Marine Biology: Sample Questions for Exam 3

What happens to the volume of a swim bladder if a fish is hauled up from 30 m depth?

• It expands about 4 times because pressure drops from 4 atm to 1 atm.

A diver descends to 10m depth. What will be the relative increase in pressure? In the ocean / in a mountain lake (air pressure 0.7 bar)

• In the ocean: pressure doubles (1 → 2 bar).

• In a mountain lake: pressure increases from 0.7 → 1.7 bar (about 2.4×).

Calculate the pressure at the bottom of the Mariana Trench.

• About 1100 bar (or 110 MPa).

• Depth ≈ 10,900 m, and pressure increases about 1 bar every 10 m.

• So, 1 + (10,900 ÷ 10) ≈ 1100 bar.

Discuss the pro’s and con’s for marine sessile animals of having a planktonic stage.

• Pros: Better dispersal and colonization of new areas; wider genetic mixing.

• Cons: Higher risk of predation and mortality during the planktonic stage.

Why are pelagic food webs more size-structured than terrestrial or benthic food webs?

• Open water offers no hiding places, so survival depends on size (eat smaller, avoid bigger).

• Food chain is mainly linear: phytoplankton → zooplankton → small fish → large fish.

• On land or seabeds, structures like trees or rocks provide shelter, creating more complex food webs.

Why would food webs be longer if mean predator: prey body size ratios are smaller?

• Smaller predator–prey size ratios mean less energy loss between levels.

• Energy is transferred more efficiently, allowing more trophic levels to exist.

The satellite picture shows chlorophyll concentration in the Pacific. A relatively narrow band of increased chlorophyll levels can be observed along the equator. Name and explain the process that causes this increased equatorial chlorophyll levels.

• Equatorial upwelling: Winds move surface water away from the equator, and deeper, nutrient-rich water rises.

• The nutrients promote high phytoplankton growth, increasing chlorophyll levels.

Describe 2 opposing effects that stratification has on phytoplankton.

• Positive: Keeps phytoplankton in the sunlit surface layer, preventing them from sinking too deep.

• Negative: Blocks nutrient mixing from deeper waters, limiting growth.

What are HNLC (High Nutrient, Low Chlorophyll) regions? Where are they found? What could explain them?

• Areas with plenty of nutrients (like nitrate and phosphate) but low phytoplankton growth.

• Found in the Equatorial Pacific, Subarctic Pacific, and Southern Ocean.

• Caused mainly by iron limitation, plus effects from grazing and low light due to deep mixing.

Describe in what way whales are keystone species in the Southern Ocean.

Whale pump: Whales feed on iron-rich krill at depth and release nutrient-rich feces at the surface, recycling iron and fertilizing phytoplankton blooms.

What is a front? Why is it often a high productivity zone?

• A front is a zone of turbulent mixing.

• Mixing brings nutrients to the surface and concentrates organisms, boosting phytoplankton growth.

Why is prey patchiness important for whales and other large planktivorous species?

• Patchy prey allows whales to feed efficiently.

• If prey were evenly spread, whales would expend more energy filtering water to catch enough food.

Zooplankton shows a diel vertical migration in the water column. Give 2 reasons why this migration benefits zooplankton growth and survival.

• Predator avoidance: Staying in deep, dark waters during the day reduces risk of being seen and eaten.

• Metabolic advantage: Cooler deep waters lower their metabolic rate, saving energy.

Explain the paradox of the plankton.

• Many plankton species coexist despite limited resources, which seems to contradict competitive exclusion.

• Viruses help by infecting the dominant species (“kill-the-winner”), preventing any one species from taking over and maintaining diversity.

Describe the principle behind active acoustic sampling (in words, no formulas needed) and give 3 possible applications of the technique.

• Principle: Sends a sound ping into the water and listens for echoes. The return time and strength reveal the distance, size, density, and type of objects.

• Applications: Mapping fish abundance, estimating zooplankton biomass, seafloor characterization.

What is Lagrangian and Eulerian sampling?

