bio 207 chapter 16: the ocean depths

mesopelagic zone

dimly lit, does not support photosynthesis, 200-1000 meters

deep sea

a region of perpetual darkness that consists of the bathypelagic, abyssopelagic and hadopelagic zones, uniformly dark, cold (35 degrees F), salinity

bathypelagic zone

1000 to 4000 meters

abyssopelagic zone

4000 to 6000 meters

hadopelagic zone

6000 meters to the benthic community, can be as deep as 11,000 meters in trenches

life in the ocean depths

reduced compared to other marine communities, due to reduction in amount of food available, low food due to lack of photosynthesis in the dark

oxygen minimum zone (OMZ)

oxygen levels are reduced due to a greater degree of respiration and lack of photosynthesis to replace the oxygen

food

in short supply, organisms rely on nutrients from surface waters to sink into deeper waters

vertical migrations

organisms spend their days in the mesopelagic and nights feeding in the epipelagic

thermocline

drastic drop in temperature that occurs with increased depth

mesopelagic animals

midwater animals, zooplankton (krill, copepods, shrimp), ostracods, amphipods, arrow worms, jellyfish, siphonophores, comb jellies, larvaceans, pteropods, squid, fish

photophores

light organs that emit light (bioluminescence)

ostracods

a group of crustaceans with a characteristic carapace that makes them look like tiny clams with legs

squid

weak or strong swimmers, possess photophores

vampire squid

looks like an octopus but is neither a squid nor an octopus, also has photophores

mesopelagic fish

typically small, 2-10 cm, bristlemouths and lanternfish, account for more than 90% of fish caught in midwater trawls, viperfish, dragonfish, barracudinas, saber-tooth fish, lancetfish, snake mackerels and cutlassfish

mesopelagic fish characteristics

long, eel-like, large mouths and eyes, photophores, less than 30 cm (lancetfish can reach 2 m), hinged, extendible jaws with fearsome teeth

Cyclothone signata

type of bristlemouths, most abundant fish on Earth

bristlemouths

named for their many bristle-like sharp teeth, have rows of photophores on their ventral surface

lanternfish

named for their rows of photophores that adorn their hands and bodies, have blunt heads, relatively large mouths and eyes

marine hatchetfish

hatchet-shaped with large eyes and mouths and ventral photophores

mesopelagic feeding

only 20% of surface primary production sinks down, fish size due to limited food, broad varied diets

non-migratory species

copepods and krill (filter out detritus and phytoplankton that sink from surface waters), shrimp, squids, mesopelagic fish (feed on fecal pellets of epipelagic grazers)

non-migrator characteristics

“sit and wait” predators - lurk in dim light and gulp anything within range
flabby, watery muscles rather than energy conserving muscles (do not swim much)
no swim bladder
soft and weak bones making them neutrally buoyant

migrating fish characteristics

swim up to epipelagic at night to feed, descend to depths during the day, safe from predators, well developed muscles and bones, swim bladder allowing for adapting to pressure changes, filled with gas or lipids

lethargic stupor

migrating fish conserving energy

tubular eyes

larger and extremely sensitive, good for upward and forward vision, not lateral vision, retina extends partway to one side of the eye to compensate

coloration

countershading and transparency (copepods, jellyfish, shrimp), silvery, black or red, black backs and silvery sides

body shape

laterally compressed bodies

bioluminescence

masks silhouettes, photophores on ventral surface breaks up silhouette and helps animal blend in with background light filtering down from the surface (counterillumination)

deep sea organism characteristics

no countershading, bioluminescence is common, small, functional eyes (some are blind), lack swim bladders, flabby muscles, light and weak skeletons, large mouths with long, pointed teeth

deep sea organism color

animals and zooplankton are drab gray or off-white, fish are black, shrimp are bright red

deep sea bioluminescence

occurrence decreases with increasing depth, used for courtship, communication or prey attraction, photophores located near or on the head

angler fish

“lure” on head that contains symbiotic bioluminescent bacteria to attract prey, male parasitism

angler fish male parasitism

males are smaller than females, males attach to females and receive their nutrition from them and fertilize their eggs

hermaphroditism

ensures reproduction occurs if encounters occur between members of the same species since each can act as male or female, important in environment where number of organisms is low

deep ocean floor

absence of sunlight, constant low temperature, great hydrostatics pressure, presence of a bottom

feeding in deep-sea benthos

sinking of large dead organisms, fecal pellets

deep sea benthos bacteria

decompose chitin of crustacean zooplankton at slower rate than surface bacteria due to pressure and cold

deep sea floor

covered in fine, muddy sediment, meiofauna abundant, suspension feeders rare, deposit feeders dominate (most are infauna, some epifauna, polychaetes, crustaceans, bivalves)

sea cucumbers

have strange, highly modified body forms with leg-like appendages

deep sea predators

sea and brittle stars, crabs, sea spiders, squids, fish

deep sea gigantism

many deep sea organisms are larger than other community counterparts, tend to grow slow, live a longer life, reproduce later in life

hydrothermal vents communities

chemical laden water escaping from cracks in the sea floor around mid-ocean ridges “feed” chemoautotrophic bacteria, provides H2S to bacteria that serve as first link in food web, can withstand temps up to 250 degrees F

black/white smokers

home to fish, shrimp, tube worms, crabs, snails, barnacles, sponges, corals

tube worms

harbor chemoautotrophic bacteria in their body to support their metabolic needs