Chapter 13 Life on the Continental Shelf. The continental shelf is the submerged edge of a...

Chapter 13Chapter 13

Life on the Continental ShelfLife on the Continental Shelf


• The continental shelf is The continental shelf is the submerged edge of the submerged edge of a continental plate. a continental plate.

• The shelf extends from The shelf extends from the low tide line to an the low tide line to an area known as the area known as the shelf break.shelf break.

• The slope of the The slope of the continental shelf is continental shelf is normally more gradual, normally more gradual, whereas, the slope whereas, the slope past the shelf break is past the shelf break is normally very steep.normally very steep.


• The slope of the shelf, the depth of the The slope of the shelf, the depth of the water at the shelf break and the distance water at the shelf break and the distance of the shelf break from shore varies of the shelf break from shore varies greatly by location. greatly by location.

• Estuaries are much more well developed Estuaries are much more well developed in areas of the world where the continental in areas of the world where the continental shelf has a gradual slope and is very wide. shelf has a gradual slope and is very wide.

• This is the case on the East Coast and Gulf This is the case on the East Coast and Gulf of the US, which is the reason for the well of the US, which is the reason for the well developed estuaries there.developed estuaries there.


• The depth of water at the shelf break The depth of water at the shelf break varies greatly with an average depth varies greatly with an average depth of around 490 feet.of around 490 feet.

• The width of the continental shelf The width of the continental shelf also varies greatly from 0.6 miles to also varies greatly from 0.6 miles to 470 miles with an average of 48 470 miles with an average of 48 miles. miles.


• The continental shelf is biologically rich.The continental shelf is biologically rich.• This is also an area of potential natural This is also an area of potential natural

resources such as oil and natural gas.resources such as oil and natural gas.• For this reason, countries wanted a way to For this reason, countries wanted a way to

protect these resources from exploitation protect these resources from exploitation by other countries. by other countries.

• In the 1950’s, the United Nations agreed In the 1950’s, the United Nations agreed that each country shall have control over that each country shall have control over the marine resources out to 200 nautical the marine resources out to 200 nautical miles (=1.15 land miles) off their coast – miles (=1.15 land miles) off their coast – this includes the continental shelf and its this includes the continental shelf and its resources.resources.


• A major portion of the fisheries global A major portion of the fisheries global catch is caught over the continental catch is caught over the continental shelf. shelf.

• The shelf and associated estuaries The shelf and associated estuaries are an important area for larvae and are an important area for larvae and juveniles of many species as well as juveniles of many species as well as adults.adults.

• A wide variety of organisms can be A wide variety of organisms can be found on/in the continental shelf.found on/in the continental shelf.


• Temperature:Temperature:– Temperature of the water over the Temperature of the water over the

continental shelf varies much more than continental shelf varies much more than the water in the deep sea (but less than the water in the deep sea (but less than in an estuary).in an estuary).

– The temperature fluctuates more The temperature fluctuates more because the water is shallower than in because the water is shallower than in the deep sea and because waves and the deep sea and because waves and currents keep the water circulating. This currents keep the water circulating. This means that warmer surface waters are means that warmer surface waters are mixing readily with the rest of the water mixing readily with the rest of the water column.column.


• Water turbulence created by waves and Water turbulence created by waves and currents keep the water column well mixed.currents keep the water column well mixed.

• This affects not only the temperature of the This affects not only the temperature of the water, but also affects the nutrients available in water, but also affects the nutrients available in the water.the water.

• Nutrients never have a chance to “rain down” Nutrients never have a chance to “rain down” on the bottom and be lost the way they do in on the bottom and be lost the way they do in the deep sea. the deep sea.

• This constant water motion means the nutrients This constant water motion means the nutrients are available to the benthic organisms as well are available to the benthic organisms as well as those in the neritic zone (the pelagic as those in the neritic zone (the pelagic environment above the continental shelf).environment above the continental shelf).

• Pelagic – water column away from Pelagic – water column away from bottom or shorebottom or shore

• Epipelagic – sea surface to depth of Epipelagic – sea surface to depth of about 200 meters about 200 meters – The epipelagic can be divided into (1) neritic The epipelagic can be divided into (1) neritic

waters over the continental shelf and (2) waters over the continental shelf and (2) oceanic waters that are past the shelfoceanic waters that are past the shelf


• Water may have less clarity due to the Water may have less clarity due to the many nutrients in the water and due to many nutrients in the water and due to suspended sediments.suspended sediments.

