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Chapter 18 The Benthos: Dwellers of the Sea Floor. 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)
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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
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)
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
18.3 High-Energy Environments • Battered by waves • Reduces predators • Moving water brings constant supply of nutrients • More productive than rain forests
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
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
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
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
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
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