Lecture 5 - Pelagic Ecosystems Flashcards
What is the neritic / sublittoral zone?
In the continental shelf region.
Found adjacent to the shore (subtidal region), always flooded by water.
How deep does the neritic zone go?
200m
What percentage of the ocean surface is composed of the neritic zone?
8%
What is the neritic zone characterised by?
Areas of high productivity; nutrient-rich areas.
What percentage of the ocean’s surface is composed of oceanic zones?
92%
What percentage of the entire Earth’s surface is composed of oceanic zones?
65%
Give the 6 oceanic zones, from shallow to deep.
- Neustic zone
- Epipelagic zone
- Mesopelagic zone
- Bathypelagic zone
- Abyssopelagic zone
- Hadal zone
What are the oceanic zones?
Deep water beyond the continental shelves.
What is the neustic zone?
The surface centimetre of the water.
Name two organisms that are adapted to live in the neustic zone.
- Jellyfish
- Portuguese man of war
How deep is the epipelagic zone?
0-200m
In which oceanic zone does the majority of primary production occur in?
The epipelagic zone
How deep is the mesopelagic zone?
200-1000m
What characterises the mesopelagic zone?
Dominated by predatory fishes.
How deep is the bathypelagic zone?
1000m-4000m
What other name is given to the bathypelagic zone?
Midnight zone
How deep is the abyssopelagic zone?
4000-6000m
Why do nutrients drop off in the North Atlantic during spring?
Because there are plankton blooms
Why is a second plankton bloom seen in autumn in the North Atlantic?
Autumn storms pick up, and nutrients are recirculated.
Thermocline begins to break down.
Nutrients available for plankton growth.
What does spatial heterogeneity mean?
An ocean water sample would be different according to wear you took it from.
Describe sargassum.
- entirely pelagic
- not attached to the seabed
- seaweeds
Give two species of sargassum.
- S. natans
- S. fluitans
Describe the work of Rooker et al (2006).
- Questioned whether sargassum were underpinning the food web.
- Isotope analysis, evidence Sargassum is not primary producer.
- Possible primary producers: Cladophora and POM.
- Composition of fatty acids in tissue of organisms; POM profile matches higher trophic levels.
Give four examples of forage fish.
- Herring
- Anchovies
- Capelin
- Menhaden
What do forage fish feed on?
- Blooms of plankton via filter feeding
- Targeting of larger copepods
Describe the migration of the North-American Eel.
Spend some time of their life in freshwater environments, from juvenile to adult stages.
Travel to Sargasso sea and spawn once, before dying.
What is the largest fish on Earth, and its size?
Whaleshark.
Grow up to 12m.
When did whalesharks originate?
60mya.
In 2000, what was the whaleshark found to be feeding on?
Euphasiid krill, found in large patches in coral reef environments.
Suggest a possible reason why whalesharks might spend a significant amount of their time near the surface.
Looking for celestial navigation cues
Describe the diving behaviour of whalesharks.
Can dive up to 1000m, experiencing 20C temperature gradient.
Ectothermic – warm up at the surface, giving them a competitive advantage when they dive deep.
How do whalesharks exploit resources?
Good at exploiting short-lived feeding events over a large scale, e.g. crab larvae of Christmas island, and krill off of Ningaloo.
