Unit 14Animals of the Benthic

Environment

Benthic organismsBenthic organisms are those that live in or on the ocean floorMore than 98% of known marine species are benthicThe vast majority of benthic species live within the shallow continental shelf…Why?

Benthic biomass closely matches surface productivity

Surface productivity

Benthic biomass

Shoreline habitatsThe type of shoreline depends on the waves, currents, and topography.Rocky shores occur along steep shorelines exposed to wave and storm actionSandy shores occur along shallow shorelines where waves and currents deposit sediments.

Rocky shoresMost organisms live on the surface (epifauna)Zonation of rocky shores:

Spray zone (rarely covered by water)High tide zoneMiddle tide zoneLow tide zone (rarely exposed)

Upper zones have mostly shelled organismsLower zones have many soft-bodied organisms and algae

Spray Zone Supratidal zoneOrganisms

Avoid drying outMany animals have shellsFew species of marine algae

Intertidal Zone OrganismsHigh tide zone

Animals have shells to avoid drying outMarine algae—rock weeds with thick cell walls

Intertidal Zone OrganismsMiddle tide zone

More types of marine algaeSoft-bodied animals

Intertidal Zone OrganismsLow tide zone

Abundant algaeMany animals hidden by sea weed and sea grassCrabs abundant in all intertidal zones

Movement of epifaunaSessile – attached to the sea floor (e.g. kelp, barnacles)Motile – move over the sea floor (e.g. crabs, snails)

Sea anemoneA vicious predator cleverly disguised as a harmless flower but armed with stinging cells

Sediment-covered shoresMost organisms burrow into the sediment (infauna)Sediment-covered shores include:

BeachesSalt marshesMud flats

Intertidal zonation and organisms

Modes of feeding

Bivalve MollusksSoft body, hard hinged shellExample: clams and musselsGreatest number in low tide regionsHow a clam burrows

Gastropod mollusksGastropods are mollusks that form the spiral-shaped sea shells we find on beachesThey move with a single foot Are found in the ocean, freshwater, and on land (slugs and snails)

Shallow offshore ocean floorExtends from the spring low-tide shoreline to the edge of the continental shelfMostly sediment-covered but contains rocky exposuresIncludes:

Kelp forestsCoral reefs

Kelp forestsKelp forests are found on rocky bottoms and provide habitat for many organismsGant brown bladder kelp Macrocystis has a strong holdfast and gas-filled floatsMacrocystis can grow up to 0.6 meter (2 feet) per day

Kelp Distribution

Coral reefsCoral reefs are hard, wave-resistant structures composed of individual coral animals (polyps)Individual coral polyps:

Are about the size of an antAre related to jellyfishFeed with stinging tentaclesLive attached to the sea floor in large coloniesConstruct hard calcium carbonate structures for protectionContain 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 actionLack 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 AlgaeCoral reefs made of algae, mollusks, foraminifers as well as coralsHermatypic coral – mutualistic relationship with algae

Algae provide foodCorals provide nutrients

Mixotrophs – derive part of nutrition from algae

Importance of Coral ReefsLargest 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 reefsImportant tourist localesFisheriesReefs 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 polypsOutbreaks (greatly increased numbers) decimatse reef

Stages of coral reef development

Coral bleachingCoral bleaching occurs when symbiotic zoothanthellae algae is removed or expelledAssociated with high water temperatures

The deep-ocean floorCharacteristics of the deep ocean:

Absence of sunlightTemperatures around freezingAverage salinityHigh dissolved oxygenExtremely high pressureSlow 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 ridgeDo not rely on food from sunlit surface watersOrganisms include:

Tube wormsClamsMusselsCrabsMicrobial mats

Alvin approaches a hydrothermal vent biocommunity

Locations of deep-sea biocommunities

Deep-sea vent biocommunity food source: ChemosynthesisDeep-sea vent biocommunities rely on bacteria and archaeon that chemosynthesize

Other deep-sea biocommunitiesLow-temperature seep biocommunities are associated with:

Hypersaline seepsHydrocarbon seepsSubduction zone seeps