The Benthic Environment

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The Benthic Environment
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Benthic Environment Habit Factors to Understand

• Sunlight penetration (solar energy supply)
• Water depth
• Substrate (material on the ocean floor where
  did it come from, what is its composition, what
  is its texture?)
• Nutrient supply and distribution
• Current and wave interactions energy from wind
  (atmosphere) or thermohaline circulation
  processes
• Pressure with depth affects not only what lives
  there (body adaptations) but also the materials
  that can be dissolved in water (carbonate
  compensation depth CCD)

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Benthic environments

• Supralittoral
• Subneritic
• Littoral zone between high tide and low tide

Fig. 12.19
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Distribution of benthic organisms
Fig. 15.1

• High concentration of benthic organisms beneath
  areas of high primary productivity
• Mainly on continental shelves (within euphotic
  zone)
• Affected by surface ocean currents and sediment
  fluxes

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Littoral zoneIntertidal zonation (rocky
shore)
Fig. 15.2 a
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Benthic organisms on rocky shores

• Epifauna
• Sessile - attached to substrate (e.g., marine
  algae)
• Mobile/Motile - move over seafloor (e.g., crabs,
  snails)
• Moderate diversity of species
• Greatest animal diversity at tropical latitudes
• Greatest algae diversity at mid-latitudes

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Intertidal zonation (rocky shore)

• Spray zone (supratidal)
• Avoid drying out
• Many animals have shells
• Few species of marine algae

Fig. 15.2b
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Intertidal zonation (rocky shore)

• High tide zone
• Avoid drying out so animals have shells
• Marine algaerock weeds with thick cell walls
• Middle tide zone
• More types of marine algae
• Soft-bodied animals
• Low tide zone
• Abundant algae
• Many animals hidden by sea weed and sea grass
• Crabs abundant in all intertidal zones

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Littoral ZoneIntertidal zonation (sandy shore)
Fig. 15.8
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Benthic organisms on sediment-covered shores

• Similar intertidal zones (littoral zone)
• Less species diversity
• Greater number of organisms
• Mostly infauna
• Burrow into sediment
• Microbial communities

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Benthic organisms on sediment-covered shores

• Coarse boulder beaches
• Sand beaches
• Salt marshes
• Mud flats
• Energy level along shore depends on
• Wave strength
• Longshore current strength
• Fine-grained, flat-lying tidal flat more stable
  than high energy sandy beach

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Sandy beaches

• Animals burrow (infauna)
• Bivalve mollusks
• Annelid worms

Crustaceans Echinoderms Meiofauna (small fauna
that live in between the substrate particles in
both fresh and saltwater)
Fig. 15-9
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Mud flats

• Eelgrass and turtle grass common
• Bivalves and other mollusks (infauna)
• Fiddler crabs (epifauna)
• This environment is also supratidal and has
  variable salinity, inundation, and temperature
  variations.

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Benthic environments

• Continental shelf
• Subneritic
• Littoral
• Sublittoral
• Inner
• Outer

Fig. 12.19
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Shallow ocean floor

• Continental shelf ( max 200 meters water depth)
• Mainly sediment covered (substrate from
  continents and weathered ocean floor)
• Kelp forest associated with rocky seafloor
• Lobsters (motile)
• Oysters (sessile)

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Coral reefs

• Most coral polyps live in large colonies
• Hard calcium carbonate structures
• Coral reefs limited to
• Warm (gt 18 C but not hot) seawater
• Sunlight (for symbiotic algae - photosynthesis)
• Strong waves or current action
• Clear seawater filter feeders
• Normal salinity
• Hard substrate (anchoring)

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Reef-building corals
Fig. 15-17
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Symbiosis of coral and algae

• Coral reefs made of algae, mollusks, foraminifers
  (zooplankton) as well as corals
• Hermatypic coral have a mutualistic relationship
  with algae
• Algae provide food
• Corals provide nutrients

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Coral reef zonation

• Different types of corals at different depths

Fig. 15.19
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Importance of coral reefs

• Largest structures created by living organisms
• Great Barrier Reef, Australia, more than 2000 km
  (1250 m) long
• Great diversity of species
• Important tourist locales
• Fisheries
• Reefs protect shorelines

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Humans and coral reefs

• Activities such as fishing, tourist collecting,
  sediment influx due to shore development harm
  coral reefs
• Sewage discharge and agricultural fertilizers
  increase nutrients in reef waters
• Hermatypic corals thrive at low nutrient levels
• Phytoplankton overwhelm at high nutrient levels
• Bioerosion of coral reef by algae-eating organisms

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Crown-of-thorns starfish and reefs

• Sea star eats coral polyps
• Outbreaks (greatly increased numbers) decimate
  reefs

Fig. 15.21
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Benthic environments

• Deep ocean benthic environments
• Suboceanic
• Bathyal
• Abyssal
• Hadal

Fig. 12.19
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Benthic organisms on the deep seafloor

• Little known habitat difficult to observe
• Bathyal, abyssal, hadal zones
• Little to no sunlight (aphotic zone)
• About the same temperature
• About the same salinity
• Oxygen content relatively high
• Pressure can be enormous
• Bottom currents usually slow (thermohaline
  currents)

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Food sources for deep seafloor

• Most food from surface waters
• Low supply (consumed before reaches deep water)

Fig. 15.22
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Deep-sea hydrothermal vent biocommunities

• First discovered 1977
• Chemosynthesis inorganic processes
• Archaea use sea floor chemicals to make organic
  matter
• Tube worms
• Giant clams and mussels
• Crabs
• Microbial mats
• Hot water and chemicals from magma at depth
  provide energy and materials for food manufacture

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Global hydrothermal vent fields
Fig. 15.24
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Deep-sea hydrothermal vent biocommunities

• Vents active for years or decades
• Animals species similar at widely separated vents
• Larvae drift from site to site
• Dead whale hypothesis
• Large carcasses may be stepping stone for larvae

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Deep-sea hydrothermal vent biocommunities

• Life may have originated at hydrothermal vents
• Chemosynthesis also occurs at low temperature
  seeps
• Hypersaline seeps
• Hydrocarbon seeps
• Subduction zone seeps

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Beneath the sea floor

• Deep biosphere
• Microbes (bacteria, viruses, and smaller) live in
  pore fluids
• Might represent much of Earths total biomass