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MAY 2011
Oceanography Ch # 15.
Animals in the Benthic Environment
Approx. 95% of marine organisms live on the sea floor, which varies from rocky to sandy to muddy.
15 -1. Distribution of Benthic Organisms
Most biomass depends on the productivity of the surface waters. Sunlight penetrates to the
bottom where the water is shallow.
15 -2. Communities along Rocky Shores
Organisms on the rocky surface (epi-fauna) are either permanently attached or move on it. The
biodiversity varies widely (algae, crabs).
The rocky shore can be divided into:
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A spray zone (supra tidal) located above the highest tide zone. Species have hard shells and
avoid drying out.
An intertidal zone. Residents in this zone include rock lice and sea roaches, and scavengers.
In the High tide zone, organisms have a protective covering to prevent drying out. Rock
weeds are among the first to colonize the area.
In the middle Tidal zone, are primarily algae and soft bodied animals. Acorn barnicles,
various mussels. Carnivorous snails and sea stars feed on the mussels. Sea anemones,
hermit crabs, sea urchins feed on algae in intermittent pools.
In the low tide zone, almost always submerged, there are abd. Algae and shore crabs, who
hide during daylight hours and feed at night.
15 -3. Communities along sediment covered shores
In-fauna organisms are abundant. They burrow into the sediment. The water infiltrates into the
sediment carrying nutrients and oxygen.
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Intertidal zones are similar to those on a rocky shore.
Sandy beaches – organisms (mollusks, worms, crustaceans) burrow into the sand, which is
moist and has a constant temp.
Mudflats have a large population of turtle grass, and fiddler crabs.
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15 -4. Communities on the shallow offshore ocean floor.
Extends from low tide to the continental shelf edge. The biodiversity ranges from low to
moderate. Benthic organisms diversity is lowest beneath upwelling waters.
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Rocky bottoms are covered by various types of macroscopic algae, kelp and forest kelp.
Lobsters and oysters are also present.
Coral reefs are constructed by polyps extracting CaCO3 . Polyps live throughout the sea, but
build structures only in warm, shallow, clean marine areas with rocky substrate. (limits N35
Deg and S 35 Deg). Polyps live in a symbiotic relationship with Algae. Water temp must be
< 86 Deg F and > 64 Deg F.
15 -5. What Communities exist on the Deep Ocean Floor?
Deep sea Hydrothermal Vents
1977 discovery. Water temp 46 to 54 Deg F. on the Galapagos Ridge. Tube worms > 1 met long.
Baja California Vent 662 Deg F. Black smoker emits sulfides, are acidic and toxic (H2S and heavy
metals)
Other vents have a limited life span.
The Dead whale Hypothesis is used to explain the movement from one vent to another.
Additional seeps are
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Hypersaline at depths 10,500 ft.
Hydrocarbons at 2300 ft.
Subduction zones the water is slightly warmer than expected
The deep biosphere is a new Frontier. Discovered microbial communities within the porous part of the
sea floor.