# Module D Quiz — Question Bank **Source:** Canvas quiz, submitted Jul 15 at 11:14 a.m. (attempt took 10 minutes) **Score:** 1.8 / 2.0 — Questions 3 and 13 answered incorrectly; all others correct. **Note:** Correct answers are marked with ✅. For multiple-choice questions the student's selection was not captured in the paste; correct answers are identified from course content. --- ## Question 1 — Why seagrass beds boost primary production ✅ Correct > Why is primary production higher in and near seagrass beds compared to areas that lack seagrasses? - Seagrasses offer protection from grazers. - Seagrasses offer substrate for primary producers. - Seagrass degradation results in more available nutrients. - **All solutions listed increase primary production.** ✅ - Seagrasses reduce wave and current energy, increasing the settling of sediment. *Rationale: Each mechanism adds production. Blades give epiphytes (diatoms, small seaweeds) a substrate. Bacterial breakdown of seagrass detritus releases nutrients back into the water. Slowed currents drop suspended sediment, clearing the water so light reaches deeper. Shelter from grazers also protects producer biomass. (If only one mechanism were accepted, the sediment-settling → clearer water → more light pathway is the one Lesson 4-4 states explicitly.)* --- ## Question 2 — Why mangroves matter to coral reefs ✅ Correct > Why are mangrove ecosystems so important to coral reef ecosystems? - **All answers are important.** ✅ - Mangroves provide a nursery for larval fish from the coral reef. - Mangroves reduce nutrients in the water column - Mangroves filter fresh water from land. - Mangroves help reduce sedimentation from erosion. *Rationale: Mangroves, seagrasses, and reefs are interdependent. Mangroves filter land runoff (fresh water, nutrients, sediment) that would otherwise smother reefs and feed phytoplankton that block coral light. They also shelter juvenile fish that later live on the reef.* --- ## Question 3 — Ocean acidity: what does NOT affect coral health ❌ Incorrect (0 / 0.1) > Most of the surface oceans are experiencing an increase in ocean acidity. This can have a negative effect on coral reef health. Which of the following factors does not affect coral reef health? - **Increased ocean acidity affects the timing of the broadcast spawning events.** ✅ (correct answer) - Increased ocean acidity decreases the linear extension rate of corals. - Increased ocean acidity decreased red coralline algae growth. - Increased ocean acidity decreases coral calcium carbonate density. - Increased ocean acidity increases the dissolution rate of the hard parts of corals. *Rationale: Spawning timing is cued by temperature, day length, and the lunar cycle — not by pH. All the other options are documented acidification effects: slower growth, weaker/less dense skeletons, faster CaCO₃ dissolution, and harm to high-magnesium calcite coralline algae (which also disrupts larval settlement).* --- ## Question 4 — How El Niño kills kelp ✅ Correct > Periodic warming trends, such as El Niño events, have been shown to cause measurable increases in kelp mortality. What is the underlying mechanism for this effect? - Warm water increases wave action to a level that breaks kelp holdfasts. - **Warm currents decrease the mixing of cold, nutrient-rich water, severely restricting nutrient availability.** ✅ - Elevated pH levels dissolve the calcium carbonate components of the kelp body. - El Niño events cause high rates of hypersalinity that kill off kelp spores. - The warm water triggers a reproductive shift in sea otters, causing them to eat kelp stipes. *Rationale: Kelp need cold, nutrient-rich water. Warm surface water strengthens stratification, cuts off nutrient resupply (and upwelling), and starves the kelp.* --- ## Question 5 — Why infauna use siphons and burrow openings ✅ Correct > Why do many infaunal organisms rely on siphons or burrow openings? - To hide from predators - To avoid competition with epifaunal species - **To obtain oxygen and food from above the sediment** ✅ - To help them move faster *Rationale: Buried sediment is often low in oxygen and dark. Siphons and flushed burrows connect the organism to oxygen-rich water (and to plankton/detritus for filter feeders).* --- ## Question 6 — The coral reef paradox ✅ Correct > The "paradox of coral reefs" refers to the fact that these highly productive, biodiverse ecosystems thrive in waters that are: - **Oligotrophic (nutrient-poor) with very low water column primary production and low phytoplankton biomass.** ✅ - Continuously shifting and lacking any hard benthic substrate for larval attachment. - Dominated by massive monocultures of competitive dominants like blue mussels. - Hypersaline, heavily polluted by coastal upwelling, and completely dark. - Subjected to extreme freezing temperatures and constant polar ice coverage. *Rationale: Reefs sit in tropical "marine deserts" — low nitrate, low chlorophyll. The zooxanthellae mutualism solves the paradox by recycling nutrients tightly between symbiont and host.