Title: Soft Substrate Communities: The intertidal and subtidal zones
1Soft Substrate CommunitiesThe intertidal and
subtidal zones
2Intertidal Habitats
3- Exposed - sand beaches
- Protected - sand and mud flats
- Sand beaches
- Appear devoid of macroscopic life
- Virtually all organisms bury themselves
- Exposed to waves, face open ocean
- Pronounced slope
- Sand and mud flats
- Large numbers of visible macroscopic life
- Facing bay or lagoon
- Little or no slope
4Sandy shores
- Defined by three factors
- Particle size, wave action, and slope
- Interrelated
- Particle size
- Water retention
- Suitability for burrowing
- Substrate movement
5Slope
- Interaction between particle size, wave action,
and swash/backswash - Swash - water running up a beach
- Carries particles
- Accretion
- Backswash
- Removes particles
6Substrate movement
- Particles are not stable
- Continually moved and sorted
- Fines settle out in low wave action
- Coarses settle immediately
- Results in zonation based on grain size
- Different beach types
7- Dissipative beach
- Strong wave action
- Energy dissipated in broad flat surf zone
- Gentle swash
- Gentle slope
- Reflective beach
- Strong wave action
- Energy is not dissipated
- Strong swash
- Steep slope
8Seasonal changes
- Changes in wave intensity change in grain size
- Common seasonal shift in beach profile
- Fine sand in summer
- Coarse beach in winter
- Substrate may be moved a meter or more
- Few large organisms occupy the surface
9- Smooth uniform profile
- Lack topographical diversity
- Uniform action of physical factors
- Temperature
- Wave action
- Dessication
10- Sand is an excellent buffer
- Temperature changes
- Salinity
- Exposure to sunlight
- Oxygen
- Not limiting on surface
- May become limiting in substrate
- Interchange of surface water with interstitial
water - Exchange
- Fine - slow
- Coarse - fast
- Tube builders and burrowers may deepen oxygen
11Sand flats
- Consist of finer grained sand and sediment
- Waves and water currents affect grain size
- Very low slope
- Oxygen generally not limited
- Unless you go deep
12Muddy flats
- Characteristic of estuaries, salt marshes
- Restricted to completely protected areas (waves)
- Slope is flat
- More stable
- Conducive to permanent burrows
- Long retention time of water in sediment
- Low exchange rate with water above
- Results in anaerobic conditions below surface
13RPDRedox potential discontinuity layer
- Rapid change from aerobic to anaerobic layer
- Characterized by greyish color, below is black
- Below decomposition by anaerobic bacteria
- Biologically significant
- Reduced compounds diffuse upward
- Oxidized by bacteria in aerobic sediment
- Incorporated into bacterial biomass
- Form basis of food chains
14Subtidal habitats
- Turbulence eliminates thermal stratification
- Waves may affect stability of of substrate
- May suspend and move particles
- Determines types of particles present
- Removes fine particles
- Salinity is variable
- Temperature shows seasonal change
- Light penetration is reduced
- just a few meters
15Topography
- Vast monotonous expanses
- Ripple marks, worm tubes, fecal mounds
- Substrate grain size and composition only major
differences - Fewer habitats for animals to occupy
- infaunal species lt epifaunal species
16- Sublittoral - subtidal zone - area not exposed in
tidal cycle but shallow (contintental shelf) - Composed of soft sediments (mud, sand, some hard
substrates) - Communities dominated by infaunal organisms
17Physical Characteristics
Sand Beach Sand flats Muddy flats Subtidal
Wave energy High Low Low Variable
Grain size Large Med Fine Variable
Slope High Low Low Low
Stability Low Med High Variable
O2 availability High High Low Variable
18Organisms
19Size of infaunal organisms
- Macrofauna gt0.5 mm
- Meiofauna 0.5-0.062 mm
- Microfauna lt 0.062 (mostly protozoans and
bacteria)
20Community organization
- Patchiness
- Time and space
- Horizontal and vertical
- Cyclical
- result of physical factors and interactions
between organisms
21Community Organization
- Grain size sets limits for organisms
- Dominated by suspension feeders (filterers) and
detritivores - Generally separated
- Detritivores in fine sand
- Filterers in clean coarse sand
- Seasonal change
22Community structure
- Changes occur through physical or biological
factors
23Parallel bottom communities
- Thorson 1955
- Similar communities in similar habitats found
