1. Chapter 13 Lecture Slides
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2. Life on the Continental Shelf
Chapter 13
Life on the Continental Shelf

3. Life on the Continental Shelf
The continental shelf is the submerged edge of a continental plate.
The shelf extends from the low tide line to an area known as the shelf break.
The slope of the continental shelf is normally more gradual, whereas, the slope past the shelf break is normally very steep.

4. Life on the Continental Shelf
The slope of the shelf, the depth of the water at the shelf break and the distance of the shelf break from shore varies greatly by location (remember active versus passive margins).
Remember from chapter 12 that estuaries are much more well developed in areas of the world where the continental shelf has a gradual slope and is very wide.
This is the case on the East Coast of the US, which is the reason for the well developed estuaries there.

5. Life on the Continental Shelf
The depth of water at the shelf break varies greatly with an average depth of around 490 feet.
The width of the continental shelf also varies greatly from 0.6 miles to 470 miles with an average of 48 miles.

6. Life on the Continental Shelf
The continental shelf is biologically the richest part of the ocean (more species present).
This is also an area of potential natural resources such as 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 off their coast – this includes the continental shelf and its resources.

7. Life on the Continental Shelf
A major portion of the fisheries global catch is caught over the continental shelf.
The shelf is an important area for larvae and juveniles of many species as well as adults.
A wide variety of organisms can be found on/in the continental shelf. Some of the most common includes sponges, cnidarians, worms, molluscs, fish and echinoderms.

8. Life on the Continental Shelf
Temperature:
Temperature of the water over the continental shelf varies much more than the water in the deep sea (but less than in an estuary).
The temperature fluctuates more because the water is shallower than in the deep sea and because waves and currents keep the water circulating. This means that warmer surface waters are mixing readily with the rest of the water column.

9. Life on the Continental Shelf
Water turbulence created by waves and currents keep the water column well mixed.
This affects not only the temperature of the water, but also affects the nutrients available in the water.
Nutrients never have a chance to “rain down” on the bottom and be lost the way they do in the deep sea.
This constant water motion means the nutrients are available to the benthic organisms as well as those in the neritic zone.

10. Life on the Continental Shelf
Water may have less clarity due to the many nutrients in the water and due to suspended sediments.
Nutrients come from many sources, including:
Autotrophs
Decaying marine organic matter
Nutrients delivered from estuaries and terrestrial ecosystems via rivers

11. 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.

12. Types of Communities on the Continental Shelf
Soft-bottomed benthic
Seagrass beds
Kelp forests
Hard-bottomed benthic

13. Life on the Continental Shelf
Soft-bottomed benthic-
Dominant bottom type on the continental shelf
Infauna, epifauna and meiofauna are present as well as neritic species above the benthos
Sessile types are rare due to lack of “hard substrate” for attachment (remember, limiting resources????)
There are more species present in this area than in the adjoining intertidal, but the distribution is often patchy

14. Life on the Continental Shelf
Soft-bottomed benthic-
Larvae are often attracted to areas where adults reside
This is thought to be the result of chemical cues in the water
If it’s good enough for the adults, its good enough for the youngsters!

15. Life on the Continental Shelf
Soft-bottomed benthic-
A few varieties of infauna and epifauna are seen at right
You may notice that many are tube-builders to assist with the stability of the habitat

16. Life on the Continental Shelf
A wide variety of organisms also live in the spaces between the particles of sediment- meiofauna
Many of these species are found no where else
As you can see at the right, these species have appendages and attachment structures to lock themselves to the grains of sediments

17. Life on the Continental Shelf
Soft-bottomed benthic-
Many species in this area are deposit feeders (directly getting nutrients from the soft bottomed material)
Many other species are suspension feeders and filter nutrients directly from the water
Both are pictured at right

18. 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, mollucs, fish and even whales
Skates and stringrays as well as sperm whales are well known for their activity as bioturbators

19. Life on the Continental Shelf
Seagrass Beds
They are best developed in sheltered, shallow waters with good water clarity
There are over 50 known species
Species have particular tolerance levels with regards to temperature, water clarity and nutrient availability that determines their distribution

21. Life on the Continental Shelf
Seagrass Beds
Due to these tolerances, species normally prefer either cool waters OR tropical/subtropical waters, but not both normally
They are often found in combination with algal species
The density of individual seagrass plants tend to be very thick (high biomass) – this can been seen at right

22. 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, which makes the turtles happy!!!!

23. Life on the Continental Shelf
Seagrass beds
Zostera or eelgrass prefers cooler, temperate waters
It is mainly found in the Pacific and the North Atlantic
Like turtle grass, it can be directly consumed by herbivores
Both species are often important to the food chain after decaying

24. Life on the Continental Shelf
Hard-bottomed subtidal-
Less common
Often, it is the result of a submerged rocky shoreline
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 subtidal communities as well

26. Life on the Continental Shelf
Hard-bottomed subtidal-
One of the best features of the hard-bottomed community is the hiding places it provides for prey and predators alike
Insert fig 13.20

28. Life on the Continental Shelf
Kelp community-
Kelps are brown algae that are restricted to cold waters in distribution
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)

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

30. Life on the Continental Shelf
Macrocystis is a large species of kelp that can grow heights of over 100 feet
It is 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

32. 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 starfish and sea otters

33. 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