L9 - Fish and aquatic ecosystem linkages Flashcards
Are fish a taxon or a functional guild?
Fish are a functional guild
What is a gill?
- 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
What are the 4 basic requirments of fish?
- Vertebrate
- Aquatic
- Have internal gills for aquatic gas exchange (some also use air)
- Fin rays made of dermal bone (instead of digits made of endochondral bone) at the terminal ends of paired appendages
What is the total percent of fish which are classed as teleosts species?
96%
How are fish grouped ecologically by their diet and habitat?
- 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.
Explain the age-related shifts in diet and habitat
- 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
Give and explain an example of age-related shifts among fish
- 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)
Why are lotic fish grouped by temperature?
- Water temperature increases with stream order (RCC)
- Freshwater lotic fish are adapted to specific water temperatures and oxygen conditions
Give an example of 2 European species which are grouped by temperature
- Trout are cold water specialists
- Bream thrive in warm water and can tolerate low oxygen
Explain how fish evolve rapidly to fill ecological niches
- 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
Give 4 examples of freshwater fish in Lake Windermere
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
How are arctic charr in windermere seen as glacial remnant?
- 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)
Why are arctic charr populations decreasing in windermere?
- Increasing water temperatures
- Eutrophication and low oxygen in the hypolimnion
- Invasive roach (compete for zooplankton food resources)
- Overfishing (now limits on minimum size)
What does CPUE stand for?
catch per unit effort
Explain how marine, freshwater, and terrestrial ecosystems are linked
- 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
What does riparian mean?
terrestrial area which is adjacent to a stream or river
What are anadromous fish?
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
What is the role of anadromous fish in the nutrient cycle in marine systems?
They carry marine nutrients and biomass inland
What are the impact of nutrients and energy transported by pacific salmon?
Studies comparing areas with and without salmon found:
Increased invertebrate biomass
Faster growth of trees
80% higher brown bear populations
What do studies estimate about the % of marine-derived N in biomass (via nitrogen isotopes), before and after spawning?
Before spawning: 75% in trout, 30% in periphyton and caddisflies
After spawning: >90% in all organisms
Explain the importance of aquatic insects
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
For birds, is it better for nets to be closer, or further from rivers?
Closer to rivers because, nests closer to rivers have more hufa in diet (EPA%) which leads to better body condition in chicks
True or false: Density of rivers increases bird colonisation and decreases bird loss
True
Why do terrestrial and aquatic prey peak at different times of the year?
Birds actively forage for aquatic macroinvertebrates
Terrestrial insects fall into streams or are predated from surface by fish
What does allochthonous mean?
from an outside source
Explain allochthonous prey consumption
Birds eat aquatic insects in autumn-winter-spring, when terrestrial insects are much less abundant
Fish eat terrestrial insects in summer, during terrestrial peak
What is the role of seabirds for aquatic ecosystems?
vectors of energy and nutrients
~ travel on average 30-500 km at sea to feed on small pelagic fishes
Some may travel up to 3,000 km
How do seabird derived nutrients boost terrestrial ecosystems?
Productivity
- Enhances soil fertility + plant growth + biodiversity
- Vegetation biomass can be 2–5 times greater with seabirds
Carbon cycle
- Guano supports dense vegetation (10–15% more carbon sequestration)
Community
- Greater insect and soil microbial diversity
How does seabird-derived nutrients support coastal ecosystems?
Pathways
- Rainfall + runoff wash guano-derived nutrients into coastal waters
Boost to Coral Reefs
- Guano fertilization increases coral growth rates by 10–50%
- Corals recover faster after bleaching
- Reefs near seabird-influenced islands in the Pacific show ~48% greater fish biomass
Balanced Nutrient Ratios
- N:P ratio close to ~10:1, matching nutrient requirements of reefs Agricultural runoff has higher N:P ratios (>20:1) -> algal blooms + oxygen depletion + eutrophication
Name species that benefit from seabird nutrients
Grasses
Spiders
Iguanas
Crabs
Fish
Plankton
Seals
Manta rays
