Benthos

• Unlike the drifting plankton and swimming nekton, benthic organisms – commonly referred to as benthos – live on or near the ocean bottom

• A benthic habitat may be shallow or deep• Most benthic organisms are sessile (immobile)

and anchored to the benthic environment; others crawl or swim over the ocean bottom

Benthos

• Of the 250,000 known species that inhabit the marine environment, >98% are benthos!

• The majority of benthic organisms live on the continental shelf; sunlit areas of relatively high primary productivity

• Benthos include animals, protists (algae) and even plants!

Intertidal Zones

• Rocky shorelines team with organisms that live on the ocean floor (epifauna)

• Typical rocky shores are divided into distinct zones, characterized by the height of the water (which is itself determined by the tides)

• So called intertidal zones are among the most densely-populated areas on Earth; hundreds of species crowd this junction of land and sea

Life in the intertidal zone is harsh!

• Adverse conditions require special adaptations of organisms to live both underwater (some of the time) and exposed to air (the rest of the time)!

• Strong wave activity, desiccation (drying out), limited space, rapid changes in temperature, salinity, pH, and oxygen content, and predation are just some of the challenges found here

Spray zone – region above the spring high tide line; covered by water only during storms

Intertidal zone – region between the high and low tidal extremes

Intertidal Zone

• High tide zone: relatively dry

• Middle tide zone: alternatively wet and dry

• Low tide zone: usually wet, but exposed during low tides

http://www.humboldt.edu/~intertid/zones.html

Mostly shelled organisms

Mostly soft-bodied organisms and algae

Life in the intertidal: High tide zone

• Most animals living in the high tide zone have protective coverings to prevent desiccation

• Seaweeds living in the high tide zone have thick cell walls to reduce water loss during low tides

• Many organisms in the high tide zone are sessile, and remain attached to bottom, competing with others for limited space

www.armofthesea.info/flora_faunaff_speciespp/moll.htm

Life in the Intertidal: Middle tide zone

• Seawater constantly bathes the middle tide zone, so a greater variety of seaweeds and soft-bodied organisms live here

• Greater biomass in middle tide zone, and so greater competition for space!

• Mussels and barnacles are common here – hard-bodied, filter-feeding organisms which require seawater to feed and to support planktonic larval stages

Crying cockles and mussels, alive, alive-O!

• The middle tide zone is also home to carnivorous snails and sea stars

• You, too, can be a sea sleuth….• Sea stars pry open clams and mussels with

hundreds of tube feet; Predatory snails bore holes with scraping tongues and suck out prey

• Hermit crabs, sea urchins, and sea anemones are also found here

Life in the Intertidal: Low tide zone

• The low tide zone is almost always submerged, so an abundance of algae (seaweed) is typically present

• Seaweeds are multi-cellular algae (protists)• Seaweeds attach themselves with a structure

known as a holdfast and use gas bladders to reach upward to sunlit surface water; photosynthetic; important source of habitat

Life in the Intertidal: Low tide zone

• Numerous crabs and shellfish live in the low tide zone

• Benthic fish swim through the low tide zone, along with larval nektonic forms which seek shelter and habitat in this protected area

Salt marshes are sediment-covered shores

• Salt marshes and estuaries (regions where freshwater and saltwater meet) are highly productive benthic habitats

• Much of this productivity comes from sea grasses, mangroves and other vascular plants

• Salt marshes form in estuaries and are characterized by specialized plants capable of surviving in (and then out of) salt water

Salt marshes: Home Sweet Home

• Salt marshes – via their specialized plants – form protective barriers against erosion, and promote new land formation as plant roots trap sediments on each tidal cycle, and filter out excess nutrients and pollutants

• Salt marshes also provide protective habitat for larval fish species, and provide food and shelter for migratory waterfowl; marsh plants also form the base of the food web via decay

Salt Marshes are Vital Habitats!

http://en.wikipedia.org/wiki/File:Bride-Brook-Salt-Marsh-s.jpg

Sand and Cobble Beach Communities

• Not all intertidal areas are rocky or muddy; some are sandy or consist of gravel or cobbles

• As benign and peaceful as sandy beaches look, they are among the most hostile environments for small organisms

• Sand grains are abrasive and many organisms must have protective coatings and/or be able to burrow below the surface for protection

Sand and Cobble Beach Communities• In fact, very few organisms survive in wave-

swept sandy beaches• Some larger crabs can outrun the crashing

waves and locate food within sand grains• Coquina shells and mole crabs are common

along Long Island sandy beaches

www.stripersonline.com/surftalkshowthread.php?t=417951

Coral Reef Communities

• Corals are animals (Cnidarians) related to anemones and jellyfish

• Most corals secrete hard skeletons of calcium carbonate and produce coral reefs

• An individual coral – known as a polyp – feeds by capturing and eating plankton that drift within reach of their tentacles

• Corals produce sexually and asexually

Coral Reef Communities

• Corals form symbiotic relationships with dinoflagellates, known as zooxanthellae

• Zooxanthellae receive nutrients and shelter from the coral, and photosynthesize, providing the coral with organic compounds

• Zooxanthellae provide corals (otherwise translucent) with their brilliant colors

www2.watertown.k12.wi.us/pagesfifth_grade_websites.cfm

Tropical coral reefs support large numbers of species

• Reef-building corals provide substrate for other organisms to attach and hide

• Corals also provide a source of food in otherwise weakly-productive regions

• Coral bleaching (the loss of the symbiotic zooxanthellae in response to environmental stress) may kill the coral, and have devastating impacts on the coral reef community

Coral Bleaching

www.cgrer.uiowa.edu/peoplecarmichael/atmos_course/ATMOS_PROJ_99/jlmichfin/main.html

Corals are stressed by environmental change

• A water temperature change of only 1°C above the normal summer high temperature for a few weeks leads to coral bleaching– Coral expels zooxanthellae or zooxanthellae

expels itself

• El Niño events can drive coral bleaching• May be reversible – corals can re-aquire new

zooxanthellae if the stress is not too severe

Want to learn more?• Take our Marine Biology and/or Marine

Habitat Ecology courses!

Until then, so long and thanks for all the fish!