L4 - River Macroinvertebrates

Question 1

What are the defining features of lotic bodies?

Answer 1

Flow and turbulence

Question 2

What is flow measured as?

Answer 2

Velocity in meters per second
Discharge in cubic meters per second

Question 3

What is turbulence?

Answer 3

when water flows in irregular paths
* this happens more in lotic systems than lentic systems

Question 4

Why do most streams and rivers have few planktonic organisms? And what is the exception to this?

Answer 4

Planktonic organisms get flushed away in lotic bodies.
Exception: very big, slow river have a few

Question 5

What is the pelagic zone ‘limited’ to?

Answer 5

Strong swimmers - mainly vertebrates such as fish because anything else gets washed away.

Question 6

‘Most stream organisms are attached or benthic’ - what does attached and benthic mean?

Answer 6

Attached = cling to hard surfaces or plants
Benthic = buried in soft sediments

Question 7

Where do boundary layers form?

Answer 7

In flowing water
- Boundary layers also form when water flows across a fixed surface
→ Water flows more slowly close the surfaces of a stream bed

Question 8

What creates a boundary layer around small organisms?

Answer 8

Viscosity of water

Question 9

Explain how attached organisms take advantage of boundary layers

Answer 9

It’s easier to stop getting washing downstream if:
- you’re very flat
- you stay pressed against the stream bed surfaces

Question 10

What is periphyton? (base of benthic/attached food web)

Answer 10

A complex mixture of algae, microbes, and detritus that grows on aquatic surfaces and sediments
*attached microbial communities

Question 11

What are macrophytes? (base of benthic/attached food web)

Answer 11

aquatic plants + macroalgae

Question 12

Explain the role of macroinvertebrates (second layer in a benthic/attached food web)

Answer 12

• grazers (the same role as zooplankton in pelagic food webs)
  *but lots of intraguild predation ( also eat each other)

Question 13

Which layer of the benthic/attached food web are vertebrate predators found?

Answer 13

Third layer e.g. fish

Question 14

Where is the attached/benthic food web found in comparison to the pelagic food web?

Answer 14

attached/benthic food web - streams and rivers
pelagic food web - lakes and oceans

Question 15

What are 2 adaptions of periphyton?

Answer 15

1. a jelly-like matrix prevents dehydration and stores nutrients
2. the community can function in and out of water - this is important for changing water levels

Question 16

State the 4 functional groups of macroinvertebrates

Answer 16

Shredders
Collectors (filter-feeding & gatherers)
Grazers/scrapers
Predators

Question 17

What are the 2 groups of collectors within lotic food webs?

Answer 17

Gathering/Gatherers
Filtering/Filterers

Question 18

What are the characteristics of filtering collectors within lotic food webs?

Answer 18

• Capture and eat FPOM (Fine Particulate Organic Matter) from suspension
• Sloughed periphyton, faeces
• Diverse mechanisms for feeding
  → Black fly larvae sticky fans

Question 19

What are the characteristics of gathering collectors within lotic food webs?

Answer 19

• Capture and eat FPOM (Fine Particulate Organic Matter) from substratum
• Sometimes called deposit feeders
• Sloughed periphyton, faeces
• Often in association with shredders (commensalism)

Question 20

What are the characteristics of grazers/scrapers in the lotic food web?

Answer 20

• Graze on, and eat periphyton
• Scrape the surface with mouthparts
  → Snails: rasping radula
  → Insects: mandibles

Question 21

What are the characteristics of Shedders in the lotic food web?

Answer 21

• Eat CPOM (coarse particulate organic matter) made of decaying leaves and macrophytes
• Many groups of insect larvae
• Conditioning increases palatability
• Microbes on the surface (periphyton)
  → help with decomposition
  → are like ”peanut butter on a cracker”

Question 22

Where does CPOM (coarse particulate organic matter) come from?

Answer 22

CPOM is detritus that comes from terrestrial plants surrounding the stream. It is also covered in periphyton, which provides important additional nutrition to shedders

Question 23

What are the characteristics of (macroinvertebrate) predators within the lotic food web?

Answer 23

• eat other macroinvertebrates
• Ambush versus hunting
  → Suspended prey
  → Damselfly larvae = ambush predators

Question 24

What are the characteristics of vertebrate predators in lotic food webs?

Answer 24

• eat macroinvertebrates

Question 25

How are streams classified?

Answer 25

Streams are classified by their order or Strahler number (bigger = bigger)
→ The Amazon is 12th order
→ 80% of streams and rivers are 1st or 2nd order

Question 26

What is the river continuum concept (RCC)?

Answer 26

Describes the way the community composition and ecological function change along the length of a river as it increases in size/order