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BENTHOS
Benthos: Definitions
– Epifauna: live on or are associated with the benthic 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, sm. amphipods)– Macrofauna: animals > 0.5 mm in size: most
familiar kinds of animals (crabs, shrimp, starfish and most mollusks)
Feeding strategies
• 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- and hard-bottom benthic communities
• Soft: little ‘relief’: ripple marks, worm tubes, fecal mounds: some differences in sediment grain size: fewer inds. And 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
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
Distribution and biomass of benthos
The Intertidal: Where the Benthos is Most Abundant
• Biomass in intertidal= 10X that of 200 m depth and several thousand that of 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 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
Benthic Biomass in relation to distance from coast and depth
Where the food comes from
Soft Sediment Communities
• Types of soft-bottom habitats
• Role of disturbance in regulating community structure
• 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 canyons
Deep seafloor
Shallow water/Shelf
Latitudinal Diffs.
Temp. = sand
Tropic. = mud
Polar. = Gravel (Arctic w/ riverine mud)
Sandy shores/beaches
Muddy shores/bays, estuaries, and lagoons
Nearshore benthic habitats (0-200 m)
Benthic diatoms
Foraminiferans
Meiofauna (few mm)
Harpacticoid copepods
polychaete worms
crustaceans
Macrofauna (mm-cm)
pycnogonids heart urchins
brittle stars bivalves
Macrofauna (mm-cm)
Biodiversity varies with depth, sediment type and biotic factors
Infaunal community
“Patchiness” is the rule
2. Physical factors: disturbance (biotic, physical, and anthropogenic)
1. Biotic interactions: predation, competition, & facilitation
Community patterns and structureTemperate/tropical Polar
Predators have a big effect on community composition
grey whales
walrus
Megafauna (cm-m)
Benthic Predators
Caging Studies
Effects of predator exclusion on the abundance of macrofaunal molluscs, worm and crustaceans
General results:1) cages have up to
500 x density2) more infaunal spp.
in cages3) no dominance by
any single species
Direct and indirect effects of predation in soft-sediment food webs
Life-history groups
Capitella captitata
Succession
Important classification for understanding effects of disturbance
Bioturbation
BURROWING SHRIMP
CallianassaBurrows of Callianassa
fecal strandsfrom polychaetes
Upogebia- anotherburrowing shrimp
Upogebia BURROW
More Bioturbators
Burrowing holothurianHarpacticoid copepod
Oligochaete: Paranais Polychaete: Nereis
The lugworm (Arenicola) and its burrow/fecal castings
More Sediment Modifiers
Facilitation
Amensalism
• Competition has a big effect on community structure- depth distribution, population distribution, abundance, and dynamics
• Competition usually for food with big effects on growth, reproduction, and survival. Density-dependence common
•Competition in a 3-d environment: rarely for space
Competition can be important in soft-sediment communities
The intermediate disturbance hypothesis
Would you expect the intermediate disturbance hypothesis to explain diversity
patterns in soft sediments?
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)
Agent of disturbance
Waves and currents
Water-borne material (sediment, logs, rocks)
Ice
Direct impacts on organisms and SubstrateSessile organisms
detached or brokenMobile animals displaced,
injured, or killedSubstrate overturnedSediment eroded
Organisms abraded, buried, crushed or detached
Organisms abraded, detachedSediment and organismsexcavated and displaced
Habitat or assemblages affectedMost, declines with depth
Most
Rocky intertidal and subtidal, Soft sediment, Seagrass beds, Salt mashes (high lat)
PHYSICAL DISTURBANCES
Agent of disturbance
Extended aerial exposure
Temperature extremes
Salinity stress and freshwater flooding
Anoxia
Direct impacts on organisms and SubstrateOrganisms 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
Habitat or assemblages effectedRocky intertidalCoral reefsSeagrass beds
Tide pools, Kelp forests, Coral reefs
Rocky intertidal,Salt marsh, Coral reef, Mangrove,Soft sediment
Soft sediment, estuaries, semienclosed seas
PHYSICAL DISTURBANCES
Agent of disturbance
Landslides, tectonic events
Lava flow, volcanic ash
Fire, lightening strikes,
Meteorite impacts
Direct impacts on organisms and SubstrateOrganisms 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
Habitat or assemblages effectedRocky intertidal and subtidal,Soft sediment, slope and rise,vents
Rocky intertidal and subtidal, Seagrass beds, Coral reefs, vents
Salt marsh, Mangrove
Global (mass extinctions)
PHYSICAL DISTURBANCES
Agent of disturbance
Accumulation of plant or animal material (wrack and carcasses)
Algal whiplash
Bioturbation
Sediment excavation by predators
Direct impacts on organisms and SubstrateOrganisms smothered, buried and shaded, chemistry
Organisms abraded, recruits vulnerable
Organisms buried, sediment load interferes with feeding
Organisms displaced, uprooted, and buriedAccumulation of debris
Habitat or assemblages effectedSalt marsh, Seagrass beds,Soft sediment
Rocky intertidal and subtidal
Soft sediment, Seagrass beds
Soft sedimentsSeagrass beds
BIOLOGICAL DISTURBANCES
Agent of disturbance
Haul out, trampling
Red tide
Direct impacts on organisms and SubstrateOrganisms smothered, buried, smashed
Organisms suffocated and poisoned
Habitat or assemblages effectedRocky intertidal
Soft sediment, coastal environments
BIOLOGICAL DISTURBANCES