Aquatic food production systems

• nutrient availability • variations in light levels (aphotic zone/ photic layer)

Deeper layers of water that receive no sunlight because they are absorbed by shallower layers.

The water layer into which light can penetrate.

Marine mammals including whales, dolphins and porpoises.

A taxon of animals that includes corals and jellyfish.

Living near the water surface eg herring, tuna.

An organism that produces high-energy food substances using sunlight in photosynthesis.

All the aquatic animals that are caught or grown to be eaten that have shells or an exoskeleton eg crustaceans and molluscs.

Living on the seabed eg cod, plaice.

living in or on the seafloor (terrestrial)

our oceans cover 70% of the earths surface very little is biologically productive.

“A measure of the yield of a system, often expressed as the yield per unit area, time or input.” - ocean productivity is affected by the availability of light and dissolved nutrients - high productivity requires both - both are not balanced in location

• light can only reach about 200 metres • temperature decreases with depth • CO2 is high at this level (most CO2 comes from the atmosphere and dissolves in the surface of the ocean) • photosynthesising algae produces most of the nutrients here • however it does not remain here, falling into the aphotic zone (CO2, nitrates) ( all organic matter sinks as they are denser than water so most nutrients are found in the bottom (cold water carries more nutrients)) • thermoclines have no drop off due to the specific heat capacity of water)

• no light but most of the nutrients are found in this level • dead algae and dissolved organic matter falls through this layer

• nutrients also accumulate around the shoreline. • runoff from rivers and disturbance of shallow sediment • this makes continental shelves more productive than open oceans (fewer coastlines = less nutrients)

• depends on the topography of the seafloor • surface water is pushed away by winds blowing on it. Water then rises up to replace the water that was pushed away. The water from the deep is usually cold and is rich in nutrients, making areas of upwelling highly productive • underwater currents move deep water this can hit the seabed due to its changing topography and cause the water to be deflected up to the surface the water carries all of its dissolved nutrients, this often happens around seamounts

it is the movement of water (with its nutrients) due to its temperature and salinity (it is linked to the global conveyor belt) temp ↓, salinity ↑ (water freezes salt left behind in remaining now very saline water) - water goes down temp ↑, salinity ↓ - water goes up (water always moves in direction of temperature)

• nutrients needed in photic zone/ nutrients are a limiting factor • nutrients at surface on continental shelf due to disturbance of seabed (currents/tides, animals. humans, coastal storms)/ runoff from land • less nutrients near surface in open oceans because dead organic matter (DOM) sinks

light - photic zone dissolved nutrients - aphotic zone, pelagic, continental shelves

shorelines/ continental shelves

river runoff, atmospheres, dead shells, photoautotrophs

As it is closer to the atmosphere, most CO2 comes from the atmosphere and dissolves in the oceans surface water.

upwelling, thermohaline circulation (dense salty water sinks)

• pelagic trawling, -demersal trawling, • purse seining, • drift netting, • long lining, • shellfish traps,