1. Chapter 11
Between the Tides

4. Intertidal or Littoral Zone
Best known
Narrow fringe along the shoreline that lies between the highest high tide and the lowest low tide
Easy to study
No specialized equipment needed
Can return to the exact same spot again

6. A unique environment
Regularly exposed to air – organisms must have a way to cope
Emersion – being out of water and exposed to air
Immersion – being submerged
Bottoms vary and determine the community that lives there

7. Substrate or substratum – material on or in
which organisms live
Can be hard and rocky or soft and muddy or sandy

8. Rocky Shore Communities

9. Occur on steep coasts without large amounts of sediment
Active margins – west coast
Glaciers moving over land and scraping away sediments
Waves and currents can carry sediments away
Hawaii – rocky because it is geologically young

10. The Organisms Live right on the rock’s surface
Epifauna – live on the surface of the substrate
Sessile – stay attached to the rock
Living on the rock’s surface, the organisms in the rocky intertidal are fully exposed to the elements – great physical stress

11. Exposure at Low Tide

12. Low tide – left high and dry, exposed to air which is much harsher environment than water
Highest part of the intertidal (only wet on high spring tides) is almost never immersed and kept wet by wave splash

13. Low intertidal – submerged most of the time
So the higher the organisms live in the intertidal, then, the more time they have to spend out of the water

14. Water Loss Desiccate – dry out if left out of the water too long
To live in the intertidal an organism must be able to prevent desiccation, tolerate it or both
They either run and hide or “clam up”

15. Organisms that run and hide
Shore crabs
Hermit crabs
Snails
Huddle in moist shady crevices

16. Tide Pools
Depressions in the rocks that hold sea water after the tide goes out
Good places to hide at low tide

18. Organisms that can’t run and hide
Seeweeds and sessile animals
Must live in moist areas all the time

19. Organisms that Clam up
Have a protective covering like a shell that they can close to hold water
Barnacles
Mussels
Limpets – clamp to the rock
Limpets can also carve out shallow depressions or “home scars” to make a more effective seal – use their radula

20. Littorina or periwinkles clamp to rocks and also seal the opening of their shelf with their operculum

21. Organisms that do nothing
Chitons – just dry up – can survive a loss of 75%
Intertidal seaweeds – Fucus – can withstand a water loss of 90% - get practically crunchy

23. Temperature and Salinity

24. Temperature
Sea temperatures are relatively constant and mild because of high heat capacity
Air temperatures can be much more extreme – hot and cold

25. Dealing with Temperature
Moist hiding places also have lower temperatures
Nerita plicata – tropical snail has pronounced ridges to help radiate heat
Color can help deal with high temperatures

26. Salinity Fluctuates widely
When it rains salinity decreases, even have to deal with fresh water
Tide pool residents – high salinity when there is a lot of evaporation – low salinity when it rains

27. Restriction of Feeding
Little sediment accumulates so deposit feeders are rare
Deposit feeder – animals that eat organic matter that settles to the bottom
Most are sessile filter feeders – can not feed when the tide is out
Filter feeders – animals that actively filter food particles from the water

28. The Power of the Sea

29. When the tide is in life is still hard in the intertidal
Ocean waves expend tremendous energy as they crash on the shore
Rocky intertidal organisms are exposed to the full power of the sea

32. There is tremendous variation in the intensity of wave impact (wave shock) from place to place along the shore
Exposure to waves strongly affects intertidal organisms

33. Coping with Wave Shock

34. Some organisms can’t withstand wave shock and are only found in sheltered locations
Some deal with wave shock by firmly anchoring themselves to the rocks

35. Ways to Anchor Seaweeds use their holdfasts or crust on the rock
Mussels hold on with byssal threads (strong fibers made of protein)
Limpets and Chitons use their muscular foot as a suction cup
Intertidal fishes lack swim bladders so they sink and stay on the bottom

36. Other Adaptations to deal with Wave Shock
Thicker shells
Compact shape to reduce impact
Low profiles that keep them close to the rocks (barnacles, mussels, limpets and chitons)
Seaweeds are flexible and can go with the flow

40. The Battle for Space

41. The intertidal has plenty of food
Shallow coastal water provide lots of light and nutrients – photosynthesis – lots of food for animals
Plankton rich water moves in at high tide
Detritus moves in with the tide

43. Limiting Factor Space Nearly all of the space is occupied
Organisms may attach to each other because space is so limiting

44. Competition for Space A dominant biological factor
Several ways to compete for space
One – get there first - be the first to colonize the area (which means an organisms must have an effective means of dispersal)
Two – take over a space that is already occupied – uncut or bulldoze the off (barnacles and limpets)