• Nutrients come from many sources, Nutrients come from many sources, including:including:– AutotrophsAutotrophs– Decaying marine organic matter or _____Decaying marine organic matter or _____– Nutrients delivered from estuaries and Nutrients delivered from estuaries and

terrestrial ecosystems via riversterrestrial ecosystems via rivers


• Thousands of animals consume nutrients on Thousands of animals consume nutrients on the seabed. the seabed.

• Several species of worms may share an area, Several species of worms may share an area, burrowing into the sediment and cementing burrowing into the sediment and cementing the grains together into tubes of all shapes the grains together into tubes of all shapes and sizes. and sizes.

• Other burrowing animals include clams, Other burrowing animals include clams, lobsters, mud shrimp, and fish. lobsters, mud shrimp, and fish.

• The abundant life in the sediment attracts The abundant life in the sediment attracts predators like cephalopods, fish, and marine predators like cephalopods, fish, and marine mammals. mammals.

Types of Communities on the Types of Communities on the Continental ShelfContinental Shelf

1.1. Soft-bottomed benthicSoft-bottomed benthic

2.2. Seagrass bedsSeagrass beds

3.3. Kelp forestsKelp forests

4.4. Hard-bottomed benthic Hard-bottomed benthic


• Soft-bottomed benthic-Soft-bottomed benthic-– Dominant bottom type on the continental Dominant bottom type on the continental

shelfshelf– Benthos of infauna, epifauna and Benthos of infauna, epifauna and

meiofauna are present as well as _____ meiofauna are present as well as _____ species (pelagic species above continental species (pelagic species above continental shelf) above the benthosshelf) above the benthos

– Sessile types are rare due to lack of “hard Sessile types are rare due to lack of “hard substrate” for attachmentsubstrate” for attachment

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


• Soft-bottomed Soft-bottomed benthic-benthic-– Infauna like Infauna like

snails, clams, snails, clams, urchins, and urchins, and annelids as annelids as well as well as epifauna like epifauna like crustaceans crustaceans and brittle and brittle stars.stars.

– Many are tube-Many are tube-builders to builders to assist with the assist with the stability of the stability of the habitat.habitat.

Life on the Continental ShelfLife on the Continental Shelf• MeiofaunaMeiofauna• Many of these Many of these

species are found species are found no where else and no where else and include protozoa, include protozoa, cnidarians, cnidarians, crustaceans, crustaceans, nematodes, & nematodes, & annelids annelids

• These species have These species have appendages and appendages and attachment attachment structures to lock structures to lock themselves to themselves to sediment grainssediment grains

Life on the Continental ShelfLife on the Continental Shelf• Soft-bottomed Soft-bottomed

benthic-benthic-– Many species in Many species in

this area are this area are deposit feeders deposit feeders (directly getting (directly getting nutrients from the nutrients from the soft bottomed soft bottomed material) in less material) in less turbulent watersturbulent waters

– Many other Many other species are filter species are filter feeders and water feeders and water turbulence brings turbulence brings in detritus and in detritus and some animals are some animals are bioturbatorsbioturbators


• Soft-bottomed benthic-Soft-bottomed benthic-– Bioturbators (organisms that disturb bottom Bioturbators (organisms that disturb bottom

sediments) constantly “churn” the bottomsediments) constantly “churn” the bottom– This churning helps to oxygenate benthic This churning helps to oxygenate benthic

soilssoils– Bioturbators can include worms, mollusks, Bioturbators can include worms, mollusks,

fish and even whalesfish and even whales– Skates and stringrays as well as sperm Skates and stringrays as well as sperm

whales are well known for their activity as whales are well known for their activity as bioturbatorsbioturbators


• Seagrass BedsSeagrass Beds– They are best developed in sheltered, They are best developed in sheltered,

shallow waters with good water clarityshallow waters with good water clarity– There are over 50 known species and most There are over 50 known species and most

common genus is common genus is Zostera, Zostera, commonly called commonly called eelgrasseelgrass

– Species have particular tolerance levels with Species have particular tolerance levels with regards to temperature, water clarity and regards to temperature, water clarity and nutrient availability that determines their nutrient availability that determines their distributiondistribution

– Many sessile animals and epiphytic algaeMany sessile animals and epiphytic algae

Life on the Continental ShelfLife on the Continental Shelf• Seagrass BedsSeagrass Beds

– Because of their different Because of their different tolerances, seagrass tolerances, seagrass species normally prefer species normally prefer either cool waters OR either cool waters OR tropical/subtropical tropical/subtropical waters, but not both waters, but not both normallynormally

