Physical Environment

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

4. 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

5. Substrate mobility • influenced by animals – burrowing, binding in tubes • cohesiveness – microbes, mucus Interstitial space – space between grains, “pores” • affects water drainage • diffusion of chemicals

6. 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

7. Chemosynthetic bacteria – use H2S Sulfate-reducing bacteria – produce H2S (fermentation)

8. 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

9. Light – when present, plants present - benthic diatoms - macroalgae - seagrasses

10. Size of infaunal organisms • Macrofauna: >0.5 mm • Meiofauna: 0.5-0.062 mm • Microfauna: < 0.062 mm

20. Clams

21. Snails

49. Suspension feeders

50. 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”