Soft Substrate Communities: The intertidal and subtidal zones

1. Soft Substrate Communities:The intertidal and subtidal zones

2. Intertidal 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

4. Sandy shores • Defined by three factors • Particle size, wave action, and slope • Interrelated • Particle size • Water retention • Suitability for burrowing • Substrate movement

5. Slope • Interaction between particle size, wave action, and swash/backswash • Swash - water running up a beach • Carries particles • Accretion • Backswash • Removes particles

6. 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

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

8. 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

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

11. 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

12. 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

13. 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

14. 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

15. 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

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

17. Physical Characteristics

18. Organisms

19. Size of infaunal organisms • Macrofauna: >0.5 mm • Meiofauna: 0.5-0.062 mm • Microfauna: < 0.062 (mostly protozoans and bacteria)

20. Community organization • Patchiness • Time and space • Horizontal and vertical • Cyclical • result of physical factors and interactions between organisms

21. 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

22. Community structure • Changes occur through physical or biological factors

23. 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”

24. Woodin 1983 • Classification of organisms into limited # assemblages • Functional groups

25. 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

26. 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

27. Infaunal animals: • Deposit feeders • Suspension feeders • Predators: • Worms • Crustaceans • Mollusks • Echinoderms • Bottom fishes

28. Adaptations

29. 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

30. 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)

31. Adaptations • Swash migration • Find food • Avoid predators

32. 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

33. Adaptations (muddy shores) • Burrow • Permanent tubes • Anaerobic adaptations • Development of oxygen carriers (hemoglobin) • Glycogen stores for anaerobic metabolism • Bring surface water down

34. Reproduction • Iteroparous > semelparous • Coordinate spawning with tides • Lunar rhythms • Stranding • Predation • Latitudinal gradient • Planktogrophic - tropics • Lecitrophic - temperate zone

35. 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

36. 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

37. 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

38. Feeding Ecology - sand flats • Productivity from microfloral films, seagrasses, macroalgae • Not grazed extensively • 90-95% broken down into detritus • Scavengers, filterfeeders, and deposit feeders

39. 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

40. 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

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

42. 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

43. Organismal Characteristics

44. Community Organization of Soft Substrates

45. What governs subtidal communities? • Predation • Disturbance • Recruitment • Recolonization • Competition

46. 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

47. Community organization - sand • Zonation present, but fuzzy • Habit of animals to migrate up and down beach • Lack of studies

48. Community organization - mud • Intertidal area extensive • Supralittoral • burrowing crabs • Midlittoral • clams and polychaetes • Infralittoral • No sharp boundary • Like midlittoral

49. Distribution • Gregarious • Crustaceans  exposed and tropical shores • Bivalves  protected and temperate shores • # macrofaunal sp.  decreasing wave exposure • Biomass  exposed beaches

50. 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