Marine Biology MCQs
Part 1 — Marine Biology MCQs (Q1–Q25)
Q1. The deepest part of the world’s oceans is:
A. Tonga Trench
• Deep but not the deepest.
B. Mariana Trench ✅
• Challenger Deep in Mariana Trench reaches ~11,000 m.
C. Java Trench
• Also deep, but shallower.
D. Puerto Rico Trench
• Deepest in Atlantic, not globally.
Q2. Organisms that live on the ocean floor are called:
A. Nekton
• Actively swimming organisms (fish, squid).
B. Plankton
• Drifting organisms.
C. Benthos ✅
• Bottom dwellers like crabs, sponges, corals.
D. Neuston
• Float at surface layer.
Q3. The primary producers in the open ocean are:
A. Seaweeds
• Confined near coasts.
B. Mangroves
• Found in estuaries, not open ocean.
C. Phytoplankton (diatoms, dinoflagellates) ✅
• Carry out photosynthesis, form oceanic food base.
D. Zooplankton
• Consumers, not producers.
Q4. Which marine organism is a filter feeder?
A. Shark
• Active predator.
B. Squid
• Predatory.
C. Mussel (bivalve mollusk) ✅
• Strains plankton from water.
D. Eel
• Predator, not filter-feeder.
Q5. Bioluminescence in marine organisms is mainly due to:
A. ATP only
• Requires enzyme-substrate reaction.
B. Luciferin–luciferase reaction ✅
• Produces visible light without heat.
C. Chlorophyll
• For photosynthesis, not light emission.
D. Carotenoids
• Pigments, not light producers.
Q6. The intertidal zone is defined as:
A. Deep ocean trench
• Incorrect.
B. Area between high and low tide marks ✅
• Alternately submerged and exposed.
C. Pelagic open waters
• Offshore zone.
D. Abyssal plain
• Very deep ocean floor.
Q7. Coral reefs are most commonly found in:
A. Shallow, warm, nutrient-poor tropical waters ✅
• Require light for symbiotic algae (zooxanthellae).
B. Polar oceans
• Too cold for corals.
C. Deep trenches
• Lack sunlight.
D. Freshwater lakes
• Corals are marine.
Q8. The symbiotic algae inside reef-building corals are:
A. Cyanobacteria
• Not primary coral partners.
B. Zooxanthellae (dinoflagellates, genus Symbiodinium) ✅
• Provide sugars via photosynthesis.
C. Green algae (Ulva)
• Not coral symbionts.
D. Diatoms
• Free-living plankton.
Q9. Upwelling zones are biologically rich because they:
A. Increase water temperature
• Not main effect.
B. Bring nutrient-rich deep water to surface ✅
• Fuels phytoplankton blooms → productive fisheries.
C. Decrease salinity
• Not always.
D. Block sunlight
• Opposite of productivity.
Q10. Which of the following is a marine mammal?
A. Salmon
• Fish.
B. Sea turtle
• Reptile.
C. Dolphin ✅
• Warm-blooded, air-breathing, produces milk.
D. Squid
• Cephalopod mollusk.
Q11. The main skeletal material in sponges is:
A. Spicules of calcium carbonate or silica ✅
• Provide structure to marine sponges.
B. Chitin
• Found in insects/fungi.
C. Keratin
• Found in hair/skin.
D. Collagen
• Present but not main skeleton.
Q12. Estuaries are important because they:
A. Are low in nutrients
• False—nutrient-rich.
B. Serve as nurseries for many marine species ✅
• High productivity, shelter for juvenile fish.
C. Are located in deep sea
• Near coasts.
D. Lack biodiversity
• Estuaries are highly diverse.
Q13. The largest living animal on Earth is:
A. Whale shark
• Largest fish.
B. Elephant
• Largest land animal.
C. Blue whale (Balaenoptera musculus) ✅
• Largest animal ever (~30 m).
D. Giant squid
• Large, but smaller.
Q14. Mangroves are specialized because they:
A. Grow in deserts
• Incorrect.
B. Tolerate saline, waterlogged soils with pneumatophores ✅
• Adapted to coastal saline conditions.
C. Need freshwater only
• False.
D. Cannot survive tidal changes
• They thrive under them.
Q15. Which marine zone has no sunlight?
A. Neritic zone
• Sunlit near coast.
B. Euphotic zone
• Sunlit surface.
