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
