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 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

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!

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

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

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!