• Lagrangian: Follow a water parcel as it moves, tracking its changes.

• Eulerian: Stay in one place and measure what passes by.

Give some examples of data that can be obtained using satellites.

• Ocean surface: sea surface temperature, ocean color, sea surface salinity.

• Physical structure & motion: sea surface height, sea ice concentration, surface winds.

• Human use & impacts: ship traffic, harmful algal blooms, oil spills.

Give 3 reasons why pelagic fisheries are potentially more sustainable than benthic fisheries

• Faster life cycles: Pelagic fish grow and reproduce quickly, allowing stocks to recover faster.

• Less habitat damage: Fishing in the water column avoids harming the seafloor.

• More connected populations: Wide dispersal and mobility help repopulate overfished areas.

Why are jellyfish-dominated ecosystems often an end product of overfishing?

• Overfishing removes jellyfish predators and competitors.

• Jellyfish populations explode and eat fish juveniles.

• This creates a stable jellyfish-dominated ecosystem that hinders fish recovery.

Describe 3 different methods to make pelagic fisheries more sustainable

• Improve fishing gear to reduce bycatch of non-target species.

• Use real-time ocean data to close areas with high juvenile concentrations.

• Create incentives for sustainable fishing practices.

What evidence can be found on continental shelves of the impact of past glaciation events? Give a specific example.

• Drowned river deltas, boulder fields, and glacial scouring of bedrock.

• Example: Large mammal bones showing hominid butchery found 40 m below current sea level in the Gulf of Mexico.

Explain how it is possible that, whereas eustatic sea level rise was 110 m after the last glacial event, in many places the relative sea level only rose by 70 m.

Isostatic adjustment: Land previously depressed by ice sheets rises as the ice melts, reducing the net relative sea level rise.

What types of challenges do benthic organisms face in response to either high or low current velocity?

• High current: Risk of being scoured, physical damage, feeding difficulty.

• Low current: Reduced food and oxygen supply.

Why are fronts often areas of high primary productivity?

• Nutrient-rich water mixes into nutrient-poor surface waters, fueling phytoplankton growth.

• High productivity attracts fish, seabirds, and marine mammals.

Explain why the continental shelf seabed should be considered a 3-dimensional, rather than a 2-dimensional habitat. What limits the upper and the lower borders of the continental shelf seabed habitat?

• Life exists above (e.g., kelp forests) and within the seabed (e.g., burrows).

• Upper limit: How far organisms extend into the water column.

• Lower limit: Depth organisms can burrow while still accessing oxygen (≈2 m).

Explain why a small patch of mussels may grow less well than a large patch of mussels, even though competition for phytoplankton may be more severe in the latter situation.

• Large mussel patches can modify local water flow, increasing food delivery.

• Small patches cannot alter flow and may get less food despite lower competition.

Discuss (in qualitative terms) the influence of bioturbators on the continental shelf seabed ecosystem.

• Oxygenate sediments via burrows.

• Recycle nutrients by moving organic matter and waste.

• Increase microbial activity on burrow surfaces.

• Alter sediment properties: porosity, stability, topography.

• Provide microhabitats for other species.

Explain why trophic cascades are unlikely to be found in marine food webs. In what situations could you find them?

• Marine food webs are complex and resilient, reducing cascade effects.

• Cascades can occur in simpler systems with strong predator–herbivore–producer links, e.g., sea otters → sea urchins → kelp forests.

Describe which physical factors determine species composition in a hard substrate community and in a soft substrate community.

• Hard substrate: Wave exposure, current velocity, light, space competition, rock stability, crevices.

• Soft substrate: Sediment grain size, wave disturbance, current velocity, sediment stability; finer sediments increase the role of biological and chemical processes.

Lake Veere is currently a saltwater lake that has some tidal influence through a connection with the Eastern Scheldt. The bottom of the lake mainly consists of fine mud. What would happen if you would dump a significant number of large stones in the lake, and which changes you would expect in the lake ecosystem.

• Dumping stones creates hard surfaces in the muddy lake bottom.

