1. Notes for Marine Biology: Function, Biodiversity, Ecology
14 -The Tidelands Rocky Shores, Soft-Substratum Shores, Marshes, Mangroves, and Estuaries
Notes for Marine Biology: Function, Biodiversity, Ecology
By Jeffrey S. Levinton
©Jeffrey S. Levinton 2001

2. ZONATION -universal feature of rocky shores,
also true of soft sediments but not as distinct
(3-dimensional nature, owing to presence of
burrowing organisms and others within the
sediment)

3. Example of zonation on rocky shore, along a gradient of
wave exposure on a site in the United Kingdom

4. 2 SPATIAL GRADIENTS:
Vertical
Horizontal - changing wave exposure

5. Vertical gradient Heat Stress, Desiccation
Gas Exchange - dissolved oxygen
Reduced feeding time
Wave shock
Biological interactions - competition, predation

6. Heat Stress/Desiccation
Varies on small spatial scales
Body size, shape are both important - reduction of surface area/volume reduces heat gain and water loss
Evaporative cooling and circulation of body fluids aids in reduction of heat loss
Well sealed exoskeletons aid in retarding water loss (acorn barnacles, bivalves)

7. Vertical Gradients
Higher intertidal organisms more resistant to heat and desiccation stress than lower intertidal organisms

8. Vertical Gradients 2
Higher intertidal organisms more resistant to heat and desiccation stress than lower intertidal organisms
Higher intertidal animals have less time to feed. Sessile forms therefore grow more slowly than lower intertidal organisms

9. Vertical Gradients 3
Higher intertidal organisms more resistant to heat and desiccation stress than lower intertidal organisms
Higher intertidal animals have less time to feed. Sessile forms therefore grow more slowly than lower intertidal organisms
Mobile carnivores can feed only at high tide, usually feed more effectively at lower tide levels, which are immersed a greater proportion of the day

10. Oxygen consumption
Intertidal animals usually cannot respire at time of low tide

11. Oxygen consumption 2
Intertidal animals usually cannot respire at time of low tide
Respiratory organs (gills of polychaetes, bivalves) must be moist to acquire oxygen, and therefore are usually withdrawn at low tide

12. Oxygen consumption 3
Intertidal animals usually cannot respire at time of low tide
Respiratory organs (gills of polychaetes, bivalves) must be moist to acquire oxygen, and therefore are usually withdrawn at low tide
Some animals greatly reduce metabolic rate at time of low tide

13. Oxygen consumption 4
Intertidal animals usually cannot respire at time of low tide
Respiratory organs (gills of polychaetes, bivalves) must be moist to acquire oxygen, and therefore are usually withdrawn at low tide
Some animals greatly reduce metabolic rate at time of low tide
Some high intertidal animals can respire from air (e.g., some mussels) even at low tide, as long as air is not too dry

14. Pacific sand bubbler crab, Scopimera inflata, has membrane
on each leg (shaded green), which exchanges gas from air
into arterial blood

15. Wave shock 1
Abrasion - particles in suspension scrape delicate structures

16. Wave shock 2
Abrasion - particles in suspension scrape delicate structures
Pressure - hydrostatic pressure of breaking waves can crush compressible structures

17. Wave shock 3
Abrasion - particles in suspension scrape delicate structures
Pressure - hydrostatic pressure of breaking waves can crush compressible structures
Drag - impact of water can exert drag, which can pull organisms from their attachments to surfaces, erode particles from beaches and carry organisms from their burrows or living positions

18. Causes of Vertical Zonation 1
Physiological tolerance of different species at different levels of the shore

19. Causes of Vertical Zonation 2
Physiological tolerance of different species at different levels of the shore
Larval and adult preference - larvae may settle at time of high tide at high levels, mobile organisms have a series of behavioral responses that keep them at certain levels of shore

20. Causes of Vertical Zonation 3
Physiological tolerance of different species at different levels of the shore
Larval and adult preference - larvae may settle at time of high tide at high levels, mobile organisms have a series of behavioral responses that keep them at certain levels of shore
Competition - species may be capable of excluding others from certain levels of the shore

21. Causes of Vertical Zonation 4
Physiological tolerance of different species at different levels of the shore
Larval and adult preference - larvae may settle at time of high tide at high levels, mobile organisms have a series of behavioral responses that keep them at certain levels of shore
Competition - species may be capable of excluding others from certain levels of the shore
Predation - mobile predators more effective usually on the lower shore: affects distributions of vulnerable prey species

22. A rocky shore in the U.K. At the time of low tide on hot dry days, the
gastropod Nucella lapillus retreats into the crack where it is moist and
cool. Note the areas cleared of mussels adjacent to the cracks.