* --- ## Question 7 — A tide pool on a hot day ✅ Correct > As the temperature of water in an isolated intertidal tide pool increases during a hot summer day, how can the abiotic conditions be affected (assume BC coast conditions and limited respiration and photosynthesis)? - Both salinity and dissolved oxygen concentration increase simultaneously. - Salinity decreases and dissolved oxygen concentration increases. - Both salinity and dissolved oxygen concentration decrease simultaneously. - **Salinity increases and dissolved oxygen concentration decreases.** ✅ - Salinity remains constant while dissolved oxygen drops to absolute zero. *Rationale: Evaporation leaves the salt behind, so the pool becomes hypersaline. Warmer water holds less dissolved gas, so oxygen falls. Both effects stress tide-pool organisms.* --- ## Question 8 — Climate change and the climax community ✅ Correct > Which of the following circumstances due to climate change will NOT affect the stability and makeup of a climax community at an intertidal ecosystem? - Increasing winter storm intensities. - Increased fresh water input from rivers. - Summer days with record hot temperatures. - Colder temperatures during winter months. - **All circumstances will affect the stability and makeup of an intertidal climax community.** ✅ *Rationale: Storms, freshwater input, heat, and cold snaps all change disturbance regimes and stress, so a truly stable climax community becomes rare.* --- ## Question 9 — Why removing Pisaster halves diversity ✅ Correct > When Pisaster ochraceus was experimentally removed from a rocky intertidal mussel bed community, the species richness of the community decreased by 50%. This occurred because: - The community instantly shifted into an early-stage bacterial film succession. - Algal mats grew uncontrolled and blocked all available surface light. - Primary productivity dropped due to a sudden lack of nutrients. - Whelks took over the lower intertidal and consumed all the barnacles. - **Mussels propagated rapidly and outcompeted other species for limited space.** ✅ *Rationale: This is the classic keystone-predator experiment. The mussel is a competitive dominant; without the seastar, it monopolizes the rock and diversity crashes.* --- ## Question 10 — Advantage of infaunal life ✅ Correct > What is a key physiological advantage enjoyed by infaunal organisms living within soft-bottom substrates compared to epifaunal organisms on rocky shores? - **Interstitial spaces retain water and remain moist, protecting them from desiccation and moderating temperature fluctuations.** ✅ - The shifting substrate allows them to photosynthesize at night. - They can completely bypass the need for oxygen by utilizing particulate organic matter directly. - Coarse sand grains provide an absolute barrier against all forms of macro-predation. - Soft sediment lacks any organic carbon, eliminating the threat of toxic bacterial blooms. *Rationale: Water held between sediment grains insulates buried organisms from drying out and from temperature swings. The trade-off is lower oxygen and less food transport.* --- ## Question 11 — Lugworms as keystone species ✅ Correct > Polychaete worms like lugworms (Arenicola sp.) are considered ecosystem engineers or keystone species in sandy bottom and mudflat communities because they: - **Bring oxygenated water into deep sediment layers through burrowing, allowing other heterotrophs to survive and process organic carbon.** ✅ - Hunt and eliminate larvae of competing species. - Act as the primary producers of the system by fixing atmospheric nitrogen. - Build hard calcium carbonate reefs that stabilize the shifting sands. - Prevent oxygen from entering the sediment, protecting anaerobic bacteria. *Rationale: Burrow irrigation oxygenates sediment that would otherwise go anoxic, letting aerobic organisms exploit the rich organic carbon in mud.* --- ## Question 12 — Zooxanthellae specificity (True/False) ✅ Correct > Zooxanthellae within a specific coral can only be one specific species. - True - **False** ✅ *Rationale: Zooxanthellae are genetically diverse (many clades and strains). One coral species can host different strains, and corals can re-acquire new strains after bleaching — the basis of the adaptive bleaching hypothesis.* --- ## Question 13 — Intermediate Disturbance Hypothesis ❌ Incorrect (0 / 0.1) > According to the Intermediate Disturbance hypothesis, which of the following will most likely have the highest diversity (assume a rocky intertidal location along the same bay). - Area on average has 5 m waves. - **Area on average has 100 cm waves.