BIOL2204 Marine Biology - Week 8

Plankton define?

Free-floating organisms that cannot swim strongly enough to overcome ocean currents drift with the water. I.e a way of life - not a taxonomic classification

What are phytoplankton?

• Microscopic, photosynthetic organisms

• Primary energy production is autotrophic (primary producers), with chloroplasts/pigments.

• They exist as single cells or in chains.

What are zooplankton?

• Drifting animals (or animal-like protists) that eat other plankton.

• Primary feeding strategy is heterotrophic: they are grazers, predators, or detritivores.

• Visible gut/ingested food.

• They frequently have cilia or appendices that enable directed swims/jumps

What are mixoplankton?

Contain both chloroplasts and vacuoles; may produce energy in an autotrophic or heterotrophic way

What are holoplankton?

• Organisms that spend their whole life as plankton.

• Drive primary productivity and grazing.

• E.g diatoms, dinoflagellates, copepods, chaetognaths, krill, jellyfish

What are meroplankton?

• Organisms that have a planktonic or larvae phase only as part of their life.

• E.g veliger (molluscs), trochophore (annelids), and naupilii/zoea (crustaceans) larvae.

What are lecithotrophic larvae?

• A type of meroplankton that only spends hours to days in the planktonic stage.

• Form larger, yolky eggs (requiring more parental investment); fed by the yolk.

• Shorter planktonic period and higher survival per larva, but shorter dispersal and lower fecundity.

Trade-off: higher investment > lower output > higher survival

What are planktotrophic larvae?

• A type of meroplankton that spends weeks to months in the planktonic stage.

• Require lower parental investment; larvae must feed in the plankton and develop rapidly.

• High mortality (predation, sensitivity to food supply)

Trade-off: low Investment → high output → low survival

Orders of magnitude of plankton?

Span 7x orders of magnitude (microscopic to jellyfish). Pico → Nano → Micro → Meso → Macro → Mega

Why does size matter for plankton?

3x main reasons:

- Nutrient uptake → A decrease in size = an increase in SA:V ratio. Results in highly efficient nutrient uptake

- Sinking rate → An increased size = increased sinking potential. Larger plankton therefore usually equipped with structures that allow floating or motion

- Predator/prey match → gear vs. gape

Different roles of plankton?

- Primary production and oxygen production

- Forming the base of marine food webs (energy flow)

- Climate and biogeochemistry → Carbon storage and nutrient cycling

- Biodiversity and connectivity

- Water quality

- Environmental monitoring → can be early indicators of climate change; sensitive to changes

What are the key adaptations required for planktonic life?

Staying afloat, feeding, avoid predators (defence), and persist (reproduce)

Staying afloat adaptations in Plankton

- Storage of low density fluids (e.g., lipids)

- Flattened and elongated shapes such as spines and chains

- Structures for motility including flagella or ciliary bands

Feeding adaptations in plankton

- Capture gear, e.g filters and nets. Includes mucus nets and oral cilia

- Raptorial/grasping tools (common in predators). Includes grasping spines, tentacles, spiny mouth parts

Defence adaptations in plankton

- Armour and shape making the organism harder to bite or have more drag (thecal plates, horns and spines, chains, colonies)

- Camouflage and optics, typically transparency or bioluminescence

- Chemical defence including toxins or noxious metabolites

- Behavioural adaptations → diel vertical migration (up at night, down by day)

Persistence adaptations in plankton

- Phytoplankton → resting stages as spores or cysts

- Zooplankton → resting eggs produced in harsh conditions; slowing metabolism

- Protected development and provisioning; embryo development in capsules or chambers or protected by a yolk rich sac.

Cyanobacteria plankton type?

Phytoplankton - photosynthetic bacteria (NOT algae/plants. No membrane bound organelles. Can cause hypoxia)

Can also convert Nitrogen to Ammonia

Cyanobacteria pigments

Chlorphyll-a + phycobiliproteins (give it an orange-red/teal colour)

Diatom plankton type?

Phytoplankton

Diatom covering?

Glassy, porous, with two box-like valves. Fine striae and no flagellar grooves. Have a silica shell (frustule: epitheca + hypotheca) covered in pores/striae

Diatom symmetry?

Radial or bilateral

Diatom motility?

Glide slowly rather than swim. Single cells may form chains.

Diatom pigments?

