Life on the Continental Shelf

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Life on the Continental Shelf
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• Continental Shelf
• shallow submerged extension of the continent

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(low tide to shelf break))
(Tidal zone)
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THE CONTINENTAL SHELVES

• Shallow part of sea floor
• Immediately adjacent to surrounding land
• Relatively smooth platform that ends in shelf
  break
• Covers 1/6 of earth surface
• Topography irregular many small hills, valleys
  and depressions
• Sediment type mainly sand- or silt-sized
  fluviatile (deposited by rivers)

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THE CONTINENTAL SHELVES

• Average width 75 km, narrower in areas with
  strong current
• Average slope 0o07
• Average depth flattest portion 60 m
• Average depth where greatest change of slope
  130 m
• Hills of 20 m or more and depression of 20 m or
  more

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SUBTIDAL ABIOTIC FACTORS

• temperature fluctuates from one area to another
  especially with depth
• 1 atm increase in pressure with 10 m depth
• strong influence of currents and waves especially
  those in the shallow depths
• turbulence may prevent stratification

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SUBTIDAL ABIOTIC FACTORS

• rich in nutrients (brought in from river
  discharges)
• influenced by sedimentation processes
  (especially shallow areas)
• - lithogenic sediments (physical and chemical
  weathering of rocks)
• - biogenic sediments (shells and skeletons of
  marine organisms)

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Sediment Runoff
River Deltas

• Feature
• Triangle deposit of sediment

Nile River Delta
Mississippi Delta
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SUBTIDAL ORGANISMS

• Plankton (suspended in water column)
• Nekton (able to swim against current)
• Benthos (on/in bottom sediment)

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SUBTIDAL ORGANISMS

• Factors that may influence subtidal organisms
• 1. Water depth
• 2. Distance from land.

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Distribution of Marine Life

• A. Pelagic

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Distribution of marine life
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Distribution of Marine Life

• A. Pelagic
• B. Benthos

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Distribution of marine life
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Distribution of Marine Life

• A. Pelagic
• B. Benthos
• 1. Demersal
• 2. Epifauna
• 3. Infauna

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Intertidal Zone
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SUBTIDAL COMMUNITIES

1. Soft-bottom Subtidal Communities
2. Hard-bottom Subtidal Communities

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SOFT-BOTTOM SUBTIDAL COMMUNITIES

• Made up of
• A. Muddy substrate
• B. Sandy substrate

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SOFT-BOTTOM SUBTIDAL COMMUNITIES

• Influenced by
• 1. Particle size distribution
• 2. Sediment stability
• 3. light
• 4. salinity
• 5. temperature

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CHARACTERISTICS OF SOFT-BOTTOM SUBTIDAL
COMMUNITIES

• Type of dominant substrate ie sand, mud etc.
• Most infauna, some epifauna and almost no sessile
  organisms

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SOFT-BOTTOM SUBTIDAL COMMUNITIES

• More abundant than soft-bottom intertidal
  communities
• Less abiotic problems
• 1. No problem with desiccation
• 2. Temperature and salinity more stable

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DISTRIBUTION OF ORGANISMS

• Particle size influence distribution of infauna
  (?)
• Particle size distribution (depending on depth)
• Easier for organisms to borrow in sand compared
  to mud (water drainage better in sand)
• Patchy sediment type patchy distribution of
  organisms

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DISTRIBUTION OF ORGANISMS

• Some larvae choose substrate before undergoing
  metamorphosis
• Some larvae can detect adults and settle close by

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SOFT-BOTTOM SUBTIDAL ORGANISMS

• 1. infauna
• Benthic organisms that bury themselves in the
  sediment
• 2. epifauna
• Organisms that inhabit the surface of the bottom
  sediment
• No. of subtidal sp. gt intertidal (more stable, no
  desiccation)
• Distribution of organisms influenced by particle
  size (mud or sand)

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Epifauna
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Soft-bottom subtidal communities

• Infauna 
• live within the sediment, mostly soft bottom 
• mostly clams and worms (polychaetes) 
• burrow tubes for food scavenging and oxygen
  supply
• Primary producers algae, mostly benthic diatoms
  and dinoflagellates
• cyanobacteria mats on mudflats
• mud more productive than sand
• macro- and meiobenthos, often detrivores, living
  of deposits from seagrasses and marshes
• birds important grazers

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Infauna
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PRODUCTIVITY

• Minimum productivity
• (by diatoms and other microalgae)
• Most communities based on detritus

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DEPOSIT FEEDERS

• 1. Polychaetes accumulation using tentacles or
  by ingestion of sediment
• 2. Sand dollars use mucus to bring food to
  mouth
• 3. Bent nosed clam collect sediment using
  siphon
• 4. Brittle stars collect detritus using
  tube-feet
• 5. Peanut worms, sea cucumber, ghost shrimp

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Tube feeding by polycheate, Arenicola Marina.
Black arrows show water flow and open arrows
show sediment flow. Sediment brought to anoxic
area, digested and deposited at upper region of
shaft
Proboscis
Gills
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SUSPENSION/ FILTER FEEDERS

• Cockles water intake via siphon
• Polychaetes and amphipods
• Brittle star traps particles using tube feet
• Sea pens traps particle from water column

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Scavenger and Predator

• Shrimps and large crustaceans (scavenger)
• Whelks dan moon snail feed on other bivalves
• Sea stars and crabs (can act as scavenger or
  predator)
• Rays and skates
• Flounder, halibut and sole

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Soft-bottom subtidal communities
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Soft-bottom subtidal communities
Examples of meiofauna in sand
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Soft bottom subtidal communities

• 32,000 polychaetes in sand/m2
• vs
• 50-500 earth worms in soil/m2
• Ecological Role
• clean sediments
• aerate soil

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HARD-BOTTOM SUBTIDAL COMMUNITIES

• Small subtidal communities
• Some time they may be in the form of coral reefs
• Hard substrate may include organisms that produce
  calcium carbonate
• Rich in epifauna but less as infauna

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HARD-BOTTOM SUBTIDAL COMMUNITIES

• Rocky shore
• Coral reefs
• Most important organisms are the sea weeds (able
  to settle on rocks/hard substrate

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PRODUCERS

• Most important communities - seaweeds
• Strong competition
• Amount of light influence distribution of sea
  weeds
• Weeds found in these areas have higher
  chlorophyll concentration

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grazers

• Invertebrates that move slowly sea urchin,
  limpets, chitons, abalone
• Algal defense against predators
• - By having food that are not tasty
• - Fast regenaration
• - Calcification (formation of calcium)

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Hard-bottom subtidal communities
Epibionts
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Hard-bottom subtidal communities
Generalized food web
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Hard-bottom subtidal communities
Examples of N. Atlantic Kelp
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Hard-bottom subtidal communities
Geographic Distribution of Kelp
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Hard-bottom subtidal communities
Life History of Kelp
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Hard-bottom subtidal communities
Distribution of Kelp
What abiotic and biotic factors affect
distribution?
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Hard-bottom subtidal communities
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1. What is the sublittoral zone?
2. What is meiofauna (infauna)?
3. How do organisms survive living in a soft bottom
   community?
4. What food source are soft-bottom communities are
   based on?
5. Why dont we see anemones and sea slugs in the
   high tide zone?