Benthos

1. 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

2. 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!

3. 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

4. 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

5. 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

6. Mostly shelled organisms 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 soft-bodied organisms and algae http://www.humboldt.edu/~intertid/zones.html

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. Salt Marshes are Vital Habitats! http://en.wikipedia.org/wiki/File:Bride-Brook-Salt-Marsh-s.jpg

15. 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

16. 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

17. 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

18. 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

19. 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

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

21. 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

22. Want to learn more? • Take our Marine Biology and/or Marine Habitat Ecology courses!

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