Chapter 13 Review Questions

Explain similarities and differences among the following: red tides, and harmful algal blooms.

A red tide is a proliferation of dinoflagellates to such an extent that they color the surface waters red. Red tides are specific to certain species of dinoflagellates. Because these dinoflagellates secrete potent biotoxins, these red tides are more correctly called harmful algal blooms. Note that not all algae will cause a harmful algal bloom because not all algae secrete potent biotoxins.

Describe the advantage that a top carnivore gains by eating from a food web as compared to a single food chain.

A top carnivore is more likely to survive eating from a food web because it has alternative foods to eat if its preferred food diminishes or disappears.

What three types of feeding strategies exist?

Filter feeding, or suspension feeding, deposit feeding, and carnivorous feeding.

Productivity in specific regions of tropical oceans is not uniformly low. What factors contribute to the higher productivity with coastal upwelling?

Coastal upwelling: Where the prevailing winds blow toward the equator and along the western continental margins, surface waters are driven away from the coast. The displaced water is replaced by nutrient-rich water surfacing from depths of 200 to 900 meters (660 to 2950 feet). This nutrient-rich upwelling promotes high primary productivity in these areas, in turn, it supports large fisheries. In the Pacific, such conditions exist along the southern coast of California and the southwestern coast of Peru; in the Atlantic, they exist along the northwestern coast of Morocco and the southwestern coast of Africa.

Describe the color difference between coastal waters and less-productive open-ocean water and explain why each has the color that it does.

Coastal waters tend to be yellow-green in color because of the presence of turbidity from continental runoff and because of the microscopic organisms that thrive in this high-nutrient environment. Open ocean water lacks this turbidity and concentrated abundance of nutrients and photosynthetic organisms and tends to be indigo blue. In addition, a physical property of deep water is that it scatters incoming solar radiation preferentially in the blue portion of the electromagnetic spectrum, making the water appear blue.

Discuss the characteristics of the coastal ocean where unusually high concentrations of marine life are found.

Conditions that result in unusually high concentrations of marine life in some coastal regions are the result of coastal upwelling. Particularly where the surface water is moved offshore by Ekman transport, water from beneath the photosynthetic zone will rise to replace it. Since there is no plant or algal life growing in these deeper waters, they are rich in plant and algal nutrients and serve to continuously supply nutrients to the sunlit surface waters.

An important variable in determining the distribution of life in the oceans is the availability of nutrients. How are the following variables related: proximity to the continents, availability of nutrients, and the concentration of life in the oceans?

Continents are a source of nutrients due to runoff from the land, specifically nitrates and phosphates, which are essential for phytoplankton. The greatest concentrations of marine organisms are proximal to the continents because the continents are a major source of nutrients. Phytoplankton use the nutrients to produce carbohydrates, fats, and proteins that make up the base of the food web.

Productivity in specific regions of tropical oceans is not uniformly low. What factors contribute to the higher productivity in coral reefs?

Coral reefs: Organisms that comprise and live among coral reefs are superbly adapted to low-nutrient conditions, in a similar manner to how some terrestrial organisms are adapted to a desert existence. Symbiotic algae living within the tissues of coral and other species allow coral reefs to be highly productive ecosystems. Additionally, coral reefs tend to hold and concentrate the low levels of nutrients in the ecosystem.

The golden algae include two classes of important phytoplankton. Compare their composition and structure of their tests.

Diatoms secrete a siliceous cell wall composed of two halves (valves) that are an important constituent of siliceous sediment called diatomaceous earth that is used in filtering devices, industrial abrasives, polishing agents, and numerous other applications. Diatomaceous earth accumulates on the sea floor beneath surface waters that are relatively low in temperature such as in high-latitude regions where equatorial upwelling occurs. Coccolithophorids are covered with tiny calcareous plates (coccoliths) that are abundant in calcareous oozes found on the sea floor beneath warm surface waters (not too deep because the calcium carbonate goes into solution below the calcite compensation depth [CCD]).

Productivity in specific regions of tropical oceans is not uniformly low. What factors contribute to the higher productivity with equatorial upwelling?

Equatorial upwelling: Where the trade winds drive westerly equatorial currents on either side of the equator, surface water diverges as a result of Ekman transport. The surface water that moves toward higher latitudes is replaced by nutrient-rich water that surfaces from depths of 200 meters (660 feet). Equatorial upwelling is best developed in the eastern Pacific Ocean.

Another important determinant of productivity is the availability of solar radiation. Why is biological productivity relatively low in the tropical open ocean, where the penetration of sunlight is greatest?

Even though there is a thicker column of sunlit water in the open ocean far from the continents than in the turbid water near their shores, photosynthesis is greatly restricted in the clear open ocean water by the lack of nutrients in surface waters.

Explain why everything in the ocean at depths below the shallowest surface water take on a blue-green appearance.

Even though there is a thicker column of sunlit water in the open ocean far from the continents than in the turbid water near their shores, photosynthesis is greatly restricted in the clear open ocean water by the lack of nutrients in surface waters.

Of the following types of seafood on a menu, which is the best choice for supporting sustainable fisheries: a) farmed salmon; b) monkfish; c) orange roughy; d) Atlantic cod; or e) Pacific halibut?

Farmed salmon is the best choice for supporting a sustainable fishery.

