• 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

• 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!

• 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

• 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

Mostly shelled organisms
Mostly softbodied organisms and algae http://www.humboldt.edu/~intertid/zones.html
• High tide zone: relatively dry
• Middle tide zone: alternatively wet and dry
• Low tide zone: usually wet, but exposed during low tides

• 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

• 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

• 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

• 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

• 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 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 – 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

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

• 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

• In fact, very few organisms survive in waveswept 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

• 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

• 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

• 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

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

• 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

• Take our Marine Biology and/or Marine
Habitat Ecology courses!