Chapter 18 The Benthos: Dwellers of the Sea Floor

1. Chapter 18 The Benthos: Dwellers of the Sea Floor

2. 18.1 Algae and Plants • General characteristics of benthic algae • Holdfast, stipe, and blades • Confined to shallow depths • Kinds of seaweeds • Green algae (shallow water) • Most similar to land plants • Store starch • Brown algae (moderate depth) • Range from microscopic chains of cells to kelps—the largest of the algae • Red algae (maximum depth) • Most advanced and varied in form • Other marine plant communities • Sea grasses • Marsh grasses • Mangroves

3. 18.2 Animals • Animals of the rocky shore • Relationship of organisms to intertidal environment (extremes)  vertical zonation • Tide pools • Small, isolated pools  specialized habitat • Deeper tide pools provide stable habitat for starfish, sea urchins, and sea cucumbers • Animals of the soft substrates • Few grazing animals (no algae) • Detritus feeders • Bioturbation • Bacteria (important source of protein)

4. 18.2 Animals, continued • Animals of the deep-sea floor • Number of species increases with depth • Fouling and boring organisms • Organisms that foul surfaces include: barnacles, anemones, tube worms, sea squirts, and algae • Shipworm and gribble are responsible for wood boring

5. 18.3 High-Energy Environments • Battered by waves • Reduces predators • Moving water brings constant supply of nutrients • More productive than rain forests

6. 18.4 Coral Reefs • Tropical corals • Colonial animals called polyps, symbiotic relationship with zooxanthellae • Tropical coral reefs • Complex assemblages, many types of algae and animals • Coral bleaching • Effect of El Niño • Predation and disease • Sea star Acanthaster • Coralline lethal orange disease, known as CLOD • Human activities • Sport divers trampling delicate corals • Deforestation and development • Use of cyanide and explosives by fishers • Deep-water corals • Coral preserves

7. 18.5 Deep-Ocean Chemosynthetic Communities • Hot vents • Discovered in 1977, using submersible Alvin • Found around the world near seafloor spreading centers • Chemosynthesis by bacteria (primary producers) • Densely populated communities • Cold seeps • Bacteria use methane and hydrogen sulfide (primary producers) • Large communities where oil and gas seep onto the sea floor

8. Boxed Reading: Deep-Sea Ice Worms • Gas hydrates: icelike deposits of methane and some hydrogen sulfide gas • Formed at cold temperature and high pressures • Mound discovered in Gulf of Mexico • Sediment free • Densely covered with worms (new species) • Worms are believed to feed on bacteria living on the ice surface

9. 18.6 Practical Considerations: Harvesting the Benthos • The animals • Valuable part of the seafood harvest • Crustaceans: crabs, shrimp, prawns, and lobsters • Mollusks: clams, mussels, oysters, and squid • Overfishing • Conservation programs difficult to implement • The algae • Food • Good source of vitamins and minerals • Not a good source of calories • Industrial uses • Biomedical products • Thousands of active compounds in marine organisms

10. Boxed Reading: Genetic Manipulation of Fish and Shellfish • Gene transfer and chromosome manipulation techniques • Produce faster growing fish • Triploid or transgenic fish • Produce bigger fish • Select gender • Prevent sexual maturation (triploid) • Resistance to disease or cold temperatures • Transgenic • Potential impact on wild populations

11. Summary • Benthic algae anchored to firm substrates • Holdfast, stipe, and photosynthetic blades • Provide food, shelter, and substrate for other organisms • Benthic animals classified into epifauna and infauna • Midlittoral zone • Crowded • Wide variety of animals • Deep-sea floor • Uniform environment • Increasing diversity of species with depth • Decreasing population with depth • High-energy coastal benthic environments • High productivity • Coral reefs • Under great stress, including human threats