23. Beaches and Wave Action
Exposed beaches - strong erosion and sediment transport
Difficult environment for macrobenthos to survive and maintain living position
Swash riding - means of moving up and down with rising and falling tide - maintain position in wet but relatively non-eroded tidal level

24. Swash Riding - found in Mole Crab Emerita, some species
of the bivalve Donax

25. The mole crab, Emerita talpoida, burrowing into
an exposed beach in North Carolina

26. Interspecific Interactions and Zonation
Why are there vertical zones, with dominance often of single sessile species within a zone?

27. Interspecific Interactions and Zonation 2
Why are there vertical zones, with dominance often of single sessile species within a zone?
Possible explanations: (1) Differences in tolerance of species at different tidal heights (2) Competitive interactions (3) other factors

28. Investigation by Field Manipulation Experiments
Classic experiments of Joseph Connell
Studied factors controlling vertical zonation by selective inclusion and exclusion of hypothesized interacting species

29. Rocky Shores of Scotland - Key Species in Connell’s study
Chthamalus stellatus - acorn barnacle, ranging from subtropical latitudes to northern British isles
Semibalanus balanoides - acorn barnacle, ranging from Arctic to southern British isles, overlapping in range with C. stellatus
Nucella lapillus - carnivorous gastropod, drills and preys on barnacles

30. Connell Field Experiment
transplant newly settled Chthamalus to all tidal levels
caged some transplants, excluded Nucella
allow Semibalanus to settle and cleaned Semibalanus cyprids off some rocks

31. Results of Connell Experiment
Chthamalus survival poorer in presence of Semibalanus
Chthamalus survival decreased where Semibalanus grew the fastest
Chthamalus survival increased in high intertidal due to its resistance to desiccation

32. Conclusions from Connell Experiments
Predation important in lower intertidal
Biological factors control lower limit of species occurrence
Physical factors control upper limit
Community structure a function of very local processes (larval recruitment not taken into account as a factor)

33. Desiccation MHW spring MHW neap Mean tide MLW neap MLW spring Physical
Chthamalus
MHW spring
MHW neap
Mean tide
MLW neap
MLW spring
Competition
Chthamalus
Semibalanus
Semibalanus
Wave Shock
Predation
Physical
factors
Interspecific effects
Adult density
Settlement of cyprids

34. Soft Sediments Zonation not as distinct as on rocky shores
Competition - demonstrated by experiments

35. Dense population of the barnacle Semibalanus balanoides

36. Mud Flat Field Experiments by Sarah Woodin
burrowing Armandia brevis versus tube builders
Cage placed on sediment with top screen: tube builders settled on screen, Armandia burrowed through and reached higher densities than when screen was absent and tube builders settled directly in sediment and established tubes

37. Soft Sediments - Vertical Stratification
Dominant species found at different levels below sediment-water interface
Experimentally reduce density of deep-dwelling clams, remaining individuals grow faster - demonstrates effect of density
Removal of shallow dwelling species of bivalves has no effect on growth of deeper-dwelling species

38. Occurrence of various bivalves at different burrowing
depths in a sand flat in southern California

39. Predation and Species Interactions
Predators reduce prey density
Prey species compete
Conclude: predation may promote coexistence of competing prey species

40. Field Experiment of Robert Paine
Rocky shores of outer coast of Washington State
Principle predator - starfish Pisaster ochraceus
Pisaster preys on a wide variety of sessile prey species, including barnacles, mussels, brachiopods, gastropods

41. Pacific coast starfish Pisaster ochraceus, flipped over
Left: eating a mussel, Right: eating barnacles

42. Paine Experiment and Results 1
Removal of Pisaster ochraceus

43. Paine Experiment and Results 2
Removal of Pisaster ochraceus
Successful settlement of recruits of mussel Mytilus californianus

44. Paine Experiment and Results 3
Removal of Pisaster ochraceus
Successful settlement of recruits of mussel Mytilus californianus
Other species greatly reduced in abundance, Mytilus californianus became dominant

45. Paine Experiment and Results 4
Removal of Pisaster ochraceus
Successful settlement of recruits of mussel Mytilus californianus
Other species greatly reduced in abundance, Mytilus californianus became dominant
Conclude: Pisaster ochraceus is a keystone species, a species whose presence has strong effects on community organization mediated by factors such as competition and predation

46. Larval Recruitment Exerts Strong Effects 1
Results from manipulative experiments usually depend upon steady recruitment of larvae of competing species

47. Larval Recruitment Exerts Strong Effects 2
Results from manipulative experiments usually depend upon steady recruitment of larvae of competing species
What if recruitment is variable?