** ✅ (correct answer) - Area dominated by blue mussels. - Impossible to tell based on the information given. - Area on average has 5 cm waves. *Rationale: Diversity peaks at MODERATE disturbance. 5 m waves = extreme disturbance (only a few stress-tolerant species survive). 5 cm waves or a mussel-dominated area = minimal disturbance (the competitive dominant takes over). 100 cm (1 m) waves are the intermediate case — enough disturbance to clear patches, not enough to exclude most species.* --- ## Question 14 — Cyanobacteria on coral reefs ✅ Correct > What role do cyanobacteria play in supporting the high productivity of coral reef environments? - They actively prey on crown-of-thorns sea stars to protect the coral polyps. - They alter local water clarity to filter out excess, damaging solar radiation. - They act as a foundation species by building massive calcium carbonate skeletons. - **They fix atmospheric nitrogen (N₂) into ammonium (NH₄⁺), a biologically usable form of nutrient.** ✅ *Rationale: In nutrient-poor tropical water, nitrogen fixation supplies the reef with usable nitrogen — a key support for reef productivity. (Note the quiz lists the crown-of-thorns distractor twice.)* --- ## Question 15 — The reef's foundation ✅ Correct > Which type of organism would most likely form the base and main structure of a coral reef? - Gorgonacea coral - **hermatypic coral** ✅ - coralline algae - ahermatypic coral - all answers are correct *Rationale: Hermatypic (stony, scleractinian) corals secrete the CaCO₃ framework that builds the reef. Coralline algae only cement it together; gorgonians (soft corals) and ahermatypic corals do not build reefs.* --- ## Question 16 — What increases the chance of an urchin barren ✅ Correct > Which of the following would INCREASE the likelihood of an urchin barren in any given area during a summer season? - increased sedimentation in the water column, reducing light in the water column - presence of a strong El Niño - **increased predation of sea otters by local orcas** ✅ - increased fishing of urchins - increased storm activity in that area *Rationale: The cascade is otters → urchins → kelp. More orca predation on otters releases the urchins from their keystone predator, so urchins multiply and mow the kelp down to a barren. (El Niño and storms damage kelp directly but do not release the urchins; fishing urchins does the opposite.)* --- ## Question 17 — Who settles a cleared patch (select all) ✅ Correct > Which of the following organisms could settle successfully in a recently cleared area patch (bare rock) in the rocky intertidal? - **barnacles** ✅ - **diatoms** ✅ - **rockweed (Fucus sp.)** ✅ - adult mussels - limpets - seastars *Rationale: Succession starts with a bacterial film, then an algal film (diatoms/cyanobacteria), then seaweeds and barnacle larvae settle. Limpets (grazers) and seastars (predators) are mobile and move in later — they do not "settle." Adult mussels are already sessile elsewhere; only their larvae settle new patches (though an adjacent mussel bed can slowly spread in).* --- ## Question 18 — Disadvantage of a tide pool at low tide ✅ Correct > Which of the following is a possible important DISADVANTAGE of inhabiting a tidepool during a low tide compared to nearby exposed locations? - limited food - UV exposure - predation - desiccation - **low oxygen** ✅ *Rationale: A tide pool solves desiccation and reduces UV, but an isolated pool can heat up fast, and warm water holds less oxygen — organisms can run out of O₂. (Salinity also spikes as water evaporates.)* --- ## Question 19 — Rule for zonation boundaries ✅ Correct > In the rocky intertidal zone, vertical zonation creates distinct visual bands. What is the general rule governing the boundaries of these zones? - The upper limit is determined by biotic factors, and the lower limit is determined by abiotic factors. - Both upper and lower limits are strictly determined by physical factors like desiccation. - **The upper limit is determined by abiotic factors, and the lower limit is determined by biotic factors.** ✅ - The limits are entirely random and depend solely on unpredictable larval settlement patterns. - Both upper and lower limits are strictly determined by biological interactions like predation. *Rationale: Abiotic stress (desiccation, heat, UV) caps how high an organism can live. Biotic pressure (predation, competition — e.g., the seastar-mussel boundary) sets how low.* --- ## Question 20 — What controls sandy-shore communities ✅ Correct > Which factor most strongly influences the types of organisms found in a sandy shore ecosystem? - Temperature - Salinity - **Sediment grain size** ✅ - Light availability *Rationale: Grain size controls drainage, oxygen, and organic (POM) content — coarse sand flushes clean but holds little food; fine mud holds food but goes anoxic. The whole community structure follows from that trade-off.*