1. Life on the Continental Shelf
Chapter 13
Life on the
Continental Shelf

3. Continental Shelf Submerged edge of the continents
Richest part of the ocean
Includes world’s most important fishing grounds (90% of total global catch)
Oil and minerals have been found on it
Profoundly affected by pollution on other activities of humans on land

5. Physical Characteristics of the Subtidal Environment

6. Subtidal or Littoral Zone
Never exposed at low tide
Extends from the low tide level on shore to the shelf break (outer edge of continental shelf)
Benthos of the continental shelf live in the subtidal zone
Plankton and nekton over the continental shelf are part of the nertic zone

8. Factors that affect subtidal organisms are linked to two of the shelf’s fundamental characteristics:

9. 1. Shallow Water
temperature varies from place to place - one of the most important factors effecting distribution of organisms
Bottom affected by waves and currents – prevents stratification and nutrients do not concentrate in the bottom layer

10. 2. Proximity to Land Nutrients are brought in by rivers
Water over the continental shelf is far more productive and plankton rich than the open ocean
Water has a greenish tint from the phytoplankton and the decaying organic matter
Freshwater runoff can lower the salinity

11. Sedimentation
Of great influence because of the proximity to land and the shallow water
The settling of sediment particles from the water
Most sediments are lithogenous (sediment that comes from the physical and chemical breakdown of rocks on land)

12. 1. Wind transported 2. Shore erosion 3. Transport by rivers 4
1.Wind transported 2. Shore erosion 3. Transport by rivers  4. Transport by ground water  5. Yields of biological and chemical processes 6. Transport by icebergs and floating ice 7. Volcanic eruptions

13. Water Clarity
Abundant phytoplankton and the sediment from rivers and stirred up by waves and currents make shelf water murkier than the open ocean
Light does not penetrate as deeply which reduces the depth that primary producers can live

14. Continental Shelf Bottom Communities

15. The type of substrate is very important in determining which particular organisms inhabit the floor of the continental shelf

16. Soft-Bottom Subtidal Communities
Sandy and muddy substrates dominate the world’s continental shelves
There are distinct communities whose distribution is greatly influenced by such factors as the particle size and stability of the sediments, light and temperature

17. Infauna predominate, some epifauna, sessile organisms are rare
There are higher numbers of organisms on soft bottoms in the subtidal zone as compared to the intertidal zone

19. Reasons for Higher Diversity
Desiccation is not a problem
No drastic temperature changes
Minimal salinity changes
Stable environment

20. Distribution of organisms
Patchy
Organisms are in distinct clumps
Caused by different sediment types

21. Unvegetated Soft-Bottom Communities
Lack significant amounts of seaweeds or sea grasses
Main primary producers are diatoms
Detritus is a very important food source for many inhabitants

22. Deposit Feeders Polychaets Trumpet worms (Pectinaria)
Bamboo worms (Clymenella)
Lugworms (Arenicola)
Heart Urchins (Spatangus)
Sand Dollars (Dendraster)
Echiurans, peanut worms, sea cucumbers and ghost shrimps (Callianassa)

24. Trumpet worm
Bamboo Worm
Sea Cucumber
Lugworm

25. Heart Urchin
Ghost Shrimp

27. Suspension Feeders (Filter Feeders)
Clams
Razor clams
Quahog (Mercenaria mercenaria)
Cockles
Soft-shelled clam (Mya arenaria)
Amphipods
Polychaetes (parchment worms and terebellids)

28. Quahog
Soft Shell clam

29. Distribution of burrowing deposit and suspension feeders is influenced by several factors:

30. 1. Type of Substrate Deposit feeders predominant in muddy sediments
Suspension feeders – sandy bottoms

31. 2. Type of Organisms present affects the establishment of others
Deposit feeders exclude suspension feeders
Bioturbators – move sediment while burrowing or feeding

32. Epifaunal Invertebrates
Deposit Feeders
Brittle stars
amphipods
Scavengers
Shrimps (Penaeus)
Predators
Whelks (Nassarius)
Moon snails (Polinices)

34. More Predators Blue crab (Callinectes sapidus)
Lady Crab (Ovalipes ocellatus)
Hermit crabs
Lobsters
octopuses
Sea Stars (Astropecten) prey on:
Clams
Brittle stars
Polychaetes
Predatory amphipod

38. Bottom Dwelling fishes of the soft bottom community
Rays
Skates
Flounders
Halibuts
Soles
Tubots

39. Flounder
Sole
Ray

40. Skate
Skate

41. Halibut

42. Sea Grass Beds
Soft bottoms along the coast are occasionally carpeted by seagrasses
Flowering plants, grass-like in appearance but unrelated to true grasses
Develop best in sheltered, shallow water along the coast
Also found in estuaries and association with mangrove forests