– They are often found in They are often found in combination with algal combination with algal speciesspecies

– The density of individual The density of individual seagrass plants provides seagrass plants provides large amounts of detrituslarge amounts of detritus


• Seagrass BedsSeagrass Beds– ThalassiaThalassia (turtle grass) is a common seagrass (turtle grass) is a common seagrass

in tropical and subtropical areasin tropical and subtropical areas– It is named turtle grass because it is often It is named turtle grass because it is often

directly consumed by green sea turtlesdirectly consumed by green sea turtles– In fact, patches of turtle grass have been In fact, patches of turtle grass have been

shown to be “farmed” by individual turtlesshown to be “farmed” by individual turtles– In this farming, green turtles bite the tops off In this farming, green turtles bite the tops off

the turtle grassthe turtle grass– When the tops grow back, they are much more When the tops grow back, they are much more

tender and easier to digest by green sea tender and easier to digest by green sea turtlesturtles


• Seagrass bedsSeagrass beds– ZosteraZostera or eelgrass prefers cooler, or eelgrass prefers cooler,

temperate waterstemperate waters– Like turtle grass, it can be directly Like turtle grass, it can be directly

consumed by herbivoresconsumed by herbivores– Both species are often important to the Both species are often important to the

food chain after decaying to form food chain after decaying to form detritusdetritus

Life on the Continental ShelfLife on the Continental Shelf• Hard-bottomed subtidal-Hard-bottomed subtidal-

– Less commonLess common– Often, it is the result of a submerged rocky Often, it is the result of a submerged rocky

shoreline creating lots of hiding placesshoreline creating lots of hiding places– Rock formations attract a wide variety of Rock formations attract a wide variety of

organisms including many sessile types organisms including many sessile types that cannot survive in soft bottomed that cannot survive in soft bottomed communitiescommunities

– Oyster reefs, worm tubes and calcareous Oyster reefs, worm tubes and calcareous algae can all serve as hard-bottomed algae can all serve as hard-bottomed communities as wellcommunities as well

Sea _____ grazing on seaweed in a hard bottomed subtidal community

Generalized food web for hard-bottomed subtidal community


• Kelp community-Kelp community-– Kelps are ____ algae Kelps are ____ algae

that are restricted that are restricted to cold waters in to cold waters in distributiondistribution

– In addition to In addition to requiring cold requiring cold water, kelps are water, kelps are very nutrient-needyvery nutrient-needy

– This is the result of This is the result of the fast growth seen the fast growth seen in these algae (up to in these algae (up to 20 inches a day)20 inches a day)


• LaminariaLaminaria is a species of kelp common in is a species of kelp common in the North Atlantic, North Pacific and the the North Atlantic, North Pacific and the Asiatic coast of the PacificAsiatic coast of the Pacific

• This is one of the smaller species of kelp at This is one of the smaller species of kelp at maximum heights of only around 10 feetmaximum heights of only around 10 feet

• Like other species, its rapid growth Like other species, its rapid growth provides an enormous amount of primary provides an enormous amount of primary production in the areas where it is foundproduction in the areas where it is found

• It can be found growing with larger kelp It can be found growing with larger kelp species in the North Pacific primarilyspecies in the North Pacific primarily


• MacrocystisMacrocystis is a large species of kelp is a large species of kelp that can grow heights of over 100 that can grow heights of over 100 feetfeet

• It is found mainly in the Pacific on the It is found mainly in the Pacific on the coasts of North and South Americacoasts of North and South America

• This species forms thick forests that This species forms thick forests that serve as a MAJOR ocean ecosystem serve as a MAJOR ocean ecosystem in the areas where it is foundin the areas where it is found

Geographic distribution of kelps


• Kelp community-Kelp community-– Sea urchins are by Sea urchins are by

far the largest direct far the largest direct consumer of kelpconsumer of kelp

– In turn, many In turn, many species feed on the species feed on the sea urchins sea urchins including their including their “cousins” the “cousins” the starfish and sea starfish and sea ottersotters

Life on the Continental ShelfLife on the Continental Shelf• The diagram The diagram

at the right at the right shows the shows the anatomy of anatomy of a kelp foresta kelp forest

• Thousands Thousands of organisms of organisms are are dependent dependent on the kelp on the kelp forests for forests for shelter shelter (habitat) or (habitat) or for trophic for trophic needsneeds

Chapter 13 Life on the Continental Shelf. The continental shelf is the submerged edge of a...

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