food webs, marine nutrient cycles, mangroves and seagrass Flashcards
+ Redfield ratio
1
Q
food web
A
pathway of consumption and energy flow from one trophic level to another
2
Q
food chain vs food web
A
chain:
- linear
- efficient transfer of energy
- simple
web:
- complex
- not efficient
3
Q
trophic levels
A
- 1° producer (autotroph)
- 1° consumer (heterotroph)
- 2° consumer (heterotroph)
- 3° consumer (top predator)
4
Q
explain why in marine ecosystems there are always only 4-5 levels
(6 marks)
A
- eating is inefficient
- 70-99% of energy is lost as heat (respiration)
- energy cannot be created so diminishes through each level
- 1° production in marine systems v large but doesn’t scaffold more levels
- long food chains are unstable
- predator design (morphology) is limited (apex predators can only be so effective)
- omnivory (eating both plant matter and animals) is common
5
Q
suggest why body size is a good indicator of trophic level
A
- ↑ body size = ↑ energetic demand of consumer
- marine 1° producers are v small and numerous (eg. phytoplankton)
BUT…
some apex predators begin life as eggs/larvae and ↑ in size by 5 orders of magnitude
6
Q
suggest reasons why marine systems have more complex food webs than on land
A
(low levels of specialism)
- openness of marine systems
- large size changes along a life history
- long lifespans – ontogenetic shifts
7
Q
what drives food web stability?
A
resource availability
eg. ↑ phytoplankton =
- ↑ copepods
- ↑ sandeels
- ↑ seabird breeding success
8
Q
what are bottom-up control webs driven by?
A
productivity
9
Q
what are top-down webs driven by?
A
predation / grazing
10
Q
top-down webs
A
- higher trophic level influences the community structure of a lower trophic level …
- … through predation
- important for ecosystem structure and function
11
Q
bottom-up webs
A
lower trophic level in biological network affects the community structure of higher trophic levels …
… by means of resource restriction
12
Q
what offers some stability in natural systems?
A
strength of interactions varies within food web
13
Q
evidence of top-down control
A
- overfishing led to depletion of cod stocks in N. Atlantic
- subsequent ↑ in abundance of shrimp, crabs, and lobster
- cod on benthic macro-invertebrates
14
Q
trophic cascade
A
- ecological phenomenon triggered by addition / removal of top predators …
- … and involving reciprocal changes in relative pops of predator and prey through food chain…
- … which often results in dramatic changes in ecosystem structure and nutrient cycling
- usually occurs in food webs with ~3 trophic levels
- likely to occur when linkages between species are strong
15
Q
describe the trophic cascade of sea otters
A
- sea otters hunted to brink of extinction for fur
- orca predation of otters ↑ due to over-fishing (less of orcas usual food source)
- ↑ sea urchin pop as less otters to eat them
- kelp forests were heavily depleted by grazing urchins -> ~10x less kelp
- sea otters protected by law -> leads to pop recovery
- significant ↓ in sea urchins -> leads to recovery of kelp forests
16
Q
mesopredator release
A
- when pops of medium-sized predators rapidly ↑ after the removal of predators
- changes in apex predator abundance can have disproportionate effects on mesopredator abundance
17
Q
describe what modelling by Yodzis (1998) predicted
A
- fur seal culling would cause ↓ in hake, horse mackerel and anchovy …
- … ↓ overall fishery yield
- seal removal -> ↑ predatory fish -> ↓ hake
18
Q
mangroves
A
- tropical inshore communities dominated by species of trees and shrubs that grow permanently in salty water
- mangrove species are terrestrial plants that have dominated fringes of sea
- buffer tropical shorelines from erosion and filter run off
19
Q
mangrove growth env
A
- grow in hostile soil env …
- soil is O₂ deficient and higher salinity than open ocean due to evaporation
- typical redox potential of aerated soil: 300mV and mangrove -200mV
20
Q
describe how mangrove species can survive in anoxic soil
root adaptations for anoxic soil
A
- shallow rooting system -> grow quickly and outwards -> (keeps roots close to surface for as much O₂ as possible)
- elongation in Rhizophora up to 9mm a day (super fast growth)
- aerial roots (above ground) -> only used so O₂ can penetrate them and transport it to areas of plant lacking it
21
Q
what would be an indication of anoxic soil env?
