directly) or flocculants that precipitate
algal cells to the water bottom.
 Reagents used in the direct killing methods can be an
inorganic agent, including cupric sulphate, hydrogen peroxide,
chlorine, sodium hypochlorite, sodium percarbonate and
ozone, or organic algicides, such as hexadecyl trimethyl
ammonium bromide (HDTMA) , sophorolipid , and aponin .
 Direct killing methods that take effect rapidly are currently
prohibited in most regions (e.g., cupric sulphate) due to their
toxic effects on the ecosystem.

41.  In recent years, researchers have started to consider using
more environmental-friendly compounds, such as those that
can rapidly decompose, including hypochloric acid, sodium
hypochlorite, sodium percarbonate and ozone, organic
algicides (e.g., carboxylic acid, organic amine, and ketone) ,
and plant extracts.
 After considering the potential environment problems and
costs, however, these chemicals are usually not recommended
to be applied in the field, except perhaps in some limited
aquaculture or localized regions, such as lakes.

42. The control strategies of HABs
Methods Principle Advantage/disadvantages
Physical methods – Skimming algae flocs
using boat after air
flotation
– Isolation by fence and oil
spill collector
– Lysis by ultrasonic and
electromagnetic waves
– Electrolysis
Advantages: simple,
easy to operate and
environmental- friendly
Disadvantages: high
cost, only can be used in
small scale waters, lysis of
toxic algae can release
toxin to waters

43. Biological methods – Predation by, e.g.,
zooplankton and filter-
feeding shellfish
– Enzymolysis or
parasitism by bacteria,
virus and/or parasitic
dinoflagellates
– Nutrient competition
or allelopathy
Advantages: environment
friendly, some virus and
parasitic dinoflagellates
are specific to algae cells
Disadvantages: may
cause invasion of alien
species, problems of
cultivation, storage,
transportation and
timeliness, not suitable to
control field HABs, low
predation rate of toxin
algae by filter feeding
animals, lysis of toxic
algae can release toxin to
waters

44. Chemical methods – Killing by, eg, inorganic
killing reagent
(cupric sulphate,
hydrogen peroxide,
sodium hypochlorite,
sodium percarbonate, and
ozone and chlorine) and
organic algicide (such
as HDTMA, sophorolipid,
and aponin)
– Flocculating by, e.g.,
flocculants setting,
including inorganic,
organic and microbial
flocculants; clay mineral
setting, such as kaolinite
and montmorillonite
Advantages:
Takes effects fast, easy to
store and transport
Disadvantages: potential
secondary pollution, non
specific, may cause harm
to non-HABs organisms,
lysis of toxic algae can
release toxin to waters

45. REFERENCE;
• Anderson DM, Gilbert PM, Burkholder JM (2002) Harmful
algal blooms and eutrophication: nutrient sources, composition
and consequences. Estuaries 25:704–726
• Satpathy KK, Nair KVK (1996) Occurrence of phytoplankton
bloom and its effect on coastal water quality.Indian J Mar
Sci 25:145–147
• https://www.noaa.gov/what-is-harmful-algal-bloom
• http://www.fao.org/fishery/topic/14759/en
• Global Ecology and Oceanography of Harmful Algal Blooms,
page no.(403-407).