globally - Similar sediments contain similar organisms
- Similar ecologically and taxonomically
- Pattern implies associations are not random
- Represent interacting systems with similar rules
24Woodin 1983
- Classification of organisms into limited
assemblages - Functional groups
25Types of organisms
- Sediment stabilizers
- Organisms that secrete mucous or roots to bind
sediment - Amphipods, phoronid worms, anemones, polychaetes
- Sediment destabilizers (bioturbators)
- motile or sedentary organisms who cause sediments
to move - Cucumbers, mobile clams, whelks
26Community organization
- Four dominant taxonomic groups of macrofauna
- Polychaetes
- Tube building worms, Burrowing worms
- Crustaceans
- Ostracods, Amphipods, isopods, decapods, mysids,
tanaids - Echinoderms
- Brittle stars, urchins, sand dollars, sea
cucumbers, sea stars - Mollusks
- Bivalves, scaphopods, gastropods
27- Infaunal animals
- Deposit feeders
- Suspension feeders
- Predators
- Worms
- Crustaceans
- Mollusks
- Echinoderms
- Bottom fishes
28Adaptations
29Adaptations
- Deep Burrowing
- Get away from sediment affected by waves
- Heavy shells - anchors
- Long siphons
- Severe storm may wash the up on beach
- Harder to get back into water and burrow quickly
- Mercenaria, Pismo clam
30Adaptations
- Fast burrowers
- More common
- Burrow as soon as wave removes organism
- Annelid worms, small clams, crustaceans
- Short bodies, limbs
- Donax, Siliqua and Ensis (razor clams)
- Emerita (mole crabs)
31Adaptations
- Swash migration
- Find food
- Avoid predators
32Adaptations
- Smooth shells - reduce resistance of sand
- Ridges - grip sediment, aid in penetration
- Reduced spines (echinoderms, sand dollars)
- Weight belts - accumulation of iron compounds -
sand dollars
33Adaptations (muddy shores)
- Burrow
- Permanent tubes
- Anaerobic adaptations
- Development of oxygen carriers (hemoglobin)
- Glycogen stores for anaerobic metabolism
- Bring surface water down
34Reproduction
- Iteroparous gt semelparous
- Coordinate spawning with tides
- Lunar rhythms
- Stranding
- Predation
- Latitudinal gradient
- Planktogrophic - tropics
- Lecitrophic - temperate zone
35Types of organisms - sand beach
- Lack of macroscopic plants
- Primary producers - benthic diatoms, surf-living
phytoplankton - Vertical migration in sediments, water column
- Polychaete worms, mollusks, crustaceans
36Feeding ecology - sand beach
- Very little primary production
- Organisms depend on phytoplankton in water,
organic debris - Filter feeders, detritus feers, scavengers
- Few resident carnivores
- Opportunistic carnivores, scavengers
37Types of organisms - sand flats
- Perrenial microscopic plants, seagrasses
- Ephemeral algae, seasonally abundant
- Large and diverse array of microflora
- Benthic diatoms, dinoflagellates, cyanobacteria
- Polychaete worms, mollusks, crustaceans
38Feeding Ecology - sand flats
- Productivity from microfloral films, seagrasses,
macroalgae - Not grazed extensively
- 90-95 broken down into detritus
- Scavengers, filterfeeders, and deposit feeders
39Types of organisms - mud flats
- Substantial plant life
- Diatoms, macroalgae, seagrasses
- Bacteria
- Highly abundant
- Sulfur bacteria (oxidize sulfur compounds for
energy) (Chemolithoautotrophic bacteria) - Two separate layers of productivity
- Macrofauna similar to sandy areas
40Feeding Ecology - mud flats
- More food available than in sand
- More large organisms
- Deposit and suspension feeders are dominant
- Deposit feeders (worms and bivalves)
- Burrow through substrate (earthworms)
- Surface feeding
41- Suspension feeders
- Mostly like others in sandy areas
- Must deal with fine suspended particles
- Partially feed on both particles and plankton
- Predators
- Fish, birds, moon snails, crabs, worms
- Few herbivores
- Trophic structure based
- detritus bacteria base
- Autotrophic base
42Types of organisms - subtidal
- Nutrients are rarely limiting
- Productivity is relatively high
- Large populations of zooplankon and benthic
organisms - Macroscopic plants contribute to primary
production - Runoff from land plays major role
- Few large grazing animals
43Organismal Characteristics
Sand Beach Sand flats Muddy flats Subtidal
Plants Low Med High Variable
Primary productivity Low Med High High
Epifaunal predators Low High High High
Detritus Low Med High Variable
44Community Organization of Soft Substrates
45What governs subtidal communities?
