Harmful algal blooms Topic 4. Learning goals To understand classification and biological sources of harmful algal blooms To learn biological mechanisms.
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Learning goals
To understand classification and biological sources of harmful algal blooms
To learn biological mechanisms of action of algal toxins
Practical implications: prediction, prevention and control
What are HABs?
Algae that produce toxins Dinoflagellates Diatoms Cyanobacteria (fresh water)
Very potent toxins (few cells per liter can produce toxic effects)
Adversely affect overall environmental quality
Environmental impacts
Toxic effects on organismsPhysical impairment of fishNuisance conditions from odors or
discoloration of water or habitats
History of HABs
HABs are not a new phenomenon!Documentation of HABs goes back to
ancient timesApparent increase of the HAB occurrence
in modern times – real or imaginary?
Toxic dinoflagellate blooms Ciguatera Fish Poisoning Diarrhetic Shellfish Poisoning Neurotoxic Shellfish Poisoning Paralytic Shellfish Poisoning
Toxic diatom blooms Amnesic Shellfish Poisoning
Harmful blooms (non-toxic or toxicity not confirmed) Fish kills
Pfiesteria, Chaetoceros, Heterosigma Brown tides
Aureococcus, Aureoumbra
Algae associated with HABs
Ciguatera Fish Poisoning
Gambierdiscus toxicus (a dinoflagellate)
Associated with weeds and coral reefs
Optimum conditions: shallow waters, 25-34°C, 25-40 ppt
Ciguatoxin and maitotoxin
Ciguatera Fish Poisoning
Common cause of food-borne poisoning~ 50% of US seafood poisoning
90% - Florida and Hawaii Spring/Summer
Ciguatera Fish Poisoning: Vectors
Usually large fish, bottom dwellers and reef fish Red snapper, Grouper, Amber Jack, Sturgeon
Toxins Bioaccumulate Stable and heat resistant Lipid soluble Highly potent (clinical effects from <1 mg)
Lag time <12 h Acute onset Early symptoms (24-48 h): Gastrointestinal
Pain, cramping, diarrhea, vomiting Late symptoms
Neurological Headache, toothache Temperature disturbance (hot-cold sensation reversal) Respiratory paralysis and seizure in severe cases
Cardiovascular Heart rate abnormalities (rare), usually bradycardia
Ciguatera Fish Poisoning: Symptoms in humans
Ciguatera Fish Poisoning: Treatment and prevention
Diagnosis Biomarkers of exposure not available
Therapy Not available
Prevention Complicated
Wide range of susceptible species Odorless, colorless, tasteless
Avoidance Large reef fish Avoiding roe, head, viscera
Diarrhetic Shellfish Poisoning
Dinoflagellates Dinophysis acuminata,
Dinophysis fortii, Prorocentrum lima
Species reported in the US but associated illnesses not reported
Okadaic acids and dinophysistoxins
Mechanisms of action
Inhibits phosphatase 1 and 2A which control Na+ secretion from intestinal cells
Loss of fluids and ions from gut epithelial cells
Diarrhetic Shellfish Poisoning: Human Symptoms
Generally mild gastrointestinal illness Diarrhea, nausea, vomiting Rapid onset, rapid resolution No neurotoxic effects Long-term effects? (Possibly tumorigenic)
FDA level in shellfish – 0.2 ppm okadaic acid plus 35-methyl-okadaic acid
Neurotoxic Shellfish Poisoning
Karenia brevis (previously Gymnodinium breve)
Florida, Gulf of Mexico
Brevetoxins
Neurotoxic Shellfish Poisoning: Human Symptoms
Similar to ciguatera poisoning Early symptoms: Gastrointestinal
Nausea, diarrhea, vomiting Late symptoms
Neurological Tingling Numbness Loss of motor control Usually not associated with human mortality
FDA level in fish – 0.8 ppm brevitoxin-2 equivalent
Brevetoxins: Ecological Impacts
Massive fish kills Harmful to birds
(pelican, seagulls, cormorants) and manatees
Brevetoxins: Economical Impacts
Human health-associated impactsClosure of shellfish bedsSkin and respiratory irritation to humans at
the seashoreLosses in commercial catch and tourism
Paralytic Shellfish Poisoning
Dinoflagellates Alexandrium spp. Gymnodinium spp. Pyrodinium spp.
Northern Atlantic and Pacific coasts
Temperate and tropicalSaxitoxins
Mechanism of action
Binds and blocks voltage-dependent sodium channels
Blocks neuron activity and affects peripheral nervous system
Paralytic Shellfish Poisoning: Human Symptoms Rapid onset (~30 min) Absence of gastrointestinal symptoms Neurological symptoms
Numbness Headache Ataxia Weakness Cranial nerve dysfunction Diaphragmatic paralysis Death by asphyxiation
Weakness can persist for weeks
Paralytic Shellfish Poisoning: Therapy and Prevention
Therapy Not available (supportive only)
FDA limit in fish 0.8 ppm
Saxitoxins: Ecological Impacts
Mass bivalve mortality (1980- 5,000,000 mussels, 1980; 1997- 50,000, Eland Bay, South Africa)
Lobster mortality (Eland Bay, South Africa)Humpback whales (Cape Cod, MA)
1997 South Africa
Amnesic Shellfish Poisoning
Pseudo-nitzschia spp. (diatoms)
Discovered in 1987 (Price Edward Isl., Canada)
Domoic acid
Mechanisms of action
Mimics a neurotransmitter (glutamic acid)
Overstimulates and eventually kills neurons in hypocampus
Stimulates voltage-dependent calcium channels
Amnesic Shellfish Poisoning: Human Symptoms Early symptoms: Gastrointestinal
Nausea, vomiting, diarrhea CNS symptoms
Dizziness Cognitive effects Disorientation Memory loss Delirium Seizures Agitation
Highly variable course 10% with permanent neurological damage
Domoic acid: Ecological Effects
1991 Monterey Bay CA - >100 pelicans and cormorants were found dead or suffering from unusual neurological symptoms
Pseudo-nitzschia australisVector: Northern Anchovie
Pfiesteria piscicida: fish kills
Unknown substances secreted by finfish and shellfish stimulate Pfiesteria to transform from benthic cysts or amoebae or non-toxic flagellated cells, to toxic zoospores
Pfiesteria in humans
Rare Narcosis Sores Nausea/vomiting Acute short-term memory loss Severe cognitive impairment
Recovery in 6-8 weeks, but may re-occurMost cases – Chesapeake fishermen and
algal researchers (aerosol!)
HABs: What can we do about it?
Prevention Complicated Public awareness (=negative publicity for fish
and shellfish industry)
Prediction Satellite tracking of red and brown tides Mathematical models predicting blooms
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