Transcript 2008, final Lecture 11 Benthos an d Soft sediment communities

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)
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
Where the food comes from
Effects of predator
exclusion on the
abundance of
macrofaunal
molluscs, worm
and crustaceans
General results:
1) cages have up to
500 x density
2) more infaunal spp.
in cages
3) no dominance by
any single species
Soft Sediment Communities
• Types of soft-bottom habitats
• Role of disturbance in regulating
community structure
• Effects of predation, competition and
facilitation
Submarine canyo
Latitudinal Diffs.
Temp. = sand
Tropic. = mud
Polar. = Gravel (Arctic w/ riverine mud)
Deep seafloor
Shallow water/Shelf
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)
pycnogonids
brittle stars
heart urchins
bivalves
High biodiversity that 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
Predators have a
big effect on
community
composition
walrus
Caging Studies
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- another
burrowing shrimp
Upogebia BURROW
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
Gastropod: Hydrobia
Gastropod 2: Ilyanassa
Sediment modifiers
Ammensalism/mutualism
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
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
Direct impacts on
organisms and
Substrate
Habitat or
assemblages
effected
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
Anthropogenic disturbances
in soft sediment habitats
Oil spills
Exxon-Valdez oil spill
•Bleigh Reef in NPWS
Ecosystem level impacts
•42 million L of oil
•1990 km of coastline and
750 km southward
Prince William Sound, AK on 24 March 1989
•14 years of intensive study
Ecological impacts of the EVOS
•New understanding of long-term effects and recovery
processes. Ecosystem-based toxicology
•Before: short-term impact assessments and lab studies of
toxic effects
•First real ecosystem impact study
General conclusions:
1) Oil persisted beyond a decade in surprising amounts and toxic
forms because of the presence of soft-sediments
2) Oil significantly bioavailable to induce chronic biological exposure
3) Longterm effects at population level
Ecological impacts of the EVOS
3 major pathways of exposure & induction:
•Acute exposure to oil during spill and subsequent
negative health effects
•Chronic persistence of oil, bio-exposure, and population
impacts to species closely associated with shallow
sediments
•Indirect effects related to predator-prey relationships,
loss of habitat
Acute effects of spill
•Oil in fur, feathers, and ingested
•1000-2800 sea otters
•~250,000 seabirds
•302 harbor seals
•Mass mortality of macroalgae, benthic invertebrates
on shore from a combination toxicity, smothering, and
physical displacement caused by high pressure clean-up
Persistence of oil
•40-45% oil grounded in 1989 on 787 km of PWS beaches
•7-11% contaminated 1203 km of Gulf of AK coastline
•2% remained on beaches after 3.5 yrs (-0.87 per yr)
•Rates of dispersion and degradation diminished through time
•Suppressed by physical barriers to disturbance, oxygenation
and photolysis
•Oil trapped in sediments and mussel beds
Effects of chronic exposure
•Chronic exposure of sediment affiliated species
•Fish embryos exposed to partially weathered oil
•Multi-ringed PAHs toxic to pink salmon eggs at 1 ppb when
exposed for months
•Toxic to herring eggs when exposed for 16 days
•Reduced salmon and herring reproduction in many areas
Effects of chronic exposure
•Led to death from compromised health, growth, or
reproduction
•Lower growth rates of salmon = reduced survival
•Abnormal growth in herring and salmon caused by
endocrine disruptors = less fat
Cascades of indirect effects
•Two most important types of cascades
•Trophic cascades in which predators reduce abundance
of their prey which releases the preys food species from
control
•Provision of biogenic habitat by organisms that serve
as or creates important physical structure in environment
•Current Risk Assessment models used for projecting
biological injury to marine communities ignore indirect
effects
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
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
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
Deposit Feeders
Sponge
Bivalve
Amphipod
Bryozoan
Hydroid
Suspension feeders
Polychaete
Tunicate
Brittlestar
Barnacle
Anemone
PARALLEL BOTTOM
COMMUNITIES
FUNCTIONAL GROUPS
(or: bioturbators)
FEEDING IN AN INFAUNAL
CUCUMBER
PREDATORS OF BENTHOS
CAGE STUDIES
COMPETITION FOR SPACE
LIFE IN THE MUDS: A
COMPLEX SITUATION
COMMUNITY CHANGES: STORM INDUCED
SEASONAL POPULATION CHANGE
LONGER-TERM OSCILLATIONS IN
ANOTHER AMPHIPOD
Biomass of benthos in relation to distance from coast and depth
RECOVERY OF
BENTHIC
COMMUNITY
FOLLOWING
DEFAUNATION
BY RED TIDE