EARTH100 Coral Reefs Exam 2

What is a fringing reef?

A reef that grows directly from the shoreline, with little or no lagoon separating it from land.

What is a barrier reef?

A reef that runs parallel to shore but is separated from it by a lagoon.

What is an atoll?

A ring-shaped reef, island, or series of islets surrounding a central lagoon, formed from sinking volcanic islands.

What is a patch reef?

Small, isolated reefs, often found inside lagoons or between larger reef structures.

What is a cay?

A small, low island of sand and coral rubble formed on the surface of a reef.

Why have most coral reefs formed after the last glacial maximum?

Sea levels rose after the last Ice Age, flooding continental shelves and creating new shallow-water habitats where reefs could grow.

How do reefs keep up with changing sea level?

By vertical growth — corals and reef organisms deposit CaCO₃ quickly enough to keep pace with rising seas.

Which scientist first developed a theory to explain atolls?

Charles Darwin

Describe the subsidence/compensation theory.

Volcanic islands form → fringing reefs develop → as island sinks, reef grows upward forming barrier reefs → complete sinking leaves atolls.

How are hot spots connected to seamounts and atolls?

Hot spots form chains of volcanoes/seamounts. Corals colonize shallow volcanoes; when islands erode and sink, reefs persist as atolls.

Why is the Great Barrier Reef expanding south?

Warming seas allow coral growth farther south along Australia's east coast.

Describe reef biodiversity.

Coral reefs house 600,000-9 million species; 25% of marine species depend on reefs; 65% of marine fishes live there.

What organisms are associated with reefs?

Stony corals, gorgonians, hydrocorals, coralline algae, calcareous green algae (Halimeda), sponges, molluscs (giant clams, scallops, snails, nudibranchs), echinoderms (sea urchins, cucumbers, starfish, crinoids), crustaceans, worms, fishes, bacteria.

Coralline algae?

Red algae, encrusting, deposit CaCO₃ in cell walls, cement reefs together, key on reef crest.

Calcareous green algae?

Halimeda; large cells, CaCO₃ in walls, fast-growing, resistant to grazing.

Filter feeders? Why important?

Organisms (sponges, bivalves) that filter plankton/particles from water. They clean water and recycle nutrients.

Octocorallia?

Cnidarians, colonial, 8 tentacles, internal skeleton, planktonic larvae.

Scallops?

Migratory bivalves, swim by clapping shells.

Giant clams?

Large bivalves, mantle holds zooxanthellae, filter feeders, epifauna/infauna.

Epifauna vs infauna?

Epifauna live on the surface (e.g., clams on reefs); infauna burrow into sediment.

Gastropods (Flamingo tongue)?

Snails; many herbivorous grazers. Flamingo tongue is carnivorous, feeds on soft corals.

Nudibranchs

Shell-less gastropods, breathe via dorsal appendages, most carnivorous.

Starfish

Radial symmetry, CaCO₃ ossicles, tube feet, predators with two stomachs.

Crinoids

Radial symmetry, filter feeders, mouth and arms on top, free swimming.

Sea cucumbers?

Scavengers, collagen body walls, can expel tubules, some host commensals.

Crustaceans?

Exoskeleton, 3 body segments, biramous limbs, nauplius larvae.

Spiny lobsters?

Social crustaceans, spiny exoskeleton, nocturnal grazers/scavengers.

Marine worms (Feather dusters)?

Tube-dwelling polychaetes, use colorful tentacle crowns to filter food/respire.

Trophic pyramid components?

Producers: algae, seagrass, phytoplankton

Primary consumers: herbivores, grazers

Secondary consumers: planktivores, small predators

Tertiary consumers: top predators (sharks, groupers)

Seagrasses & seagrass beds?

Flowering plants, not algae. Grow in shallow sandy/muddy bottoms, ecosystem engineers, provide food/habitat.

Plankton?

Microscopic organisms. Phytoplankton = photosynthetic, producers. Zooplankton = animal-like, consumers.

What is bioerosion?

Breakdown of coral skeletons by organisms (parrotfish, boring sponges, urchins).

Examples of protection?

Reef structures shelter organisms from predators.

Other mutualisms?

Cleaner fish/shrimp with clients, clams with zooxanthellae.

Examples of disturbance?

Sea star outbreaks, urchin die-offs, bleaching.

How does fish biodiversity vary by ocean?

Highest in Indo-Pacific; Atlantic reefs are relatively species-poor.

Day-night changes in fish populations?

Day: planktivores swarm above reef.Night: planktivores hide; nocturnal predators feed on benthos.

Adaptations of nocturnal fish?

Large eyes, mouths, reddish/silver coloration, hide in caves.

Feeding strategies of reef fish:

Herbivores (scrapers, grazers, bioeroders, browsers)

Planktivores

Predators (corallivores, invertebrate feeders, piscivores: pursuit, stalking, ambush)

Scrapers (parrotfish):

Beak-like teeth, scrape algae/sediment, prevent algal overgrowth.

Bioeroders (parrotfish)

Large, eat corals + algae, produce sand.

Grazers (surgeonfish, angelfish)

Remove turf algae, help reef resilience, don't damage substrate.

Browsers (tangs, damselfish):

Feed on macroalgae; damselfish farm algae patches, territorial.

Planktivores (wrasses, Moorish idols)

Small, feed on inverts or benthic inverts, some symbiotic cleaners.

Corallivores (butterflyfish, puffers)

Obligate or facultative coral feeders, often territorial.

Invertebrate feeders (triggerfish, lionfish):

Strong jaws, precision feeders, adapted to crush shells.

Pursuit predators (snappers, jacks)

Fast swimmers, torpedo bodies, hunt in open water.

Stalking predators (trumpetfish, barracuda):

Camouflaged, ambush with surprise bursts.

Ambush predators (frogfish, groupers):

Camouflaged, rely on lures or suction feeding.

Cleaning stations?

Wrasses/shrimps remove parasites from "client" fish; mutualism.

Schooling behavior?

Fish group together for predator defense, better swimming efficiency, and feeding advantage.

Why are reefs important?

Protect coasts, support fisheries, tourism, medicine, biodiversity.

Present status?

~11% lost, 16% severely damaged, ~60% threatened by humans, no pristine reefs left. Caribbean: coral cover declined from ~50% to ~10% since 1970s.

Predicted losses?

70% of reefs could disappear within 50 years. Economic losses in fisheries, tourism, shoreline protection.

Main challenges?

Natural: bleaching, pathogens, storms, predators, bioerosion, El Niño.Human: pollution, runoff, coastal development, overfishing, aquarium trade, climate change.

Coral bleaching?

Stress response where corals expel zooxanthellae, leaving white skeleton visible. Triggered by high temps, UV, salinity changes, runoff.

Recovery?

Possible if stress is brief; corals can regain zooxanthellae.

Common coral diseases?

Black band disease, yellow band disease, aspergillosis in sea fans.

How hurricanes affect reefs?

Cause breakage, smothering, freshwater poisoning—but can cool waters, reducing bleaching.

Other disturbances?

Tsunamis, earthquakes, volcanoes, predation, algal competition.