C. Aphotic zone ✅
• Below ~1000 m, perpetual darkness.
D. Intertidal zone
• Gets sunlight.
Q16. The term nekton refers to:
A. Floating plants only
• That’s phytoplankton.
B. Bottom-dwellers
• That’s benthos.
C. Active swimmers like fish, squid, whales ✅
• Can move independently of currents.
D. Microscopic drifters
• Plankton.
Q17. The largest coral reef system in the world is:
A. Mesoamerican Reef
• Second largest.
B. Red Sea Coral Reef
• Important but smaller.
C. Great Barrier Reef (Australia) ✅
• >2,300 km long, visible from space.
D. Florida Reef Tract
• Smaller.
Q18. A key feature of echinoderms is:
A. Bilateral symmetry as adults
• They are radial as adults.
B. Water vascular system with tube feet ✅
• Unique hydraulic locomotion system.
C. Exoskeleton of chitin
• Arthropods, not echinoderms.
D. Segmented body
• Not segmented.
Q19. Which of the following organisms is a cartilaginous fish?
A. Tuna
• Bony fish.
B. Shark ✅
• Belongs to class Chondrichthyes.
C. Salmon
• Bony fish.
D. Eel
• Bony fish.
Q20. Salinity of seawater averages around:
A. 1‰ (0.1%)
• Too low.
B. 10‰ (1%)
• Too low.
C. 35‰ (3.5%) ✅
• Standard ocean salinity.
D. 70‰ (7%)
• Hypersaline lagoons only.
Q21. The largest phylum in marine biodiversity is:
A. Echinodermata
• Large but not biggest.
B. Arthropoda ✅
• Crustaceans, insects, copepods dominate ocean diversity.
C. Cnidaria
• Important, not most numerous.
D. Porifera
• Smaller group.
Q22. Which whale species was nearly driven to extinction by whaling but has recovered under protection?
A. Humpback whale ✅
• Heavily hunted, populations rebounded after 1986 IWC moratorium.
B. Orca
• Less hunted.
C. Beluga
• Arctic, smaller populations.
D. Narwhal
• Limited hunting.
Q23. Which of these is a keystone predator in kelp forest ecosystems?
A. Sea cucumber
• Detritivore.
B. Sea otter ✅
• Controls sea urchin populations, maintains kelp forests.
C. Anchovy
• Small fish.
D. Starfish
• Important, but in rocky shores.
Q24. El Niño events negatively affect marine ecosystems because they:
A. Increase upwelling
• Actually suppress upwelling.
B. Reduce nutrient supply → fisheries collapse ✅
• Warm water blocks nutrients, disrupting food webs.
C. Decrease sea level
• Not main effect.
D. Increase coral growth
• Often cause coral bleaching.
Q25. The primary cause of coral bleaching is:
A. Heavy metals
• Contribute, but not main.
B. Thermal stress from rising sea surface temperature ✅
• Expulsion of zooxanthellae under stress.
C. Ocean currents
• Not direct cause.
D. Predation by fish
• Not bleaching.
Part 2 — Marine Biology MCQs (Q26–Q50)
Q26. The mid-ocean ridge ecosystem is known for:
A. Coral reefs
• Found in shallow, sunlit zones.
B. Hydrothermal vent communities with chemosynthetic bacteria ✅
• Use hydrogen sulfide instead of sunlight.
C. Mangrove swamps
• Coastal, not deep-sea.
D. Polar ice algae
• Found in cold surface waters.
Q27. The primary producers in deep-sea vent ecosystems are:
A. Phytoplankton
• Require sunlight, absent here.
B. Chemosynthetic bacteria ✅
• Use sulfur compounds for energy.
C. Seaweeds
• Need light, grow near coasts.
D. Zooplankton
• Consumers, not producers.
Q28. Which fish is famous for its bioluminescent lure in the deep sea?
A. Tuna
• Surface predator.
B. Mackerel
• Open ocean fish.
C. Anglerfish ✅
• Has glowing lure to attract prey in darkness.
D. Swordfish
• Active predator near surface.
Q29. Organisms that can tolerate wide salinity ranges are called:
A. Stenohaline
• Narrow salinity tolerance.
B. Euryhaline ✅
• Adapt to variable salinity (e.g., salmon, estuarine fish).
C. Osmophilic
• Tolerant of high osmotic pressure.
D. Thermophilic
• Heat-tolerant, not salinity.
