week 3- planktonic organisms

the substrate (mud, rock, sand)

the water column (the watery bit)

Pelagic organisms that can maintain their position against water currents

Pelagic organisms that cannot maintain their position against currents

Plant-like (i.e., capable of primary production via photosynthesis)

Animal-like (i.e., derive nutrition by consuming other organisms)

Mega-plankton 20 cm + Macro-plankton 2cm – 20 cm Meso-plankton 200 µm - 2cm Micro-plankton 20-200 µm Nano-plankton 2 - 20 µm Pico-plankton 0.2 - 2 µm

Diatoms Dinoflagellates Coccolithophorids Cyanobacteria

-The cyanobacteria capable of photosynthesis and are typically <1 to ~5 µm in size - Many can use N2 gas as a source of nitrogen (i.e., they ‘fix nitrogen’) - Cyanobacteria can occur as single cells, filaments, or colonies

• The dominant primary producer in the oceans • Many are food for small zooplankton • Some are toxic, and if they bloom they can impact whole ecosystems

The coccolithophorids are single celled eukaryotes (aka protists) capable of photosynthesis - Coccolithophorids are typically small (<20 µm) and are characterised by calcium carbonate coccoliths

• Form blooms that look chalky white in open ocean • Major contribution to calcium carbonate sedimentation

The diatoms are single celled eukaryotes (aka a protist) capable of photosynthesis * Diatoms are typically 5- 200µm and fast growing (1-3 generations per day) * Characterised by producing a silica ‘box’ around the cell The silica box is composed of two halves called ‘valves’ or ’frustules’ * Diatoms can also occur as single cells or chains

• Important food source for zooplankton and larval fish • On Geological timescales sedimentation of dead diatoms leads large silica deposits (diatomaceous earth)

• Forensics (diagnose location of drowning) • Diatomaceous earth used as abrasive in toothpaste and polishes, absorbent for nitroglycerin, filtration of liquids (e.g., beer)

Also single celled eukaryotes. Typically 10- 200 µm and characterised by two whip-like flagella

Some are phytoplankton, some zooplankton, some are both (called mixotrophy) * Can eat smaller cells and are food for larger zooplankton * Can form harmful blooms Bloom forming species can cause disease in wildlife and humans, e.g., Pfiesteria hysteria causes skin lesions and mass mortality in many fish species

• Viruses &bacteria (pico-) • Ciliates, dinoflagellates and metazoan larvae (micro-) • Copepods (meso-) • Gelatinous zooplankton (macro-)

Whilst the phytoplankton are typically unicellular the zooplankton span microbes to metazoans

Viruses are the most abundant ‘life form’ in the ocean (estimated 1030 viruses) * Every second, approximately 1023 viral infections occur in the ocean * Major source of mortality and disease in organisms from phytoplankton to whales

Bacteria are important heterotrophic decomposers (although the cyanobacteria are important autotrophs) * Bacteria play a critical role in major element cycles (e.g., the carbon and nitrogen cycles)

Small metazoan and protozoa (i.e., heterotrophic unicellular eukaryotes) form a critical link in marine food webs * Consume bacteria and nano-phytoplankton * Feed mesozooplankton & larval fish

• Characterised by ‘hair-like’ cilia on the cell surface associated with movement and feeding • Important grazers in the marine plankton

• The mesozooplankton are exclusively metazoan (i.e., animals) • Most animal phyla are represented in plankton, but one dominant group • Copepods are small crustaceans and account for ~95% of the planktonic biomass