L7 - The Open Ocean Flashcards
The open ocean - What is the oceanic zone?
Above the deep sea; beyond the shelf break. Further divided by how much light can reach a certain depth.
What is the open ocean?
A large, unbounded environment where organisms move and live in 3 dimensions. Nowhere to attach, burrow or hide
Where is the patchiness in the open ocean?
Physical properties, biological production, biomass.
How much of the earth does the ocean cover?
71%
What is the epipelagic zone?
It is a pelagic zone. Sunlit/euphotic/upper ocean. Surface to 200m. High biomass overall, high diversity. Enough sunlight to sustain photosynthesis. Most of the life in the ocean is reliant on the productivity within this zone.
What is the mesopelagic zone?
Twilight zone, only 1% of incident light reaches this zone. In most areas of the world, the epipelagic-mesopelagic transition is marked by a thermocline (rapid temperature change over a short distance). Photic zone is well-mixed by wind and waves. Deeper waters are more stable. Result = stratification.
What is the mesopelagic zone? pt 2
The depth varies with seasonality, can restrict nutrient upwelling and limit productivity. Organisms moving through the water column have to deal with large, sudden temp change.
What is the bathypelagic zone?
‘Midnight’ zone, No light. Constant temp 4 deg C.
What is the abyssopelagic zone?
Extends 300,000,000 square km ~40% of the global surface. Near constant conditions. Abyssal waters originate at the air-sea interface in the polar regions. Much of the life here is benthic. Fuelled by marine snow.
What is the Hadalpelagic zone?
From 6,000m to the very bottom. Deepest point is the mariana trench, off the coast of Japan.
What zone shows considerably more food to other ecosystems?
Pelagic zone. Ocean currents carry plankton and nutrients into shallower waters. Detritus sinks to the deep sea sediments.
Depth present variability in…… Light?
Photosynthesis, UV damaging at surface, predation style.
Depth present variability in…… Pressure?
1 atm of Pressure per 10 metres of depth
Depth present variability in…… Oxygen?
Oxygen at certain depths depleted by bacteria breaking down sinking material
What is the pelagic enviro home to?
Plankton and Nekton marine organisms
What are plankton?
Passively transported by the ocean currents. Planktonic plants = phyloplankton, Planktonic animals = zooplankton.
What are Nekton?
Free swimmers, marine mammals, fish, invertebrates, reptiles, and birds.
Plankton - What are phytoplankton?
The foundation of most food webs in the pelagic zone are the phytoplankton. >95% of the ocean’s photosynthesis.
Plankton - How do you classify by size?
A gradient of moveability - the smaller you are, the ‘stickier’ seawater is and the more energy needed to move. Movement can especially occur vertically.
Plankton - What is zooplankton?
Usually microscopic, but some are larger e.g. jellyfish. Are heterotrophs (consumers). Zooplankton are the link between primary production and larger organisms. Might be Halo-plankton : all of life cycle in water column, Mero-plankton : part of the life cycle in the water column.
What do echogram show?
Density of animals in the water column.
Plankton - What is the Diel Vertical Migration?
In terms of biomass, DVM is the largest daily migration on the planet. DVM is the result of a trade-off by zooplankton to avoid visual predators and damaging UV light.
Plankton - How do you sample?
Traditionally sampled using towed nets. Finer mesh for phytoplankton, coarser net for zooplankton.
What are new techniques used to sample plankton?
Genomics (the study of DNA sequences, underwater photography, satellites, sonar.
What are there not in the pelagic zone?
Deposit feeders, instead there are Pelagic suspension feeders, active pursuit.
What are Nekton?
Carnivorous, planktivorous nekton. Fish, whale and basking sharks, baleen whales, lanternfish.
What species of Nekton eat other Nekton?
Fishes, mammals, squids, crustacea
What are the problems with staying afloat?
Cells, tissues, shells and skeletons are generally heavier than water. Solutions are either keep swimming, increase water resistance, increase buoyancy.
How does water resistance help staying afloat?
It creates drag, amount of drag depends on, how much water a moving organism pushes in front of it, the amount of friction between it and the water
How does increasing buoyancy help staying afloat?
Store lipids (oils and fats are less dense than water). Diatoms, fish larvae, and eggs (oil droplets), sharks (in liver), whales, seals etc. have blubber. Gas pockets, swim bladders (most bony/teleost fish), cyanobacteria can control gas in vacuoles. Change in composition of body fluids, SO42- and Mg2+ excreted and replaced with NH4+ and Cl-, many planktonic species do this. We know very little about the diet of most epipelagic species.
What do we know about epipelagic food webs?
Many epipelagic organisms consume across multiple trophic levels. E.g. capepods consume both herbivores and carnivores. Tuna can be anything from a secondary consumer (eating krill) to a fourth level consumer (e.g. eating mackerel).
What are epipelagic food webs complicated by?
Life stage - different stages of development will predate on, and be prey for, diff organisms - ontogenetic changes. Location - tropical food webs, usually have more steps than colder waters.
What do patterns of epipelagic organisms follow?
Patterns of primary production.