• Sessile animals (mussels, barnacles, tubeworms) can settle, forming a small reef.

• The reef provides shelter for fish and crustaceans, increasing biodiversity.

• Filter feeders improve water clarity by removing particles.

• Local water flow changes, trapping some mud and altering sediment.

• Overall, the lake shifts from a simple mud habitat to a more complex reef-like ecosystem.

Discuss the options that exist for Carbon Capture and Storage (CCS) in the deep sea. For each option, give an advantage and a disadvantage.

• Direct Ocean Storage: Inject CO₂ into deep water.

  • Advantage: Speeds up CO₂ absorption by the ocean.

  • Disadvantage: Can quickly acidify deep water.

• Deep-Sea Sediments: Store CO₂ in porous seabed sediments.

  • Advantage: CO₂ can stay trapped for a long time.

  • Disadvantage: Risk of leaks or harming marine life.

• Deep-Sea Basalt Aquifers: Inject CO₂ into basalt rocks where it turns into minerals.

  • Advantage: Very secure, becomes solid.

  • Disadvantage: Expensive and limited locations.

What is bioluminescence? Name 4 functions of bioluminescence.

• Bioluminescence: Light produced by a chemical reaction in an organism (using luciferin and luciferase).

• Functions: Finding mates, finding food, avoiding predators, counter-illumination (camouflage).

What 3 types of currents can be observed on the deep-sea floor?

• Tidal currents: Reach the seabed near continental slopes, create ripple patterns.

• Oceanic conveyor: Large, steady currents driven by thermohaline circulation.

• Coriolis currents: Caused by Earth’s rotation affecting water movement at the seabed.

Compare and contrast the challenges faced by a deep-sea organism to those faced by an estuarine organism.

• Abiotic conditions:

  • Deep sea: Stable environment with constant darkness, low temperature, high pressure, and stable salinity/pH. Main challenge: coping with extreme conditions and scarce food.

  • Estuary: Highly variable environment with changing salinity, temperature, and turbidity due to tides. Main challenge: coping with rapid environmental changes.

• Biotic conditions:

  • Deep sea: Low population densities and biomass; less competition and predation; rely on unpredictable sinking food from above.

  • Estuary: High productivity and biomass; intense competition for space and food; direct access to primary producers like plants and algae.

What food sources are available to deep-sea organisms?

• Particulate Organic Matter (POM) / Marine snow / Phytodetritus (main source)

• Large food falls (whale, fish, squid carcasses)

• Plant and wood debris from land and sea

• Dissolved Organic Matter (DOM) for some species

• Chemosynthetic production at hydrothermal vents, cold seeps, and whale falls

Discuss why large parts of the seafloor are nevertheless seasonal environments.

• Surface primary production in temperate and polar regions is highly seasonal (spring bloom).

• This organic material sinks as marine snow over 1–2 months.

• The deep seafloor receives a seasonal pulse of food (phytodetritus), making it a seasonal environment.

Draw a graph of year-round POM deposition on the ocean floor in a tropical ocean, under a mid-oceanic gyre, and on the seafloor of a temperate ocean near the continental slope.

• Tropical Ocean: Low, relatively flat line, little seasonal change.

• Mid-Oceanic Gyre: Very low, flat line (low productivity).

• Temperate Ocean near Continental Slope: Low most of the year, with a single large peak in summer (July/August) from spring bloom phytodetritus.

Discuss the difference between life history characteristics of benthic deep-sea organisms in a tropical ocean and in a temperate ocean.

• Temperate deep sea: Seasonal, abundant food pulses; organisms reproduce and grow seasonally, often R-selected (fast growth, opportunistic).

• Tropical deep sea / gyres: Constant but low food supply; organisms grow slowly, reproduce late, and live longer, often K-selected (stable, food-limited environment).

Describe a method for estimating species diversity in the deep sea.

• Use ROVs or other vehicles to record video or still images along a transect.

• Identify and count all visible species in a known area.

• Calculate diversity indices from these counts.

Give 2 reasons why cold-water coral reefs are often found on continental slopes, rather than on the abyssal plain.

• Hard substrate: Slopes provide rock and other surfaces needed for coral attachment; abyssal plains are mostly soft sediment.

• Enhanced food supply: Slopes have stronger currents and are closer to productive waters, bringing more suspended food (POM) to the corals.

Discuss 2 potential explanations for deep-sea gigantism.

• Metabolism (Kleiber’s Law): Cold temperatures slow metabolism; larger body size is more energy-efficient, helping organisms survive on limited food.

• Food limitation & delayed reproduction: Scarce food causes slow growth and late reproduction; indeterminate growth over long lifespans leads to larger final body sizes.

Name the 3 different types of hydrothermal vents and give a brief description of each.

• Black Smokers: Hottest vents; emit dark, smoke-like plumes rich in metal sulfides; water up to 350°C.

• White Smokers: Cooler than black smokers; emit lighter plumes with barium, calcium, and silicon; lower water temperatures.

• Diffuse Vents: Hot water seeps through cracks; much cooler; mixes quickly with surrounding seawater.

What animal groups are found at thermal vents?

• Siboglinid tubeworms (e.g., Riftia)

• Bivalve molluscs (e.g., Calyptogena clams, Bathymodiolus mussels)

• Decapod crustaceans (e.g., Bythograea crabs, Rimicaris shrimp, squat lobsters)

• Polychaete worms (e.g., Pompeii worm Alvinella)

• Amphipods (e.g., Halice)

• Fish (e.g., Thermarces)

• Other sessile/sedentary fauna (e.g., sponges, anemones)

What fuels hydrothermal vents?

• Cold seawater seeps into cracks in the ocean floor, is heated by magma, and reacts with rocks.

• Hot water dissolves minerals and gases, which are released when it exits the vent.

How are the chimneys formed?

• Super-hot, mineral-rich water meets freezing cold seawater.

• The sudden temperature change causes minerals (like sulfur) to solidify, forming chimney structures.

Where are hydrothermal vents found?

• Along mid-ocean ridges.

What is chemosynthesis?

• Process that replaces photosynthesis in the deep ocean.

• Bacteria use chemical energy (e.g., hydrogen sulfide) to produce nutrients instead of sunlight.

What is the difference between black and white smokers?

• Black smokers: Dark water (sulfide minerals), hotter.

• White smokers: Light-colored water (calcium, silicon), cooler.

What is the maximum water temperature at hydrothermal vents? Why doesn’t the water boil?

• Maximum temperature ≈ 375 °C.

• High pressure from the overlying ocean prevents boiling, keeping water liquid.

What are the characteristics of a mangrove tree? Are mangroves a polyphyletic or a monophyletic group? Explain your answer.

• Characteristics: Woody trees/shrubs at the sea–land interface in the tropics; have aerial roots (pneumatophores, knees) to cope with salt and waterlogged mud.

• Group type: Polyphyletic – the mangrove habitat evolved independently at least 16 times.

Describe 2 problems that mangroves, being terrestrial plants, encounter in their natural environment. Describe how mangroves solve these problems.

• Problem: Waterlogged, anoxic sediment → Solution: Aerial roots (pneumatophores, knees) for oxygen.

• Problem: High salt levels → Solution: Exclude salt at roots, tolerate salt in tissues, excrete excess salt through leaves or bark.

What is vivipary? In what way does vivipary benefit mangroves?

• Vivipary: Seeds germinate and develop while still attached to the parent.

• Benefit: Seedlings (propagules) are ready to survive floating in seawater, aiding dispersal.

Why are mangroves only found in the tropics?

• High energy cost of growth, salt tolerance, and coping with waterlogged soil requires year-round sunlight for photosynthesis, which is only available in the tropics.

What is bio-logging? Name 3 applications of bio-logging.

• Bio-logging: Attaching small devices to animals to track their movements and behavior.

• Applications:

  • Track foraging trips of seabirds (e.g., gannets).

  • Discover migration routes of large fish (e.g., basking sharks).

  • Study physiology and behavior of diving animals (e.g., penguin breathing and feeding patterns).

What are mudskippers? What makes them special?

• Amphibious fish related to gobies.

• Can live out of water, "walk" on mud using fins, breathe air, live in burrows, and transport air to their eggs.

What is the ecological role of crabs in mangrove communities?

• Process mangrove leaf litter.

• Burrow, aerating sediments (bioturbation).

• Improve sediment chemistry and promote mangrove growth.

• Store leaves in burrows, keeping carbon in the system.

Name 2 beneficial effects that mangroves have on adjacent coral reefs.

• Coastal protection: Reduce wave energy and trap sediment/runoff that could smother reefs.

• Nursery grounds: Provide refuge and food for juvenile fish, increasing reef fish biomass.

List some of the ecosystem services of mangroves.

• Nursery grounds for fish.

• Coastal protection from waves and storms.

• Trap sediment and filter runoff.

• Export carbon to coastal food webs.

Explain the features of seagrasses that enable them to live permanently submerged in seawater.

• Leaves with sheaths to withstand strong water movement.

• Hydrophilous pollination to reproduce underwater.

• Extensive lacunar (air) system to transport oxygen to roots in oxygen-poor sediments.

What factors determine the upper and lower boundary of seagrass meadows?

• Lower boundary: Light availability for photosynthesis; depends on water clarity.

• Upper boundary (intertidal): Desiccation, UV damage, wave exposure, and ice scour.

What happens when seagrass ecosystems become eutrophic?

• Excess nutrients cause algal overgrowth.

• Algae shade seagrass, reducing light and productivity.

• Seagrass may die due to insufficient light.

What are the general characteristics of an invasive species?

• Non-native and harmful to economy, environment, or health.

• Rapid reproduction (sexual & asexual), fast growth, high dispersal.

• Tolerant of wide conditions, freed from native predators.

• High propagule pressure (frequent introductions).

What are the main threats to seagrass ecosystems?

• Eutrophication leading to algal overgrowth.

• Invasive species (e.g., Caulerpa taxifolia).

• Physical damage from boats and anchors.

• Disease (e.g., Labyrinthula zosterae “wasting disease”).

• Heavy grazing by animals like sea urchins.

Describe the effect of grazing by dugongs on seagrass meadows.

• Dugongs eat entire seagrass plants, creating feeding trails.

• Prefer fast-growing species like Halophila.

• Grazing disturbs dominant seagrass, allowing Halophila to recolonize.

• Dugongs return to feed on new growth—this cycle is called cultivation grazing.

Describe the differences between hermatypic and ahermatypic corals.

• Feeding: Hermatypic – symbiotic zooxanthellae; Ahermatypic – plankton feeders.

• Environment: Hermatypic – build reefs; Ahermatypic – don’t build reefs.

Why are there coral reefs in the Caribbean but not on the west coasts of Africa or NE South America?

Cool upwelling lowers water temperature below coral tolerance; Caribbean and Indo-Pacific lack strong upwelling.

Difference between spawning and brooding corals; benefits/drawbacks.

• Spawning: Release gametes → long dispersal, high mortality.

• Brooding: Internal fertilization → high survival, limited dispersal.

Five factors affecting hermatypic coral distribution.

• Light: Needed for photosynthesis (<30 m).

• Temperature: Optimal 26–28 °C.

• Salinity: Stable 33–35 ppt.

• Sediment: Smothers corals, blocks light.

• Wave energy: Can damage but brings nutrients.

Effect of overfishing parrotfish.

• Less grazing → algal overgrowth → corals lose space/light → reefs dominated by algae.

Factors driving high coral reef productivity.

• Nutrient recycling: Grazers/algae recycle nutrients.

• Island mass effect: Upwelling/seabird nutrients boost phytoplankton.

Harmful effects of rising CO₂ on corals.

• Warming: Bleaching → death.

• Acidification: Harder to build skeletons → reef erosion.