2. Continental Shelf:
Area of the ocean found between the bottom of the intertidal zone and the shelf break

3. CONTINENTAL SHELVES Average width – 150 km (80 miles)
Broad along passive margins
Narrow along active margins
Average depth 150 m (500 ft)

4. Passive Margin – continental margin on the edges of diverging plates
Active Margin – continental margin facing converging or sliding plates

5. slope continental shelf rise abyssal plain abyssal hills ridge
Notice the narrow shelf by Florida
Transform faults- fractures along which the lithosphere slides horizontally past one another
ridge
transform fault

6. Life on the Continental Shelf
Biologically rich
major portion of the fisheries global catch is caught over the continental shelf
Rich in potential natural resources
oil and natural gas
For this reason, countries wanted a way to protect these resources from exploitation by other countries
In the 1950’s, the United Nations agreed that each country shall have control over the marine resources out to 200 nautical miles (230 land miles) off their coast – this includes the continental shelf and its resources

7. Pelagic – water column away from bottom or shore
Epipelagic – sea surface to depth of about 200 meters – divided into:
neritic waters over the continental shelf
oceanic waters that are past the shelf

8. Marine areas that are never exposed during low tide
SUBTIDAL ECOSYSTEMS
Marine areas that are never exposed during low tide
always submerged

9. SUBTIDAL ABIOTIC FACTORS
rich in nutrients
autotrophs
decaying marine organic matter
brought in from rivers
Lithogenous sediments are formed by the weathering process and are made up of small particles of weathered rocks and oceanic volcanoes. They are often formed together when metal and silicate ions bond. There are two types of lithogenous sediments; terrigenous and “red clay” and they are different because of the process behind their existences. For instance, terrigenous sediments are produced as a result of the weathering process of rocks above the water. These eroded particles are carried by the wind and other natural means to the oceans and are deposited at the bottom. Although it can be easily found in river beds, not much of this finds its way to the deep ocean. Red clay lithogenous sediment, on the other hand, is plentiful in the ocean. It is reddish-brown (hence the name) and is a combination of terrigenous material and volcanic ash. It is transported to the oceans by currents and wind and it settles in deep places along the ocean floor.
Biogenous sediments are formed from the insoluble remains of past life forms and parts such as bones and teeth. In many areas where the water is shallow, a majority of these sediments are the remains of shells or fragments from shelled sea creatures as well as corals. In the deep sea where there is no such a high concentration of these life forms, biogenous sediment is made from the microscopic shells that are deposited by tiny plants, animals, and plankton that live on the water’s surface and eventually make their way down to the ocean floor.
Nile River Delta
Mississippi Delta

10. SUBTIDAL ABIOTIC FACTORS
Influenced by sedimentation processes (especially shallow areas)
lithogenic / terrigenous sediments
physical and chemical weathering of rocks (turbidities, volcanic ash, red clay)
brought in by rivers, reworked by waves
biogenic sediments
shells and skeletons of marine organisms

11. Abiotic/Physical Features
temperature – varies from place to place; affects distribution of organisms
more affected by waves and currents than deep water
turbulence – water motion – mixes up nutrients so they don’t accumulate on bottom = highly productive
substrate
sandy or muddy dominate
rocky

12. Pelagic Benthic SUBTIDAL ORGANISMS Plankton (floaters)
Nekton (swimmers)
Benthic
Demersal (hover)
Epifauna (on)
Infauna (in)

13. Distribution of marine life
Pelagic
Benthic

14. Sampling the Benthic Habitat
Bottom trawls
Grabs
Dredges

15. SUBTIDAL COMMUNITIES Soft-bottom Subtidal Seagrass Beds
Hard-bottom Subtidal
Kelp Forests

16. SOFT-BOTTOM SUBTIDAL COMMUNITIES
Dominant substrate sand & mud

17. Soft-Bottom Subtidal Communities
Dominates the world’s continental shelves
Animals are distributed in this community based on:
sediment particle size
sediment stability
salinity
light and temperature
Organisms usually occur in patches, due to planktonic settlement
Metamorphose and “tasting settlement sites”

18. Soft-Bottom Subtidal Communities
Notable absence of large plants and algae
Occasional green algae
Main producers are diatoms
Detritus important food source
there is little benthic primary production
filter and suspension feeders rely on detritus brought in from estuaries
Deposit feeders and bacteria dominate fine sediments due to high organic content

19. SOFT-BOTTOM SUBTIDAL ORGANISMS
Mostly infauna, some epifauna, almost no sessile organisms (nothing to hold onto)
Infauna – benthic organisms that bury themselves in the sediment
Epifauna – organisms that inhabit the surface of the bottom sediment
No. of subtidal species > intertidal (more stable, no desiccation)
Distribution of organisms influenced by particle size (mud or sand)

20. Soft-bottom subtidal communities
Infauna: 
live within the sediment, mostly soft bottom; 
mostly clams and worms (polychaetes) 
burrow tubes for food scavenging and oxygen supply
primary producers: algae, mostly benthic diatoms and dinoflagellates
detritus important food source

21. Infauna

22. Epifauna

23. Soft-bottom subtidal communities

24. Life on the Continental Shelf
Meiofauna – live between sediment grains
Many of these species are found no where else and include protozoa, cnidarians, crustaceans, nematodes, & annelids
These species have appendages and attachment structures to lock themselves to sediment grains

