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Soft Substrate Communities soft sediment = substrate of sedimentary particles; uncemented, unconsolidated or loosely consolidated epifauna – on the surface infauna – in the sediment. Physical Environment. Grain size - particle size high energy = large grain size; sand

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Soft Substrate Communitiessoft sediment = substrate of sedimentary particles; uncemented, unconsolidated or loosely consolidatedepifauna – on the surfaceinfauna – in the sediment

physical environment
Physical Environment
  • Grain size - particle size

high energy = large grain size; sand

low energy = small grain size; mud

median grain size – sandy silt, silty sand

sorting – range of particle sizes, biological sorting

Substrate mobility
  • influenced by animals – burrowing, binding in tubes
  • cohesiveness – microbes, mucus

Interstitial space – space between grains, “pores”

  • affects water drainage
  • diffusion of chemicals
Organic Matter

- % organic matter

- substrate for microbial decomposition, detritus feeders

  • Oxidation-reduction state

redox potential discontinuity layer (RPD)

- measured by electrode (Eh)

Above RPD – oxygen present

Below RPD – oxygen absent


Chemosynthetic bacteria – use H2S

Sulfate-reducing bacteria – produce H2S (fermentation)

Organisms affect the depth of the RPD layer

in irrigated tubes, extend RPD into sediments

  • Organisms must adapt to anaerobic conditions
    • Bring oxygenated water down
    • Tolerate H2S
Light – when present, plants present

- benthic diatoms

- macroalgae

- seagrasses

size of infaunal organisms
Size of infaunal organisms
  • Macrofauna: >0.5 mm
  • Meiofauna: 0.5-0.062 mm
  • Microfauna: < 0.062 mm
trophic structure
Trophic Structure
  • Suspension Feeders (filter feeders)

- primary food = plankton

- generalists, size selection by filter

  • Deposit Feeders
    • animal that feeds by consuming particles in or on the substrate
    • “detritivore”
types of deposit feeders
Types of deposit feeders
  • Surface deposit feeders
  • Burrowing or deep

Microbial Stripping Theory – deposit feeders don’t digest detritus, just digest microorganisms on the detritus and sediment particlesFenchel: - low assimilation efficiency detritus (1-10%) - high assimilation efficiency microbes (40-80%)

logical argument for microbial stripping
Logical argument for microbial stripping
  • Composition of the detritus

- sources, age

- temporal variation

  • Digestion detritus vs microbes
  • Constancy and quality of microbes
    • microbial colonization

- protein

renewal rates microbes
Renewal rates - microbes
  • Animal must not ingest again until microbes recolonize
  • pelletization
physical or biological
Physical or biological?
  • Soft bottom benthic communities structured by ???
  • Expt evidence
Physical –
  • Oliver 1979
    • Subtidal zoned on gradient of wave energy
    • < 14m – regular disturbance, small molbile crustaceans
    • > stable, tube polychaetes
both biological and physical
Both biological and physical
  • Mills 1969 – sandy area, low biomass, density of IF
  • Illyanassa – mech disturbance by snails
  • Low Illyanassa density – colonization by Ampeleisca tube building amphipod – exclude Illyanassa
  • Selective deposit feeding produces fine sediments, tubes create topo diversity, promotes colonization by polychaetes
  • Winter storms, destabilize Ampelisca mats
  • Illyanass recruits in spring,
biological factors
Biological factors
  • Competition
  • direct displacement – rare ( no hard surface to push against) , no colonials
  • Food/space – evidence form regular spacing of individuals
  • interference- Levinton 1977
  • Direct: Active Bivalve Yoldia limulata disrupts burrows of less mobile Solemaya velum; Illyanassa and Ampleisca
indirect more common
Indirect : more common
  • Burrowing DF – muddy sand w/high [OM]
  • Where DF present in high no. SF absent
  • DF burrow, fecal material, create loose surface layers, unstable, easily resuspended
  • Clogs SF feeding
  • Buries SF larvae, DF larvae OK
  • Exclusion of one trophic group by another
rhoads and young 1970
Rhoads and Young 1970
  • Reworked sediments by 3 sp DF clams, Yoldia, Nucula, Macoma – excludes DF
  • Soft sediment animals affect the sediment they live in
  • Functional groups – animals that use/affect the environment in the same way
    • Trophic groups
    • Sediment stabilizers/destabilizers
types of organisms
Types of organisms
  • Sediment stabilizers
    • Organisms that secrete mucous or otherwise bind sediment; roots
    • Amphipods, phoronid worms, anemones, polychaetes
  • Sediment destabilizers (bioturbators)
    • motile or sedentary organisms who cause sediments to move
    • Sea cucumbers, mobile clams, whelks
Deposit feeders produce fluid fecal rich surface
  • Easily resuspended by low velocity currents
  • Instability might interfere with suspension feeders:
    • Experiments with Mercenaria in trays above bottom
    • Deposit feeder larvae not affected
trophic group amensalism
Trophic Group Amensalism
  • Interaction between two trophic groups in which one group is inhibited while the other is not
    • Inhibitors = deposit feeders; exclude suspension feeders
    • Physical instability of the sediment – clogs filters, buries newly settled suspension feeder larvae/juveniles; can’t maintain life position; disturbed or eaten by deposit feeders
rhodes and young 1971
Rhodes and Young 1971
  • Molpadiaoolotica – large, high density, sedentary, silt-clay mud, heads down DF
  • Ingest sediment at depth. Deposit loose fecal matter, form mounds
  • Reworking produces loose high water content easily susp. sediment
  • Areas between – highly unstable
  • Cones – stable, fecal pellets, bound material

