L4 - Deposit Feeders Flashcards

1
Q
A
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2
Q
  • Organisms that feed on organic matter in the sediments
  • Dominate macrofauna in finer-grained (muddy) sediments
  • Many phyla represented – highly diverse feeding guild
  • Significant ecosystem process
A
  • Annelids (primarily polychaetes)
  • Molluscs (bivalves & gastropods)
  • Arthropods (crustaceans)
  • Echinoderms
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3
Q

Food from sediment

  • Plant and macroalgae detritus (coastal/shelf only)
  • Benthic microalgae (coastal only)
  • Organic detritus (dead phytoplankton & animals, faecal pellets)
  • Bacteria
  • In deeper environments quality and quantity of food available to deposit-feeders is low
A
  • Major paradigm
  • Bulk sediment properties very low in particulate organic matter (POM) - typically < a few %
  • Much of the organic matter has low nutritional value
  • POM C:N ratios > 20, living tissue ~ 7
  • How can deposit-feeders can grow rapidly on this poor food source?
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4
Q

Microbial stripping

  • Early hypothesis: For POM to be nutritional for deposit-feeders it must be decomposed by microbes and converted into microbial tissue
  • Decomposition:
  • Fragmentation increases surface area:volume ratios
  • Leaching
  • Microbial decay increases N content
  • However in many habitats heterotrophic bacteria abundance in sediments is not high enough meet all the energy demands of many species
A
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5
Q

Microbial gardening

  • A form of microbial stripping
  • Deposit-feeder activities enhance microbial productivity (reduce competition, free up resources)
  • N absorbed by bacteria from water is made available to deposit-feeders
A

Microbial gardening

• Even with microbial gardening bacteria abundance in sediments is still not that high but may be very important for specific fatty acids, amino acids & vitamins

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6
Q

Feeding strategies

  • Process large volumes of sediment – typically one body weight day-1
  • Even at low nutritional value if you consume enough you will survive
  • Particle selection
  • Many species will select smaller particles (higher surface area:volume ratio) which are associated with higher food quality (i.e. more bacteria) especially tentaculate feeders
  • Fluidising sediment sorts particles
  • Many particles are rejected for ingestion
  • Modify gut retention times depending on particle quality – intracellular digestion retains nutritious particles
  • Specialist enzymes to detach microbes from sediments
  • Still much to learn due to identifying what exactly many deposit-feeders are eating and how to assess food quality
A
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7
Q

Ecological significance – chemical gradients

• Burrows alter the amount of oxidised surface area influencing nutrient cycles in sediment

Burrows oxygenated sediment, speeds up break down of inorganic materials

A
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8
Q

Ecological significance – chemical gradients

A

Intricate network system left behind by burrowing crab

oxygenates network altering nutrience cycle and creating habitats

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9
Q

Ecological significance – chemical gradients

Sub-surface deposit-feeders: Arenicola marina (lug worm)

(Feeds head town tail up to avoid predation from birds)

A
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10
Q

Ecological significance – sediment transport

• Alter grain size at surface, oxidise sediment at depth enhancing microbial activity

A
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11
Q

Ecological significance – sediment transport

  • Benthic algae
  • Primary producre
  • Migrates through sediment
  • Produces carbohydrates which bind algae together and creates more stable less errosive susceptible environments.
A

Ecological significance – sediment transport

• High densities of deposit-feeder affect sediment stability, erosion rates

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12
Q

Ecological significance – primary production

Cinerarium – heart urchin

  • Common sub-tidal species
  • Bulldozes top 5 cm of sediment
  • Homogenizes sediment
  • Complex feedback with bacteria & benthic algae
A
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13
Q

Ecological significance – primary production

A
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14
Q

Ecological significance – primary production

A
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15
Q

Macrofaunal abundance by feeding type in Long Island Sound (Sanders 1958)

  • Trophic group amensalism – Rhodes & Young (1970)
  • Reworking of sediment by deposit-feeders destabilises sediment making it stressful to suspension-feeders (clogs gills, reduces food quality)
  • Modified by Woodin (1976) to include adult/larval interactions
A
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16
Q

Ecological significance – community interactions

  • As a hypothesis it makes sense but data lacking
  • Mixed communities often occur due to spatial refuges
  • Some organisms capable of switching between deposit- and suspension-feeding
  • Absence does not imply exclusion (e.g. larvae not available)
  • Other processes (e.g. predation may be important)
  • See discussion in Grey for more details

A
17
Q

Summary

•Feeding types

•Food sources

•Feeding strategies

•Ecological interactions

A