Adaptation to low food - pelagic Flashcards
Large filter feeders - explain whale sharks adaptations
- Whale sharks suck in a mouthful of water, closes its mouth and expels the water through its gills.
- During the delay between closing the mouth and opening the gill flaps, plankton is trapped against the dermal denticles which line its gill plates and pharynx.
- This fine sieve-like apparatus prevents the passage of anything but fluid out through the gills (anything above 2 to 3 mm in diameter is trapped).
- Any material caught in the filter between the gill bars is swallowed.
- Whale sharks have been observed “coughing” presumably a method of clearing a build up of food particles in the gill rakers.
Large filter feeders - the basking shark
The basking shark is a passive filter feeder.
- It filters zooplankton, small fish and invertebrates from up to 2000 tons of water per hour.
- Basking sharks possess large olfactory bulbs that may guide it in the right direction.
- Basking sharks are often associated with thermal and chlorophyll-a fronts, which influence their movement and maximises their feeding.
- Unlike the other large filter feeders, it relies only on the water that is passed through the gills by swimming.
- Basking sharks are passive filter feeders while other sharks can suck or pump water through their gills.
Describe the structure and function of gill rakers.
- Gill rakers in the fish project from the branchial arch (gill arch) filter small prey.
- Rakers are usually present in two rows, projecting from both the anterior and posterior side of each gill arch.
- They prevent food particles from exiting the spaces between the gill arches.
- The structure and spacing of gill rakers in fish determine the size of food particles trapped and correlates with feeding behaviour.
How may diet effect gill raker size?
Early gill rakers strain large particles and diverted them to the oesophagus to prevent potentially damaging solid material going through the gill slits and over the gill filaments.
Carnivores and omnivores often have more widely spaced gill rakers with secondary projections.
Describe filter feeding in krill.
Antarctic krill consume minute phytoplankton cells through filter feeding, using developed front legs.
The six thoracopods form a very effective “feeding basket” used to collect phytoplankton from the open water.
In areas were phytoplankton is abundant, krill can filter in a stationary position.
In low density areas the krill actively push through the water with the feeding basket in an opened position.
The the food is combed to the mouth opening with special setae on the inner side of the thoracopods
What adaptation gives Antarctic krill and advantage?
Filter feeding Krill
Antarctic krill can also scrap algae off sea ice using ice rakers at the end of their thoracopods.
This additional adaptation gives it a competitive advantage over other pelagic filter feeders like the salp Salpa thompsoni.
Jellyfish
Most jelly fish have trailed tentacles covered in a grid of fibres which are slowly dragged through the water.
The tentacles are very fine in order to avoid disturbance in the water.
The fibres of, for e.g. moon jellies circumvent the body.
Planktonic prey are unaware of the presence of such a fine trap and become entangled and consumed by the jellyfish.
Very energy efficient foraging strategy in food environment.
Mouth size as an adaptation to low food availability.
- Large gap and mouth size is another adaptation to low food availability in the deep pelagic.
Many predators have disproportionally large mouths and teeth relative to the rest of the body.
The fangtooth, Anoplogaster cornuta, has some the longest teeth relative to body size of all fish.
It contains special sockets to house the teeth when the mouth closes.
What adaptations does the fangtooth have for locating prey?
- The fangtooth is thought to use chemoreceptors for assisting in locating food.
- These are believed to be situated at the front of the head above the mouth.
- Pores in some species of angler fish used for detecting prey in the water column.
- Other sensory appendages are used to detect prey in vicinity.
Fish with a big mouth
- The pelican eel (Eurypharynx pelicanoides)
- Notable feature is its large mouth, which is much larger than its body.
- The mouth is loosely hinged, and can be opened wide enough to swallow fish much larger than the eel itself.
- The pouch-like lower jaw resembles that of a pelican, hence its name.
- The lower jaw is hinged at the base of the head, with no body mass behind it, making the head look disproportionately large.
- Water that is ingested is expelled via the gills.
Descibe the adaptations the this fishes locomotion
- Angler fish are not mobile predators.
- They ambush prey using their lure.
- The body shape and fins do not appear to be designed for long distance movement through the water or locomotion.
- The large caudal fins of the angler fish are more likely to used as a rudder to change position in the water column.
- The pectoral fins are probably stabilisers in order to keep it up-right.
What may the uses of the pelican eels jaws be?
The jaws are ~1/4 of the total length, but has only small teeth, which would not be consistent with a regular diet of large fish.
The large mouth may be an adaptation to allow the eel to eat a wider variety of prey when food is scarce: used like a large net.
The eel can swim into a large groups of crustaceans with its mouth wide open, scooping them up as it goes.
Adaptations of jaws that can open past 90 degrees
Dragonfish including posses highly adapted jaws which can open to an angle greater than 100o.
The dragonfish has an occipital-vertebral hinge structure which allows the mouth to open really wide.
The protractor hyoideus muscle is used to open and close the jaw but there is no mandible membrane either side of the muscle which makes the mouth quicker to close.
kind of summary
Bathypelagic predation
Many deep-water pelagic fauna are ambush predators.
Sensitive pores on the body detect movement in the water.
Teeth act as cages/restrictors, not for ‘biting’.
Teeth can be hinged on one of both directions.
Targets tend to get swallowed whole.
Do not appear to distinguish prey from other objects.
Extreme sexual dimorphism.
