Algal toxins & its effects

1. Algal Toxins & its Effects
Jitendra Kumar
College of Fisheries Mangalore

2. What is algal toxin?
 Algal toxins are organic molecules produced by a
variety of algae in marine, brackish and fresh waters.
 They are a problem in Fisheries when they are
produced in sufficient quantities, with sufficient
potency, to kill cultured organisms, decrease feeding
and growth rates, cause food safety issues, or
adversely affect the quality of the product.

3. environment
 Algal toxins do not enter the marine environment
from an external source but are generated during
blooms of particular naturally occurring marine
algal species.
 Algal
species,suchas Alexandrium and Dinophysis can
cause poisoning through the food chain when
shellfish ingest these algae (and their toxins) and
are then subsequently consumed by fish, birds
and potentially humans.
 The occurrence of toxic algae is perfectly natural
but there are concerns that increases in the
supply of essential nutrients through human
activities may be contributing to the increased
frequency and magnitude of these events.

4. Different
syndromes:- NSP - neurotoxic shellfish poisoning;
 PSP - paralytic shellfish poisoning;
 ASP - amnesic shellfish poisoning;
 DSP - diarrhoetic shellfish poisoning;
All are caused by toxins synthesized by
dinoflagellates, except for ASP, which is
produced by diatoms of the genus
Pseudonitzschia

5. Fate and behaviour in the
marine environment
 Released either when algal cells are ingested by
filter feeding animals, or when algal cells are broken
down after a bloom crashes.
 Some dinoflagellate species of toxic algae form cysts
that can accumulate in the sediment and act as an
inoculums for a new population when conditions
favour germination of the cysts.

6. Effects on the marine
environment
Effects on marine organisms:-
 sub-lethal and lethal toxicity, especially to fish, birds
and sea mammals;
 physical damage to fish gills.
Toxic phytoplankton can be filtered from the water by
shellfish, such as clams, mussels, oysters, or scallops,
which then accumulate the algal toxins to levels
which can be lethal to consumers, including humans.

7. Algae have also been implicated in fish kills by the
following direct methods:
◦ Mechanical damage to gills by algal spines,
notably the serrated spines of Chaetoceros spp.
◦ Irritation of gills resulting in over-production of
mucilage within the gills leading to suffocation.
◦ Physical blocking of the secondary lamellae of
fish gills.
◦ Increased water viscosity due to the secretion
of polysaccharides.

8. The indirect effects arise from changes in the oxygen
balance. super saturation with oxygen during the day
and oxygen depletion during the night. Algae have
been implicated in fish kills by the following indirect
methods:
◦ Asphyxiation caused by oxygen depletion.
◦ Gas bubble trauma from extreme oxygen super saturation.

9. Bioaccumulation
 Many algal toxins readily bio accumulate in marine
animals and significantly bio magnify through food
chains posing a hazard to consumers at higher trophic
levels (fish, birds and sea mammals).

10. Common types of algal poisoning:-
Ciguatera poisoning:-
 caused by potent neurotoxins produced by
Gambierdiscus toxicus,a dinoflageletes.
These toxins build-up in the food chain, starting from
small fish grazing on algae on coral reefs which are
then eaten by larger top-order predators such as coral
trout, red bass, chinaman fish, mackerels etc.

11. Paralytic shellfish poisoning:-
 Paralytic shellfish poisoning (PSP) is probably the
best known of all the shellfish poisonings.
Around 20 species of dinoflagellates have been
implicated in producing the alkaloid toxin saxitoxin,
a potent neuromuscular blocking agent that finds its
way through shellfish to humans.
Dinoflagellate species known to produce this toxin
include Gymnodinium catenatum, Alexandrium
catenella, A. minutum etc.

12. Diarrhetic shellfish poisoning:-
Dinophysis fortii and D. acuminate identified as
responsible.
Eating shellfish contaminated with diarrhetic shellfish
toxins (akodoic acid, dinophysistoxins and
pectenotoxins) causes severe gastrointestinal
problems.

13.  Amnesic shellfish poisoning
 The amnesic shellfish toxin, domoic acid, is produced
by the diatoms Nitzschia pungens, Nitzschia
pseudodelicatissima which accumulate in shellfish
and affect their consumers.
 High-performance liquid chromatography or mouse
bioassay techniques can be used to detect the toxin.
Shellfish containing more than 20 parts per million
domoic acid are considered unfit for human
consumption

14. Cyanobacterial toxins
 Most cyanotoxins are either neurotoxins or
hepatotoxins.
 Neurotoxins are produced by several genera of
cyanobacteria including Anabaena, Microcystis,
Arthrospira, Phormidium and Oscillatoria.
 Neurotoxins usually have acute effects in vertebrates,
with rapid paralysis of the peripheral skeletal and
respiratory muscles. Other symptoms include loss of
coordination, twitching, irregular gill movement,
tremors, altered swimming, and convulsions before
death by respiratory arrest.

15. Contro
l
 Identification of the conditions that trigger harmful
algal blooms may aid in developing strategies to
prevent red tides or freshwater cyanobacterial blooms
 Controlling nutrient loading through reduced
fertilizer use, improved animal waste control, and
improved sewage treatment may reduce the number,
or likely locations, of toxic algal blooms.

16. References:-
 http://www.nwhc.usgs.gov/publications/field_manual
/chapter_36.pdf
 http://www2.ca.uky.edu/wkrec/AlgalToxinsPond.pdf
 http://www.ukmarinesac.org.uk/activities/water-
quality/wq8_50.htm
 http://www.jstor.org/discover/10.2307/3454638?sid=
21104911699901&uid=2&uid=4&uid=3737496