Soft substrate communities the intertidal and subtidal zones
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Soft Substrate Communities: The intertidal and subtidal zones. Intertidal Habitats. 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

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Soft Substrate Communities: The intertidal and subtidal zones

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Soft Substrate Communities:The intertidal and subtidal zones


Intertidal Habitats


  • 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


Sandy shores

  • Defined by three factors

    • Particle size, wave action, and slope

    • Interrelated

  • Particle size

    • Water retention

    • Suitability for burrowing

  • Substrate movement


Slope

  • Interaction between particle size, wave action, and swash/backswash

  • Swash - water running up a beach

    • Carries particles

    • Accretion

  • Backswash

    • Removes particles


Substrate 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


  • 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


Seasonal 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


  • Smooth uniform profile

  • Lack topographical diversity

  • Uniform action of physical factors

    • Temperature

    • Wave action

    • Dessication


  • 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


Sand 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


Muddy 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


RPDRedox 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


Subtidal 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


Topography

  • 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 < epifaunal species


  • 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


Physical Characteristics


Organisms


Size of infaunal organisms

  • Macrofauna: >0.5 mm

  • Meiofauna: 0.5-0.062 mm

  • Microfauna: < 0.062 (mostly protozoans and bacteria)


Community organization

  • Patchiness

    • Time and space

    • Horizontal and vertical

    • Cyclical

    • result of physical factors and interactions between organisms


Community 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


Community structure

  • Changes occur through physical or biological factors


Parallel 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”


Woodin 1983

  • Classification of organisms into limited # assemblages

  • Functional groups


Types 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


Community 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


  • Infaunal animals:

    • Deposit feeders

    • Suspension feeders

  • Predators:

    • Worms

    • Crustaceans

    • Mollusks

    • Echinoderms

    • Bottom fishes


Adaptations


Adaptations

  • 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


Adaptations

  • 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)


Adaptations

  • Swash migration

    • Find food

    • Avoid predators


Adaptations

  • 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


Adaptations (muddy shores)

  • Burrow

  • Permanent tubes

  • Anaerobic adaptations

    • Development of oxygen carriers (hemoglobin)

    • Glycogen stores for anaerobic metabolism

    • Bring surface water down


Reproduction

  • Iteroparous > semelparous

  • Coordinate spawning with tides

    • Lunar rhythms

    • Stranding

    • Predation

  • Latitudinal gradient

    • Planktogrophic - tropics

    • Lecitrophic - temperate zone


Types 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


Feeding 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


Types 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


Feeding Ecology - sand flats

  • Productivity from microfloral films, seagrasses, macroalgae

  • Not grazed extensively

  • 90-95% broken down into detritus

  • Scavengers, filterfeeders, and deposit feeders


Types 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


Feeding 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


  • 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


Types 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


Organismal Characteristics


Community Organization of Soft Substrates


What governs subtidal communities?

  • Predation

  • Disturbance

  • Recruitment

  • Recolonization

  • Competition


Community 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


Community organization - sand

  • Zonation present, but fuzzy

    • Habit of animals to migrate up and down beach

    • Lack of studies


Community organization - mud

  • Intertidal area extensive

  • Supralittoral

    • burrowing crabs

  • Midlittoral

    • clams and polychaetes

  • Infralittoral

    • No sharp boundary

    • Like midlittoral


Distribution

  • Gregarious

  • Crustaceans  exposed and tropical shores

  • Bivalves  protected and temperate shores

  • # macrofaunal sp.  decreasing wave exposure

  • Biomass  exposed beaches


McLachlan 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


Community 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


  • Most sand beach animals are opportunistic

  • Few indigenous invertebrate predators

    • Few exclusion experiments, diversity 

  • Filter feeders - ample food


Community 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


  • Seasonal weather changes

    • Migration to deep water

    • Sea ice - scouring

  • Prime factors are:

    • Predation

    • Competition

    • Disturbance

  • Predation, predation/disturbance significant


Wiltse 1980

  • Moon snail (Polinices duplicatus)

    • Active predator of bivalves

  • Soft shell clam (Mya arenaria)


Wiltse 1980

  • Removed moon snail

  • Increase in Mya

  • Increase in infauna


Virnstein 1977

  • Green crab (Caenus maenas)

  • Blue crab(Callinectes sapidus)

  • Crabs which dig in sediment for food


Virnstein 1977

  • Exclusion resulted in an increase in infaunal densities


Woodin 1978

  • Horseshoe crab (Limulus polyphemus)

  • Digs distinctive pits in search of food


Whelks (Busycon spp.)

  • Devastating to sand flat clam populations

  • Consume all sizes of clams

  • No size refuge


Refugia? Woodin 1978

  • Tube-forming worm Diopatra cuprea

  • Forms upright tubes

  • Effectively deters both Limulus and Calinectes

  • Infaunal abundances greater around tubes


Peterson and Peterson (1979)

  • Effects of deposit feeders in NC

  • Hemichordate worm (Balanoglossusaurantiacus)

  • Funnel feeder, digs u-shaped burrow

  • Ingests sediment


Peterson and Peterson (1979)

  • Consumes small infaunal organisms

  • Causes death of others it does not ingest

  • Keeps # of infaunal organisms low

  • Compounded by sea cucumber (Leptosynaptatenuis)

  • Also ingests sediment


Adult-larval interactions (Woodin 1976)

  • Predatory interactions


Direct 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


Brenchley and Carlton (1983)

  • Littorina littorea (European), Ilyanassaobsoleta (native)

  • Spatial segregation

  • Littorina destroys egg capsules of Ilyanassa


Grant (1981)

  • Two amphipod species

    • Acanthohaustorius - lives in oxidized layer

    • Pseudohaustorius - lives in anoxic layer

  • Both prefer oxidized layer

  • Acanthohaustorius superior competitor


Predators (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


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