The Deep Sea

Physical characteristics of deep sea

  • Dark, no light deeper than 1000m

  • Cold

  • Constant salinity

  • Oxygen available

  • High nutrients

  • High pressure 1 atm/10 m

  • Slight seasonality

Sampling

  • Bathysphere off Bermuda

  • Alvin submersible, Woods Hole Oceanographic Institute

Focal Components of Pelagic Deep Sea

  • Deep sea benthic communities

  • Hydrothermal vents

  • Cold seeps

95% of all marine species are benthic

Substrate Types

Hard Rock

  • Uncommon in deep sea.

  • Spreading centers - hydrothermal vents

  • Active faults

  • Sides of Seamounts

  • On other organisms

  • Offshore banks

  • Manganese nodules

Sediments

  • Different origins: terrigenous (near shore), biogenic (skeletal remains), aeolian (atmosphere), cosmic (meteors)

  • Deposition rates: open ocean - mm/1000y. coastal - cm/1000y

Organisms

Epifauna - sediment surface

Errant species - movile ( echidnoderms, fish, crustaceans )

Sessile species - non mobile (barnacle, worm, sponge)

Infaunal (living in sediment) organisms are the dominant organisms. Macro (snails)>meio (ciliates or worms)>micro

Benthic boundary layer - the water layer immediately above the seafloor. Upward from 10 to 100m above the bottom. Area of high re-suspension, favorable for suspension feeders.

Adaptations for little food

  • Detritus (marine snow, big particles, pieces of other organisms): plants, animals, fecal pellets, molts, etc. Called detritivores

  • Ladder of vertical migration. Bands of organisms can migrate up/down at certain depths

  • Chemosynthesis - hydrothermal vents. Deep sea primary production

Dominant feeding modes

  • Suspension feeding - Prevalent down to 2-3km depth then becomes less abundant, especially on sandy sediments. Ex. Crinoids

  • Deposit feeding - Increases with depth - less energy expensive - very common on muddy sediments. ex. Polychaetes

Oddities of the Deep: Gigantic Scavengers (ex. giant isopod), Detritivores and herbivores can become carnivorous (ex. Carnivorous Ascidian)

Hydrothermal Vents

  • Discovered 1977 - temperature anomaly detected by geologists

  • Same year as Submersible Alvin

  • Spots for high biomass

  • Vent areas 20-60m²

  • 95% of species are endemic to vents

  • Gigantism

  • Free living bacteria in plumes= 10^5 - 10^6 cells per mL

  • 1993 → outpourings of hyperthermophilic bacteria discovered, rich in Archaea (Archaea tolerates >90 degrees C, extremophiles)

  • Some filter feeders use bacteria as food source

Main organisms at vents

  • Worms - tube worms grow up to 3m in length, can grow 85cm/year - have no guts or mouth… how do they survive?? Chemosynthesis

  • Giant Clams - Calyptogena up to 30cm length

  • Other mussels

Black smokers

  • 400 degrees C, 750 degrees F

  • Reduced saltwater components - iron related, metal

  • Lifetime of vent: several years to decades

  • Chimneys grow 10cm/DAY, total height 45ft. lifetime is around 10 years

White smokers

  • Carbonate precipitates out - white chimney

100’s of km between vents … how do organisms get to the next site? Whale corpses.

Cold seeps

  • Discovered in 1990s

  • Slow continued seepage of reduced chemical compounds from the ocean floor (mainly methane)

  • Similar taxa but different species than at hydrothermal vents (mssels, tube worms)

  • NO extremophiles at seeps.

  • Chemosynthetic bacteria at base of food web, bacterial extensive mats are common

  • Not short lived like hydrothermal vents.