Soft Substrate CommunitiesSoft Substrate Communities

soft sediment = substrate of soft sediment = substrate of sedimentary particles; sedimentary particles; uncemented, unconsolidated uncemented, unconsolidated or loosely consolidatedor loosely consolidated

epifauna epifauna – on the surface– on the surfaceinfauna infauna – in the sediment– in the sediment

Physical EnvironmentPhysical Environment

1.1. Grain size - particle sizeGrain size - particle size

high energy = large grain size; sandhigh energy = large grain size; sand

low energy = small grain size; mudlow energy = small grain size; mud

median grain size – sandy silt, silty median grain size – sandy silt, silty sandsand

sortingsorting – range of particle sizes, – range of particle sizes, biological sortingbiological sorting

Substrate mobilitySubstrate mobility– influenced by animals – burrowing, influenced by animals – burrowing,

binding in tubesbinding in tubes– cohesiveness – microbes, mucuscohesiveness – microbes, mucus

Interstitial spaceInterstitial space – space between – space between grains, “pores”grains, “pores”– affects water drainageaffects water drainage– diffusion of chemicalsdiffusion of chemicals

2.2. Organic MatterOrganic Matter- % organic matter- % organic matter- substrate for microbial - substrate for microbial decomposition, detritus feedersdecomposition, detritus feeders

3.3. Oxidation-reduction stateOxidation-reduction stateredox potential discontinuity layer redox potential discontinuity layer (RPD)(RPD)

- measured by electrode (Eh)- measured by electrode (Eh)Above RPD – oxygen presentAbove RPD – oxygen presentBelow RPD – oxygen absentBelow RPD – oxygen absent

Chemosynthetic bacteria – use H2S

Sulfate-reducing bacteria – produce H2S (fermentation)

• Organisms affect the depth of the Organisms affect the depth of the RPD layerRPD layer

in irrigated tubes, extend RPD in irrigated tubes, extend RPD into into sedimentssediments

• Organisms must adapt to anaerobic Organisms must adapt to anaerobic conditionsconditions– Bring oxygenated water downBring oxygenated water down

– Tolerate HTolerate H22SS

4.4. Light – when present, plants Light – when present, plants presentpresent

- benthic diatoms- benthic diatoms

- macroalgae- macroalgae

- seagrasses- seagrasses

Size of infaunal organismsSize of infaunal organisms

•Macrofauna: Macrofauna: >0.5 mm>0.5 mm

•Meiofauna: Meiofauna: 0.5-0.062 0.5-0.062 mmmm

•Microfauna: Microfauna: < 0.062 < 0.062 mmmm

Clams

Snails

Suspension feeders

Trophic StructureTrophic Structure

• Suspension Feeders (filter feeders)Suspension Feeders (filter feeders)

- primary food = plankton- primary food = plankton

- generalists, size selection by filter- generalists, size selection by filter

• Deposit FeedersDeposit Feeders- animal that feeds by consuming animal that feeds by consuming

particles in or on the substrateparticles in or on the substrate- ““detritivore”detritivore”

Types of deposit feedersTypes of deposit feeders

• Surface deposit feedersSurface deposit feeders

• Burrowing or deepBurrowing or deep

Microbial Stripping Theory Microbial Stripping Theory – – deposit feeders don’t digest deposit feeders don’t digest detritus, just digest detritus, just digest microorganisms on the detritus microorganisms on the detritus and sediment particlesand sediment particles

Fenchel:Fenchel: - - low assimilation efficiency detritus low assimilation efficiency detritus

(1-10%)(1-10%)

- high assimilation efficiency microbes - high assimilation efficiency microbes (40-80%)(40-80%)

Logical argument for microbial Logical argument for microbial strippingstripping

• Composition of the detritusComposition of the detritus

- sources, age- sources, age

- temporal variation- temporal variation

• Digestion detritus vs microbesDigestion detritus vs microbes

• Constancy and quality of microbesConstancy and quality of microbes- microbial colonizationmicrobial colonization

- protein- protein

Renewal rates - microbesRenewal rates - microbes

• Animal must not ingest again until Animal must not ingest again until microbes recolonizemicrobes recolonize

• pelletizationpelletization

Predators

Physical or biological? Physical or biological?

• Soft bottom benthic communities Soft bottom benthic communities structured by ???structured by ???