Q30. The biggest threat to global fisheries today is:
A. Natural predation
• Part of ecosystem balance.
B. Overfishing and unsustainable harvest practices ✅
• Depletes fish stocks globally.
C. Coral reef growth
• Not a threat.
D. Strong ocean currents
• Do not cause collapse.
Q31. Which adaptation allows deep-sea fishes to survive high pressure?
A. Hollow bones
• Found in birds.
B. Flexible cell membranes and pressure-resistant enzymes ✅
• Prevent damage under extreme pressure.
C. Air-filled lungs
• Would collapse under pressure.
D. Strong skeletons of calcium phosphate
• Not main adaptation.
Q32. Cetaceans include:
A. Seals and sea lions
• These are pinnipeds.
B. Whales, dolphins, porpoises ✅
• Belong to order Cetacea.
C. Penguins
• Birds.
D. Sharks
• Fish.
Q33. The main pigment responsible for oxygen transport in marine invertebrates like mollusks and crustaceans is:
A. Hemoglobin
• Found in vertebrates.
B. Hemocyanin ✅
• Copper-based, blue when oxygenated.
C. Myoglobin
• Oxygen storage in muscle.
D. Chlorocruorin
• Rare, in some annelids.
Q34. Whale migration usually occurs for:
A. Escaping predators
• Not the main reason.
B. Breeding and calving in warmer waters ✅
• Travel thousands of km seasonally.
C. Seeking light
• Not relevant.
D. Avoiding storms
• Secondary reason at best.
Q35. The fastest marine mammal is:
A. Dolphin
• Fast but not the fastest.
B. Orca (killer whale) ✅
• Can reach ~55 km/h.
C. Sea lion
• Slower.
D. Narwhal
• Arctic species, not very fast.
Q36. Bycatch in fisheries refers to:
A. Illegal fishing
• Broader term.
B. Non-target species accidentally caught during fishing ✅
• Includes turtles, dolphins, seabirds.
C. Overfishing
• Different issue.
D. Aquaculture harvest
• Controlled, not bycatch.
Q37. Which shark species is filter-feeding?
A. Great white shark
• Apex predator.
B. Hammerhead shark
• Predator.
C. Whale shark ✅
• Largest fish, eats plankton.
D. Tiger shark
• Predator.
Q38. Eutrophication in marine ecosystems results mainly from:
A. Ocean acidification
• Caused by CO₂, not nutrients.
B. Excess nutrient runoff → algal blooms → oxygen depletion ✅
• Dead zones form, killing fish.
C. Melting glaciers
• Freshwater input, not main cause.
D. Increased salinity
• Not related.
Q39. The main adaptation of marine mammals for diving is:
A. Lungs that store more air
• Lungs actually collapse to avoid nitrogen issues.
B. High myoglobin content in muscles for oxygen storage ✅
• Enables long dives.
C. Air bladders
• Fish, not mammals.
D. Salt glands
• Present in birds, reptiles.
Q40. Which zone has the highest biodiversity in the ocean?
A. Abyssal zone
• Low diversity.
B. Coral reef ecosystems ✅
• Comparable to tropical rainforests.
C. Open ocean
• Lower density of life.
D. Polar seas
• Seasonal productivity, but not richest.
Q41. Krill are ecologically important because they:
A. Produce oxygen directly
• That’s phytoplankton.
B. Form a crucial link between phytoplankton and higher predators (whales, seals, fish) ✅
• Keystone prey species.
C. Decompose organic matter
• Not their role.
D. Are apex predators
• They are primary consumers.
Q42. Red tides are caused by:
A. Diatoms
• Usually non-toxic blooms.
B. Dinoflagellates producing harmful algal blooms ✅
• Can release neurotoxins, kill fish.
C. Cyanobacteria
• Cause blooms, but not classic red tide.
D. Seaweeds
• Not planktonic.
Q43. The largest group of marine reptiles today are:
A. Crocodiles
• Few species, mostly freshwater.
B. Sea turtles ✅
• Widely distributed, multiple species.
C. Sea snakes
• Numerous, but smaller group.
D. Marine iguanas
• Found only in Galápagos.
Q44. Ocean acidification occurs because:
A. Volcanoes increase ocean pH
• Incorrect.
B. Absorption of excess atmospheric CO₂ → carbonic acid formation ✅
• Lowers pH, harms corals/shellfish.
C. Salt dissolves in water
• Salinity does not reduce pH.
