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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 • 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 • Macrofauna: >0.5 mm • Meiofauna: 0.5-0.062 mm • Microfauna: < 0.062 mm
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”