Harmful algal blooms

Topic 4

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?

HABs in US:

Pre- and post-1972

“Red” Tide

World-wide occurrence

Algae: Dinoflagellates Diatoms

“Brown” Tide World-wide occurrence Algae

Chrysophyta (“golden-brown algae”)

Aureococcus Aureoumbra

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

Ciguatoxin

Mechanism of action

Selective activation of voltage-sensitive Na+ channels

Ciguatera Fish Poisoning

Mechanism of action

Selectively activates voltage dependent calcium channels

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

Diarrhetic Shellfish Poisoning

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

Mechanism of action

Selective activation of voltage-sensitive Na+ channels

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

Paralytic Shellfish Poisoning

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

Amnesic Shellfish Poisoning

Domoic AcidGlutamic 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: Distribution in the US

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

Satellite images: Karenia brevis in NC, 1987

Staellite images: Red tide in FL, 1978