44. 50 to 60 species of sea grasses
Most are tropical and subtropical
Several species are common – Eelgrass (Zostera marina)
Form thick luxuriant beds
Their roots keep them anchored in the face of turbulence

45. Eel Grass

46. Stabilize the soft bottom
Leaves cut down wave action and currents
More and finer sediment can be deposited which affects colonization by other organisms

47. Sea grass beds have a higher primary production than anywhere else on soft bottoms
Rank among the most productive communities in the entire ocean
Part of the reason: true roots – able to absorb nutrients from sediment
Increased by algae growing on the surface of the sea grass - epiphytes

48. Herbivores that eat seagrass:
Sea turtles
Mantees
Sea urchins (Diadema, Lytechinus)
Parrotfishes (Sparisoma)
Birds

50. Diadema

53. Ways that animals take advantage of high primary production of seagrasses:
Feed on the large amounts of decaying leaves and seaweeds
Offer shelter
Animals live on the leaves: hydroids, snails, tiny tube dwelling polychaetes, amphipods, shrimps

55. Larger animals that live among the plants:
Queen conch (Strombus)
Clams
Pen shell (Pinna carnea)
Nurseries for commercially available species

56. Queen conch (Strombus)
Pen shell (Pinna carnea)

58. Hard-Bottom Subtidal Communities

59. Relatively small portion of the continental shelf
In some cases a significant component of the hard substrate is provided by calcareous algae, tubes of polychaete worms and oyster shells
Often called reefs

60. Rocky Bottoms Never subject to desiccation Wider variety of organisms
are rich and productive
Seaweeds – most conspicuous inhabitants

61. Types of Seaweeds Brown and red Filamentous (Chordaria, Ceramium)
Branched (Agardhiella, Desmarestia)
Thin and leafy (Porphyra, Gigartina)
Encrusting (Lithothamnion)
All have holdfasts

62. Chordaria
Agardhiella

64. Lithothamnion

65. One of the main problems for seaweeds and sessile animals in the subtidal is to find a place to attach
There is intense competition for living space
Rich epifauna and poor infauna

66. Organisms Sponges Hydroids Sea anemones Soft corals Bryozoans
Tube-dwelling polychaetes
Barnacles
Sea squirts

67. Bryozoans

68. Sea Squirts

69. Grazers Small, slowing moving invertebrates
Sea urchins (Arbacia, Diadema, Stronglyocentrotus)
Chitons
Limpets
Sea hares
Abalones

70. Abalones

71. Seaweed defenses against grazing
Chemicals such as sulfuric acid and phenols
Can rapidly regrow
Tough and leathery
Calcareous algae (Lithothamnion, Clathromorphum, Halimeda) deposit calcium carbonate in their cell walls

73. Carnivores Feed on attached invertebrates
Sea urchins – seaweeds and flimsier attached invertebrates
Crabs
Lobsters
Fish
Grazers and predators strongly influence the composition of hard-bottom communities

74. Kelp Communities
Kelps are a group of large brown seaweeds that live in relatively cold water and are restricted to temperate and sub polar regions
True giants
Home to a vast assortment of organisms

76. Laminaria
North Atlantic and Asiatic coast
Blades 3 m or 10 ft long

78. Giant Kelp Macrocystis Pacific coasts of north and south America
Stipe – 20 to 30 m in length

79. Kelp beds – large dense patches of kelp
Kelp forests – when the fronds of the kelp beds float at the surface
Canopy – floating tops of kelps at the surface

80. Physical Factors that influence kelp Communities
Temperature – must be cool
Do not do well where there is heavy wave action – fragile
Prefer to attach to deep bottoms where wave action is reduced

81. Kelps can grow very fast with the giant kelp growing as fast as 50 cm/day ( 20 in/day)
Kelp communities are very productive

82. Organisms found within the kelp beds
Polychaetes
Small crustaceans
Brittle stars
Tube-dwelling polychaetes
Lace-like bryozoans (Membranipora)
Sponges
Sea squirts
Lobsters
Crabs
Hermit crabs
Sea stars
Abalones
octopuses

83. Fishes of the Kelp Community
Rockfishes (Sebastes)
Kelp bass (Paralabrax clathratus)
California sheephead (Semicossyohus pulcher) eats sea urchins, crabs)
Surf perches (Rhacochilus, Brachyistius)
Topsmelts (Atherinops) – plankton feeders

84. Small Algae are grazed by:
Snails
Crabs
Sea urchins
Fishes
Few eat kelps

85. Sea urchins Most important grazers in kelp communities
Most important species – red (Strongylocentrotus franciscanus), purple (S. purpuratus) and green sea urchin (S. droebachiensis)

86. Populations sometimes explode (known as plagues)
Normally urchins feed on drifting kelp
During a plague urchins eat attached kelp and can clear large areas – urchin barrens or urchin deserts
Sea otters can help maintain urchin populations

89. The End …..