Life on the Continental Shelf

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Chapter 13

• Life on the Continental Shelf

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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.

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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).

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• 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

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Types of Communities on the Continental Shelf

1. Soft-bottomed benthic
2. Seagrass beds
3. Kelp forests
4. Hard-bottomed benthic

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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

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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.

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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

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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

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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

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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

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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

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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

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Sea _____ grazing on seaweed in a hard bottomed
subtidal community
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Generalized food web for hard-bottomed subtidal
community
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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)

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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

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Geographic distribution of kelps
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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

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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