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 3

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 4

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 13

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

Sandy shores/beaches

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) heart urchins pycnogonids brittle stars bivalves

Biodiversity varies with depth, sediment type and biotic factors

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

Community patterns and structure Temperate/tropical Polar

Megafauna (cm-m) grey whales walrus Predators have a big effect on community composition

Benthic Predators

Caging Studies

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

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

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

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

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

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

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 structure- depth distribution, population distribution, abundance, and dynamics

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)

PHYSICAL DISTURBANCES 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 Habitat or assemblages affected Most, 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 Substrate Organisms injured or killed by desiccation, heat, UV by heat or cold. Bleaching by osmotic stress by metabolic stress 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

PHYSICAL DISTURBANCES 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 by heat Direct impact and climate change 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)

BIOLOGICAL 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 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 Habitat or assemblages effected Salt marsh, Seagrass beds, Soft sediment Rocky intertidal and subtidal Soft sediment, Seagrass beds Soft sediments Seagrass beds

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