45. Three – grow over the competitors making them vulnerable to waves, smothering them, or blocking their sunlight

46. Vertical Zonation

47. The rocky intertidal community is usually divided into distinct bands or zones at characteristic heights in the intertidal
Vertical zonation - A given species is only found in a particular vertical range

48. Zonation is Caused by:
Complex interaction of physical and biological factors
Upper limit determined by physical factors
Lower limit determined by biological factors

50. Organisms of the Upper Intertidal
Lichens
Cyanobacteria (Calothrix)
Filamentous green alga (Ulothrix)
Periwinkles (Littorina) which graze on algae
Limpets – hardy grazers
Predators- birds raccoons and rats from land

51. Organisms of the Intertidal
Acorn barnacles
Little gray barnacles (Chthamalus)
Rock Barnacles (Balanus, Semibalanus)
Little gray barnacles live higher up than rock barnacles – upper limit physical factor – emersion
Lower limit – biological factors (competition and predation) – rock out compete little gray – rock are eaten by Whelks

53. Brown seaweeds –rock weeds (Fucus, Pelvetia)
Mussels
Gooseneck barnacles
Brown seaweeds –rock weeds (Fucus, Pelvetia)
Sea stars (Pisaster, Asterias) eat mussels
Lower limit of mussels is set by predation of sea stars
Spiny lobsters – eat mussels
Pelvetia

55. Gooseneck Barnacles
Pisaster

56. Lower Intertidal Organisms
Seaweeds
Light and space are important resources
Green alga (Entromoropha)
Irish moss (red alga) Chondrus crispus
Kelps
Coralline algae (Corallina, Lithothamnion)
Sea urchins

57. Chondrus crispus
Corallina

58. Sea anemones (Metridium, Anthopleura)
Polychaete worms (Spirorbis, phragmatopoma)
Snails (Tegula, Nucella)
Sea Slugs (Aplysia, Dendronotus)
Gobies, clingfishes, sculpins, pricklebacks and gunnels

59. Spirorbis
Metridium
Spirorbis
Sculpin
Aplysia

60. Soft-Bottom Intertidal Communites

61. Soft bottom – bottom composed of sediment – organisms can burrow in it easily
Whether and what type of sediment accumulates depends on how much water motion there is and on the source of the sediment
The type of sediment strongly influences the community

62. The Shifting Sediments

63. Unstable, constantly shifting
Organisms do not have a solid place to attach
Few seaweeds, some areas have sea grass beds
Most burrow in the mud – infauna (live in the sediment)

64. Important Physical Factor of Soft Bottom Communities
Kind of sediment
Size of the grains (gravel, sand, silt, clay)
Sediment composition is directly related to the degree of water motion
Fine sediment remains suspended longer and can be kept suspended with a small amount of water motion

66. Living in the Sediment

67. Advantages Stays wet when the tide goes out
Desiccation is not as critical
Course sand however will dry out quickly

68. Oxygen Availability
Amount of organic matter in bottom sediments is particularly important to deposit feeders
Few primary producers, detritus is the main source of food
Deposit feeders extract this organic matter from the sediments
Smaller grain sizes contain more organic matter

69. Grain size also affects the amount of oxygen available in the sediments
Oxygen is used through respiration and decay bacteria

70. Problems for Muddy Bottoms
More organic matter to decay and use up oxygen
Flow of water that brings in new oxygen is reduced
Except for the upper few centimeters of mud the interstitial water (water between the grains) is deficient of oxygen

71. Anoxic – sediments with absolutely no oxygen
Anaerobic bacteria can break down organic matter without oxygen – hydrogen sulfide is produced as a byproduct
H2S – smells like rotten eggs and turns things black

72. Adaptations of Infauna to low oxygen levels
Pump oxygen rich water from the sediment surface with siphons or through their burrows
Adaptation of hemoglobin to low oxygen levels – can extract as much oxygen as possible
Sluggish – reduces the need

73. Getting Around Muscular foot pulls the organism into the sediment
Burrow or plough along
Jointed appendages to dig – crustaceans
Eating their way through the sediment – sea cucumbers and certain worms

74. Feeding Detritus is the main food source
Diatoms sometimes form highly productive mats
Plankton brought in by the tides
Deposit feeding – burrowing through the sediments and eat them
Tube feet to pick up particles – sand dollars
Siphons to filter feed

75. Plankton
Diatoms
Sand Dollar

77. Zonation Not as obvious as it is on the rocky intertidal
Best seen on sandy beaches where water drains quickly
Hardiest to see in muddy areas where the area is flat

78. The End ……