• Expt evidenceExpt evidence

Physical – Physical –

• Oliver 1979Oliver 1979– Subtidal zoned on gradient of wave Subtidal zoned on gradient of wave

energy energy – < 14m – regular disturbance, small < 14m – regular disturbance, small

molbile crustaceansmolbile crustaceans– > stable, tube polychaetes> stable, tube polychaetes

Both biological and physicalBoth biological and physical• Mills 1969 – sandy area, low biomass, Mills 1969 – sandy area, low biomass,

density of IFdensity of IF

• Illyanassa – mech disturbance by snailsIllyanassa – mech disturbance by snails

• Low Illyanassa density – colonization by Low Illyanassa density – colonization by Ampeleisca tube building amphipod – Ampeleisca tube building amphipod – exclude Illyanassaexclude Illyanassa

• Selective deposit feeding produces fine Selective deposit feeding produces fine sediments, tubes create topo diversity, sediments, tubes create topo diversity, promotes colonization by polychaetes promotes colonization by polychaetes

• Winter storms, destabilize Ampelisca Winter storms, destabilize Ampelisca matsmats

• Illyanass recruits in spring, Illyanass recruits in spring,

Biological factors Biological factors • Competition Competition

• direct displacement – rare ( no hard direct displacement – rare ( no hard surface to push against) , no colonialssurface to push against) , no colonials

• Food/space – evidence form regular Food/space – evidence form regular spacing of individualsspacing of individuals

• interference- Levinton 1977interference- Levinton 1977

• Direct: Active Bivalve Yoldia limulata Direct: Active Bivalve Yoldia limulata disrupts burrows of less mobile Solemaya disrupts burrows of less mobile Solemaya velum; Illyanassa and Ampleiscavelum; Illyanassa and Ampleisca

Indirect : more commonIndirect : more common• Burrowing DF – muddy sand w/high [OM]Burrowing DF – muddy sand w/high [OM]

• Where DF present in high no. SF absentWhere DF present in high no. SF absent

• DF burrow, fecal material, create loose DF burrow, fecal material, create loose surface layers, unstable, easily surface layers, unstable, easily resuspendedresuspended

• Clogs SF feedingClogs SF feeding

• Buries SF larvae, DF larvae OKBuries SF larvae, DF larvae OK

• Exclusion of one trophic group by Exclusion of one trophic group by another another

Rhoads and Young 1970Rhoads and Young 1970• Reworked sediments by 3 sp DF clams, Reworked sediments by 3 sp DF clams,

Yoldia, Nucula, Macoma – excludes DFYoldia, Nucula, Macoma – excludes DF

• Soft sediment animals affect the Soft sediment animals affect the sediment they live insediment they live in

• Functional groups – animals that Functional groups – animals that use/affect the environment in the use/affect the environment in the same waysame way– Trophic groupsTrophic groups– Sediment stabilizers/destabilizersSediment stabilizers/destabilizers

Types of organismsTypes of organisms• Sediment stabilizersSediment stabilizers

– Organisms that secrete mucous or Organisms that secrete mucous or otherwise bind sediment; rootsotherwise bind sediment; roots

– Amphipods, phoronid worms, Amphipods, phoronid worms, anemones, polychaetesanemones, polychaetes

• Sediment destabilizers (bioturbators)Sediment destabilizers (bioturbators)– motile or sedentary organisms who motile or sedentary organisms who

cause sediments to movecause sediments to move– Sea cucumbers, mobile clams, whelksSea cucumbers, mobile clams, whelks

• Deposit feeders produce fluid fecal Deposit feeders produce fluid fecal rich surfacerich surface

• Easily resuspended by low velocity Easily resuspended by low velocity currentscurrents

• Instability might interfere with Instability might interfere with suspension feeders:suspension feeders:– Experiments with Experiments with Mercenaria Mercenaria in trays in trays

above bottomabove bottom– Deposit feeder larvae not affectedDeposit feeder larvae not affected

Trophic Group AmensalismTrophic Group Amensalism

• Interaction between two trophic Interaction between two trophic groups in which one group is groups in which one group is inhibited while the other is notinhibited while the other is not– Inhibitors = deposit feeders; exclude Inhibitors = deposit feeders; exclude

suspension feederssuspension feeders– Physical instability of the sediment – Physical instability of the sediment –

clogs filters, buries newly settled clogs filters, buries newly settled suspension feeder larvae/juveniles; can’t suspension feeder larvae/juveniles; can’t maintain life position; disturbed or eaten maintain life position; disturbed or eaten by deposit feedersby deposit feeders

Rhodes and Young 1971Rhodes and Young 1971• Molpadia oolotica – large, high Molpadia oolotica – large, high

density, sedentary, silt-clay mud, density, sedentary, silt-clay mud, heads down DFheads down DF

• Ingest sediment at depth. Deposit Ingest sediment at depth. Deposit loose fecal matter, form moundsloose fecal matter, form mounds

• Reworking produces loose high water Reworking produces loose high water content easily susp. sedimentcontent easily susp. sediment

• Areas between – highly unstable Areas between – highly unstable

• Cones – stable, fecal pellets, bound Cones – stable, fecal pellets, bound materialmaterial