What conditions create ocean eutrophication (dead zones)?

Increased inorganic nutrient input, primarily nitrogen and phosphorus, from terrestrial sources (agriculture, urban run-off) stimulates coastal algal blooms. Eutrophication is caused by excess nutrient input into marine systems. Excessive algal growth pulls oxygen out of the water, producing low dissolved oxygen levels (less than 2.0 g/ml, hypoxia). When oxygen levels drop to 0 g/ml, a dead zone is created.

Describe the yearly productivity pattern in polar oceans, including the main factor that limits productivity in polar oceans.

Many parts of the polar ocean experience darkness, and hence no photosynthetic phytoplankton, for about 3 months of the year. When sunlight is able to penetrate the ocean deep enough, plankton will start to develop and other organisms will feed on them. The Antarctic has somewhat greater productivity than the Arctic because North Atlantic Deep Water upwells near Antarctica with its high nutrient concentration. The main limiting productivity factor in polar oceans is the availability of solar energy.

Define overfishing. When a species is overfished, what changes are there in the standing stock, the size of individuals in the remaining fish population, and the maximum sustainable yield?

Overfishing happens when fish are removed from the population so quickly that the remaining population is not yet sexually mature enough to reproduce, resulting in a decline in the fish population and the general size of the fish in that population. The maximum sustainable yield will be significantly reduced as well.

What is the average efficiency of energy transfer between trophic levels? Use this efficiency to determine how much phytoplankton mass is required to add 1 gram of new mass to a killer whale, which is a fourth-level carnivore.

The efficiency of energy transfer between trophic levels averages 10% (0.10). To add 1 gram of new mass to a killer whale at the fourth trophic level requires: 1÷ 0.10 ÷ 0.10 ÷ 0.10 ÷ 0.10 = 10,000 grams of phytoplankton mass

Why is the productivity in tropical oceans uniformly low year-round?

The main limiting productivity factor in tropical oceans is the availability of nutrients.

Describe trends that occur in number of individuals, total biomass, and organism size at successive trophic levels going up a biomass pyramid.

The number of individuals is greatest at the bottom of a biomass pyramid. Total biomass decreases the higher up they are found in the pyramid but organism size increases.

How does the flow of energy through the biotic community differ from the manner in which mass is moved through the ecosystem?

The unidirectional flow of energy prevents the recycling of energy within the system once it has been released from its chemical state. Mass moved through the ecosystem is different because the energy represented by the mass of organic matter that is decomposed to inorganic forms is recyclable through the biological uptake of photosynthesis and chemosynthesis.

Describe the yearly productivity pattern in middle-latitude oceans.

There are pronounced seasonal variations at temperate latitudes, and this variation produces a more complex pattern of productivity than in either polar or tropical regions. During the winter, thermal stratification may be minimal, and the surface waters are rich in nutrients as a result of mixing between the deep- and surface-water layers. Productivity is low, however, due to the low angle at which the Sun's rays strike the ocean surface. Very little solar radiation penetrates the water column, producing a low photosynthetic rate. As the Sun rises higher in the sky during the spring, sufficient sunlight penetrates the water column, producing a spring phytoplankton bloom. The increased availability of solar radiation also results in the development of a thermocline that prevents the continued supply of nutrients from deep water, and productivity decreases until fall cooling begins to weaken the thermocline. Mixing again occurs, and a smaller fall phytoplankton bloom occurs. It is soon limited by decreased amounts of solar radiation because the Sun is lower in the sky and the day length decreases.

What is/are the limiting factor(s) for the spring phytoplankton bloom at temperate latitudes? What is/are the limiting factor(s) for the fall phytoplankton bloom?

There is a high level of spring productivity that is limited by a reduced supply of nutrients, and a fall increase in productivity that comes to an end because of the lack of solar radiation.

Describe three examples of unintended consequences that have occurred in marine ecosystems when top predators are removed.

Top predators keep smaller, lower trophic level fish populations from overrunning ocean ecosystems to the point of destruction. Top predators also keep marine ecosystems healthy because they will prey first on the sick, lame, and old members of lower trophic levels. A coral reef ecosystem may be affected if top carnivores are removed because smaller fish may proliferate and allow for an increase in algae on the corals, which in turn suppresses the coral growth.

Compare the macroscopic algae in terms of color, maximum depth to which they grow, and size.

• Phaeophyta (brown algae): The dominant color is brown to black. They may grow attached to ocean bottoms at depths of 30 meters (100 feet) or more. The brown algae range in size from the small genus Ralfsia that is a common encrusting form on intertidal rocks to the 30-meter (100-foot) long Pelagophycus (bull kelp). In the Sargasso Sea, a free-floating brown alga gives the area its name, Sargassum. • Chlorophyta (green algae): The dominant color is green, and green algae are found in the shallow intertidal zone only. The majority of species are less than 30 centimeters (12 inches) in maximum dimension. Ulva, sea lettuce, is common in tidal pools in colder waters while Codium, sponge weed, is widely distributed in warm water coastal areas. • Rhodophyta (red algae): The dominant color is pink to dark red. These algae can use short blue and green wavelengths of light for photosynthesis; they are the group of algae found growing attached to the ocean floor at the lower portion of the photic zone. They have been found at depths up to 268 meters (880 feet), and Corallina is common in rocky intertidal areas.