Harmful algal blooms & phycotoxins Flashcards
How widespread is the production of toxins in marine organisms?
- Very, and had evolved many time simultaneously
- 1,000+ marine families containing poisons & toxins.
- Maybe x500 more venomous species in tropics that temperate regions.
- Mostly contain proteins, peptides & other pharmacologically active
substances.
What is a poison?
- An umbrealla term, can be any substance that produces a detrimental biological response in another/same organism.
- They are very stable.
- They exhibit a very wide range of toxicities.
- Their efficiency and effectiveness is very variable but include some of the most toxic substances known.
What is venom?
Venom, unlike toxins which are chemically and biologically very stable, are the reverse and break down very easily.
But they are also incredibly highly evolved and efficient at what they do.
Holocrine venom
- Really are not true venom.
- Venomous, posinous subtances
- For example spines that you brush against, cause physical harm and release a poisonous substance. Not intentional but more incidental.
Stings / Bites
- True venom requires a direct and deliberate mode of venom transfer, generally a bite or a sting.
- Generally unstable
- Generally very efficient and effective
Why is it hard to pick up trends from medical history?
- Effects on humans are perceptive i.e. one person’s pain is another’s discomfort.
- Much information is historical, and therefore dubious in terms of accuracy.
- Symptoms – heart & respiratory failure – 50 yrs ago would not be distinguished from other conditions.
- Trends may suggest that the number of cases in increasing, which may be explained this
- Know less about marine toxins now than was known about medicine in dark ages.
- Sediment cores show toxic algal blooms from 2000 BC.
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How do harmfull macroalgal blooms fit into the food web?
How many marien alage are there (10 yeras ago)
- Over 5,000 spp marine microalgae described to date.
- new molecular techniques = reclassification e.g. Skeletonema
- Approx 300 sp. develop into ‘algal blooms’
- Defined as can discolour the water – so called ‘red tides’ & ‘brown tides’.
- Cell densities can exceed millions of cells per litre.
- Duration can last from hours to months
- Algal cell density is also affected by oceanographic forcing e.g. upwelling, wind drive circulation etc.
Do all harmful algal blooms produce toxins?
- Of the 300 blooming species, over 100 produce potent toxins which are harmful to plants, animals and humans these are termed ‘Harmful Algal Blooms’.
- ‘Nuisance Algal Blooms’ (branch within algal blooms) = don’t produce toxins but cause major problems e.g. reduced O2 concentration or damage (when they die they deoxygenate the water) to fish gills.
- Chaetoceros sp. Long, sharp spines can penetrate fish gills resulting in excess mucus production & death by asphyxiation. May also result in secondary infections.
Incidences of HABS are increasing globally, why is this?
Possible reasons include:
- Increased scientific awareness of toxic species.
1. More people listening to scientists
2. More goverments taking notice
3. More monitoring equipment
4. Better diagnosis assays
- Increased scientific awareness of toxic species.
- Increased utilisation of coastal waters for aquaculture.
1. Utilise more of our inshore waters for food production
2. Harvesting for bivalves, crustaceans ect
- Increased utilisation of coastal waters for aquaculture.
- Stimulation of plankton blooms by cultural eutrophication &/or unusual climatological conditions.
1. Fueling the system by adding nutrients
- Stimulation of plankton blooms by cultural eutrophication &/or unusual climatological conditions.
- -Transport of dinoflagellates as resting cysts either in ships’ ballast water or associated with translocation of shellfish stocks from one area to another.
- Ballast water
- Aquaculture moving broodstock
What types of algae produce toxins?
- 5 main algal classes identified as toxin producers**:
1) Dinoflagellates – 90 species
2) Diatoms – 10 species
3) Haptophytes – 9 species
4) Raphidophyceans– 7 species
5) Cyanobacteria / blue-green algae – **not true algae** - 10 species
Dinoflagellates
Dinoflagellates:
Saxitoxins, neosaxitoxins, gonyautoxins, okadaic acid, yessoensis toxins, azaspiracids, ciguatoxins, maitotoxins, brevetoxins, Pfiesteria toxin (plus several other less frequently occurring compounds).
- Huge range of toxins produced by dinoflagellates (many in each group)
- Chemically and toxiologicaloly diverse
Diatoms:
Domoic acid; oxylipins
Primarily talking about domoic acid, as a neurotoxin.
The most potent toxins are neurotoxins, which attack the central nervous system.
Haptophytes:
Prymnesin & prymnesin-like toxins
A range of neuro and cycotoxins
Cyanobacteria: (says interesting things are happening - exam)
Cyanobacteria:
Anatoxins, saxitoxins, microcystins, nodularins, cylindrospermopsins,
β-N-methylamino-L-alanine, debromoaplisiatoxin, lyngbyatoxin,
lipopolysaccharides.
- Alot of toxins, alot of overlap with dinoflagelllates, but also alot of toxins unique to themselves.
- Some of them are contact skin toxins
Paralytic shellfish poisoning (PSP)
Causative organisms –Alexandrium, Gymnodinium, Gyrodinium,
Gonyaulax & Pyrodinium.
- The life cycle has the hypnocyst (resting stage.) - is transportable e.g. ballast water & therefore may increase biogeographic range & frequency of PSP incidents.
- Saxitoxin one of only 2 natural toxins on UN agreement on biological weapons (Schedule 1 Chemical Warfare Agents – other is ricin.)
- Dose of only 0.2 mg can be fatal.
- 2 main groups of PSP toxins – saxitoxins (STX) & neosaxitoxins.
- STX first isolated from Saxidoma mollusc.
- Change in R- groups radically change the toxicity.
- 14 structural forms of STX & 9 for neosaxitoxins. It also includes the gonyautoxins. The degree of toxicity varies with each structural form.
- Epimerization is an isomer change of H & S groups which alters potency.
- This change in chemistry can happen within the algae, the animal that digests or within us.
- The acid in the stomach will make saxitoxin around six times as toxic. This makes regulatory control and guidance in terms of fisheries and public health very very difficult.
- You can freeze, cook or extract it out.
Gyrodinium aureolum – annual North Sea bloom. Caused PSP incident in Newcastle in 1968 (mussels) also notable fatalities among the sea bird population of Farne Islands. (yearly bloom around UK shores from cysts in the firthe of fourth - monitoring for this unlike developing countries)
How does saxitoxin work?
- Very fast-acting, and works by sitting in the sodium channels in your nervous system and stop the movement of sodium ions across your nerves.
- Saxitoxins are specific & potent sodium channel blockers preventing propagation of action potentials.
- STX found in widely differing groups e.g. pufferfish, Californian newt, red alga Jania sp. & blue-ringed octopus.
- STX not produced by these organisms, but rather bacteria living in/on the organisms.
- Also, evidence that it is not in fact the dinoflagellate which produces PSP toxins, but bacteria.