• attracts SF polychaete Euchone, other attracts SF polychaete Euchone, other SF tube buildersSF tube builders

• SF tube builders stabilize sediment, SF tube builders stabilize sediment, extend downwards into substrateextend downwards into substrate

• Stabilize cones, prevent resuspnsion Stabilize cones, prevent resuspnsion attract more tube SFattract more tube SF

• High tube density prevent settlement of High tube density prevent settlement of large DF/ burrowers – can’t penetratelarge DF/ burrowers – can’t penetrate

• Indirect restriction – competitive Indirect restriction – competitive interferenceinterference

• Also filter out and prey on larvae of DFAlso filter out and prey on larvae of DF

Coexistence is possibleCoexistence is possible• SF prefer more sandy areas – firmer, SF prefer more sandy areas – firmer,

easier to build sfc tubeseasier to build sfc tubes

• Sand: DF not favored, low [OM], difficult Sand: DF not favored, low [OM], difficult to burrowto burrow

• Areas where both can live – sharp Areas where both can live – sharp boundaries but no physical differences boundaries but no physical differences

• Patches – removal of residents (rays, Patches – removal of residents (rays, storms)storms)

• Little asexual reproduction - colonize by Little asexual reproduction - colonize by larval recruitment or adult immigrationlarval recruitment or adult immigration

Woodin 1976Woodin 1976

Suggests there are 3 major functional Suggests there are 3 major functional groups:groups:

• Mobile (burrowing) deposit feedersMobile (burrowing) deposit feeders

• Suspension feedersSuspension feeders

• Tube buildersTube builders

None have overlapping distributions – None have overlapping distributions – why?why?

Adult-larval interactionsAdult-larval interactions

• Deposit feeders – change nature of Deposit feeders – change nature of sediment (trophic group sediment (trophic group amensalism), feed at surfaceamensalism), feed at surface

• Suspension feeders – consume larvae Suspension feeders – consume larvae while filteringwhile filtering

• Tube builders – dense assemblage Tube builders – dense assemblage creates mat that larvae can’t creates mat that larvae can’t penetrate; feed at surfacepenetrate; feed at surface

Leads to:Leads to:

• Strong dominance by year classesStrong dominance by year classes

• Inhibition model of succession – Inhibition model of succession – multiple stable states multiple stable states

IlyanassaIlyanassa ( (NassariusNassarius) – mud snail, ) – mud snail, mobile DFmobile DF

AmpeliscaAmpelisca – amphipod, tube builder – amphipod, tube builder

Sand vs MudSand vs Mud

Role of Predation and Role of Predation and Competition in Soft Sediment Competition in Soft Sediment

CommunitiesCommunities

• Sediments – 3DSediments – 3D

• Refuge form non-digging predatorsRefuge form non-digging predators

• Ability to divide resource and avoid Ability to divide resource and avoid competitioncompetition

Woodin – predator trophic Woodin – predator trophic typestypes• Surface –, juveniles vulnerable, affect Surface –, juveniles vulnerable, affect

size classes., esp those with refuge in size classes., esp those with refuge in size/depthsize/depth

• Browsers – nippers, rob energyBrowsers – nippers, rob energy

• Burrowers – “weasel” predators Burrowers – “weasel” predators (nemerteans, Pisaster brevispinis) (nemerteans, Pisaster brevispinis)

• Digging – excavate holes, change Digging – excavate holes, change sediments, indiscriminate sediments, indiscriminate

• Infaunal – burrowing nemerteans, Infaunal – burrowing nemerteans, polychaetespolychaetes

Large predator/disturbersLarge predator/disturbers

Caging Results:Caging Results:

• Virnstein 1977– crabs/epifaunal or sfc Virnstein 1977– crabs/epifaunal or sfc predators: change in numbers but predators: change in numbers but not compositionnot composition

• Ambrose 1991 – infaunal – reduce Ambrose 1991 – infaunal – reduce infaunal populations, eat other infaunal populations, eat other predators, multiple layers of predators, multiple layers of predatorspredators

Cage results overall – Cage results overall – removal of predatorsremoval of predators

• Increase in total densityIncrease in total density

• Increase in species richnessIncrease in species richness

• No tendency for competitive No tendency for competitive exclusionexclusion

Why No Competitive Why No Competitive Exclusion?Exclusion?

