Toxic algae

what are algae?

  • they are polyphyletic → not a single evolutionary group

  • they are defined functionally: photosynthetic organisms without true roots, stems, or leaves

  • they are found as:

    • phytoplankton (microalgae drifting in water)

    • macroalgae/seaweed

    • benthic microalgae (on substrate)

what is an algal bloom?

  • an algal bloom = increased phytoplankton biomass caused by:

    • high growth rates

    • accumulation in stable water

    • low loss rates (low grazing or sinking)

  • algae are primary producers in the marine foodweb, supporting bacteria → zooplankton → fish

what are HABs?

  • some algal blooms become harmful called HABs

  • these can 

    • colour water red, brown or green

    • produce toxins

    • kill fish

    • contaminate shellfish

    • create foams and surface scums

    • harm ecosystems and humans

  • four HAB types:

    • toxin producers

      • toxins accumulate up the foodweb → harmful to humans/mammals

    • Icthyotoxic algae 

      • toxic to fish and gill breathing organisms (but not humans)

    • high biomass blooms

      • not toxic but can cause harm via hypoxia, shading, gelling of water, and clogging gills

    • eocosystem disruptive species

      • both toxic + bloom forming + wide ecological effects

  • only 2% of microalgae are harmful

  • in norway, some harmful groups are:

    • dinoflagellates

    • haptophytes

    • dictyophytes

    • diatoms

shellfish toxins

  • PSP → paralytic shellfish poisoning → diarrhea, nausea, vomiting, tingling, respiratory and muscular paralysis

  • DSP → diarrhetic shellfish poisoning → gastrointestinal symptoms (diarrhoea, nausea, vomiting, abdominal pain), headache

  • ASP → amnesic shellfish poisoning → gastrointestinal symptoms, head ache, disorientation, amnesia

  • NSP → neurotoxic shellfish poisoning

  • CFP → Ciguatera

  • AZP → Azaspiracid poisoning

Icthyotoxins

  • these are toxins that kill fish but are not harmful to humans

non toxic but harmful blooms

  • examples.

    • pseudochattonella farcimen → sever blooms affecting aquaculture

    • phaeocystis foam → clogs fishing nets, causes stench

    • lepidodinium bloom (oslofjord 2021) → waters turn green

monitoring in norway

  • norway has an excellent HABs monitoring system

  • blue mussle warning

  • monitoring prevents human poisoning and helps aquaculture respond early

why are HABs increasing?

  • increased awarness and reporting

  • more aquaculture activity

  • eutrophication, altered N:P:Si ratios

  • ballast water spread, transportation

  • climate change, warming, stratification → favours flagellates

  • overfishing → changes grazing pressure

the paper - Karlsson et al (2021)

  • the paper goes through three core questions:

    • which HAB species occur in northern europe?

    • what types of harm do they cause?

    • how have HABs changed over time (frequency, distribution, severity)

  • northern europe has seen an increase in reported harmful algal events over teh past decades

  • the paper defines four harmful bloom types (the same mentioned above)

  • alexandrium spp → PSP toxins

  • Dinophysis spp → DSP toxins