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