4.3 Aquatic food production systems

Question 1

What are the zones that the Ocean can be divided into ? (HINT: son 5) (EMBAH – metele tu memorizada con la tecnica Valed)

Answer 1

• Epipelagic zone
• Mesopelagic zone
• Bathypelagic zone
• Abyssalpelagic zone
• Hadalpelagic zone

Question 2

Epipelagic zone - Depth y facts

Answer 2

• (depth of 0 to 200m): into which light penetrates allowing primary produces to grow
• It is the most productive zone, with little photosynthesis occurring outside this area

Question 3

Mesopelagic zone - Depth y facts

Answer 3

• (depth of 200m to 1,000m)
• where there is insufficient light penetration to allow for plant growth

Question 4

Bathypelagic zone - Depth y facts

Answer 4

• (depth of 1,000m to 4,000m):
• also known as the dark zone because of absence of light apart from that produced by any bioluminescent organisms present.

Question 5

Abyssalpelagic zone - Depth y facts

Answer 5

• (depth of 4,000m to 6,000m)
• is dark and the water temperature is just above freezing.
• Few organisms can withstand the high pressure in this zone

Question 6

Hadalpelagic zone - Depth y facts

Answer 6

• (depth of more than 6,000m):
• includes trenches and canyons.
• The water again is very cold and life here needs to be adapted to extremely high pressure.

Question 7

Outline the basics of a marine ecosystem. state an example for each trophic level

Answer 7

1. Primary producers :
   a. phytoplankton and seaweed
2. Primary consumers
   a. zooplankton
3. Secondary consumers
   a. small predators/small fish (like sardines
4. Tertiary consumers
   a. large fish (sharks)

Question 8

What is primary production dependent on (in aquatic ecosystems

Answer 8

Primary production is dependent on the amount of sunlight, suitable temperature and available nutrient levels

Question 9

What nutrients is primary production dependent in

Answer 9

nitrates
phosphates
silicates

Question 10

What is therman stratification

Answer 10

• Tiny particles, such as nutrients, gradually sink down from the upper layers of the water
• When the weather is calm and warm, the water in a body of water (like a lake or ocean) can separate into layers based on temperature
• This is called thermal stratification
• The thermal stratification stops the nutrients from moving up into the upper layer of the water, which is called the epipelagic zone. This is where many of the organisms that rely on sunlight live

Question 11

When does thermal stratification occurr

Answer 11

• Sunlight heats the upper layer of water and surface movements create a layer with a fairly consistent temperature
• Water movement below the surface mixed layer is reduced due to the calm weather and the sun continues to warm the water. Sunlight penetration declines with depth resulting in a temperature variation from the top to the bottom of the thermocline
• Strong winds and coastal currents can cause mixing of the water and break up the thermocline and redistribute nutrients back into the water column
• This process is referred to as upwelling, and contributes to an increase in primary production. El Nino events reduce surface current and wind driven upwellings, which has a negative effect on productivity in the area
• In high latitudes during the winter vertical mixing also occurs when the surface waters gets cold and sinks. In the tropics, thermal stratification is fairly stable and production levels tend to be lower but constant

Question 12

Why are coastal waters more productive

Answer 12

• Coastal waters are typically shallower than open ocean waters, allowing more sunlight to penetrate
• nutrient-rich runoff from the land

Question 13

What are the zones in lake ecosystems

Answer 13

• Littoral zone
• Limnetic zone
• Euphotic zone
• Profundal zone
• Benthic zone

Question 14

What is the Littoral zone?

Answer 14

the shallow area of the lake that goes up to the shore area

Question 15

What is the Limnetic zone?

Answer 15

covers the open water in the lake where there is enough light for phytoplankton to photosynthesize

Question 16

What is the Euphotic zone?

Answer 16

includes both the littoral and limnetic zone where there is sufficient light for photosynthesis to occur

Question 17

What is the Profundal zone?

Answer 17

thedeep water where there is no light penetration

Question 18

What is the Benthic zone?

Answer 18

the lake bottom, where organisms live within the sediments or on thesurface of the lake sediments.

Question 19

Learn / study diagram of the lake zones!

