1. A Brief Overview of Freshwater Harmful Algal Blooms
Paul Zimba
United States Department of Agriculture
Agricultural Research Service
Catfish Genetics Research Unit
Stoneville, MS

2. Types of Harmful Algal Blooms
Produce dense blooms leading to oxygen stress.
Dinoflagellates, diatoms, raphidophytes, prymnesiophytes
Cyanobacteria (prokaryotic microbes)
Produce potent toxins—illness and death via food chain or biomass accumulation.
Paralytic shellfish poisoning (PSP)
Diarrheal shellfish poisoning (DSP)
Neurotoxic shellfish poisoning (NSP)
Ciguatera fishfood poisoning (CFP)
Estuary-associated syndrome (EAS)
Dinoflagellate
Diatom
Amnesic shellfish poisoning (ASP)
Cyanobacterial Toxin Poisoning (CTP) 

3. Etiologic agents associated with drinking water outbreaks, in surface water– United States, (n = 175) 5%
25%
Agricultural Impacts
Bacteria
Chemicals
Paramecium/Protozoa
Viruses
Algae
23% 2% 2%
43%

4. Freshwater Toxins
Hepatotoxins – microcystin, cylindrospermopsin, nodularins(?)
Neurotoxins – anatoxin-a, prymnesin, anatoxin-a(s), saxitoxin, BMAAs??
Bioactive peptides (ex. anabaenopeptins, anabaenopeptilides)
4) Dermal irritants(?)

5. Microcystins: polypeptide that has >70 structural variants that alter
potential toxicity by 20-fold. Principal damage to liver with inhibition
of protein phosphatase 2a enzyme. Identification by enzyme inhibition,
antibody binding, or HPLC/MS.
Mass: AMU
Most common
substitution sites
Impact: Direct Toxic to zooplankton, fish, mammals, plants
IndirectAltered food webs

6. Microcystin in Aquaculture Systems
Microcystin can kill fish at ng/mL
Two clonal populations – one strain blooms
in winter, whereas the other strain blooms
in summer
Around 50% of all ponds have measurable
microcystin levels based on survey of
485 ponds during July-August (3% of total).
1% of ponds have blooms that exceed
WHO guidelines
Recently shrimp kill in Texas at <20 ng/mL!

7. Anatoxin-a Neurotoxin that disrupts nerve conductance by
irreversibly binding to Na+ channels. Affected organisms
include mammals, birds, and fish.
Commonly produced by Anabaena, Planktothrix spp.
Mass: 164 AMU, requires precolumn
derivatization for HPLC identification
Direct effect: paralysis, or death.

8. ANATOXIN-a in Aquaculture systems
Producers are from Planktothrix aghardii complex
Production is limited to temperatures below 16 C
Toxin detected in gut contents and water, no extraction method
optimized for tissue analyses

9. Prymnesin toxin Produced by Prymnesium parvum (brackish water
flagellate species-grows in <2 ppt water)
Toxin structure not known, no standards available
Toxic to striped bass, channel catfish
Confirmed cases in NC, LA, and TX (USA), common
in Europe, Asia
Forms resting stages-drop salinity <1.5 ppt for control
Direct effect: toxicity?, lowered dissolved oxygen/fish kills
Indirect effect: food chain alterations

10. “Euglenophycin” produced by E. sanguinea
Neurological toxin affecting fish equilibria
Structure not fully resolved
Toxic to: tilapia, striped bass, catfish, killifish,
mammalian tissue culture cell line(s)
Cells densities between 800-1,500/mL in surface algal
scum during fish mortality events
Fish mortalities confirmed using clonal cultures
Confirmed mortality events in TX, AR, NC, and MS (USA)
and Argentina
Direct effect: fish mortalities

11. It is important to appreciate that toxin
production is from a microbial
community, so understanding role of
bacteria, and cyanobacteria is critical.
In other consortia, bacteria can
stimulate toxin production by four-fold!

12. Other toxins:
Cylindrospermopsin: documented from FL, WI (USA), common in
Europe, Australia, Africa
Producers: Cylindrospermopsis raciborski, Uzbecka spp.
Saxitoxin: documented from AL water reservoirs, common in Europe
Producers: benthic Lyngbya, Anabaena species
Bioactive peptides: serine/threonine inhibitors, neurotoxins/cytotoxins
Producers: Microcystis, Oscillatoria, Nostoc

13. Blooms differ (benthic,
sub-surface, surface)
and recognition of a
bloom often occurs
late, even after the
event!

14. Harmful Algal Blooms include non-toxin producing
situations
Blooms that increase biomass above baseline levels-
in Florida Bay, algal blooms of 10 µg/L exceed the normal
chlorophyll concentration by 5-fold.
Shading by planktonic algae can shade benthic
diatom mats, resulting in replacement by cyanobacteria
Dinoflagellate blooms in estuaries result in higher
BOD requirements and reduce dissolved oxygen, resulting
in rough fish replacing desirable species

15. SPOTTER/
ALIGNMENT
MOTOR
PLATFORM
SENSOR SYSTEM

16. Basic Remote Sensing principles

17. Overflight using
AISA push-broom
sensor on a Piper
Saratoga operated
by CALMIT, Univ.
of Nebraska
Cost : 10K

18. Alternatives: Hand held sensors: convenient light-weight
if dual-head – no worries of atmospheric
correction- can be used in most weather!
cost - $7 – 90K
quick – 18 ponds in 1 hr!

19. Note three pronounced features from catfish ponds:
705nm suspended solids MAX
676nm chl a trough
624nm phycocyanin trough

22. By optimizing model fit for the water body,
a necessary step for Case 2 waters, it is
possible to improve model performance.

24. It is critical to realize that one technique does not answer all
questions. For instance, counting
potentially toxic algae does
not tell you if toxins are present,
and measuring toxins does not
tell which species are involved.