Marine Biology

What is the epipelagic zone?

The upper layer of the ocean where light penetrates and photosynthesis occurs.

What is the mesopelagic zone?

The twilight zone below the epipelagic, extending from 200m to 1000m.

What defines net primary production in the epipelagic zone?

The total organic matter produced by photosynthesis minus respiration.

What are phytoplankton?

Microscopic, single-celled photosynthetic organisms drifting in water.

Name two major groups of phytoplankton.

Diatoms and dinoflagellates.

What are zooplankton?

Small, drifting animals that feed on phytoplankton or other zooplankton.

What is holoplankton?

Organisms that spend their entire life cycle as plankton.

What is meroplankton?

Organisms that spend only a larval or early stage as plankton.

What is bacterioplankton?

Free-living bacteria and archaea in the pelagic zone playing key roles in the microbial loop.

What is the microbial loop?

A pathway in pelagic food webs where dissolved organic matter is channeled back through bacteria to higher trophic levels.

How do pelagic food webs typically scale in trophic efficiency?

About 10% energy transfer efficiency between trophic levels.

What is a microbial food web?

A complex network dominated by microscopic producers, heterotrophic bacteria, and protozoans.

What is Daily Vertical Migration (DVM)?

A synchronized movement of mesopelagic animals up to the surface at night to feed and down at dawn to hide.

What drives DVM?

Predation avoidance in the bright upper layers by day and feeding opportunities at night.

What is the Deep Scattering Layer (DSSL)?

A layer of marine organisms that reflects sonar pulses, largely composed of DVM migrators.

Name three common animal groups found in the DSSL.

Myctophids (lanternfishes), krill, and siphonophores.

How do pelagic animals maintain buoyancy using lipids?

Accumulating oils, fats, or low-density lipids like squalene.

How do teleost fish maintain buoyancy?

By using a gas-filled swim bladder.

What is a disadvantage of a gas-filled swim bladder in the mesopelagic?

Rapid pressure changes during DVM make volume regulation difficult.

How do gelatinous zooplankton achieve neutral buoyancy?

By excluding heavy sulfate ions and replacing them with lighter ammonium ions.

What is countershading?

A camouflage pattern with a dark dorsal side and a light ventral side.

How does countershading protect epipelagic fish?

They blend into the dark depths from above and the bright sky from below.

What is transparency?

A common camouflage strategy in gelatinous pelagic organisms where light passes through them.

How do silvery sides help mesopelagic fish?

They reflect ambient light like tiny mirrors, obscuring the fish's silhouette.

What is counterillumination?

Producing light on the ventral surface to match downward-filtering sunlight.

Which group commonly uses counterillumination?

Midwater animals like lanternfish and squids.

What sensory organ do fish use to detect vibrations and water motion?

The lateral line system.

How do odontocetes locate prey in the open ocean?

Through echolocation or biosonar.

What is the function of the melon in toothed whales?

A fatty organ in the forehead that focuses and directs echolocation clicks.

What is a neuston?

Organisms that live right at the air-water interface.

What is a pleuston?

Organisms that project partially into the air like Velella.

What is the microbial loop's role in recycling nutrients?

It remineralizes dissolved organic carbon into inorganic nutrients.

What is a high-nutrient, low-chlorophyll region?

Oceanic areas with abundant macronutrients but low primary productivity due to iron limitation.

Which iron source stimulates productivity in HNLC regions?

Wind-blown dust from continental deserts.

What is a copepod?

A tiny crustacean that dominates zooplankton biomass in most oceans.

What is a gelatinous zooplankton?

Soft-bodied animals like jellyfish, ctenophores, and salps.

How do salps feed?

By filtering water through a fine mucous net.

What are pteropods?

Pelagic snails with muscular wings used for swimming.

What is the shell composition of thecosome pteropods?

Calcium carbonate aragonite, making them vulnerable to ocean acidification.

What is a siphonophore?

A colonial marine cnidarian resembling a single organism.

What is a common epipelagic apex predator?

Sharks, billfish, and tunas.

How do tunas maintain high swimming speeds?

Streamlined bodies, regional endothermy, and rigid fins.

What is regional endothermy in pelagic fishes?

The ability to keep red swimming muscles warmer than ambient water using countercurrent heat exchangers.

Why is regional endothermy advantageous for tuna?

It increases metabolic rate and muscle power output for high-speed hunting.

What is the epipelagic nekton?

Free-swimming animals that can move against ocean currents.

What is the main structural challenge for open ocean organisms?

Lack of physical hiding places leading to specialized camouflage.

How do mesopelagic fish eyes typically differ from epipelagic fish eyes?

They have large, tubular eyes optimized to capture faint light.

What is the oxygen minimum zone?

A mid-depth layer between 200m and 1000m where dissolved oxygen is lowest.

What causes the oxygen minimum zone?

High microbial respiration breaking down organic matter combined with limited circulation.

How do organisms survive within the OMZ?

Specialized metabolic adaptations or vertical migration.

What are chaetognaths?

Arrow worms, common carnivorous plankton.