- Predation
- Disturbance
- Recruitment
- Recolonization
- Competition
46Community organization - sand
- Grain size sets limits for organisms
- Dominated by suspension feeders (filterers) and
detritivores - Generally separated
- Detritivores in fine sand
- Filterers in clean coarse sand
- Seasonal change
47Community organization - sand
- Zonation present, but fuzzy
- Habit of animals to migrate up and down beach
- Lack of studies
48Community organization - mud
- Intertidal area extensive
- Supralittoral
- burrowing crabs
- Midlittoral
- clams and polychaetes
- Infralittoral
- No sharp boundary
- Like midlittoral
49Distribution
- Gregarious
- Crustaceans ? exposed and tropical shores
- Bivalves ? protected and temperate shores
- macrofaunal sp. ? decreasing wave exposure
- Biomass ? exposed beaches
50McLachlan 1983
- Abundance and diversity correlated with particle
size and slope - Faunas ?if beach is dissipative
- Wave action dissipated in surf zone
- Flat slopes
- Less movement
- High biomass of filter feeders
51Community regulation - sandy beaches
- Sandy beaches - not studied so extensively
- Competition for space not major contributor to
patterns - Three dimensional space
- Extreme patchiness
- Competition for food
- Abundant plankton
- Sparse populations
52- Most sand beach animals are opportunistic
- Few indigenous invertebrate predators
- Few exclusion experiments, diversity ?
- Filter feeders - ample food
53Community regulation - sand and mud flats
- Physical factors important
- Grain size
- Trophic group amensalism
- Exclusion of one trophic group by another
- Deposit feeders exclude suspension feeders
- Burial of newly settled suspension feeder larvae
by deposit feeders
54- Seasonal weather changes
- Migration to deep water
- Sea ice - scouring
- Prime factors are
- Predation
- Competition
- Disturbance
- Predation, predation/disturbance significant
55Wiltse 1980
- Moon snail (Polinices duplicatus)
- Active predator of bivalves
- Soft shell clam (Mya arenaria)
56Wiltse 1980
- Removed moon snail
- Increase in Mya
- Increase in infauna
57Virnstein 1977
- Green crab (Caenus maenas)
- Blue crab (Callinectes sapidus)
- Crabs which dig in sediment for food
58Virnstein 1977
- Exclusion resulted in an increase in infaunal
densities
59Woodin 1978
- Horseshoe crab (Limulus polyphemus)
- Digs distinctive pits in search of food
60Whelks (Busycon spp.)
- Devastating to sand flat clam populations
- Consume all sizes of clams
- No size refuge
61Refugia? Woodin 1978
- Tube-forming worm Diopatra cuprea
- Forms upright tubes
- Effectively deters both Limulus and Calinectes
- Infaunal abundances greater around tubes
62Peterson and Peterson (1979)
- Effects of deposit feeders in NC
- Hemichordate worm (Balanoglossus aurantiacus)
- Funnel feeder, digs u-shaped burrow
- Ingests sediment
63Peterson and Peterson (1979)
- Consumes small infaunal organisms
- Causes death of others it does not ingest
- Keeps of infaunal organisms low
- Compounded by sea cucumber (Leptosynapta tenuis)
- Also ingests sediment
64Adult-larval interactions (Woodin 1976)
65Direct Competition
- Levinton et al. (1985)
- Hydobia totteni (Eurpoean), Ilyanassa obsoleta
(native mud snail) - H. totteni lives in high intertidal
- Avoids Ilyannasa
- H. totteni is an inferior competitor
66Brenchley and Carlton (1983)
- Littorina littorea (European), Ilyanassa obsoleta
(native) - Spatial segregation
- Littorina destroys egg capsules of Ilyanassa
67Grant (1981)
- Two amphipod species
- Acanthohaustorius - lives in oxidized layer
- Pseudohaustorius - lives in anoxic layer
- Both prefer oxidized layer
- Acanthohaustorius superior competitor
68Predators (Petersen 1991)
- Rocky intertidal
- Starfish, mollusks
- Slow moving
- Limited to inundated parts
- Soft intertidal
- Dominated by highly mobile predators
- Crabs, fishes, birds
- Ranges throughout intertidal