Answer 19

Mira la foto 6 en el docs

Question 20

Why aquatic food systems are seen as less productive than terrestrial food systems - STATE ARGUMENT IN FAVOR

Answer 20

• Primary producers in aquatic systemsreceive less light than terrestrial plants because some of the incoming light is absorbed or reflected by the water.
• Compared to terrestrial foods, humans generally tend to eat organisms from higher up in the aquatic food chain.

Question 21

Why aquatic food systems are seen as less productive than terrestrial food systems - STATE ARGUMENT AGAINST

Answer 21

In aquatic systems less of the biomass may be lost as indigestible skeletal material (e.g. jellyfish have no skeleton) resulting in more efficient energy transfer

Question 22

How did capture fisheries attempt to meet rising fish demand

Answer 22

• Growth in number and size of fishing fleets
• Improvements in shipping vessels which allowed fishing to occur further from the shore and in deeper waters
• Larger ships allowing for longer periods at sea resulting in greater harvest of fish
• Development of sonar, radar and satellite technology to detect and track schools of fish
• The ability to process, preserve and freeze aquatic produce on the ship whilst still out at sea

Question 23

State the 3 types of Fishing Nets

Answer 23

• Trawler nets
• Purse - seine nets
• Drift nets

Question 24

Impact of Trawler nets

Answer 24

• funnel shaped net along the seabed.
• damages sea bed and gets other animals caught

Question 25

Impact of Purse - seine nets

Answer 25

• fish are surrounded by the net, which is then closed like a draw string purse to trap the fish
• also has a lot of bycatch

Question 26

Impact of Drift nets

Answer 26

• referred to as “curtains of death”
• worst ones

Question 27

When are fish stocks renewable

Answer 27

• Fish stocks are only renewable if the rate of their removal does not exceed their growth rate
• The maximum sustainable yield (MSY) is the optimum harvest that can be obtained annually without affecting the standing stock and its ability to replenish itself

Question 28

How can the maximum sustainable yield still lead to overfishing

Answer 28

The calculated MSY can be overestimated as it may be based on inaccurate or incomplete datasets and due to gaps in our understanding of fish ecology

Question 29

why is overfishing still so popular (HINT: 2)

Answer 29

• Property rights: Fish do not respect national boundaries.
  
  • People often do not want to spend money on conserving the fish, if other competing countries will harvest them.
• Zero sum game: this is the idea that in many situations someone gains at the expense of others.
  
  • In order to conserve fish stocks you need to convince people to sacrifice short term gain to benefit in the future.
  • For this to be a favourable option, the long term gain needs to be sufficiently lucrative and low risk.

Question 30

Outline 3 ways to manage fish stocks and overfishing

Answer 30

• Use of quotas + limitation
• Reduction in fishing effort size
• Exclusion zones: Marine Protected Areas (MPAs)

Question 31

What is aquaculture ?

Answer 31

Farming of aquatic organisms

Question 32

What are the two types of aquaculture systems

Answer 32

• Open based system
• Semi-closed systems

Question 33

Outline open based system

Answer 33

• most popular
• farming the organisms within a natural aquatic ecosystem such as the sea or a lake
  • through: fish cages, clam beds and oyster rafts that are submerged in the water
• issues with this is that the farmers have no control over abiotic factors such as temperature and no control over biotic factors such as predation (or poaching)

Question 34

Outline Semi-closed systems

Answer 34

the abstraction and use of water from the sea or lakes within tanks or ponds situated on land

Question 35

enviromental impact of aquaculture (HINT: 6 main impacts)

Answer 35

1. Loss of habitats (to make way for aquaculture)
2. Increase in organic sediments (waste)
3. Increase in available nutrients
4. Use of medicine
5. Use of antifouling agents
6. spread of disease

Question 36

• Actions to reduce the environmental impacts of fish farming

Answer 36

• Reducing waste from uneaten feed by not overfeeding (e.g. timing feeding session)
  • More effective application of any medicines to reduce losses to the environment.
  • Regular removal of any dead fish from the cages.
  • Moving the cages at regular intervals to prevent build-up of organic sediments at bottom and give the area time to recover.
  • Locate fish farms where there is sufficient movement and exchange of water to:
    
    • Reduce nutrient levels in the water.
    • Reduce phytoplankton levels in the water and disperse any blooms.
    • Reduce build-up of waste by dispersing it.
  • Aerate the water to prevent anoxic conditions
    
    • anoxic = depleated of oxygen
  • Removing the deposited waste from below the fish cages.