Life in the Pelagic: An introduction to the Plankton

Size classifications and terminology

• Classification of planktonic organisms is generally based upon size – rather than function (most methods involve filtration which distinguishes organisms based upon size rather than species).

• This can be problematic because in the plankton, trophic position is not always determined by size (size ratios between predator and prey are not constant).

Abundance of living organisms

6x106 in Washington StateHumans (2m)

Typical abundanceOrganism and size

10 to 104 per mlPhytoplankton (20-200um)

10 to 102 per mlProtizoan plankton (20-50um)

102 to 104 per mlNanoflagellates (1-10um)

105 to 107 per mlBacterioplankton (~1um)

Bacterioplankton in Aquatic Systems

• Found in all natural waters

• Non-pathogenic!

• Small (≤1µm) yet abundant (>106 cells ml-1)

• Comparable in biomass to phytoplankton

• Fundamental in nutrient & carbon cycling

• Drive water quality parameters (i.e. anoxia, nutrient

availability)

• Extremely diverse

(DAPI stained slide of bacterioplankton from Chesapeake Bay)10 µm

•Diverse and ubiquitous viral community in the marine environment

•Significant role suspected (certainly impact bacteria and may also impact primary production and higher trophic levels, viruses suspected in some marine mammal beachings).

•Viruses may be important agents in demise of some phytoplankton blooms (e.g., Trichodesmium)

•Viruses are important agents for DOM release and nutrient cycling

0.1um

Bacteriophage

Femtoplankton (0.02 – 0.2 µm)

Bacteria•Very important role in marine food webs, especially degradation and recycling

•Ubiquitous in ocean (~106 / ml)•Various forms (motile, rods, spiral, coccoid)

Archaea•Distinct RNA•Early evolutionary separation•Favoring extreme environments•Recently discovered in ocean

Picoplankton (0.2 – 2 µm)

Vertical distribution of Bacteria and Archaea cell abundance at HOTS (Karner et al 2001).• Opposite patterns of distribution• Archaea are ubiquitous, but biogeochemical significance is poorly understood

Picoplankton (0.2 – 2 µm)

Cyanobacteria – “blue-green algae”

Photosynthetic bacteriae.g. Synechococcus spp. • Up to 106/ml in euphotic zone• In both coastal and oceanic waters• In temperate and tropical oceans• Can play major role in primary production, especially open ocean

Prochlorophytes

•Prochlorococcus marinus•Abundant at base of the euphotic zone in open ocean (106 / ml)•Ubiquitous distribution•Can play a major role in primary production, especially in the open ocean•Different strains have been identified that live in different depths in the water column and have different metabolic capabilities particularly with respect to what forms of nutrients they can use, i.e., NH4 vs. NO3.

Note: Prochlorococcus is currently believed to be the most abundant form of plant life on earth.

2µm

More on Picoplankton (0.2 – 2 µm)

Mostly small eukaryotic phytoplankton

Dominate more oligotrophic open ocean environments

small pennate diatom

small centric diatomdinoflagellates

coccolithophorid

Nanoplankton (2 – 20 µm)

Large eukaryotic phytoplankton

Prominent in productive coastal / upwelling zones

centric diatom

chain-forming diatoms

large dinoflagellates

Microphytoplankton (20 – 200 µm)

Heterosigma

These are heterotrophic and mixotrophic protozoans

•Large group and taxonomically diverse• ciliates• dinoflagellates• heterotrophic nanoflagellates (HNFs)• radiolarians (silica) and foraminifera (calcite)

•Same size as the microphytoplankton (2 – 200 µm)

•Heterotrophic and mixotrophic forms

•Very important consumers in marine environments!!!

Microzooplankton (2 – 200 µm)

Tintinnid ciliate

Oxyrrhis marina

bodonidschoanoflagellates

Heterotrophic nanoflagellates

Protoperidinium Gyrodinium spiraleNoctiluca scintillans

Dinoflagellates

Leegaardiella sp.

Laboea strobila

http://www.aslo.org/photopost

Ciliates

Favella-like tintinnid

Favella-like tintinnid

Eutintinnis

Let’s talk about grazing…

Sarcodines: foraminifera

Sarcodines

heliozoa

radiolaria

amoebae

Mesozooplankton (200 um – 2 mm)

• Relatively large, planktonic heterotrophs (200 µm – 2 mm)• Huge, diverse group…

• Larger protozoans• Coelenterates• Cheatognaths• Annelids• Molluscs• Arthropods• Copepods• Amphipods• Euphausiids• Small larvaceans and salps• Pteropods and heteropods

Meroplankton•As opposed to holoplankton or true plankton•Eggs, larvae and juvenile stages of benthic invertebrates and fish•Time spent in the plankton may be minutes to months•Especially important in coastal and estuarine waters as you will see on the zooplankton lab

Barnacle nauplius

Polycheate larvae

Crab zoea

Crab megalopaBarnacle cypris

Sea urchinlarvae

Snail veliger

Starfish larvae

Macroplankton (2-20 cm) and Megaplankton (20-200 cm)

• “Jellyfish” are prominent examples• Most are classified as plankton• Hydrozoan, Scyphozoan and Cubozoan medusae• Ctenophores• Salps• Larvaceans• Pteropods and Heteropods

Scyphozoan medusa (Chrysaora)(megaplankton)

Ctenophores like Mnemiopsis and Beroe(macroplankton)

Major Phytoplankton Groups

Major Phytoplankton Groups

1) Diatoms (20um to 2mm)• Most abundant, rapidly dividing organisms, bloomers• Silicate frustrule (shell) – pennates (motile) and centrics• Solitary and chain forming

2) Dinoflagellates (20 – 40um)• Motile with flagella• Auto, mixo, hetero-trophic• HABs (paralytic shellfish poisoning, Gymnodinium, red tides

(Prorocentrum), Pfiesteria piscicida, zooxanthellae• Noctiluca sp. (bioluminescence)

3) Microflagellates (2-30um) • Coccolithophores, primnesiophytes, cryptophytes

4) Picophytoplankton (<2um)• Prochlorococcus and Synechococcus

Diatoms

Thalassiosira anguste Chaetoceros convolutus

Pseudo-nitszchiamultiseries Chaetoceros debilis

Cylindrotheca sp.

Dinoflagellates

Ceratium tripos

Dinophysis

Gymnodinium spp.

Protoperidinium

Other phytoflagellates

cryptomonadsChrysochromulina

bergeriEmiliania huxleyi

Pyramimonas

Phaeocystisglobosa

Heterosigma akashiwo

ChlorellaDunaliella

Euglena

Chlorophytesand other coastal

taxa

Picophytoplankton

Synechococcus

Prochlorococcus

Mixed assemblage under epifluorescence

N2-fixing cyanobacteria

Trichodesmium spp.

as endosymbionts in the diatom Rhizosolenia