pelagic ecology Flashcards
what are neuston
animals that live at the ocean’s surface - drifting in currents and driven by winds
- Ocean clean up scheme uses net to collect plastic at the surface – but also collects neuston
what are plankton
Drift in currents but usually able to swim weakly, and especially move vertically in the water
what is the Diel Vertical Migration (DVM)
- Largest migration in terms of biomass on the planet - anti-predator strategy by zooplankton (Predator evasion hypothesis)
- Animals occur in deeper water in the day and
Move to shallower water at night
what is the clear cost to Diel Vertical Migration (DVM)
movement at a low Reynold’s number (small organisms) is energetically expensive
what are the 2 Additional support for the predator evasion hypothesis
- Interspecific differences (bigger or more pigmented species show more pronounced DVM)
- Ontogenetic differences (smaller developmental stages of the same species show less pronounced DVM)
what is the Proximate cue that DVM changes for
- light intensity
- Depth of DVM had been observed changing with varying cloud cover, eclipses and phases of the moon
- plankton have been observed to spend more time at the surface in the winter where nights are longer
what is Reverse DVM
- Associated with invertebrate predators that use tactile (non-visual) stimuli to locate prey - so still predator avoidance (but non visual ones)
- move deeper during night, higher during day
what are the 4 things Differences in foraging patterns are attributed to
- Differences in ambient light levels at prey depths during the diel cycle
- Differences in the visual activity at low light levels
- Differences in the escape abilities of the different prey, so that ambient light levels are more important for the predator in one case than the other
- Differences in the amplitude of different prey (how deep they go) species - commuting costs in reaching the prey vary for these different divers
what are Ladders of migration
multiple, stacked layers move up and down in a complicated pattern (predators follow prey)
- Four-dimensional game of cat and mouse (including inverse DVM)
what are nekton
active swimmers - Able to move independently of water currents
- mainly crustaceans and cephalopods
- Invertebrate nekton occupy similar trophic levels to fish
what is distinct about a squids diet
- Can occupy several trophic levels
- Role reversal: young squid are eaten by a range of predators but eat those same predator species as they grow
what is the main nektonic crustacean
krill
- swimming crabs and shrimp also included
what are ‘Wasp-waist’ systems
Dominated by a mid trophic- level species that is thought to exert top-down control on its food and bottom-up control on its predator - aka loads of diversity of species on top and bottom of trophic level but 1 species on mid tropic level linking the two
what is the most dominant of the seven Southern Ocean krill species in terms of biomass
Euphausia superba
summarise the krill life cycle
- females birth in the summer and the embryos sink to the sea floor and hatch
- larvae then rise to the surface so that the first feeding stage appears at the same time as the summer phytoplankton boom
- Juveniles will then rely on winter sea ice for shelter and food (ice algae)
**Adult krill are able to reduce their metabolism by 3-fold during winter and survive off their own lipids
what is the Calyptopis and Six furcilia stagesin krill
Calyptopis stage: first with a mouth and feeding appendages
Six furcilia stages: before the metamorphosis into juveniles
how will global warming affect krill abundance
there is less ice for feeding and shelter
- the animals that eat krill e.g. whales will also by affected
