ZOOPLANKTON Diverse -- protozoans and others Nutrition modes: Herbivores (graze on phytoplankton) Carnivores (predators) Radiolaria Foraminifera Zooplankton: 1. Protozoans: Foraminifera and Radiolarians -warm waters 2. Crustaceans Copepods Most numerous and wide-spread multi-cellular zooplankton Copepods.. relatively small (few mm) Euphausids - e.g., shrimp-like "krill" - important food source at high latitudes,...for whales, etc....maybe for humans! Euphausia- Krill 1
Other representative zooplankton: Jellyfish, Portuguese man-of-war Colonies of distinct organisms Other zooplankton: Planktonic snails.. (Pteropods) "foot" has become a wing-like fin More zooplankton: Meroplankton: Eggs and larval stages of molluscs, fish, crustaceans Importance: dispersal of offspring food for predators 2
Vertical migration of some zooplankton (crustaceans, protozoans) Rise at night to feed Sink during day -> "Deep Scattering Layer" at 500 m Must be light-triggered (they descend during full moon, rise during a solar eclipse) Why? Possible reasons... 1. Evade predators (feed at night) 2. Rest in cooler, deeper waters during day 3. In some areas, subsurface currents return them to their proper habitat BACTERIA Present on everything Role: Decompose organic matter Release nutrient elements Bacteria as food resources: - Eaten by zooplankton Chemosynthetic bacteria Energy derived from chemical reactions Occurrence: 1. Hydrothermal vents: Oxidation of hydrogen sulfide in vent fluids Producers for an entire community of organisms 2. Cold seeps of oil and natural gas: Oxidation of methane gas Lecture 34 -- The Oceans NEKTON General characteristics Representatives Invertebrates Fish Cetaceans -- whales and porpoises Other mammals Reptiles Migration during life cycle -- some examples 3
GENERAL CHARACTERISTICS Nektonic organisms are swimmers Mode of nutrition: Herbivores Carnivores (predators, scavengers) Vertebrates dominate INVERTEBRATE NEKTON Different evolutionary branch from vertebratescan track this evolution through fossils in ocean sediments Examples: Large shrimp (Arthropods) Cephalopods (class of Mollusca): Chambered Nautilus Cuttlefish Squid FISH -- THE DOMINANT NEKTON - Distributed world-wide - Occur at all depths - Concentrated in the epipelagic zone (0-200m) - Deep-water and bottom dwellers also Cartilagenous fish: (Skeletons of cartilage, not bone) Sharks- well adapted (evolved over 300 Million Years ago!) Wide-spread, epipelagic Active predators (some are plankton feeders) Skates and rays Shallow-bottom dwellers Carnivores AND plankton feeders 4
Bony fish: (includes most eels) Epipelagic representatives (commercially fished) Tuna, Salmon -- predators Herring, Anchovy -- plankton feeders Coastal bottom-dwellers (commercially fished) Halibut, Sole Deep-sea Bony fish (>200m = Dark) Habitat: Below the photic zone All species are carnivorous Food comes down from photic zone Scarce food below about 1000m Competition Need to attract prey Need to eat large prey- as large as possible Need to conserve energy between meals Deep-sea Bony fish (>200m = Dark) General features -- adaptations: Large, light sensitive eyes Small (<10 cm), Low rates of metabolism Large mouths, well-developed teeth Luminsecent -- light-producing organs Attraction of prey Mate selection Deep-Sea Bony Fish: Representatives Cyclothone, Lantern fish: Abundant in mesopelagic (200-1000m) Feed on Euphausids (Krill) and Copepods migration Hatchetfish- Eyes and mouth directed upward Angler fish- Deeper (>1000m) Luminous moveable lure Parasitic male attached to body of female 5
CETACEANS Evolved from a common terrestrial ancestor 1. Baleen whales -- filter-feeders (plankton, small fish) 2. All other whales, plus porpoises, dolphins Toothed Fast-swimming predators Fig. 11.19 Baleen OTHER MARINE MAMMALS 1. Pinnepeds ("feather-footed") common ancestors Seals, Sea Lions, Walruses Habitat: polar, midlatitudes Require shore and/or sea-ice areas 2. Sea cows -- Manatees, Dugongs: tropical herbivores 3. Sea otters Habitat: cold, coastal waters Nutrition: carnivores of benthos 6
MARINE REPTILES Few species, but successful Representatives: Turtles Crocodiles Snakes Marine Iguanas MIGRATION OF NEKTONIC SPECIES -- SOME NOTABLE EXAMPLES WHY MIGRATION? Migration links...... regions appropriate for reproduction... regions of feeding for adults Examples: California Grey Whales- Mexico to Alaska Pacific Salmon- fresh water spawning Atlantic Eels- salt water spawning- opposite Atlantic Green Turtles- nesting sites vs. foraging 7