13 Benthic Life Habits Notes for Marine Biology: Function, Biodiversity, Ecology

13 Benthic Life Habits

• Notes for Marine Biology: Function, Biodiversity, Ecology

• By Jeffrey S. Levinton

Important benthic lifestyles

• 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

• 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

Life in Mud and Sand

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

Burrowing in sediment 4

Burrowing in sediment 5

Burrowing in sediment 8

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

Soft-Sediment Microzone

• Strong vertical chemical gradients

• Gradients strongly affected by biological activity

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

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

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

Suspension Feeders

• Feed on small particles, low Reynolds number

• Passive versus active suspension feeders

Suspension Feeders 2

Suspension Feeders 3

Suspension Feeders 4

Suspension Feeders 4

Carnivores

Herbivores

Cellulose feeder

The End

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