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  1. Benthos

  2. Benthos: Definitions • Epifauna: live on or are associated with the surface • Infauna: live within the substrate • Microfauna: animals <0.1 mm in size (e.g. protozoa/bacteria) • Meiofauna: animals <0.5 mm in size: “interstitial” (e.g. nematodes, small amphipods) • Macrofauna: animals > 0.5 mm in size: most familiar kinds of animals (crabs, shrimp, starfish and mollusks)

  3. Benthic Feeding Modes Deposit feeders: feed on organically enriched sediments: continuous “reworking” of sediments to extract nutrients: analogous to earthworms: can live in very fine sediments Suspension feeders: filtering devices or mucus nets collect detritus or plankton: need coarser sediments or hard bottom Grazers/predators/scavengers

  4. Soft Bottom Communities

  5. Soft sediments: Modes of feeding

  6. Soft- versus hard-bottom benthic communities Soft: little ‘relief’: ripple marks, worm tubes, fecal mounds: some differences in sediment grain size: fewer inds. Fewer infauna and more epifauna in sand: more individuals in mud and most are deposit feeders Hard: more ‘relief” and more habitat diversity: increase in suspension feeders

  7. Soft Bottom Benthic Communities

  8. Abiotic Factors Affecting Benthos (to 200 m depth)) • Wave action: influence distribution of sediments and physically affect animals • Sediments: vary according to wave action (particle size sorting): terrigenous and marine origin (“allochthonous” and “autochthonous”): fine clays go to deeps • Salinity and temperature: FW influences; more thermal variability

  9. Benthic Biomass in relation to distance from coast and depth

  10. The Intertidal: Where the Benthos is Most Abundant • Biomass in intertidal= 10X that of 200 m depth and several thousand times that of the abyss! • Not without a cost: wave shock; desiccation; cold; osmotic issues; and land predators. But at high tide: plenty of O2; nutrients; light; and wastes washed away. • More vertical relief and habitat diversity= more species diversity

  11. Reproduction and Dispersal • Broadcast spawning vs. brooding- varying amounts of energy invested, and value of dispersal • Where to settle? 1) chemical attractants: settle near your own kind 2) bottom types: settle in appropriate substrates

  12. Patterns of Diversity with Depth

  13. Soft Sediment Communities • Community structure • Types of soft-bottom habitats • Effects of predation, competition and facilitation

  14. Four groups of dominant macrofauna in soft bottoms Class Polychaeta: most numerous: tube-building and burrowing Subphylum Crustacea: ostracods, amphipods, isopods, tanaids, mysids, small decapods Phylum Mollusca: burrowing bivalves and scaphopods, gastropods at surface Phylum Echinodermata: brittle stars, heart urchins, sand dollars, sea cukes

  15. Submarine canyons Shallow water/Shelf Deep seafloor Latitudinal Diffs. Temp. = sand Tropic. = mud Polar. = Gravel (Arctic w/ riverine mud)

  16. Sandy shores/beaches

  17. Muddy shores/bays, estuaries, and lagoons

  18. Nearshore benthic habitats (0-200 m)

  19. Meiofauna (few mm) Benthic diatoms Harpacticoid copepods Foraminiferans

  20. Macrofauna (mm-cm) polychaete worms crustaceans

  21. Macrofauna (mm-cm) heart urchins pycnogonids brittle stars bivalves

  22. grey whales walrus Megafauna (cm-m) Predators have big effects on community composition

  23. Biodiversity varies with depth, sediment type and biotic factors

  24. Community patterns and structure Temperate/tropical Polar

  25. Benthic Predators

  26. Caging Studies

  27. Effects of predator exclusion on the abundance of macrofaunal molluscs, worm and crustaceans • General results: • Caged areas have up to 500 x density • more infaunal spp. in cages • no dominance by any single species

  28. Direct and indirect effects of predation in soft-sediment food webs

  29. Succession Capitella captitata Important classification for understanding effects of disturbance Life-history groups

  30. Bioturbation Upogebia- another burrowing shrimp Upogebia BURROW fecal strands from polychaetes Burrows of Callianassa BURROWING SHRIMP Callianassa

  31. More Bioturbators Harpacticoid copepod Burrowing holothurian Polychaete: Nereis Oligochaete: Paranais

  32. The lugworm (Arenicola) and its burrow/fecal castings

  33. Amensalism Facilitation More Sediment Modifiers

  34. Competition can be important in soft-sediment communities • Competition in a 3-d environment: rarely for space • Competition usually for food with big effects on growth, reproduction, and survival. Density-dependence common • Competition has a big effect on community structure- depth distribution, population distribution, abundance, and dynamics

  35. The intermediate disturbance hypothesis

  36. Types and scales of disturbances in soft-sediments

  37. Disturbance caused by eutrophication

  38. Iceberg scour disturbance

  39. On frequently scoured seafloor, what functional groups would you expect?

  40. Re-colonization • Different mechanisms: • Vegetative regrowth of survivors • Recruitment from propagules (including spore and seed bank) • Influence of patch characteristics: • Size and shape • Substrate characteristics (e.g. rock or sediment types, topographic complexity, biogenic structures) • Patch location (environmental conditions and proximity to propagule sources) • Timing of patch creation (availability of propagules and differences in conditions)

  41. PHYSICAL DISTURBANCES Habitat or assemblages affected Most, declines with depth Most Rocky intertidal and subtidal, Soft sediment, Seagrass beds, Salt mashes (high lat) Agent of disturbance Waves and currents Water-borne material (sediment, logs, rocks) Ice Direct impacts on organisms and Substrate Sessile organisms detached or broken Mobile animals displaced, injured, or killed Substrate overturned Sediment eroded Organisms abraded, buried, crushed or detached Organisms abraded, detached Sediment and organisms excavated and displaced

  42. PHYSICAL DISTURBANCES Habitat or assemblages effected Rocky intertidal Coral reefs Seagrass beds Tide pools, Kelp forests, Coral reefs Rocky intertidal, Salt marsh, Coral reef, Mangrove, Soft sediment Soft sediment, estuaries, semienclosed seas Agent of disturbance Extended aerial exposure Temperature extremes Salinity stress and freshwater flooding Anoxia Direct impacts on organisms and Substrate Organisms injured or killed by desiccation, heat, UV Organisms injured or killed by heat or cold. Bleaching Organisms injured or killed by osmotic stress Organisms injured or killed by metabolic stress

  43. PHYSICAL DISTURBANCES Habitat or assemblages effected Rocky intertidal and subtidal, Soft sediment, slope and rise,vents Rocky intertidal and subtidal, Seagrass beds, Coral reefs, vents Salt marsh, Mangrove Global (mass extinctions) Agent of disturbance Landslides, tectonic events Lava flow, volcanic ash Fire, lightening strikes, Meteorite impacts Direct impacts on organisms and Substrate Organisms abraded, crushed, displaced, or smothered Organisms injured or killed by lava, smothered by ash Organisms injured or killed by heat Direct impact and climate change

  44. BIOLOGICAL DISTURBANCES Habitat or assemblages effected Salt marsh, Seagrass beds, Soft sediment Rocky intertidal and subtidal Soft sediment, Seagrass beds Soft sediments Seagrass beds Agent of disturbance Accumulation of plant or animal material (wrack and carcasses) Algal whiplash Bioturbation Sediment excavation by predators Direct impacts on organisms and Substrate Organisms smothered, buried and shaded, chemistry Organisms abraded, recruits vulnerable Organisms buried, sediment load interferes with feeding Organisms displaced, uprooted, and buried Accumulation of debris

  45. BIOLOGICAL DISTURBANCES Habitat or assemblages effected Rocky intertidal Soft sediment, coastal environments Agent of disturbance Haul out, trampling Red tide Direct impacts on organisms and Substrate Organisms smothered, buried, smashed Organisms suffocated and poisoned

  46. Infaunal communities: a Summary “Patchiness” is the rule 1. Biotic interactions: predation, competition, & facilitation 2. Physical factors: disturbance (biotic, physical,and anthropogenic)

  47. Where the food comes from