The Benthic Zone

1. The Benthic Zone Benthic zone is the substrate (floor) on both the shallow continental shelf and the abyss.

2. The substrate is composed of 4 types of sediment: 1. Biogenous or organic • greater than 30% organic material • Oozes • Contain skeletal & fecal remains • Terrigenous or lithogenous • greater than 30% inorganic products of weathering & volcanic ash. • Hydrogenous or authogenic • minerals precipitated from chemical compounds in seawater • Cosmogenous • materials that fall from space.

3. These different types of sediments, called patchiness, determine where animals will live on the ocean floor. • Grains of sediment become sorted depending upon how long they have been around and the transportation mechanisms.

4. Porosity • the amount of pore spaces for air, food, and water held between grains. • More spaces = better environment • Sorting • measure of uniformity of grain size • Poorly sorted grains are many different sizes and have better porosity • Well-sorted grains are less porous, are nearly the same size and provide poor habitat. • Poorly-sorted grains are good because they provide better habitats, hold more food & water.

5. Maturity • measures the age of the sediments • Older sediments will have been exposed to heavy erosion • Younger sediments show less erosion

6. Characteristics of the Benthic Zone: • 90% of organisms on continental shelf • 10% in the abyss • Mesopelagic zone - 99% of the organisms are bioluminescent (produce light by chemical reaction) • Very stable environment - increases with depth. • Lack of light is a major limiting factor - reducing food, predation, and mating.

7. Diversity increases with depth - more niches are created because resources are limited. • Oxygen is supplied from cold, saline waters of the poles. • Biomass decreases with depth - this low population density is directly related to food scarcity.

8. Communities entirely composed of consumers and scavengers • Producers are found only in photic zones • Decomposers like bacteria are more common in mid-water mesopelagic zone.

9. Hydro-Thermal Vent Communities • The exception in benthic communities’ producers are the chemosynthetic bacteria around hydrothermal vents. • 1977 - scientists (DSV Alvin - Project FAMOUS) discovered unique hydrothermal vent communities. • Vent communities found in all oceans at depths 1-2 miles down.

10. Bacteria living near the vent use hydrogen sulfide dissolved in seawater to build organic molecules in a process called chemosynthesis. • Animals clustered near the vents grow to huge sizes; can withstand temperature differences from 36o to 662o F. • The community also has many suspension-feeders attached to the hard rock bottom which is unusual in the deep sea

11. Vents last 100 years - when supply of H2S is exhausted, the ecosystem dies. • Cold Seeps - methane and sulfur-rich fluids seep into the ocean floor where symbiotic bacteria use sulfur oxidation for survival. • Cold Seeps are home to millions of benthic worms, crabs, and mollusks.

12. Summary Questions • How is biomass and diversity related to an increase in depth? • Why is the herbivore trophic level absent in deep sea benthic pyramids? • How do the sizes of organisms living around the hydrothermal vents compare with other benthic organisms?

13. Adaptation of Benthos Benthos is the name of organisms living on the substrate. They obtain food by: • Suspension feeding - • filter food suspended in water column • Sandy & course sediments where currents contain large quantities of food and stable (don’t clog feeding mechanism) • Corals living below the light

14. Deposit feeding • Eat food particles lying in sediments • Dominants in muddy, fine sediments • Scavengers or Croppers • Quickly locate dead animals falling from above. • Go for long periods without food. • Will eat deposit feeders

15. Other Adaptations include: • Special respiratory & feeding appendages that keep animals above the sediment to prevent clogging or smothering in the substrate. • Expandable mouth and bodies to accommodate large but infrequent meals.

16. Air bladders are small or missing as buoyancy is not needed. Pressure is required for proper enzyme functioning. • Evisceration (expelling) internal organs to provide predator with a meal while they escape to regenerate lost parts.

17. Lights and lures to attract prey, mates or frighten predators. • Blind creatures occur where sight is of no advantage.

18. Reproductive Strategies: • Dispersal of planktonic larvae • common only on the shelf. • Adv: chance for larvae to land on the best substrate • Disadv: heavy predation

19. Direct development (brooding) • internal fertilization is common in cold, deep water where food is scarce. • Adv: protection of an adult • Disdv: is adult is eaten, all the offspring are lost

20. Asexual reproduction • Budding • Adv: solves the problem of finding a mate • Disadv: lacks the adaptability provided by variety in a gene pool

21. Summary Questions • How do benthic organisms reproduce? • Name 4 adaptations for benthic marine life. • Why are benthic organisms difficult to study?

22. Phylum Mollusca Second largest phylum behind Arthropoda General Characteristics: • Many are benthic • Complete digestive tract • Open circulatory system • Usually separate sexes • Cephalization (having a head) • Soft bodies; mantle secretes a shell

23. Class Gastropoda • Gastro = stomach • Pod = foot • Univalvia (one shell) • Ex: snail, abalone, conch • Most are benthic herbivores • Dog welk is carnivirous • Radula (tongue) with a ribbon of flexible teeth works like a mini-chain saw

24. Class Pelecypoda • Bivalvia (two-footed, also two shells) • Ex: clams, oysters, scallops • Benthic planktivores • Filter sea water through an inccurrent & excurrent pore. • Sessile (oyster) • Swim by opening & closing both shells (scallop)

25. Class Cephalopoda • Cephalo = head • Pod = foot • Squid, octopus, cuttlefish, chambered nautilus • Have the most advanced brain of all invertebrates. • Mouth has a sharp beak for eating worms & fish

26. Moves by jet-propulsion - mantle fills with water which can be squirted out to propel them backwards. • Chromatophoresin the skin change colors when the animal is alarmed and for camouflage.

27. Ink gland is used as a “smoke screen” for quick escape. • Eyes have a cornea, lens and retina; excellent vision.

28. Squid • Internal shell (pen) that is clear and flexible. The only hard part of their body is their beak. • Has 2 tentacles with flat paddles.

29. Octopus • A soft, flexible body allows the octopus to hide in very small spaces. • Very shy & do not attack humans nor eat ships • Enjoy human contact in captivity • Octupus’ head has 8 regenerative arms

30. Octopus • Octopus reproduction is by internal fertilization. • During the 30 days until hatching, the female carefully aerate, cleans and watches the eggs - never leaving (even to eat). • The female usually dies from exhaustion and starvation soon after they hatch.

31. Cuttlefish • The cuttlefish has an internal shell that is sold in pet stores as a source of calcium for birds.

32. Chambered Nautilus • The spiraled shell is lined with mother-of-pearl and perfectly proportioned. • The walls (septa) divide a series of compartments in the shell and are pierced by a tube (siphuncle) connected to the nautilus. • Gas & liquid exchange occurs through the siphuncle walls and allows the nautilus to regulate it buoyancy.

33. Summary Questions • Identify three members of the phylum Mollusca. • Why do squids ink? • Which type of mollusk has bilateral symmetry?