What is a dinoflagellate bloom?

A rapid proliferation of dinoflagellates sometimes resulting in red tides.

What is a silicoflagellate?

A type of phytoplankton with an internal skeleton made of silica.

What is a coccolithophore?

Microscopic algae covered in calcium carbonate plates called coccoliths.

What is the primary pigment used by photosynthetic phytoplankton?

Chlorophyll-a.

What is secondary production in the pelagic zone?

The generation of biomass by heterotrophic consumers feeding on primary producers.

What are tunicates?

Chordate zooplankton including larvaceans and salps.

What is a larvacean house?

A delicate mucus structure built to filter food, regularly discarded and sinking as marine snow.

How does light attenuation work in the water column?

Red and infrared light are absorbed first while blue and green penetrate deepest.

What is another name for the euphotic zone?

The epipelagic zone where net photosynthesis exceeds respiration.

What is marine snow?

A continuous shower of organic detritus falling from the upper ocean to the deep sea.

What composes marine snow?

Fecal pellets, dead plankton, mucus houses, and skeletal fragments.

Why is marine snow important to the deep sea?

It serves as the primary food and energy source for deep-sea benthic organisms.

What is deep-sea gigantism?

The tendency for deep-sea invertebrates to grow much larger than shallow-water relatives.

What are possible causes of deep-sea gigantism?

Low temperatures, high pressure, scarce food, and delayed maturity.

How do deep-sea fish compensate for scarce food?

Reduced metabolic rates, flabby water-rich muscles, and massive stomachs.

What is bioluminescence?

The production and emission of light by a living organism through a chemical reaction.

What two primary chemicals are involved in bioluminescence?

Luciferin and luciferase.

What are photophores?

Specialized light-producing organs found in many deep-sea animals.

Give three functions of bioluminescence in the deep sea.

Predator deterrence, prey attraction, and conspecific communication.

What is the oxygen profile in the deep ocean below the OMZ?

Oxygen levels rise again due to cold, well-oxygenated polar deep-water currents.

What are hydrothermal vents?

Fissures on the seafloor where geothermally heated mineral-rich water is discharged.

Where are hydrothermal vents commonly found?

Along mid-ocean ridges and tectonic plate boundaries.

What is the base of the food web at hydrothermal vents?

Chemosynthetic bacteria and archaea.

How do chemosynthetic microbes produce energy at vents?

By oxidizing hydrogen sulfide or methane instead of using sunlight.

What is Riftia pachyptila?

The giant tube worm found at hydrothermal vents.

How does Riftia survive without a mouth or gut?

It harbors symbiotic sulfur-oxidizing bacteria in a trophosome.

What is a trophosome?

An internal organ in Riftia packed with bacteria providing organic molecules.

What are cold seeps?

Seafloor areas where hydrocarbon-rich fluids leak out slowly.

What supports life at cold seeps?

Chemosynthetic microbes utilizing methane and hydrogen sulfide.

What are seamounts?

Underwater mountains rising from the seafloor, acting as biodiversity hotspots.

How do seamounts affect ocean currents?

They deflect deep currents, creating upwelling that brings nutrients upward.

What are deep-sea trenches?

Long, narrow, steep depressions representing the deepest parts of the ocean.

What environmental conditions characterize the hadal zone?

Extreme hydrostatic pressure, near-freezing temperatures, and total darkness.

How do piezophilic organisms adapt to high pressure?

Specialized cell membranes rich in unsaturated fatty acids and pressure-resistant proteins.

What is an abyssal plain?

A vast, flat region of the deep ocean floor between 3,000 and 6,000 meters.

What is the bathypelagic zone?

The ocean layer from 1,000 to 4,000 meters deep with perpetual darkness.

What is the abyssopelagic zone?

The layer from 4,000 to 6,000 meters deep covering abyssal plains.

What is the benthic boundary layer?

The layer of water immediately overlying the seafloor influenced by bottom friction.

What is benthic-pelagic coupling?

The exchange of energy and nutrients between the water column and seafloor.

How do deep-sea anglerfish find mates in darkness?

Through extreme sexual dimorphism where tiny parasitic males fuse to females.

What is the function of the esca in anglerfish?

A bioluminescent lure dangling above the mouth to attract prey.

What is a deep-sea ooze?

Pelagic sediment composed of at least 30% skeletal remains of microorganisms.

What is calcareous ooze?

Sediment rich in calcium carbonate shells absent below the CCD.

What is siliceous ooze?

Sediment rich in silica shells found in high productivity areas.

What is the Carbonate Compensation Depth?

The depth where calcium carbonate dissolution equals supply rate.

What is a whale fall community?

An ecological succession of organisms colonizing a sinking whale carcass.

Name the stages of a whale fall ecosystem.

Mobile scavenger, opportunistic reef, sulfophilic, and bone stage.

What organisms dominate the sulfophilic stage of a whale fall?

Chemosynthetic bacteria utilizing hydrogen sulfide from bones.

How do deep-sea corals differ from shallow-water corals?

They lack zooxanthellae, grow slowly, and inhabit cold deep waters.