A Brief Overview of Freshwater Harmful Algal Blooms
Paul Zimba
United States Department of Agriculture
Agricultural Research Service
Catfish Genetics Research Unit
Stoneville, MS
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)
– Amnesic shellfish poisoning (ASP)
 – Cyanobacterial Toxin Poisoning (CTP)
Dinoflagellate
Diatom
Etiologic agents associated with drinking water outbreaks,
in surface water– United States, 1989-2000 (n = 175)
5%
25%
Agricultural Impacts
Bacteria
Chemicals
Paramecium/Protozoa
Viruses
Algae
23%
2%
2%
43%
Freshwater Toxins
1) Hepatotoxins – microcystin, cylindrospermopsin, nodularins(?)
2) Neurotoxins – anatoxin-a, prymnesin, anatoxin-a(s), saxitoxin,
BMAAs??
3) Bioactive peptides (ex. anabaenopeptins, anabaenopeptilides)
4) Dermal irritants(?)
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: 950-1185 AMU
Most common
substitution sites
Impact:
Direct Toxic to zooplankton, fish, mammals, plants
IndirectAltered food webs
Microcystin in Aquaculture Systems
Microcystin can kill fish at 60-70 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!
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.
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
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
“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
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 fourfold!
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
Blooms differ (benthic,
sub-surface, surface)
and recognition of a
bloom often occurs
late, even after the
event!
Harmful Algal Blooms include non-toxin producing
situations
1) Blooms that increase biomass above baseline levelsin Florida Bay, algal blooms of 10 µg/L exceed the normal
chlorophyll concentration by 5-fold.
2) Shading by planktonic algae can shade benthic
diatom mats, resulting in replacement by cyanobacteria
3) Dinoflagellate blooms in estuaries result in higher
BOD requirements and reduce dissolved oxygen, resulting
in rough fish replacing desirable species
SPOTTER/
ALIGNMENT
MOTOR
PLATFORM
SENSOR SYSTEM
Basic Remote Sensing principles
Overflight using
AISA push-broom
sensor on a Piper
Saratoga operated
by CALMIT, Univ.
of Nebraska
Cost : 10K
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!
Submersed Reflectance (OO)
8.5
7.5
5.5
4.5
3.5
2.5
1.5
nm
744.41
685.59
625.08
562.95
499.27
434.12
-0.5
367.56
0.5
nm
Reflectance
6.5
55
54
45
53
44
52
43
51
42
50
41
49
40
48
39
47
38
Note three pronounced
features from catfish
ponds:
705nm suspended solids MAX
676nm chl a trough
624nm phycocyanin trough
20
y = 0.0018x + 4.3392
R2 = 0.23
R440/R550
16
12
8
4
0
0
500
1000
1500
2000
Chlorophyll, mg/m3
2500
3000
3500
RMSE, mg.m3
500
Step 1
l01 =670 nm
450
400
350
300
680
700
720
740
760
l3
780
800
RMSE, mg.m3
500
450
Step 2
l3 =726 nm
Step 4
l3 =714 nm
By optimizing model fit for the water body,
a necessary step for Case 2 waters, it is
possible to improve model performance.
400
350
300
600
620
640
l1
660
680
700
RMSE, mg.m3
500
Step 3
l1 =650 nm
450
400
350
300
680
700
720
740
l3
760
780
800
2.0
(R-1650)xR740 = 0.0004xChl + 0.4797
R2 = 0.71, RMSE = 369 mg/m3
Models
1.5
1.0
0.5
(R-1650-R-1710)xR740 = 0.0003xChl - 0.0052
R2 = 0.78, RMSE = 319 mg/m3
0.0
0
500
1000
1500
2000
Chlorophyll, mg/m3
2500
3000
3500
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.