attracts SF polychaete Euchone, other SF tube builders

  • SF tube builders stabilize sediment, extend downwards into substrate
  • Stabilize cones, prevent resuspnsion attract more tube SF
  • High tube density prevent settlement of large DF/ burrowers – can’t penetrate
  • Indirect restriction – competitive interference
  • Also filter out and prey on larvae of DF
coexistence is possible
Coexistence is possible
  • SF prefer more sandy areas – firmer, easier to build sfc tubes
  • Sand: DF not favored, low [OM], difficult to burrow
  • Areas where both can live – sharp boundaries but no physical differences
  • Patches – removal of residents (rays, storms)
  • Little asexual reproduction - colonize by larval recruitment or adult immigration
woodin 1976
Woodin 1976

Suggests there are 3 major functional groups:

  • Mobile (burrowing) deposit feeders
  • Suspension feeders
  • Tube builders

None have overlapping distributions – why?

adult larval interactions
Adult-larval interactions
  • Deposit feeders – change nature of sediment (trophic group amensalism), feed at surface
  • Suspension feeders – consume larvae while filtering
  • Tube builders – dense assemblage creates mat that larvae can’t penetrate; feed at surface
leads to
Leads to:
  • Strong dominance by year classes
  • Inhibition model of succession – multiple stable states

Ilyanassa (Nassarius) – mud snail, mobile DF

Ampelisca – amphipod, tube builder

Sand vs Mud


Sediments – 3D

  • Refuge form non-digging predators
  • Ability to divide resource and avoid competition
woodin predator trophic types
Woodin – predator trophic types
  • Surface –, juveniles vulnerable, affect size classes., esp those with refuge in size/depth
  • Browsers – nippers, rob energy
  • Burrowers – “weasel” predators (nemerteans, Pisasterbrevispinis)
  • Digging – excavate holes, change sediments, indiscriminate
  • Infaunal – burrowing nemerteans, polychaetes
caging results
Caging Results:
  • Virnstein 1977– crabs/epifaunal or sfc predators: change in numbers but not composition
  • Ambrose 1991 – infaunal – reduce infaunal populations, eat other predators, multiple layers of predators
cage results overall removal of predators
Cage results overall – removal of predators
  • Increase in total density
  • Increase in species richness
  • No tendency for competitive exclusion
why no competitive exclusion
Why No Competitive Exclusion?
  • Reduced opportunity for interference competition
vertical distribution
Vertical distribution
  • Competition for food and space SF and DF
  • Subtidal – food abundant – detritus
  • SF – partition space by depth, feeding structure (callianassa)
  • DF – feed at different levels
  • Peterson 1977
    • –removal of some sp from a depth level – increase in abundance of other sp at that strata – competition
    • Adding sp to a depth level caused emigration by others – vertical spacing and maintain density
why no competitive exclusion86
Why No Competitive Exclusion?
  • Reduced opportunity for interference competition
  • Extreme importance of adult-larval interactions
why no competitive exclusion88
Why No Competitive Exclusion?
  • Reduced opportunity for interference competition
  • Extreme importance of adult-larval interactions
  • Developmental plasticity of marine invertebrates
  • Lack of clear competitive dominant
caging artifacts
Caging Artifacts
  • How could these change the results?
wilson 1991
Wilson 1991
  • No evidence for both predation and competition affecting benthic community structure
  • No evidence for a competitive dominant in any soft bottom system
  • Can’t fully predict effects of predation or competition
  • Lack knowledge of growth, life spans, trophic types, pop dynamics , esp DF
  • No unifying theroy of community organization for sof bottom envtsd
multiple stable states
Multiple Stable States
  • Long term stability – eg Molpadia
  • Cyclic oscillation – Mills – Illynassa – Ampelisca, biological and physical factors
  • Multi- year long term – Baltic - alternating states affected by variable recruitment
  • Pontoporeia affinis – Macoma baltica
  • High Pontoporeia keeps out Macoma, poor year for Pontiporea allows Macoma, keeps out Pontoporea
  • Predators affects r selected species
recruitment dynamics
Recruitment Dynamics
  • Loss of larvae in the water column
  • Larvae as passive particles
  • Larval site selection
  • Adult-larval interactions
  • Meiofauna-macrofauna interactions
meiofauna macrofauna interactions watzin 1983
Meiofauna – Macrofauna Interactions (Watzin 1983)
  • Larval/Juvenile macrofauna are the same size meiofauna (temporary meiofauna)
  • Among the meiofauna are potential predators and competitors
meiofauna macrofauna interactions watzin 198397
Meiofauna – Macrofauna Interactions (Watzin 1983)
  • Manipulations in small boxes
    • Increased densities of turbellarian predators
    • Increased densities of “other meiofauna” – potential competitors
  • Exposed to recruitment for one week
    • Macrofauna larvae avoid treatments, or lower survival of juveniles after settlement
  • Must survive the “meiofauna bottleneck” – escape in size
other roles of meiofauna
Other Roles of Meiofauna
  • Meiofauna as food for deposit feeders
  • Meiofauna stimulate bacterial productivity
    • Speed break-down of detritus
    • Ingest bacteria – turnover
    • Mucus – release of DOM
  • Trophic group amensalism
  • Disturbance
  • Predation
  • Competition
  • Recruitment