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 Diatom • 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 • Amnesic shellfish poisoning (ASP) • Cyanobacterial Toxin Poisoning (CTP)
Agricultural Impacts Bacteria Chemicals Paramecium/Protozoa Viruses Algae Etiologic agents associated with drinking water outbreaks, in surface water– United States, 1989-2000 (n = 175) 5% 25% 23% 2% 2% 43%
Freshwater Toxins • Hepatotoxins – microcystin, cylindrospermopsin, nodularins(?) • Neurotoxins – anatoxin-a, prymnesin, anatoxin-a(s), saxitoxin, BMAAs?? • 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 IndirectAltered 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 four-fold!
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 • 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
SPOTTER/ ALIGNMENT MOTOR PLATFORM SENSOR SYSTEM
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!
Note three pronounced features from catfish ponds: 705nm suspended solids MAX 676nm chl a trough 624nm phycocyanin trough
By optimizing model fit for the water body, a necessary step for Case 2 waters, it is possible to improve model performance.
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.