• Reduced opportunity for interference Reduced opportunity for interference competitioncompetition

Vertical distributionVertical distribution• Competition for food and space SF and Competition for food and space SF and

DFDF

• Subtidal – food abundant – detritusSubtidal – food abundant – detritus

• SF – partition space by depth, feeding SF – partition space by depth, feeding structure (callianassa)structure (callianassa)

• DF – feed at different levels DF – feed at different levels

• Peterson 1977 Peterson 1977 – ––removal of some sp from a depth level – removal of some sp from a depth level –

increase in abundance of other sp at that increase in abundance of other sp at that strata – competitionstrata – competition

– Adding sp to a depth level caused Adding sp to a depth level caused emigration by others – vertical spacing and emigration by others – vertical spacing and maintain densitymaintain density

Why No Competitive Why No Competitive Exclusion?Exclusion?

• Reduced opportunity for interference Reduced opportunity for interference competitioncompetition

• Extreme importance of adult-larval Extreme importance of adult-larval interactionsinteractions

Why No Competitive Why No Competitive Exclusion?Exclusion?

• Reduced opportunity for interference Reduced opportunity for interference competitioncompetition

• Extreme importance of adult-larval Extreme importance of adult-larval interactionsinteractions

• Developmental plasticity of marine Developmental plasticity of marine invertebratesinvertebrates

• Lack of clear competitive dominantLack of clear competitive dominant

Caging ArtifactsCaging Artifacts

• How could these change the How could these change the results?results?

Wilson 1991 Wilson 1991 • No evidence for both predation and No evidence for both predation and

competition affecting benthic competition affecting benthic community structurecommunity structure

• No evidence for a competitive dominant No evidence for a competitive dominant in any soft bottom systemin any soft bottom system

• Can’t fully predict effects of predation or Can’t fully predict effects of predation or competitioncompetition

• Lack knowledge of growth, life spans, Lack knowledge of growth, life spans, trophic types, pop dynamics , esp DFtrophic types, pop dynamics , esp DF

• No unifying theroy of community No unifying theroy of community organization for sof bottom envtsdorganization for sof bottom envtsd

Multiple Stable StatesMultiple Stable States• Long term stability – eg MolpadiaLong term stability – eg Molpadia

• Cyclic oscillation – Mills – Illynassa – Cyclic oscillation – Mills – Illynassa – Ampelisca, biological and physical factors Ampelisca, biological and physical factors

• Multi- year long term – Baltic - alternating Multi- year long term – Baltic - alternating states affected by variable recruitmentstates affected by variable recruitment

• Pontoporeia affinis – Macoma balticaPontoporeia affinis – Macoma baltica

• High Pontoporeia keeps out Macoma, poor High Pontoporeia keeps out Macoma, poor year for Pontiporea allows Macoma, keeps year for Pontiporea allows Macoma, keeps out Pontoporea out Pontoporea

• Predators affects r selected species Predators affects r selected species

• END END

Recruitment DynamicsRecruitment Dynamics

• Loss of larvae in the water columnLoss of larvae in the water column

• Larvae as passive particlesLarvae as passive particles

• Larval site selectionLarval site selection

• Adult-larval interactionsAdult-larval interactions

• Meiofauna-macrofauna interactionsMeiofauna-macrofauna interactions

Meiofauna – Macrofauna Meiofauna – Macrofauna Interactions (Watzin 1983)Interactions (Watzin 1983)

• Larval/Juvenile macrofauna are the Larval/Juvenile macrofauna are the same size meiofauna (temporary same size meiofauna (temporary meiofauna)meiofauna)

• Among the meiofauna are potential Among the meiofauna are potential predators and competitorspredators and competitors

Meiofauna – Macrofauna Meiofauna – Macrofauna Interactions (Watzin 1983)Interactions (Watzin 1983)

• Manipulations in small boxesManipulations in small boxes– Increased densities of turbellarian Increased densities of turbellarian

predatorspredators– Increased densities of “other meiofauna” – Increased densities of “other meiofauna” –

potential competitorspotential competitors

• Exposed to recruitment for one weekExposed to recruitment for one week– Macrofauna larvae avoid treatments, or Macrofauna larvae avoid treatments, or

lower survival of juveniles after settlementlower survival of juveniles after settlement

• Must survive the “meiofauna Must survive the “meiofauna bottleneck” – escape in sizebottleneck” – escape in size

Meiofauna as Food for Bottom-Meiofauna as Food for Bottom-feeding Fishesfeeding Fishes

Other Roles of MeiofaunaOther Roles of Meiofauna

• Meiofauna as food for deposit Meiofauna as food for deposit feedersfeeders

• Meiofauna stimulate bacterial Meiofauna stimulate bacterial productivityproductivity– Speed break-down of detritusSpeed break-down of detritus– Ingest bacteria – turnover Ingest bacteria – turnover – Mucus – release of DOMMucus – release of DOM

ConclusionsConclusions

• Trophic group amensalism Trophic group amensalism

• DisturbanceDisturbance

• PredationPredation

• CompetitionCompetition

• RecruitmentRecruitment