Transcript 2011 final Lecture 9-1 Benthos an d Soft sediment communities

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?