D. Oil spills
• Polluting, not acidification.
Q45. Which is the largest marine phylum in biomass?
A. Cnidaria
• Numerous, but not the most biomass.
B. Copepods (Crustacea, Arthropoda) ✅
• Tiny but abundant → huge global biomass.
C. Mollusca
• Diverse, but smaller biomass.
D. Echinodermata
• Smaller.
Q46. Which structure helps sharks in detecting electrical signals of prey?
A. Lateral line
• Detects water movement, not electric fields.
B. Ampullae of Lorenzini ✅
• Electroreceptive organs around snout.
C. Swim bladder
• For buoyancy.
D. Spiracle
• For breathing when buried.
Q47. Which marine zone contains the continental shelf?
A. Abyssal zone
• Too deep.
B. Neritic zone ✅
• Shallow waters over continental shelf.
C. Oceanic zone
• Beyond continental shelf.
D. Hadal zone
• Deep trenches.
Q48. The oxygen minimum zone (OMZ) in oceans is found:
A. At mid-depths (~200–1000 m), due to high respiration and low mixing ✅
• Depleted oxygen region.
B. Surface waters
• Oxygenated by photosynthesis.
C. Deep trenches
• Cold, oxygen-rich due to mixing.
D. Coral reefs
• Highly oxygenated.
Q49. Which adaptation helps penguins survive in marine environments?
A. Hollow bones
• Seen in flying birds.
B. Dense bones, streamlined body, insulating fat layer ✅
• Adapted for diving/swimming.
C. Salt glands only
• Present, but not main adaptation.
D. Air bladders
• Fish, not birds.
Q50. Which ocean phenomenon is worsened by global warming and threatens corals?
A. Tides
• Natural cycles.
B. Mass bleaching due to heat stress and acidification ✅
• Warming + CO₂ acidification weaken reefs.
C. Plate tectonics
• Geological, not coral stress.
D. Lunar eclipses
• No effect.
Part 3 — Marine Biology MCQs (Q51–Q75)
Q51. Which marine organism is a rich source of agar used in biotechnology?
A. Brown algae (Fucus)
• Source of alginates, not agar.
B. Green algae (Ulva)
• Used as food, not agar.
C. Red algae (Gelidium, Gracilaria) ✅
• Agar is extracted from red seaweeds.
D. Blue-green algae
• Cyanobacteria, not agar producers.
Q52. Sponges (Porifera) are important in biotechnology because they:
A. Store oxygen
• Not their role.
B. Produce bioactive compounds with antimicrobial and anticancer properties ✅
• Many marine drugs come from sponges.
C. Fix nitrogen
• Cyanobacteria do this.
D. Filter oxygen from water
• They filter-feed, not oxygen.
Q53. A common marine biofuel source is:
A. Coral reefs
• Not used for fuel.
B. Microalgae producing lipids (e.g., Nannochloropsis) ✅
• Algal oils → biodiesel.
C. Sea turtles
• Not energy source.
D. Jellyfish
• Not used for fuel.
Q54. Marine biotechnology often uses extremozymes from:
A. Mangroves only
• Not main source.
B. Deep-sea hydrothermal vent microbes ✅
• Enzymes stable at high temperature/pressure.
C. Penguins
• Animals, not enzyme source.
D. Dolphins
• Not used for biotech enzymes.
Q55. Carrageenan, widely used as a food thickener, is extracted from:
A. Brown algae
• Source of alginates.
B. Red algae (Rhodophyta) ✅
• Carrageenan is a polysaccharide from red seaweeds.
C. Green algae
• Not carrageenan source.
D. Cyanobacteria
• Not correct.
Q56. Which marine plant is crucial for carbon sequestration (“blue carbon”)?
A. Sea lettuce (Ulva)
• Green algae, less contribution.
B. Seagrasses (e.g., Posidonia, Zostera) ✅
• Store large carbon stocks in sediments.
C. Mangrove fungi
• Contribute indirectly.
D. Polar ice algae
• Important but smaller carbon sink.
Q57. The International Whaling Commission (IWC) was established to:
A. Promote commercial whaling
• The opposite.
B. Regulate and eventually ban commercial whaling ✅
• Moratorium since 1986.
C. Conserve mangroves
• Not related.
D. Protect coral reefs
• Different body.
Q58. A marine endangered reptile listed by IUCN is:
A. Komodo dragon
• Land reptile.
