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Planktivory
Planktivory
Suspension feeders:
Animals that process large quantities of water through a
feeding apparatus (gill rakers, baleen).
Gill rakers trap particles such as zooplankton,
phytoplankton and detritus.
Includes: manta rays, basking shark, whale shark,
megamouth, paddlefish, gizzard shad, menhaden, and
bighead carp.
Feeding strategies:
A) Obligate and faculative planktivores:
Most fish are planktivorous at some point in their life,
either as holoplankton or meroplankton.
•
Facultative planktivores: (ex. sunfishes) are
opportunistic feeders. Prey selection depends on food
availability
•
Obligate planktivores: (ex. blueblack herring, Atlantic
Menhaden) feed exclusively on plankton
B) Ram feeding and suction feeding
Ram feeding: creates a forward motion in which water is
delivered into the mouth; opens mouth wide as
possible and rams prey
•
continuous ram feeders
•
intermittent ram feeders
Suction feeding: predator remains relatively stationary,
comes close to prey and then sucks prey in.
•
continuous suction feeders
•
intermittent suction feeders
Suction feeder
Nonsuction feeder
Jaw Protrusion
Sling-jaw wrasse
Ram Feeders
• Continuous
• Intermittent
Continuous ram feeders (tow-net)- water passes
continuously through mouth, over gills and exits through gill
slits or operculum.
~20 species fish
In fish: extensive elaboration of the branchial (gill) apparatus
Manta Ray:
• They have no teeth.
• Cephalic flaps channel water containing plankton into
mouth
• To prevent gills from clogging, a screen of small tiny
protuberances located in the throat, hold the food
until it can be swallowed.
Megamouth, Basking Shark and Whale Shark- Generally
these planktivorous sharks have tiny numerous teeth and
elongated gill rakers. The gill rakers help to strain plankton.
Basking shark- (10 meters long)
•
Swims about 2 knots with mouth open and bristle-like
gill rakers erect while filtering particulate matter
•
It then closes its’ mouth forcing water over the gills; it
is an indiscriminate planktivore
•
Has five pairs of gill slits and can filters ~540 liters
zooplankton/day and over 1500 gallons of water/ hour
(1850 m3 water/hour)
•
Basking sharks caught between Oct. And Dec., no
visible gill rakers were found, but had immature or
functionless, incompletely developed rakers (possibly
has a resting, non feeding stage). Re-grows gill rakers
by February.
Paddlefish- Order Acipenseriformes
• freshwater, rarely brackish; found in China and the US
• gill rakers are long and in the hundreds- used for
plankton feeding, minute teeth are present
Polyodon spathula (US- Mississippi drainage)- planktonfeeding; non protrusible mouth
Psephurus gladius (China- Yangtze River)- piscivorous
with a protrusible mouth
Continuous ram feeding
Intermittent ram feeders
• takes one gulp of water at a time, extracts
particles and repeats the process
• In using this method, the predator needs to be
able to grab prey before it moves out of the way.
• Seen in whales, not sure about in fish????
Suction Feeders
• Continuous
• Intermittent
Continuous suction feeders (pump filter feeders)creates and osculatory pump and draws water in over
sieving device. Animal remains still while suctioning.
Ammocetes (lamprey larvae)-spends 3-7 years filter
feeding and burrows into sand;
Feeding:
• a current of water is drawn in by muscular action
• water enters buccal cavity and washes over gills
• uses gills to filter particles for food
• in ammocetes, filtering linked to breathing.
Intermittent suction feeders (intermediate
feeding):
• relatively unspecialized
• intermediate condition between ram and
suction feeding on individual prey
• they don’t alter their swimming speed or
direction to focus attention on individual
plankton.
Diurnal and Nocturnal
Planktivores
Diurnal Planktivores
Typically feed by forming aggregations in the water column
prey- swimming crustacea, larvaceans and fish eggs
• largely transparent except for some pigments on eyes or
gut and usually small size (< 3mm in size)
Planktivore:
• find modifications to jaw, head and dentition:
usually small mouth, reduced or absent teeth
• jaw protrusion mainly functions to produce suction
• In Chromis viridis- uses ram-jaw, low suction to capture
evasive prey, but decrease jaw protrusion and increase
suction when prey are less evasive
Diurnal Planktivory
adaptations - streamlining and deeply forked
caudal fins; aggregation
ecology-feed along the reef edge mainly on
transient zooplankton from open water; the
fish depend on water currents to supply them
with food; may feed in stationary aggregations
Crepuscular changeoverdiurnal fish leave typically in order of:
small fish first….mid sized …. then large
Very active time.
In nocturnal species- fish enter waters
above the reef at night fall by size order
(small to larger)
Nocturnal Planktivores
Difficulty in visually locating prey in dim light
• adaptation- large eyes ex. squirrel fish
• Feed on larger zooplankton: Hobson & Chess found
that even the smallest nocturnal reef planktivores are
limited to zooplankters larger than 1 mm; whereas
diurnal planktivores with similar feeding structures have
been found to feed primarily on organisms smaller than
1 mm.
Possibly due to:
1.) inability to see smaller ones
2.) more efficient
3.) prey more vulnerable
Adaptations to nocturnal threats from predators:
• streamlined bodies and deeply forked tails are less
developed- possibly due to less threat to attack after
dark
• less aggregation occurs at night
• countershading using luminescent organs
Nocturnal planktivores more widespread throughout reef
than diurnal counterparts
ctenophore