food webs & the microbial loop Flashcards
different plankton from smallest to biggest
- femo
- pico
- nano
- micro
- meso
- macro
- mega
what is the base of marine food webs
Phytoplankton - almost every organism in sea is dependent on its energy
why aren’t most food webs straight forward and simple
things like stratification, changes in nutrient levels increase the number of niches available
what’s bottom-up control
Abundance at a particular trophic level is controlled by resources (food) availability at the next lower level – what you are eating
what’s top-down control
Abundance at a particular trophic level is controlled by predation from the next higher level – what is eating you
what’s a trophic cascade
Top-down control of community structure by predators; conspicuous indirect effects two or more links distant from the primary one
what’s an example of top down control leading to trophic cascade
- 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
explain the classical food chain
- 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
what’s the problem with the classic food chain
- Prior to the 1980’s methods for quantifying microbial abundance, biomass and production = very poor
- At best, estimated 10% of actual bacterial numbers
what’s The microbial loop
Channelling of energy through microbes - additional loop to what we have in classical food web
how were we able to confirm the microbial loop
- Since early 80’s view of food chains altered dramatically - Improved techniques: Bacteria
how were techniques post 80’s used to calculate abundance and production of bacteria
- Abundance -> acridine orange, DAPI (stains)
- Production (how quick they grow) -> thymidine incorporation
explain the additional loop to what we see in classical food web
- hetero flagellates feed on bacteria
- Cilliates eat hetero flagellates + autotroph flagellates
- Copepods eat Cilliates
**Energy gets chanelled into higher parts of planktonic food web
why are bacteria beneficial in the microbial loop
- phytoplankton exude up to 60% of PP as DOM
- Bacteria = good scavengers of DOM at low conc - Large SA/volume ratio
except for phytoplankton what’s the majority of PP
blooms of dinos & diatoms
why are the majority of dinoflagellate species
heterotrophic
3 mechanisms of heterotrophic dino feeding
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)
heterotrophic dino feeding characteristics
- Many feed optimally on large prey (1:1)
- Compete with copepods
- Growth rates: dinos > metazoans
- Respond more quickly to phyto bloom
mixotrophic meaning
Both photosynthesise & feed
how do Mixotrophic Ciliates photosynthesise
by hijacking chloroplasts of consumed phytoplankton
Mixotrophic Ciliates nutrient cycling
1) Regenerate nutrients: heterotrophic
2) Require DIN: endosymbionts
2 things Mixotrophic Flagellates get from feeding on bacteria
1) Aquire essential nutrients
2) Eat their competitor
what is marine snow
- 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
importance of marine snow
- 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
what’s the Ultimate source of DOM
phytoplankton
- Directly: lysis, leaking (25%)
- Protozoa: egest phyto dissolved products (53%)
- Mesozoo: Sloppy feeding (12%)
- Viral infection (10%)
4 things DOM composes of
- Carbohydrates: Mono-, oligo- & polysaccharides
- Nitrogenous compounds (aa, peptides, proteins)
- Organic acids (glycollate)
- Lipids
what happens to >90% DOM released
consumed & respired
- but some DOM resists microbial degradation & accumulates to form a large, unused pool of organic carbon
what organisms are involved in the complex microbial food web
- Picoeukaryotes
- Heterotrophic Dinoflagellates
- Mixotrophic Ciliates
- Mixotrophic Flagellates
- Viruses
what makes a Microbial food web a WEB
- Much more complex than simple ‘add on chain’
- Some organisms function more than 1 trophic level
- Models: Quantitatively assess importance of interactions