B. Leatherback turtle (Dermochelys coriacea) ✅
• Largest sea turtle, critically endangered.
C. Crocodile
• Semi-aquatic, not strictly marine.
D. Iguana
• Land/Island reptile.
Q59. Marine protected areas (MPAs) are created to:
A. Stop all human activity
• Some activities allowed.
B. Conserve biodiversity and manage sustainable use of marine resources ✅
• Reduce overfishing and habitat loss.
C. Increase oil drilling
• Opposite purpose.
D. Promote plastic use
• Not correct.
Q60. Which pollutant is most harmful to marine birds due to feather coating?
A. Heavy metals
• Toxic, but not feather-related.
B. Oil spills ✅
• Damage waterproofing, cause hypothermia and death.
C. Plastics
• Cause ingestion problems, not feather issues.
D. Fertilizers
• Cause eutrophication, not feather damage.
Q61. Microplastics are dangerous because they:
A. Float harmlessly
• Incorrect.
B. Enter food webs, absorb toxins, and bioaccumulate ✅
• Harm organisms and humans.
C. Dissolve quickly in seawater
• Persistent for decades.
D. Benefit plankton
• Harmful, not beneficial.
Q62. Which is the largest living structure made by organisms in the ocean?
A. Mangrove forest
• Plant-based.
B. Great Barrier Reef (coral polyps + symbionts) ✅
• Largest biological structure visible from space.
C. Kelp forest
• Large, but smaller scale.
D. Hydrothermal vent
• Not a structure.
Q63. The main adaptation of marine birds like albatrosses is:
A. Strong claws for climbing
• Terrestrial adaptation.
B. Large wingspans for dynamic soaring over oceans ✅
• Can glide for days.
C. Ability to live underwater
• They are surface feeders.
D. No need for salt glands
• They have salt glands for osmoregulation.
Q64. Osmoregulation in marine bony fish involves:
A. Drinking only freshwater
• They live in seawater.
B. Drinking seawater, excreting excess salt via gills and kidneys ✅
• Maintain osmotic balance.
C. Not drinking water at all
• Would dehydrate.
D. Storing salt in tissues
• Not true.
Q65. Which marine animal uses echolocation for navigation and hunting?
A. Sea turtle
• No echolocation.
B. Shark
• Uses electroreception, not echolocation.
C. Dolphins and whales ✅
• Emit sound waves and interpret echoes.
D. Jellyfish
• No sound system.
Q66. The phenomenon of coral reef death due to high temperature and CO₂ is called:
A. Red tide
• Algal bloom.
B. Ocean overturning
• Circulation phenomenon.
C. Coral bleaching ✅
• Loss of zooxanthellae → reef collapse.
D. Upwelling
• Nutrient rise, not bleaching.
Q67. Bioaccumulation of mercury in marine food chains is most dangerous for:
A. Seaweeds
• Do not accumulate much.
B. Top predators (e.g., tuna, swordfish) ✅
• Biomagnification at higher trophic levels.
C. Krill
• Lower in chain.
D. Filter-feeding bivalves only
• Accumulate, but less than top predators.
Q68. The term “dead zone” in coastal oceans refers to:
A. High biodiversity area
• Opposite meaning.
B. Hypoxic areas where oxygen levels are too low for most life ✅
• Often from nutrient pollution.
C. Places without sunlight
• Deep sea, but not dead zone.
D. Coral reefs
• Usually productive, not dead.
Q69. Which marine mammal is known as the “sea cow”?
A. Dolphin
• Fast swimmer, not “sea cow.”
B. Seal
• Carnivorous predator.
C. Manatee/Dugong ✅
• Herbivorous, grazing seagrass.
D. Orca
• Predator, not herbivore.
Q70. The lateral line system in fish detects:
A. Light
• Detected by eyes.
B. Electric fields
• Sharks use ampullae for this.
C. Water vibrations and movement ✅
• Important for schooling and predator detection.
D. Temperature
• Not primary function.
Q71. Overharvesting of sea cucumbers threatens ecosystems because they:
A. Eat fish
• Incorrect.
B. Recycle nutrients and oxygenate sediments ✅
• Essential for benthic ecosystem health.
C. Produce coral reefs
• Not correct.
D. Have no ecological role
• False—very important.
Q72. Which marine organism produces the potent neurotoxin tetrodotoxin?
A. Jellyfish
• Produce venom, not TTX.
