Unit 14
Animals of the Benthic
Environment
Benthic organisms
Benthic organisms are those that live in or
on the ocean floor
More than 98% of known marine species
are benthic
The vast majority of benthic species live
within the shallow continental shelf…Why?
Benthic biomass closely matches
surface productivity
Surface productivity
Benthic biomass
Shoreline habitats
The type of shoreline depends on the waves, currents, and
topography.
Rocky shores occur along steep shorelines exposed to
wave and storm action
Sandy shores occur along shallow shorelines where waves
and currents deposit sediments.
Rocky shores
Most organisms live on the surface (epifauna)
Zonation of rocky shores:
Spray zone (rarely covered by water)
High tide zone
Middle tide zone
Low tide zone (rarely exposed)
Upper zones have mostly shelled organisms
Lower zones have many soft-bodied organisms
and algae
Spray Zone
Supratidal zone
Organisms
Avoid drying out
Many animals have
shells
Few species of
marine algae
Intertidal Zone Organisms
High tide zone
Animals have shells to avoid drying out
Marine algae—rock weeds with thick cell walls
Intertidal Zone Organisms
Middle tide zone
More types of marine algae
Soft-bodied animals
Intertidal Zone Organisms
Low tide zone
Abundant algae
Many animals hidden by sea weed and sea grass
Crabs abundant in all intertidal zones
Movement of epifauna
Sessile – attached to the sea floor (e.g. kelp,
barnacles)
Motile – move over the sea floor (e.g.
crabs, snails)
Sea anemone
A vicious
predator
cleverly
disguised as a
harmless
flower but
armed with
stinging cells
Sediment-covered shores
Most organisms burrow into the sediment
(infauna)
Sediment-covered shores include:
Beaches
Salt marshes
Mud flats
Intertidal zonation and organisms
Modes of feeding
Bivalve Mollusks
Soft body, hard hinged shell
Example: clams and mussels
Greatest number in low tide regions
How a clam burrows
Gastropod mollusks
Gastropods are mollusks that form the spiral-shaped sea
shells we find on beaches
They move with a single foot
Are found in the ocean, freshwater, and on land (slugs and
snails)
Shallow offshore ocean floor
Extends from the spring low-tide shoreline
to the edge of the continental shelf
Mostly sediment-covered but contains
rocky exposures
Includes:
Kelp forests
Coral reefs
Kelp forests
Kelp forests are found on
rocky bottoms and provide
habitat for many organisms
Gant brown bladder kelp
Macrocystis has a strong
holdfast and gas-filled floats
Macrocystis can grow up to
0.6 meter (2 feet) per day
Kelp Distribution
Coral reefs
Coral reefs are hard, wave-resistant structures
composed of individual coral animals (polyps)
Individual coral polyps:
Are about the size of an ant
Are related to jellyfish
Feed with stinging tentacles
Live attached to the sea floor in large colonies
Construct hard calcium carbonate structures for
protection
Contain symbiotic photosynthetic zooxanthellae algae
Conditions for coral reef development
Coral reefs need:
Warm water: 18-30°C (64-86°F)
Strong sunlight (for symbiotic algae)
Strong wave/current action
Lack of turbidity (clear seawater)
Normal salinity (not too fresh or salty)
Hard substrate for attachment
Coral reef distribution and
diversity
Coral reef zonation
Symbiosis of Coral and Algae
Coral reefs made of algae,
mollusks, foraminifers as well
as corals
Hermatypic coral –
mutualistic relationship with
algae
Algae provide food
Corals provide nutrients
Mixotrophs – derive part of
nutrition from algae
Importance of Coral Reefs
Largest structures created by living organisms
Great Barrier Reef, Australia, more than
2000 km (1250 miles) long
Great diversity of species--25% of all marine
species found on reefs
Important tourist locales
Fisheries
Reefs protect shorelines
Humans and Coral Reefs
Fishing, tourist collecting, and sediment influx due to
shore development harm coral reefs.
Sewage discharge and agricultural fertilizers increase
nutrients in reef waters.
Crown of Thorns Phenomenon
Sea star eats coral
polyps
Outbreaks (greatly
increased numbers)
decimatse reef
Stages of coral reef development
Coral bleaching
Coral bleaching
occurs when
symbiotic
zoothanthellae
algae is removed
or expelled
Associated with
high water
temperatures
The deep-ocean floor
Characteristics of the deep ocean:
Absence of sunlight
Temperatures around freezing
Average salinity
High dissolved oxygen
Extremely high pressure
Slow bottom currents (except abyssal storms)
Low food supply
Food sources for deep-sea
organisms
Deep-sea hydrothermal vent
biocommunities
Found in deep water near black smokers along the
mid-ocean ridge
Do not rely on food from sunlit surface waters
Organisms include:
Tube worms
Clams
Mussels
Crabs
Microbial mats
Alvin approaches a hydrothermal
vent biocommunity
Locations of deep-sea
biocommunities
Deep-sea vent biocommunity
food source: Chemosynthesis
Deep-sea vent biocommunities rely on bacteria
and archaeon that chemosynthesize
Other deep-sea biocommunities
Low-temperature seep biocommunities are
associated with:
Hypersaline seeps
Hydrocarbon seeps
Subduction zone seeps