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marine bio > food webs, marine nutrient cycles, mangroves and seagrass > Flashcards

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

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2
Q

food chain vs food web

A

chain:

  • linear
  • efficient transfer of energy
  • simple

web:

  • complex
  • not efficient
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3
Q

trophic levels

A
  1. 1° producer (autotroph)
  2. 1° consumer (heterotroph)
  3. 2° consumer (heterotroph)
  4. 3° consumer (top predator)
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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
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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

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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
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7
Q

what drives food web stability?

A

resource availability

eg. ↑ phytoplankton =

  • ↑ copepods
  • ↑ sandeels
  • ↑ seabird breeding success
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8
Q

what are bottom-up control webs driven by?

A

productivity

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9
Q

what are top-down webs driven by?

A

predation / grazing

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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
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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

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12
Q

what offers some stability in natural systems?

A

strength of interactions varies within food web

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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
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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
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15
Q

describe the trophic cascade of sea otters

A
  1. sea otters hunted to brink of extinction for fur
  2. orca predation of otters ↑ due to over-fishing (less of orcas usual food source)
  3. ↑ sea urchin pop as less otters to eat them
  4. kelp forests were heavily depleted by grazing urchins -> ~10x less kelp
  5. sea otters protected by law -> leads to pop recovery
  6. significant ↓ in sea urchins -> leads to recovery of kelp forests
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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
Q

evolution of seagrass

A
  • 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
Q

seagrass growth env

A
  • 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
Q

describe how seagrass is useful near coral reefs in tropical regions

A

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
Q

seagrass p/s

how do they generate carbon

A
  • 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
Q

how are seagrasses such effective photosynthesisers and 1° producers

A
  • able to use bicarbonate (HCO₃⁻) as CO₂ source
  • HCO₃⁻ makes up 89% of CO₂ availability in seawater
30
Q

redfield departures

A
  • variations / deviations from classic Redfield ratio
  • these departures can occur due to adaptations and ecological factors influencing nutrient stoichiometry of plankton
31
Q

adaptations of plankton that can cause redfield departures?

A
  • 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
Q

seafloor carbon stocks

A
  • Transitional vegetated zones
    -> salt marsh, mangroves
  • Non-vegetated sea floor
    -> bare sediment, maerl beds
  • Vegetated sea floor
    -> kelp forests, seagrass beds
33
Q

blue carbon

A

carbon stored in ocean sinks

34
Q

human influence on nutrient cycles are represented by…

A
  • ocean acidification
  • formation of gulf of mexico dead zones (expanding yearly)
35
Q

what results in dead (hypoxic) zones?

A

excessive nutrition addition

36
Q

3 forms of dissolved inorganic carbon (DIC)

A
  • carbonate ion (CO₃⁻)
  • bicarbonate ion (HCO₃⁻)
  • CO₂[aq] -> which inc Carbonic acid (H₂CO₃)

marine bio (11 decks)

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