B. Pufferfish (Tetraodontidae) ✅
• Deadly neurotoxin, blocks sodium channels.
C. Squid
• Ink, not TTX.
D. Sea otter
• No toxin.
Q73. Which human activity causes ocean acidification most directly?
A. Burning fossil fuels → increased CO₂ absorption by oceans ✅
• Carbonic acid lowers pH.
B. Plastic pollution
• Serious, but not acidification.
C. Oil spills
• Pollute, not acidify.
D. Overfishing
• Depletes stocks, not acidification.
Q74. The process where marine animals dive deep and return to surface daily is called:
A. Coral bleaching
• Not migration.
B. Diel vertical migration (by zooplankton/fish) ✅
• Largest animal migration on Earth by biomass.
C. Red tide
• Algal bloom.
D. Bioremediation
• Pollution cleanup.
Q75. Which group of marine mammals lacks external ears and uses blubber for insulation?
A. Seals (true seals, Phocidae) ✅
• Streamlined, no external ear flaps.
B. Sea lions
• Have external ear flaps.
C. Dolphins
• Have auditory openings but not pinnae.
D. Polar bears
• Semi-marine, not fully aquatic.
Part 4 — Marine Biology MCQs (Q76–Q100)
Q76. The main driver of sea level rise is:
A. Increased rainfall
• Local effect, not global rise.
B. Thermal expansion of water and melting ice sheets ✅
• Both add to sea level rise.
C. Submarine volcanoes
• Cause local uplift, not global.
D. Tides
• Daily fluctuations, not long-term rise.
Q77. The primary cause of ocean deoxygenation is:
A. Coral bleaching
• Symbiont loss, not oxygen depletion.
B. Warming oceans reducing oxygen solubility and circulation ✅
• Less mixing, less dissolved oxygen.
C. Salinity increase
• Has small effect only.
D. Tsunamis
• Short-term events.
Q78. Which current is called the “global conveyor belt”?
A. Gulf Stream alone
• Part of it, not the whole.
B. Thermohaline circulation ✅
• Driven by temperature & salinity differences.
C. Equatorial Counter Current
• Surface flow only.
D. El Niño
• Climatic oscillation, not steady conveyor.
Q79. Ocean gyres contribute most to:
A. Coral reef growth
• Not directly.
B. Accumulation of floating plastics in “garbage patches” ✅
• Example: Great Pacific Garbage Patch.
C. Whale migration
• Influenced by currents, but not gyres alone.
D. Upwelling
• Found on eastern boundaries, not gyres.
Q80. The largest carbon sink on Earth is:
A. Rainforests
• Important, but smaller than oceans.
B. The world’s oceans ✅
• Absorb ~25–30% of atmospheric CO₂.
C. Deserts
• Store little carbon.
D. Freshwater lakes
• Minor contribution.
Q81. Ballast water from ships often introduces:
A. Nutrients
• Not main concern.
B. Invasive marine species ✅
• Example: zebra mussels, harmful algae.
C. Freshwater only
• Not relevant.
D. Oxygen
• Not major impact.
Q82. Which international treaty focuses on conserving migratory marine species?
A. Kyoto Protocol
• Climate change, not species.
B. CMS (Convention on Migratory Species / Bonn Convention) ✅
• Protects whales, turtles, seabirds.
C. CITES
• Trade in endangered species, broader.
D. UNCLOS
• Law of the sea, not species-specific.
Q83. UNCLOS (United Nations Convention on the Law of the Sea) grants nations rights to resources within:
A. 12 nautical miles
• That’s territorial waters.
B. 200 nautical miles (Exclusive Economic Zone, EEZ) ✅
• EEZ covers fisheries, oil, and seabed rights.
C. Entire ocean
• International waters shared.
D. Continental slope only
• Incorrect.
Q84. Illegal, Unreported, and Unregulated (IUU) fishing mainly threatens:
A. Coral reefs only
• Broader impact.
B. Global fish stocks and food security ✅
• Leads to depletion and economic loss.
C. Marine mammals only
• Affects entire ecosystems.
D. Polar regions only
• Occurs worldwide.
Q85. Marine snow refers to:
A. Frozen seawater
• Sea ice, not marine snow.
B. Continuous shower of organic debris sinking to deep sea ✅
• Food source for deep benthos.
C. Coral bleaching
• Different phenomenon.
D. Salt precipitates
• Not correct.
