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The Taxonomic Groups of Phytoplankton

A. An Overview

1. Bacteria (= prokaryotic cells)

  • Eubacteria (heterotroph)
  • Archebacteria or Archaea (heterotroph)
  • Cyanobacteria (phototroph, phytoplankton!)
    • "real Cyanobacteria"
      • filamentous cyanobacteria, fix nitrogen 
      • coccoid cyanobacteria
    • Prochlorophytes
  • 2. Algae (= eukaryotic cells)
    • Chromophyta (possess chlorophyll a and c)
      • Cryptophyceae
      • Dinophyceae
      • Chrysophyceae
      • Prymnesiophyceae
      • Bacillariophyceae (diatoms)
    • Chlorophyta (possess chlorophyll a and b)
      • Chlorophyceae
      • Prasinophyceae
      • Euglenophyceae
    B. Diatoms = Bacillariophyceae
    • Plankton, benthos, and epiphyton
    • Centric (round) – mostly plankton 

      • pennate (long) – mostly benthos, epiphyton
    • Size 2 mm to 1 mm; single, chains, colony
    • Silica frustle – important in Si cycle and deposit of silica on sea floor (ooze)
    • Taxonomy: based on pores in frustle
    • Predominant in phytoplankton spring bloom in temperate and polar seas
    • Non-motile – prefer turbulent waters
    • Cell division – replacement of one frustle half; daughter cells become smaller; at certain size sexual reproduction, formation of auxospore
    • Some species produce resting spore with thickened frustle, which rests on sea floor (shallow seas) upon adverse conditions
    C. Dinoflagellates = Dinophyceae
    • Also referred to as Pyrrophyta
    • Can be autotrophic (phototrophic), but 50% of dinoflagellates are heterotrophic; some chlorophyll-carrying species complement nutrition by phagotrophy (mixotrophic); parasitic forms (on or within zooplankton or sucking out diatoms)
    • Mostly single cells, some form chains; motile by 2 flagella
    • “hate” turbulence
    • Naked forms and thecate forms; theca consists of several thick cellulose plates
    • Typically abundant in summer, fall blooms, oligotrophic (nutrient-poor) open ocean
    • Proliferation by cell division, theca may divide with daughter cells building new half or may be lost prior to division
    • Sexual reproduction leads to resting spores, deposited in sediment
    • Systematics of dinoflagellates based on number and structure of cellulose plates and spines
    • Cell divided in posterior and anterior half by deep grove = girdle
    • One flagellum extends free posteriorly from cell (forward movement), the other wraps transversally around cell in the girdle (rotation)
    D. Red Tides, Dinoflagellate Blooms
    • Mass development of dinoflagellates (>108 cells l-1) discolor water; mostly related to nutrient input by rain or drainage from fields and pig/chicken farms
    • Paralytic Shellfish Poisoning (PSP): Algal cells contain highly lethal saxitoxin; accumulation of toxin in clams, mussel, scallops, fish lead to poisoning of humans; symptoms neurological, heart arrest in most severe cases after 24 hrs; closure of mussel beds
    • Neurotoxic Shellfish Poisoning (NSP): algal toxin is brevetoxin (Gymnodinium breve); neurological & gastrointestinal symptoms; aerosols can produce asthma; no deaths reported
    • Diarrhetic Shellfish Poisoning (DSP): Okadaic acid, Dinophysis sp.; gastrointestinal symptoms (diarrhea, cramps) 30 min after consumption of toxic shellfish, not lethal, recovery ca. 3 days
    • Ciguatera Fish Poisoning (CFP): Ciguatoxin, gastrointestinal, neurological, and cardiovascular symptoms; paralysis and death documented, but usually less severe; mostly tropical waters


    E. Prymnesiophyceae

    • Major oceanic bloom formers; some mixotrophic
    • Naked cells, mostly single; motile, 2 flagella and 1 haptonema (also referred to as Haptophytes)

    • Phaeocystis gelatinous colony-forming, extended blooms in North Sea, Atlantic, and Southern Ocean

    • Coccolithophorids: single cells with external shell of calcareous plates (coccoliths)

    • only one or several plate types plates (sytematics) 
    • mostly <20 mm (nanoplankton)
    • Blooms visible from space by discoloration
    • Major transport of carbonate to the sea floor; sediments up-lifted to surface known as chalk (White Cliffs, Dover)
    • Longitudinal cell division /w shell divided
    F. Chrysophyceae
    • Also referred to as golden (brown) algae;
    • Usually single cells with 1 flagellum, small, few colony-forming species in freshwater
    • Posses small scales on cells used for taxonomy
    • Silicoflagellates: possess internal skeleton of silicous spines; few species, mostly cold water
    G. Chlorophyta (Chlorophyceae, Prasinophyceae)
    • Marine species mostly single cells with two flagella; colony-forming, aflagellate cells abundant in freshwater
    • Contain chlorophyll b, by which they can be distinguished in pigment analyses (HPLC)
    • Less important in typically marine systems but abundant in Florida Bay and eutrophic coastal and estuarine areas
    H. Cyanobacteria
    • Also reffered to as blue-green algae; however, they are procaryotic organisms (bacteria, no algae)
    • Single cells, colonies, filaments, aggregates
    • Tropical oceans: Trichodesmium (Oscillatoria) – ability to fix nitrogen (N2), important for N cycle
    • Baltic Sea: also blooms of filamentous, N2-fixing cyanobacteria during summer to fall (yellow and red color)

    • Ubiquitous and important: Synechococcus spp. (coccoid, <2 mm size) and Prochlorococcus spp. (coccoid, 0.5 mm) – major part of photosynthetic picophytoplankton


      • (Epifluorescence micrograph of Synechococcus)
    • Mats of filamentous cyanobacteria can form stromatolites in the tidal zone


    I. Links to photo collections on the web: