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Benthos 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) 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 Soft Bottom Communities Soft sediments: Modes of feeding 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 Soft Bottom Benthic Communities 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 Benthic Biomass in relation to distance from coast and depth 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 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 Patterns of Diversity with Depth Distribution and biomass of benthos Soft Sediment Communities • Community structure • Types of soft-bottom habitats • Effects of predation, competition and facilitation 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 Submarine cany Latitudinal Diffs. Temp. = sand Tropic. = mud Polar. = Gravel (Arctic w/ riverine mud) Deep seafloor Shallow water/Shelf Muddy shores/bays, estuaries, and lagoons Nearshore benthic habitats (0-200 m) Meiofauna (few mm) Benthic diatoms Harpacticoid copepods Foraminiferans Macrofauna (mm-cm) polychaete worms crustaceans Macrofauna (mm-cm) pycnogonids brittle stars heart urchins bivalves Megafauna (cm-m) grey whales walrus Predators have big effects on community composition Biodiversity varies with depth, sediment type and biotic factors Community patterns and structure Temperate/tropical Polar Benthic Predators Caging Studies Effects of predator exclusion on the abundance of macrofaunal molluscs, worm and crustaceans General results: 1) Caged areas have up to 500 x density 2) more infaunal spp. in cages 3) no dominance by any single species Direct and indirect effects of predation in soft-sediment food webs Life-history groups Important classification for understanding effects of disturbance Succession Capitella captitata Bioturbation Upogebia BURROW Upogebia- another burrowing shrimp fecal strands from polychaetes Burrows of Callianassa BURROWING SHRIMP Callianassa More Bioturbators Harpacticoid copepod Oligochaete: Paranais Burrowing holothurian Polychaete: Nereis The lugworm (Arenicola) and its burrow/fecal castings Tube feeding by polycheate, Arenicola Marina. Black arrows show water flow and open arrows show sediment flow. Sediment brought to anoxic area, digested and deposited at upper region of shaft Proboscis Gills More Sediment Modifiers Amensalism Facilitation 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 structuredepth distribution, population distribution, abundance, and dynamics Where the food comes from The intermediate disturbance hypothesis Types and scales of disturbances in soft-sediments Disturbance caused by eutrophication Iceberg scour disturbance On frequently scoured seafloor, what functional groups would you expect? 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) PHYSICAL DISTURBANCES Agent of disturbance Direct impacts on organisms and Substrate Habitat or assemblages affected Waves and currents Sessile organisms detached or broken Mobile animals displaced, injured, or killed Substrate overturned Sediment eroded Most, declines with depth Water-borne material (sediment, logs, rocks) Organisms abraded, buried, crushed or detached Most Ice Organisms abraded, detached Sediment and organisms excavated and displaced Rocky intertidal and subtidal, Soft sediment, Seagrass beds, Salt mashes (high lat) PHYSICAL DISTURBANCES Agent of disturbance Direct impacts on organisms and Substrate Habitat or assemblages effected Extended aerial exposure Organisms injured or killed by desiccation, heat, UV Rocky intertidal Coral reefs Seagrass beds Temperature extremes Organisms injured or killed by heat or cold. Bleaching Tide pools, Kelp forests, Coral reefs Salinity stress and freshwater flooding Organisms injured or killed by osmotic stress Rocky intertidal, Salt marsh, Coral reef, Mangrove, Soft sediment Anoxia Organisms injured or killed by metabolic stress Soft sediment, estuaries, semienclosed seas PHYSICAL DISTURBANCES Agent of disturbance Direct impacts on organisms and Substrate Habitat or assemblages effected Landslides, tectonic events Organisms abraded, crushed, displaced, or smothered Rocky intertidal and subtidal, Soft sediment, slope and rise,vents Lava flow, volcanic ash Organisms injured or killed by lava, smothered by ash Rocky intertidal and subtidal, Seagrass beds, Coral reefs, vents Fire, lightening strikes, Organisms injured or killed by heat Salt marsh, Mangrove Meteorite impacts Direct impact and climate change Global (mass extinctions) BIOLOGICAL DISTURBANCES Agent of disturbance Direct impacts on organisms and Substrate Habitat or assemblages effected Accumulation of plant or animal material (wrack and carcasses) Organisms smothered, buried and shaded, chemistry Salt marsh, Seagrass beds, Soft sediment Algal whiplash Organisms abraded, recruits vulnerable Rocky intertidal and subtidal Bioturbation Soft sediment, Organisms buried, sediment load interferes with feeding Seagrass beds Sediment excavation by predators Organisms displaced, uprooted, and buried Accumulation of debris Soft sediments Seagrass beds BIOLOGICAL DISTURBANCES Habitat or assemblages effected Agent of disturbance Direct impacts on organisms and Substrate Haul out, trampling Organisms smothered, buried, Rocky intertidal smashed Red tide Organisms suffocated and poisoned Soft sediment, coastal environments Infaunal communities: a Summary “Patchiness” is the rule 1. Biotic interactions: predation, competition, & facilitation 2. Physical factors: disturbance (biotic, physical, and anthropogenic) Would you expect the intermediate disturbance hypothesis to explain diversity patterns in soft sediments?