Q86. The primary energy source in hydrothermal vent ecosystems is:
A. Sunlight
• Absent in deep sea.
B. Chemical energy from oxidation of hydrogen sulfide ✅
• Used by chemosynthetic bacteria.
C. Oil seeps
• Not primary.
D. Wave action
• Not energy source for life.
Q87. The largest migration on Earth by biomass is:
A. Whale migration
• Impressive, but smaller.
B. Bird migration
• Large, but smaller biomass.
C. Diel vertical migration of zooplankton ✅
• Billions move daily from deep to surface.
D. Salmon runs
• Local scale.
Q88. Which adaptation allows penguins to dive deep?
A. Hollow bones
• Seen in flying birds.
B. Dense bones and high myoglobin storage ✅
• Prevent buoyancy and extend oxygen supply.
C. Salt glands only
• Osmoregulation, not diving.
D. Large lungs
• Collapse during dives.
Q89. Which marine mammal uses tusks for dominance and ice-breaking?
A. Seal
• No tusks.
B. Walrus ✅
• Tusks are elongated canines.
C. Dugong
• Sea cow, no tusks.
D. Orca
• Predator, no tusks.
Q90. Sirenia includes:
A. Whales
• Cetacea, not Sirenia.
B. Seals
• Pinnipeds, not Sirenia.
C. Manatees and dugongs (sea cows) ✅
• Order Sirenia.
D. Penguins
• Birds.
Q91. The biggest threat to sea turtles worldwide is:
A. Saltwater intake
• Adapted for salt.
B. Loss of nesting beaches and bycatch in fishing nets ✅
• Human activities threaten populations.
C. Predation by sharks
• Natural, but not biggest threat.
D. Low reproductive output
• Naturally offset by many eggs.
Q92. Which gas forms clathrate hydrates in deep-sea sediments?
A. Oxygen
• Not stable in hydrates.
B. Methane ✅
• Trapped as methane hydrates in sediments.
C. Nitrogen
• Not hydrate-forming at seabed.
D. Argon
• Inert gas, not hydrate.
Q93. Primary productivity in the open ocean is generally low because:
A. No sunlight
• Sunlight exists in surface waters.
B. Low nutrient availability in surface waters ✅
• Nutrients trapped at depth.
C. Lack of CO₂
• Oceans rich in CO₂.
D. Strong currents
• Not main limiting factor.
Q94. The deep scattering layer is composed of:
A. Floating plastics
• Not living.
B. Migrating fish, squid, zooplankton reflecting sonar ✅
• Appears as false bottom in sonar.
C. Corals
• Fixed organisms.
D. Submarine ridges
• Geological.
Q95. Which ocean phenomenon leads to global climate effects?
A. Tides
• Local effect.
B. El Niño–Southern Oscillation (ENSO) ✅
• Alters rainfall, temperature worldwide.
C. Monsoons
• Regional only.
D. Hurricanes
• Regional storms.
Q96. Keystone species in kelp forests are:
A. Krill
• Important, but not keystone here.
B. Sea otters controlling sea urchin populations ✅
• Maintain kelp forests.
C. Sharks
• Predators, but less impact.
D. Mussels
• More relevant to rocky shores.
Q97. Mangrove roots provide:
A. No ecological function
• Wrong.
B. Nursery habitat for juvenile fish and coastal protection ✅
• Reduce erosion, high biodiversity.
C. Open ocean food source
• Not directly.
D. Only timber
• Secondary benefit.
Q98. Which adaptation helps polar bears survive marine life?
A. Hollow fur only
• Provides insulation, but not sole adaptation.
B. Thick blubber, hollow hairs, large paws for swimming ✅
• Semi-aquatic adaptations.
C. Gills
• Mammals don’t have gills.
D. Salt glands
• Not present.
Q99. The mesopelagic zone is also called:
A. Sunlit zone
• That’s euphotic.
B. Twilight zone (~200–1000 m, dim light) ✅
• Enough light to see, not photosynthesis.
C. Abyss
• Deeper zone.
D. Intertidal
• Coastal zone.
Q100. The future of marine conservation depends on:
A. Ignoring climate change
• Opposite of solution.
B. Global cooperation in reducing CO₂, protecting MPAs, and regulating fisheries ✅
• Integrated, international effort needed.
C. Unlimited harvesting
• Unsustainable.
D. Removing marine mammals
• Not conservation.
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