L9 - Fish and aquatic ecosystem linkages

Question 1

Are fish a taxon or a functional guild?

Answer 1

Fish are a functional guild

Question 2

What is a gill?

Answer 2

• A respiratory organ used by an aquatic organism to exchange dissolved oxygen for carbon dioxide and other waste products
• Gills can be made of different tissues and function very differently (e.g. in fish versus insects)
• All gills have a large surface area for gas exchange

Question 2

What are the 4 basic requirments of fish?

Answer 2

1. Vertebrate
2. Aquatic
3. Have internal gills for aquatic gas exchange (some also use air)
4. Fin rays made of dermal bone (instead of digits made of endochondral bone) at the terminal ends of paired appendages

Question 3

What is the total percent of fish which are classed as teleosts species?

Answer 3

96%

Question 4

How are fish grouped ecologically by their diet and habitat?

Answer 4

• Planktivores versus piscivores
• Benthic, pelagic and littoral species
• Both of these attributes can change, over a species’ lifespan or seasonally!
• Individual fish are mobile and can move around looking for food.

Question 5

Explain the age-related shifts in diet and habitat

Answer 5

• Ontogenetic (has to do with their development) diet shifts from planktivory to piscivory are common due to gape limitation
• Shifts from littoral (safer) to pelagic (more dangerous) habitat use are common due to less need for predator avoidance
• This is because the bigger you are the less need to hide from predators

Question 6

Give and explain an example of age-related shifts among fish

Answer 6

• Smaller perch mostly eat zooplankton, larger perch mostly eat fish
• Small perch eat around 80% zooplankton, but as they search for macroinvertebrates, and when in large size class, the diet contains smaller fish > cannibalism is also common among piscivores. (diet changes with age, and size)

Question 7

Why are lotic fish grouped by temperature?

Answer 7

• Water temperature increases with stream order (RCC)
• Freshwater lotic fish are adapted to specific water temperatures and oxygen conditions

Question 8

Give an example of 2 European species which are grouped by temperature

Answer 8

• Trout are cold water specialists
• Bream thrive in warm water and can tolerate low oxygen

Question 9

Explain how fish evolve rapidly to fill ecological niches

Answer 9

• Cichlids are the most species-rich family of vertebrates (> 1600 species)
• Recent rapid radiation in the African great lakes
• Represent every type of habitat use (littoral, pelagic, benthic), diet source (piscivore, planktivore, herbivore), and foraging strategy (digging in sand, scraping periphyton, etc.)
• Huge variety of morphology in body, jaws, and teeth
• Other examples of fish radiations: stickleback, arctic charr

Question 10

Give 4 examples of freshwater fish in Lake Windermere

Answer 10

Perch: small, littoral and pelagic; mostly plankton then mostly fish

Roach: small, mostly littoral; mix of plankton, detritus and macrophytes; invasive (having a potential negative impact on arctic charr)

Pike: large, mostly pelagic; ambush predators; major sporting fish

Arctic charr: medium, mostly pelagic; mix of plankton, insects, and fish; one of UK’s most rare/threatened fish

Question 11

How are arctic charr in windermere seen as glacial remnant?

Answer 11

• Arctic charr are cold-water specialist salmonids that live in or near the arctic
• Some populations are anadromous, migrating from marine to freshwater habitats to spawn
• In the UK (the southernmost part of their range), they only live in deep, cold lakes – “glacial refuges” – where they have been trapped since the last ice age (and do not migrate to the sea)

Question 12

Why are arctic charr populations decreasing in windermere?

Answer 12

• Increasing water temperatures
• Eutrophication and low oxygen in the hypolimnion
• Invasive roach (compete for zooplankton food resources)
• Overfishing (now limits on minimum size)

Question 13

What does CPUE stand for?

Answer 13

catch per unit effort

Question 14

Explain how marine, freshwater, and terrestrial ecosystems are linked

Answer 14

• Nutrients from catchment run-off into freshwater habitats, and are carried to the ocean
• Mobile organisms can carry nutrients and energy across habitat boundaries
• These fluxes can have important impacts of ecosystem function

Question 15

What does riparian mean?

Answer 15

terrestrial area which is adjacent to a stream or river

Question 16

What are anadromous fish?

Answer 16

Fish which migrate from freshwater rivers to the ocean, but then return to spawn (freshwater) e.g. salmon
* - 95% of their body mass is marine derived
- All Pacific salmon die after spawning, while ~25% of Atlantic salmon return to the sea
- Salmon carcasses are consumed by inland organisms, transporting large amounts of marine nutrients and energy to riparian habitats

Question 17

What is the role of anadromous fish in the nutrient cycle in marine systems?

Answer 17

They carry marine nutrients and biomass inland

Question 18

What are the impact of nutrients and energy transported by pacific salmon?

Answer 18

Studies comparing areas with and without salmon found:
Increased invertebrate biomass
Faster growth of trees
80% higher brown bear populations

Question 19

What do studies estimate about the % of marine-derived N in biomass (via nitrogen isotopes), before and after spawning?

Answer 19

Before spawning: 75% in trout, 30% in periphyton and caddisflies
After spawning: >90% in all organisms

Question 20

Explain the importance of aquatic insects

Answer 20

Aquatic insects are juveniles that emerge as adults
- These adult insects provide an important food source, particularly for birds (which has an aquatic origin)
- Highly Unsaturated Fatty Acids (HUFAs) are an important nutritional resource that is more abundance in aquatic organisms

Question 21

For birds, is it better for nets to be closer, or further from rivers?

Answer 21

Closer to rivers because, nests closer to rivers have more hufa in diet (EPA%) which leads to better body condition in chicks