Transcript 13 Benthic Life Habits

13 Benthic Life Habits
Notes for Marine Biology:
Function, Biodiversity, Ecology
By Jeffrey S. Levinton
©Jeffrey S. Levinton 2001
Important benthic lifestyles
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Benthos
Epibenthic
Burrowers
Borers
Infaunal, Semi-infaunal
Benthic swimmers
Interstitial
Benthos - size classification
• Macrobenthos - shortest dimension < 0.5
mm
• Meiobenthos - smaller than 0.5 mm,
greater than 0.1 mm
• Microbenthos - < 0.1 mm
Feeding Classification
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Suspension feeders
Deposit feeders
Herbivores (macroalgae or microalgae)
Carnivores
Scavengers
Food classification ambiguities
• Herbivores could be classified as
suspension feeders who feed on
planktonic microalgae
• Carnivores could be classified as
suspension feeders who feed on
zooplankton
Life in Mud and Sand
Life in Mud and Sand
Particle size - important parameter
Current strength
Sorting - variation of current strength, poor
versus well sorted sediment
Life in Mud and Sand
Particle size - measures
Median grain diameter - measured usually
by sieving and weighing size fractions
Silt-clay fraction - % of weight of sediment
< 62m
Sedimentary Structures
Ripple marks on an intertidal sand flat
Burrowing in sediment
• Burrowers use hydromechanical and
mechanical digging mechanisms to move
through the sediment
• Watery sediments with high silt clay
content have thixotropy - as you move
through sediment it takes yet less force to
continue to move
Burrowing in sediment 2
• Hydromechanical burrowing - combines
muscle contraction working against rigid,
fluid filled chamber (skeleton)
• Form penetration anchor first to allow
further extension of body into sediment
• Form terminal anchor to allow pulling of
rest of body into the sediment
Burrowing in sediment -bivalve
foot
Muscle contraction
Longitudinal
muscles
PA
Circular
muscles
PA = penetration anchor
TA = terminal anchor
TA
Hydromechanical
burrowing
Lugworm, Arenicola marina
Longitudinal muscle
contracting
Terminal
anchor
Eversion of
pharynx
Circular muscle
contracting
Pentetration
ancthor
Burrowing in sediment 4
Inarticulate brachiopod burrows by scissoring
2 valves back and forth, which displaces sediment
Mechanical displacement
burrowing
Burrowing in sediment 5
Biogenic structures - burrowing and processing
of sediment affects sedimentary structures
1. Burrowing in mud increases water
content of sediment
2. Increases grain size (pellets)
3. Alters vertical and 3-D mechanical, chemical
structure
Burrowing in sediment 8
Biogenic graded bedding
Annelid ingests small particles at depth and deposits them on surface
Interstitial animals
• Live in the pore waters of sediment,
usually sand grains
• Belong to many taxonomic groups
• All share elongate, wormlike form, in
order to move through tight spaces
Interstitial animals 2
Harpacticoid
copepod
Polychaete
Gastrotrich
Hydroid
Opisthobranch
gastropod
Soft-Sediment Microzone
• Strong vertical chemical gradients
• Gradients strongly affected by biological
exchange
activity
Oxic
Redox Potential
Discontinuity
Anoxic
Soft-Sediment Microzone 4
Soft-Sediment Microzone 5
• Microbial types also vary with depth
below the sediment water interface
• Towards the surface, aerobic bacteria
dominate (energetically most efficient to
use oxidation)
• Deeper, bacteria present that can live in
the absence of oxygen and can produce
energy through various chemical means
Soft-Sediment Microzone 6
Aerobic bacteria (use oxygen to break down organic substrates)
RPD
RPD
Fermenting bacteria (break down organic cpds. --> alcohols,fatty acids)
Sulfate reducing bacteria (reduce SO4 to H2S)
Methanogenic bacteria (break down organic cpds. --> methane)
Benthic Feeding Types
Deposit Feeders
• Feed upon sediment, within the sediment
or at sediment surface
• Head-down deposit feeders feed within
the sediment at depth, usually on fine
particles, defecate at surface
• Surface browsers often feed on surface
microorganisms such as diatoms
Deposit Feeders 2
Surface tentacle
feeding polychaete
Tentacle feeding
bivalve
Deep feeding
polychaete
Surface feeding
amphipod
Surface siphonate
feeding bivalve
Deep feeding polychaete
feces
Burrow
opening
Surface trace of burrow of the
Lugworm, Arenicola marina
(Anglesey, North Wales)
Arenicola marina burrow cross section
Deposit feeders 3
• Microbial stripping hypothesis: deposit
feeders are most efficient at digesting and
assimilating benthic microbes (diatoms,
bacteria)
Deposit feeders 4
• Microbial stripping hypothesis: deposit
feeders are most efficient at digesting and
assimilating benthic microbes (diatoms,
bacteria)
• In some sediments non-living organic
matter is abundant, so even a low
assimilation efficiency returns some
nutrition for deposit feeders
Deposit feeders 5
• Microbial stripping hypothesis: deposit
feeders are most efficient at digesting and
assimilating benthic microbes (diatoms,
bacteria)
• At some times of years, fresh
phytoplankton sinks and is added to the
bottom: another source of non-living food
for deposit feeders
Deposit feeders 6
• Microbial stripping hypothesis: deposit
feeders are most efficient at digesting and
assimilating benthic microbes (diatoms,
bacteria)
• Detritus from seaweeds is probably more
digestible than detritus from seagrasses
and marsh grasses, which have much
relatively indigestible cellulose
Deposit feeders 7
• Deposit feeders feed on sedimentary
grains, microbial organisms living on
particulate organic particles
• Feeding activity accelerates
microbial attack - grazing stimulates
microbial metabolism, results in tearing
apart of organic particles
Deposit feeders 9
Egestion
Transport to
surface of
deep sediment
Microbial
consumption
POM deposition
Free-burrowing bivalve
Sediment
stirring
RPD
Stimulation
of microbial
growth
Tube
POM,
Metal, sulfur,
(mechanically, dissolved organic
Chemically, carbon exchange
Transformed)
Metal, sulfur,
dissolved organic
carbon exchange
Ingestion of sediment
Suspension Feeders
• Feed on small particles, low Reynolds
number
• Passive versus active suspension feeders
Suspension Feeders 2
Bivalve, x-section
Polychaete Serpula
Barnacle
Suspension Feeders 3
Sea squirt Styela montereyensis
Passive suspension feeding mechanism
Suspension Feeders 4
Motile
particle
deposition
Direct
interception
Sieving
Inertial
impaction
= fiber
Gravitational
deposition
Encounters of particles with fibers
Suspension Feeders 4
Motile
particle
deposition
Direct
interception
Sieving
Inertial
impaction
= fiber
Gravitational
deposition
Encounters of particles with fibers
Carnivores
Bivalve Cuspidaria
oystercatcher
Gastropod Nucella
Polychaete
Glycera
Crab Callinectes sapidus
Herbivores
Polychaete Nereis vexillosa
Parrot fish
radula
Chiton
Urchins
Cellulose feeder
Bivalve Teredo
foot
Greatly elongated mantle
Obtains nitrogen
with symbiotic
nitrogen fixing bacteria
The End