single cell plankton

plankton are taxonomically and functionally diverse

  • plankton include viruses → bacteria/archaea → unicellular eukaryotes → multicellular organisms

  • protists (single-cell eukaryotes) are extremely diverse in morphology, metabolism, and ecological roles

traditional calssification (phytoplankton, zoo, bacterioplankton) is inadequate

  • problems

    • too simplistic

    • taxonomically inconsistent

    • doesnt reflect nutrition, reproduction, trophic roles

  • thus → size based and function based systems are better

plankton size classes

femto

viruses (<0.2µm)

pico

<2-3 µm

nano

2-20µm

micro

20-200µm

meso

200µm - 2 mm

macro

2-20 cm

mega

>20 cm

  • sampling methods depend on size

  • size relates to trophic interactions and metabolism

  • imaging tools target specific size fractions

plankton are functionally diverse

  • phytoplankton

    • photosynthetic: cynaobacteria + microeukaryotes

    • base of marine food webs

  • zooplankton

    • heterotrophic: protozooplankton + metazooplankton

  • mixoplankton

    • can combine autotrophy and heterotrophy

    • wide range of strategies

protists = single cell eukaryotes

  • huge morphological and ecological diversity

  • protists hold approx. 4 gigatons of carbon, more than all animals combined

  • they form the engine of marine ecosystems

    • photosynthesis

    • grazing

    • parasitism

    • viral interactions

    • export of carbon (POM, aggregates)

protist evolution and the eukaryotic tree

  • modern eukaryotic tree = supergroups

    • Amorphea

    • Archaeplastida

    • Haptista

    • Cryptista

    • TSAR

    • Orphan taxa (discoba, metamonoda)

archaeplastida - origin of chloroplasts

  • primary endosymbiosis 1.6 billion years ago

  • a eukaryote engulfed a cyanobacterium → chloroplasts

  • gave rise to:

    • glaucophytes

    • red algae (rhodophyta)

    • green algae (chlorophyta + streptophytes → land plants

orphan taxa: discoba

  • includes euglenozoa, which are:

    • 1500 species

    • ubiquitous flagellates

    • wide nutritional strategies: phagotrophy, autotrophy

    • rigid pellicle → characteristic metaboly movement

  • also includes symbiontids, deep-sea anaerobes with sulfur-oxidising epibionts

amorphea - opisthokonts + amoebozoa

  • opisthokonts include

    • animals

    • fungi

    • choanoflagellates (sister group to animals)

    • fish parasites (icthyosporeans)

  • huge diversity of unicellular forms

cryptista - cryptophytes

  • plastids from secondary endosymbiosis (red algal origin)

  • plastid surrounded by 4 memebranes

  • nucleomorph (residual nucleus of red algal endosymbiont)

  • important marine picoplankton

  • produce PUFA → valuable in aquaculture

haptista - includes haptophytes

  • third appendage haptonema

  • major planktonic group

  • many covered with coccoliths (CaCO3 plates)

  • key players in global carbonate cycle and biological pump

  • blooms visible from space

TSAR - the secret rulers of our world

  • TSAR = telonemids + stramenopiles + alveolates + rhizaria

  • one of the largest, mot diverse eukaryotic assemblages

alveolata

  • shared character: cortical alveoli under the membrane

ciliophora (ciliates)

  • nuclear dualism: micronucleus + macronucleus

  • conjugation

  • many with elaborate cilia strucutres

  • tintinnids form lorica with debris + fossil record

apicomplexa

  • parasites (plasmodium, toxoplasma)

  • retain apicoplast (non photosynthetic plastic) → evidence of algal ancestry

dinophyta (dinoflagellates)

  • 50% photosynthetic

  • dinokaryon: permanently condensed chromosomes

  • thecate vs athecate forms

  • recurrent plastid gains/losses (kleptoplasty common)

rhizaria

  • traits: ameoboid forms with filopodia/reticulopodia

foraminifera

  • benthic, test-forming

  • microfossil archive

  • many host symbiodinium

radiolaria

  • siliceous skeletons

  • excellent carbon sinkers

stramenopila

  • shared character: tripartite tubular hairs on flagella (mastigonemes)

  • includes:

    • diatoms

      • silceous frustules

      • heterokont flagellated stage in sexual reproduction

      • 10000 species

      • 20% of global primary production

    • brown algae

    • heterotrophic protists groups (some parasitic or commensal)

summary: why do protists matter?

  • protists are the backbone of marine ecosystems:

    • base of food webs

    • key in biogeochemical cycles (carbon, silica, nitrogen)

    • major drivers of marine productivity

    • huge evolutionary diversity

  • this lecture focuses on

    • diversity (size, function, phylogeny)

    • evolutionary origins of photosynthesis

    • major eukaryotic supergroups

    • ecological relelvance of protist groups