48. Larval Recruitment Exerts Strong Effects 3
Results from manipulative experiments usually depend upon steady recruitment of larvae of competing species
What if recruitment is variable?
Competitively superior species might not take over, owing to low rates of recruitment

49. Larval Recruitment Exerts Strong Effects 4
Results from manipulative experiments usually depend upon steady recruitment of larvae of competing species
What if recruitment is variable?
Competitively superior species might not take over, owing to low rates of recruitment
Recruitment might be reduced if currents are not favorable, high water flow results in flushing of larvae from inshore habitates, poor year for phytoplankton results in poor year for success of plankton-feeding larvae

50. The effects of variation of tidal flushing on larval recruitment in
Higher phytoplankton
Higher suspension feeder
Growth
Higher recruitment
Lower phytoplankton
Lower suspension feeder
Growth
Lower recruitment
High freshwater flow,
tidal flushing
Low freshwater flow,
tidal flushing
The effects of variation of tidal flushing on larval recruitment in
a semi-enclosed coastal area, such as a bay

51. Disturbance as a Factor in Intertidal Community Structure 1
Disturbances are physical events that influence the distribution and abundance of organisms

52. Disturbance as a Factor in Intertidal Community Structure 2
Disturbances are physical events that influence the distribution and abundance of organisms
Disturbances may reduce abundance of competing species

53. Disturbance as a Factor in Intertidal Community Structure 3
Disturbances are physical events that influence the distribution and abundance of organisms
Disturbances may reduce abundance of competing species
Disturbances may therefore allow coexistence of competitively inferior species, or may allow colonization of species adapted to disturbance

54. Postelsia palmaeformis, the palm seaweed, invades
rocks that have been severely disturbed by storms, Spores are
released and travel just a few cm fromthe plant, allowing local
spread of a colonizing individual

55. Spatial Scale of Disturbance is Crucial in Subsequent Colonization events 1
A very small scale disturbance in a mussel bed might just result in the mussels moving and sealing off the opened patch

56. Spatial Scale of Disturbance is Crucial in Subsequent Colonization events 2
A very small scale disturbance in a mussel bed might just result in the mussels moving and sealing off the opened patch
Larger patches might be colonized by other species and the patch might last many months or even indefinitely

57. Spatial Scale of Disturbance is Crucial in Subsequent Colonization events 3
A very small scale disturbance in a mussel bed might just result in the mussels moving and sealing off the opened patch
Larger patches might be colonized by other species and the patch might last many months or even indefinitely
Therefore, spatial scale of disturbance might affect the spatial pattern of dominance of species, creating a mosaic of long-lived patches

58. Disturbance and spatial scale: events following the
California mussels
California mussels
California mussels
Small
Newly
Opened
Patch
California mussels
California mussels
California mussels
Bay
Mussels
And
Seaweeds
Large
California mussels
California mussels
California mussels
Disturbance and spatial scale: events following the
opening of a small and large patch in a Pacific coast
mussel bed

59. Estuaries Geologically ephemeral but biologically rich
Biodiversity declines with decreasing salinity, especially in so-called critical salnity range of 3-8 o/oo
Estuarine flow tends to wash species toward ocean - larval vertical migration can retard loss

60. Estuaries 2
Species in estuaries often have expanded range of resource exploitation, owing to elimination of species from open coast. Usually estuarine species also occur on open coast, although there are some species found only in low salinity estuarine conditions

61. Estuaries - Biodiversity
Diversity of marine-related estuarine species declines as you move up the estuary, towards areas of declining salinity

62. Estuaries - Biodiversity 2
There is a critical salinity range, ca. 3-8 o/oo, where diversity is at a minimum

63. Estuaries - Biodiversity 3
At lower salinities, biodiversity increases again, and typical freshwater species are encountered

64. Estuaries - Biodiversity 4
It is believed that the critical salinity range is so species-poor because normal marine species cannot survive there very well, nor can freshwater species, which lack adaptations for dealing with salt, can survive well here either.
It has been also suggested that the critical salinity range has very unusual ratios of common inorganic elements (e.g., Cl, Na), which creates further physiological difficulties

65. Biodiversity along a salinity gradient in the Randerfjord, Denmark

66. Salt Marshes dominated by Spartina spp.
Salt marshes are accretionary environments
Colonization of sediment by salt marsh plants is followed by trapping of fine particles, accretion of sediments
Marsh Spartina spp. plants spread by means of a rhizome system - plants are interconnected and often consist of broad stands of the same genotype

67. As initial colonization of Spartina alterniflora results in spread and
trapping of sediment, marsh sediment surface rises, creating a higher
intertidal environment, which favors colonization of a shorter form
Of Spartina alterniflora distant from the water (SAS) and higher marsh
Species, Spartina patens (SP).

