Life on the Continental Shelf Shipley Marine Biology.

Life on the Continental ShelfLife on the Continental Shelf

Shipley Marine BiologyShipley Marine Biology

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.

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.


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.


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.


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.


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.


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.


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


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.


1. Soft-bottomed benthic2. Seagrass beds3. Kelp forests4. Hard-bottomed benthic

Types of Communities 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 substrat

e” for attachment (remember, limiting resources????)

There are more species present in this area than in the adjoining intertidal, but the distribution is often patchy



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!


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

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

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

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


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


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

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!!!!


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


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


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



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)

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


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



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


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

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Life on the Continental Shelf Shipley Marine Biology.

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