A
pungent smell of eggs -> from H₂S, NH₃, CH₄
^ these are by-products of decomposition of organic matter
22
Q
describe how mangrove species can survive in saline soils
root adaptations for saline soil
A
- causes osmotic changes that plant cells must adapt to …
- (osmotic stuff)
- to counteract salt water uptake: root systems have -ve hydrostatic Pa by transpiring salts at leaves using salt glands
-> eg. Avicennia and Acanthus have visible salt crystals on leaves
23
Q
seagrass
A
- monocotyledonous with straw like leaves
- ## can be intertidal or subtidal -> stabilise sediment of seabed (as massive root systems called rhizomes) and provide source of 1° production (really good at converting CO₂ + light->biomass) and habitat
24
Q
describe seagrass distribution
A
grows pretty much everywhere
- tropical belt has most numbers of species
- temperate northern/southern hemisphere has 1-2 dominating species -> eg. UK: zostera marina is v common
- hard to determine how much space seagrass meadows cover as its mostly underwater -> approx 160,000-500,000 km²
25
evolution of seagrass
- fully adapted to life in sea -> all are **adapted** to be fully submerged (**subtidal**) BUT species such as *Zostera* can grow intertidally
- represented by 60 species in 12 genera -> V **LOW DIVERSITY**
- evolved from single lineage of monocot flowering plant .....
- been under lots of **pressure to adapt to surroundings** -> so found in loads of places
26
seagrass growth env
- most grow in mud and sediment -> *Phyllospadix* can be found on **rocky shores**
- seagrasses make life easier for others!
-> ↓ turbidity
-> trap suspended sediment
^improves **water quality** and **clarity** => **↑ light penetration** => **↑ p/s** rate for plankton, organisms with face incisors and any plants/algae
27
describe how seagrass is useful **near coral reefs** in tropical regions
some species might spend night in seagrass to...
- be **protected from env**
- keep **predators** from **ruining** coral reefs
in day: return to coral reef to **feed**
28
seagrass p/s
| how do they generate carbon
- need **11% irradiance for p/s**
- leaves **lack stomata** and produce **thin, porous cuticle** to absorb CO₂ from water...
... but CO₂ levels are really low because of humans (despite us pumping in CO₂ from anthropogenic release)
29
how are seagrasses such effective photosynthesisers and 1° producers
- able to use **bicarbonate (HCO₃⁻)** as **CO₂ source**
- HCO₃⁻ makes up **89%** of CO₂ availability in seawater
30
redfield **departures**
- variations / **deviations** from classic Redfield ratio
- these departures can occur due to **adaptations** and **ecological factors** influencing nutrient stoichiometry of plankton
31
**adaptations of plankton** that can cause redfield departures?
- the "survivalist"
-> ↑ N:P ratio, can sustain growth when nutrients are low, contains lots of **resource-aquisition machinery**
- the "bloomer"
-> ↓ N:P ratio, adapted for exponential growth (contains lots of **growth machinery**)
- the "generalist"
-> N:P ratio near Redfield ratio, balances growth & aquisition machinery
32
seafloor carbon stocks
- **Transitional** vegetated zones
-> salt marsh, mangroves
- **Non**-vegetated sea floor
-> bare sediment, maerl beds
- **Vegetated** sea floor
-> kelp forests, seagrass beds
33
blue carbon
carbon stored in ocean sinks
34
human influence on nutrient cycles are represented by...
- ocean **acidification**
- formation of **gulf of mexico dead zones** (expanding yearly)
35
what results in dead (hypoxic) zones?
**excessive** nutrition addition
36
3 forms of dissolved inorganic carbon (DIC)
- carbonate ion **(CO₃⁻)**
- bicarbonate ion **(HCO₃⁻)**
- **CO₂[aq]** -> which inc Carbonic acid **(H₂CO₃)**
