food webs & the microbial loop

Question 1

different plankton from smallest to biggest

Answer 1

• femo
• pico
• nano
• micro
• meso
• macro
• mega

Question 2

what is the base of marine food webs

Answer 2

Phytoplankton - almost every organism in sea is dependent on its energy

Question 3

why aren’t most food webs straight forward and simple

Answer 3

things like stratification, changes in nutrient levels increase the number of niches available

Question 4

what’s bottom-up control

Answer 4

Abundance at a particular trophic level is controlled by resources (food) availability at the next lower level – what you are eating

Question 5

what’s top-down control

Answer 5

Abundance at a particular trophic level is controlled by predation from the next higher level – what is eating you

Question 6

what’s a trophic cascade

Answer 6

Top-down control of community structure by predators; conspicuous indirect effects two or more links distant from the primary one

Question 7

what’s an example of top down control leading to trophic cascade

Answer 7

• sea otter usually at the top of the food chain – they eat sea urchins - these eat kelp and other algae
• Less sea otters from capture lead to an urchin barren food web (they increase) - kelp and other algae decrease

Question 8

explain the classical food chain

Answer 8

• Single celled diatoms + dinoflagellates soak up any DIN in the water collumn
• These photosynthesise – produce baby dinoflagellates + diatoms
• Shortly afterwards copepods (zooplankton) come along to eat the phytoplankton
• Fish can then eat the zooplankton
• All of these things will eventually die – create DOM + POM
• Bacteria will feed on the organic material – convert it into inorganic material for diatoms to feed on

Question 9

what’s the problem with the classic food chain

Answer 9

• Prior to the 1980’s methods for quantifying microbial abundance, biomass and production = very poor
• At best, estimated 10% of actual bacterial numbers

Question 10

what’s The microbial loop

Answer 10

Channelling of energy through microbes - additional loop to what we have in classical food web

Question 11

how were we able to confirm the microbial loop

Answer 11

• Since early 80’s view of food chains altered dramatically - Improved techniques: Bacteria

Question 12

how were techniques post 80’s used to calculate abundance and production of bacteria

Answer 12

• Abundance -> acridine orange, DAPI (stains)
• Production (how quick they grow) -> thymidine incorporation

Question 13

explain the additional loop to what we see in classical food web

Answer 13

• hetero flagellates feed on bacteria
• Cilliates eat hetero flagellates + autotroph flagellates
• Copepods eat Cilliates
  **Energy gets chanelled into higher parts of planktonic food web

Question 14

why are bacteria beneficial in the microbial loop

Answer 14

• phytoplankton exude up to 60% of PP as DOM
• Bacteria = good scavengers of DOM at low conc - Large SA/volume ratio

Question 15

except for phytoplankton what’s the majority of PP

Answer 15

blooms of dinos & diatoms

Question 16

why are the majority of dinoflagellate species

Answer 16

heterotrophic

Question 17

3 mechanisms of heterotrophic dino feeding

Answer 17

1) Ingestion of whole cells
2) Use of a feeding tube: peduncle (to eat the inside directly OR use as anchor to be able to feed on it)
3) Use of a cytoplasmic veil: pallium (external stomach that wraps around diatom – digestion over time)

Question 18

heterotrophic dino feeding characteristics

Answer 18

• Many feed optimally on large prey (1:1)
• Compete with copepods
• Growth rates: dinos > metazoans
• Respond more quickly to phyto bloom

Question 19

mixotrophic meaning

Answer 19

Both photosynthesise & feed

Question 20

how do Mixotrophic Ciliates photosynthesise

Answer 20

by hijacking chloroplasts of consumed phytoplankton

Question 21

Mixotrophic Ciliates nutrient cycling

Answer 21

1) Regenerate nutrients: heterotrophic
2) Require DIN: endosymbionts

Question 22

2 things Mixotrophic Flagellates get from feeding on bacteria

Answer 22

1) Aquire essential nutrients
2) Eat their competitor

Question 23

what is marine snow

Answer 23

• aggregates: Chunks of organic material that eventually end up sinking to sea bed
• Contain both planktonic & benthic species – act as a floating sea bed
• Sites of enhanced microbial activity: bacteria, cyanobacteria, phytoplankton, HNAN, ciliates

Question 24

importance of marine snow

Answer 24

• Responsible for most of the particulate flux in the oceans
  1) Supply DIN & DOM to pelagic microbes
  2) Support sp of bacterivorous protozoa that are unable to survive in water column
  3) Provide food source to larger zoo: dinos, copepods, ostracods, invert larvae

Question 25

what’s the Ultimate source of DOM

Answer 25

phytoplankton
- Directly: lysis, leaking (25%)
- Protozoa: egest phyto dissolved products (53%)
- Mesozoo: Sloppy feeding (12%)
- Viral infection (10%)

Question 26

4 things DOM composes of

Answer 26

• Carbohydrates: Mono-, oligo- & polysaccharides
• Nitrogenous compounds (aa, peptides, proteins)
• Organic acids (glycollate)
• Lipids

Question 27

what happens to >90% DOM released

Answer 27

consumed & respired
- but some DOM resists microbial degradation & accumulates to form a large, unused pool of organic carbon

Question 28

what organisms are involved in the complex microbial food web

Answer 28

• Picoeukaryotes
• Heterotrophic Dinoflagellates
• Mixotrophic Ciliates
• Mixotrophic Flagellates
• Viruses

Question 29

what makes a Microbial food web a WEB

Answer 29

• Much more complex than simple ‘add on chain’
• Some organisms function more than 1 trophic level
• Models: Quantitatively assess importance of interactions