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

2. 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.

3. Life on the Continental Shelf
Water turbulence created by waves and currents keep the water column well mixed.
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 (the pelagic environment above the continental shelf).

4. Pelagic – water column away from bottom or shore
Epipelagic – sea surface to depth of about 200 meters
The epipelagic can be divided into (1) neritic waters over the continental shelf and (2) oceanic waters that are past the shelf

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

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

7. Life on the Continental Shelf
Soft-bottomed benthic-
Infauna like snails, clams, urchins, and annelids as well as epifauna like crustaceans and brittle stars.
Many are tube-builders to assist with the stability of the habitat.
Generalized Food Chain
Detritus from other communities->meiofauna
(ciliate)->deposit (polychaete) & filter feeders (clam)

8. Life on the Continental Shelf
Meiofauna
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

9. 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 stringrays as well as sperm whales are well known for their activity as bioturbators

10. 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 and most common genus is Zostera, commonly called eelgrass
Species have particular tolerance levels with regards to temperature, water clarity and nutrient availability that determines their distribution
Many sessile animals and epiphytic algae

12. Life on the Continental Shelf
Seagrass Beds
Because of their different tolerances, seagrass 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 provides large amounts of detritus

13. 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 that bite the tops off the turtle grass. When the tops grow back, they are more tender and easier to digest by green sea turtles
Seagrass (Eelgrass)->Detritus->Filter (clams) and Deposit Feeders (polychaetes)->Herbivores (Sea urchins and fish)->Carnivores (Sea stars, fish, and seabirds)

14. Life on the Continental Shelf
Hard-bottomed subtidal-
Less common
Often, it is 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

15. Sea _____ grazing on seaweed in a hard bottomed subtidal community

16. Generalized food web for hard-bottomed subtidal community

17. Life on the Continental Shelf
Kelp community-
Kelps are ____ 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)

18. 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

19. Geographic distribution of kelps

20. 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

21. 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