68. Spartina sediment and adaptations
Sediment is often anoxic
Aerenchymal tissue allows Spartina to exchange gases, even when surrounded by anoxic soil
Presence of fiddler crab burrows enhances Spartina growth, perhaps owing to aeration of the soil

69. Fiddler crab, Uca pugilator, in a Spartina salt marsh.
Crab burrows enhance Spartina growth

70. The ribbed marsh mussel, Geukensia demissa,
lives semi-infaunally in marsh sediments. Its
presence also enhances Spartina growth, perhaps
owing to deposition of nutrient rich feces and
pseudofeces.

71. Wrack on the surface of a salt marsh. The
role of this material in the nutrient dynamics
of salt marsh ecosystems is controversial.

72. Cross-section of Spartina below sediment - note
aerenchymal tissue - allows gas exchange

73. Grazing on Spartina spp.
Grazing by invertebrates appears to be relatively slight
This may be a response to the tough leaves, rich in cellulose, which also has silica
Grazing on flowers, however, may be far greater, resulting in frequent failures of seed set

74. Grazing on Spartina spp. 2
Recent research suggests that the presence of the snail Littorina irrorata (found in SE USA) does damage to leaves. This species rises onto the leaves at the time of high tide to avoid predation by crabs

75. Salt Marsh Creeks
Older, mature salt marshes consist of meadows with interspersed creeks
The creeks have high nutrient input, support large populations of invertebrates and are often nursery grounds for juvenile fishes and crustaceans

76. Subhabitats of the Spartina salt marsh environment
Short S.
alterniflora
Spartina patens
Tall S. alterniflora
MHW
Eroding
creek
edge
Peat
Geukensia
demissa
Peat
Peat
Ilyanassa
obsoleta
MLW
Creek
Fundulus
heteroclitus
Subhabitats of the Spartina salt marsh environment

77. Vertical zonation
Salt marshes exhibit the intertidal phenomenon of vertical zonation
From low to high intertidal one often finds: S. alterniflora, S. patens, Distichlis spicata, and Juncus gerardi
The borders between zones are often quite sharp

78. Vertical zonation 2
Lower intertidal species such as Spartina alterniflora, are more salt tolerant than high intertidal forms, but low intertidal forms are not physiologically limited from growing in high intertidal area
High intertidal species are competitively superior to lower intertidal forms, but are not able to survive the longer exposure lower down to salt

79. The border between the Spartina alterniflora zone
And the Spartina patens zone, in West Meadow Creek,
Long Island, New York

80. Salt Pans
Accumulations of wrack on the upper shore may kill salt marsh grass beneath

81. Salt Pans 2
If wrack is carried away by currents, evaporation may result in high concentrations of salt, which kills seedlings and prevents recolonization of salt marsh grass species

82. Salt Pans 3
Recolonization quite difficult unless there are heavy rains, dissolving the salt, or an incursion of grass, which creates shade and traps moisture, thus enhancing dissolution of salt

83. A salt marsh salt pan, at a high intertidal
site in Rhode Island

84. Mangrove Forests
Dominated by species of mangroves, common in subtropical and tropical protected shores around the world
Mangroves broadly rooted but only to shallow depth, in quite anoxic soils
Underground roots have projections into air that allow gathering of oxygen

85. Roots types, leaves, fruits and seedlings of a mangrove
Aerial
roots
Pneumatophores
seedling
Anchoring roots
Roots types, leaves, fruits and seedlings of a mangrove

86. Salt gland
Mangroves are very salt-rolerant plants, and leaves have
a salt gland (left), which can excrete salt from cell cytosol to the
leaf surfaces (right)

87. Mangrove Forests: Important Features
High primary productivity
High supply of particulate organic matter, especially falling leaves, which subsidize animal growth
Zonation of mangrove species
Roots support a rich assemblage of sessile marine invertebrates

88. Mangrove forest along a salt creek in Mexico

89. The End