Chlorophyll a + c and fucoxanthin (give it a golden brown colour)

Diatom resting stage?

Resting spore. Made of silica; heavy, look glassy/refractive

Diatom shapes?

Centric - radial symmetry; drift

Pennate - bilateral symmetry, many have a raphe slit and glide along a surface via the raphe

Dinoflagellate plankton type?

Mixoplankton

Dinoflagellate covering?

Cellulose thecal plates with two flagellar grooves. Grooves are cingulum (belt) + sulcus (vertical). Transverse flagellum in the cingulum = spin motion. Longitudinal flagellum in the sulcus = forward steer motion

Dinoflagellate symmetry/shape?

Asymmetrical, often due to their unequal flagella

Dinoflagellate motility?

Swim with flagella, spin + drift motion

Dinoflagellate pigments?

Generally have chlorophyll

Dinoflagellate resting stage?

Resting cyst. Spiny, not glassy, with organic walls

Dinoflagellate shapes?

Thecate (armoured) - have cellulose plates and visible sutures. Often with horns/spines

Athecate (unarmoured/naked) - smooth

Ciliate plankton type?

Zooplankton (some are mixoplankton)

Key features of ciliates?

Single-celled eukaryotes with hair-like cilia (movement and feeding)

Feeding gear: Adoral zone of membranelles = a collar/arc of fused cilia that creates feeding currents

Rapid life cycles - ability to respond quickly to changes - rapid growth at warm temps

Reproduction: Mostly binary fission; conjugation for gene exchange

Generally exhibit directional, fast swimming

Ciliate shapes?

Oligotrich/Choreotrich (naked) = Soft, naked cell. Free-swimming, agile; rotate & dart

Tintinnids (loricate) = sit in a lorica "vase". Pulse water with cilia; can exit/re-enter, slow swimmers

Foraminifera plankton type?

Zooplankton

Foraminifera key characteristics?

Single-celled organisms

Build complex shells around themselves from minerals in the seawater - adding chambers as they grow

Feed using their reticulopodia nets to trap small plankton

Some host algal symbionts, which can give a faint golden hue and provide extra energy

Radiozoa plankton type?

Zooplankton

Radiozoa key characteristics?

Single-celled predators that build ornate mineral skeletons

Spherical, amebae-like body with a spiny skeleton of silica

Feed using axopodia—stiff, microtubule-supported threads

Delicate 3D lattices with radial spines; no chambers (≠ forams); no glassy valves/striae (≠ diatoms).

Copepod plankton type?

Zooplankton (they are small crustaceans and the dominant holoplankton)

Copepod life stages?

Nauplius → copepodite → adult

Copepod body plan?

Teardrop body (prosoma + urosome), large antennules, 5 pairs of swimming legs; escape jumps

Copepod reproductive structures?

Strong sexual dimorphism (males with geniculate antennules). Females carry egg sacs or broadcast eggs.

Copepod feeding strategies?

Calanoids = filter grazers/omnivores (feathery setal basket, create feeding currents)

Cyclopoids = raptorial/ambush (fewer, stouter spines)

Harpacticoids = mostly benthic scrapers (occasionally planktonic)

Amphiblastula larvae

The larvae stage of Porifera. Sexually produced.

Planula larvae

The larvae stage of Cnidarians

Cydippid larvae

The larvae stage of Ctenophores

Pilidium larvae

The larvae stage of Nemerteans

Trochophore larvae

The first larvae stage of Annelids and Molluscs

Polytroch larvae

The second larvae stage of Annelid worms (specifically Polychaeta)

Veliger larvae

The second larvae stage of Molluscs

Cyphonautes larvae

The larvae stage of Bryozoa

Lobate larvae

The larvae stage of Brachiopods

Actinotroph larvae

The larvae stage of Phoronids

Cuticular loricate larvae

The larvae stage of Priapulida

Naupilus/Zoea larvae

The larvae stage of Arthropods (Crustacea)

Tadpole larvae

The larvae stage of Chordates

Tornaria larvae

The larvae stage of Hemichordata

Doliolaria larvae

The larvae stage of Crinoidea

Bipinnaria larvae

The larvae stage of Asteroidea

Ophiopluteus larvae

The larvae stage of Ophiuroidea

Echinopluteus larvae

The larvae stage of Echinoidea

Auricularia larvae

The larvae stage of Holothuroidea