25. Life on the Continental Shelf
Thousands of animals consume nutrients on the seabed
Several species of worms may share an area, burrowing into the sediment and cementing the grains together into tubes of all shapes and sizes
Other burrowing animals include clams, lobsters, mud shrimp, and fish
The abundant life in the sediment attracts predators like cephalopods, fish, and marine mammals

26. Soft bottom subtidal communities
32,000 polychaetes in sand/m2 vs
earth worms in soil/m2
Polycheate Ecological Role:
clean sediments
aerate sediments

27. Life on the Continental Shelf
Soft-bottomed benthic-
Bioturbators (organisms that disturb bottom sediments) constantly “churn” the bottom
This churning helps to oxygenate benthic soils
Bioturbators can include worms, mollusks, fish and even whales
Skates and stingrays as well as sperm whales are well known for their activity as bioturbators

28. Carnivore feeders

29. Herbivore feeders

30. Deposit-feeders

31. Suspension-feeders

32. Soft-bottom subtidal communities
Generalized food web

33. Seagrass beds Areas that are carpeted by flowering plants
They develop best in sheltered shallow areas along the coast
Eel grass is the most common representative

34. Seagrasses Many sessile animals and epiphytic algae
Thick mats of eel grass provide lots of habitat for animals to hide
By stabilizing the sediment it decreases the turbidity
Dead sea grasses provide lots of detritus that benefit suspension, deposit and filter feeders
Many sessile animals and epiphytic algae

35. Soft-bottom subtidal communities
Epibionts
Seagrasses support many sessile animals and epiphytic algae

36. Life on the Continental Shelf
Seagrass Beds
Thalassia (turtle grass) is a common seagrass in tropical and subtropical areas
It is named turtle grass because it is often directly consumed by green sea turtles
In fact, patches of turtle grass have been shown to be “farmed” by individual turtles
In this farming, green turtles bite the tops off the turtle grass
When the tops grow back, they are much more tender and easier to digest by green sea turtles

37. Life on the Continental Shelf
Seagrass beds
Zostera or eelgrass prefers cooler, temperate waters
Like turtle grass, it can be directly consumed by herbivores
Both species are often important to the food chain after decaying to form detritus

38. Sea Grass Food Web

39. Hard-Bottom Subtidal Communities
Less common than soft-bottomed
Often, the result of a submerged rocky shoreline creating lots of hiding places
Rock formations attract a wide variety of organisms including many sessile types that cannot survive in soft bottomed communities
Oyster reefs, worm tubes and calcareous algae can all serve as hard-bottomed communities as well

40. Sea urchins grazing on seaweed in a hard bottomed subtidal community

41. PRODUCERS Most important communities - seaweeds Strong competition
Amount of light influence distribution of seaweeds
Seaweeds found in these areas have higher chlorophyll concentration

42. GRAZERS
invertebrates that move slowly: sea urchins, limpets, chitons, abalone
defense against predators
- by having food that is not tasty
- fast regeneration
- calcification (formed of calcium carbonate)

43. Generalized food web for hard-bottomed subtidal community

44. Kelp Forests
Animals that are present have the same characteristics as those of the rocky intertidal
Kelp is a macroalgae which can reach amazing sizes

45. Kelp and Kelp Forests

47. Air sack
holdfast

49. Life on the Continental Shelf
Kelp community-
Kelps are macroalgae that are restricted to cold water distributions
In addition to requiring cold water, kelps are very nutrient-needy
This is the result of the fast growth seen in these algae (up to 20 inches a day)

50. Life on the Continental Shelf
Laminaria - species of kelp common in the North Atlantic, North Pacific and the Asiatic coast of the Pacific
one of the smaller species of kelp at maximum heights of only around 10 feet
its rapid growth provides an enormous amount of primary production in the areas where it is found
can be found growing with larger kelp species in the North Pacific primarily

51. Life on the Continental Shelf
Macrocystis is a large species of kelp that can grow heights of over 100 feet
found mainly in the Pacific on the coasts of North and South America
This species forms thick forests that serve as a MAJOR ocean ecosystem in the areas where it is found

52. Kelp Communities Several species of kelp-community
fishes sheltering near giant kelp, Macrocystis.
© Galina Barskaya/ShutterStock, Inc.

54. Life on the Continental Shelf
The diagram at the right shows the anatomy of a kelp forest
Thousands of organisms are dependent on the kelp forests for shelter (habitat) or for trophic needs

55. Kelp Communities
Below the effects of waves and tides, kelp communities dominate in temperate areas
General structure of a West Coast kelp forest, with a complex
understory of plants beneath the dominant Macrocystis or Nereocystis.

56. Hard-bottom subtidal communities
Examples of N. Atlantic Kelp

57. Geographic distribution of kelp

58. Life on the Continental Shelf
Kelp community-
Sea urchins are by far the largest direct consumer of kelp
In turn, many species feed on the sea urchins including their “cousins” the seastars, and sea otters

59. Figure 14. 4: Sea urchins, bane of the kelp beds
Figure 14.4: Sea urchins, bane of the kelp beds. The urchins can absorb carbohydrates that leak from the algae or gnaw the stipes and holdfasts with their teeth. Too many urchins can destroy a kelp forest by releasing the kelp from its holdfasts.

61. Sea Urchins What leads to population explosions?
Absence of their predators
Overfishing, less seals & sea lions, killer whales eat sea otters, more urchins

64. Pictoral Food Web Example

65. Figure 16-7 Kelp Forest Community
Figure 16-7 Kelp Forest Community. Kelps provide both habitat and food for a large number of marine organisms.