Chapter 15 Questions

Describe the environmental conditions required for development of coral reefs.

An environment suitable for coral reef growth must have a minimum average monthly temperature that exceeds 18°C (64°F) throughout the year. Reef building corals rely on photosynthetic dinoflagellates (zooxanthellae) that live within their tissues. As a result of this relationship, corals survive only in sunlit waters. Strong water circulation assures an adequate supply of food and oxygen. The water must also have normal salinity and have relatively low turbidity (low amount of suspended sediment) because suspended clay, silt, and detritus particles block light and can smother the coral. Additionally, corals need a hard substrate for attachment.

Which adverse conditions of rocky intertidal zones seem to be most important in controlling the distribution of life?

An organism's success is closely tied to its ability to cope with the physical water conditions, the ocean floor, and other members of the biological community. One of the most prominent variables affecting species diversification of benthic organisms may be temperature. As well, the distribution of benthic biomass closely mirrors the distribution of photosynthetic productivity in the surface waters. This suggests that life on the ocean floor is very much dependent upon the primary photosynthetic productivity within the ocean's surface waters.

What is coral bleaching? How does it occur?

Coral bleaching is the loss of color in coral reef organisms that causes them to turn white. The cause of coral bleaching is due to the removal or expulsion of the coral's symbiotic partner, the zooxanthellae (endosymbiotic dinoflagellates), due to elevated seawater temperature or other environmental stresses.

Describe the zones of the reef slope and the characteristic coral types.

From the surface to a depth of 20 meters (66 feet), there is high-energy wave action and more than 60% of the surface light available. Massive branching corals and algae are found in this "buttress zone." Between the depths of 20 meters (66 feet) and 50 meters (164 feet), the light level drops to 20% of the surface light, and wave energy decreases. Massive head corals are common in this zone. Light levels drop to about 4% of surface light at 150 meters (492 feet). Wave energy is also minimal at this depth and delicate plate corals are common in this zone.

Describe the characteristics of hydrothermal vents.

Hydrothermal vents occur along the crest of the mid-ocean ridge where the lithosphere is thin and volcanic activity is common. They exist in complete darkness at water depths ranging from 1525 meters (5000 feet) to 3600 meters (11,800 feet). Hydrothermal vents emit hot water up to 350°C (662°F) that is so rich in metal sulfides that it colors the water black, giving these features the name "black smokers." The chimneys associated with these vents were first observed in 1979 and are composed primarily of copper sulfides, zinc sulfides, and silver sulfides. Hydrothermal vents are often colonized by unusual life forms that comprise the hydrothermal vent biocommunities.

What are the major differences between the conditions and biocommunities of the hydrothermal vents and the cold seeps?

In hydrothermal vent fields, water temperatures range as high as 12°C (54°F), while the temperatures at the cold water seeps are near ambient values of local water conditions (usually just a few degrees above freezing). Hydrothermal vents are found only in association with springs at the base of the Florida Escarpment, at hydrocarbon seeps, and at subduction zones where trench sediments have been folded. Additionally, the producers at hydrothermal vents are exclusively sulfur-oxidizing bacteria, while at the cold seeps, sulfur- and methane-oxidizing bacteria are important.

One of the most noticeable features of the middle tide zone's long, rocky coasts is a mussel bed. Describe general characteristics of mussels and include a discussion of other organisms that are associated with mussels.

Mussel beds of the genera Mytilis and Modiolus attach to the middle tide zone rocks by secreting hair-like byssal threads. The base of the mussel bed is often very abrupt. A common and visible member of the mussel bed is the goose barnacle, Pollicipes. The mussels are preyed upon by the sea stars, Pisaster and Asterias. Less visible algae, snails, hydroids, worms, clams, and crustaceans are also found in the mussel beds.

What is the "dead whale hypothesis"?

The "dead whale hypothesis" suggests that when large animals such as whales die and sink to the deep ocean floor, they may provide a temporary stepping-stone for organisms that inhabit the hydrothermal vent fields separated by large distances. Decomposition of a whale carcass provides an energy source for these organisms that breed and release their larvae, some of which make it to the next hydrothermal vent site.

Discuss the dominant species of kelp, their epifauna, and animals that feed on kelp in Pacific coast kelp forests.

The dominant species of kelp found in Pacific coast kelp forests are Macrocystis (giant brown bladder kelp) and Nereocystis. Smaller varieties of red and brown algae grow on the larger varieties along with hydroids and bryozoans. Nudibranchs feed on hydroids and bryozoans. Very few animals feed directly on living kelp plants. The sea hare, Aplaysia, and sea urchins do feed on living kelp.

How does the diversity of species on sediment-covered shores compare with that of the rocky shore? Suggest at least one reason why this occurs.

There are more species living on rocky shores than sediment-covered shores. A possible reason for this is that there are more environmental niches on rocky shores than on sediment-covered shores. An environment that has many niches creates conditions that produce high species diversity.

Describe how sandy and muddy shores differ in terms of energy level, particle size, sediment stability, and oxygen content.

This information is summarized in the table below: a. Sandy Shores b. Muddy Shores Energy Level a. High b. Low Particle Size a. Medium- to Coarse-Grained b. Fine-Grained Sediment Stability a. Low b. High Oxygen Content a. High b. Low Sediment salinity increases and permeability (the ability of a substance to pass fluid) decreases with decreased particle size. The higher sediment stability of mud flats results from the high cohesive attraction between clay particles and the lower energy longshore current in mud flat regions. The fact that sand-sized particles are rounder and clay-sized particles are flat results in the higher permeability of muddy sediment. Large amounts of organic material must be anaerobically decomposed in these deposits. This often results in sediment from mad flats having a black color and a strong hydrogen sulfide odor.

Where does the food come from to supply organisms living on the deep-ocean floor? How does this affect benthic biomass?

With the exception of chemosynthetic productivity that occurs around hydrothermal vents, all deep-ocean floor organisms receive their food from the surface waters above. Low food availability, and not low temperature, low oxygen concentration, or high pressure, limits deep-sea benthic biomass.

In which intertidal zone of a steeply sloping, coarse-sand beach would you find each of the following organisms: clams, beach hoppers, ghost shrimp, sand crabs, and heart urchins?

• Clams: Low through middle tide zones • Beach hoppers: Supratidal zone • Ghost shrimp: Middle and high tide zones • Sand crabs: Low and middle tide zones • Heart urchins: low tide zone