Chapter 17 Key Concepts

Sea grasses are marine angiosperms, or flowering plants, that are confined to very shallow water and extend mainly by subsurface rhizome systems within the sediment.
Sea grasses grow best in conditions of relatively high light and modest current flow.
Sea grasses have a complex relationship with microbial organisms on leaves and within sediments.
Sea grass beds have high primary production and support a diverse group of animal species.
Sea grass beds reduce current flow, deter the entry of some predators, and may enhance the growth and abundance of infaunal suspension feeders.
Benthic suspension feeders may enhance sea grass growth through feeding and biodeposition, but burrowing shrimp may exert negative effects on sea grasses. Sea grasses are grazed to variable degrees.
Sea grass meadows are diverse in lower latitudes and interact strongly with coexisting seaweeds, which are grazed by many species.
Nutrient addition and loss of suspension feeders both have a negative impact on sea grass.
Predation is important in sea grass beds, but strong top-down trophic cascade effects are variable, and sometimes very strong.
Disease was a major cause of eelgrass decline. Now, many sea grasses are declining because of pollution and water turbidity.
Sea grasses perform important ecosystem services, especially supporting juvenile stages of commercial fisheries and carbon sequestration to mitigate carbon dioxide–driven climate change.
Kelp forest–rocky reefs are often dominated by kelps and seaweeds in shallow waters and by epifaunal animals in deeper waters.
Rocky subtidal reefs harbor abundant communities of algae and invertebrates and are often dominated by colonial invertebrates.
Rocky reefs often are very patchy, with alternations of rocks dominated by rich invertebrate assemblages and turf-forming calcareous red algae.
Subtidal rock-wall patches of animals often are short on space, suggesting the importance of competition.
Rocky reefs are grazed more intensely, mainly by sea urchins, on horizontal benches.
Kelp forests are dominated by a few species of brown seaweeds of the group Laminariales with fantastic growth rates.
Kelp forests are biologically diverse and support many seaweed and animal species.
Kelp communities are often strongly affected by a combination of storms, presence or absence of sea otters, and behavioral changes in herbivores.
Predation from an offshore source has introduced a new trophic level to some eastern Pacific kelp forests.
In Alaskan kelp forests, succession depends on the interplay of grazing pressure, disturbance, and competition for light.
In lower-latitude California kelp forests, a larger diversity of predators beyond sea otters exerts top-down effects. Kelps vary widely in their susceptibility to grazing.
Coral reefs are constructional wave-resistant features that are built by a variety of species and are often cemented together. The growth of these structures is aided by zooxanthellae, algae that are symbiotic with the reef-building corals.
Reef-building corals belong to the calcium carbonate–secreting Scleractinia. Hermatypic corals contribute most to reef growth and have abundant endosymbiotic zooxanthellae.
Zooxanthellae are symbiotic with many invertebrates, and they are crucial as a source of nutrition for reef- building corals.
Zooxanthellae provide nutrition and aid in calcification of their coral hosts. The benefit obtained by zooxanthellae may relate to protection from grazing and access to nutrients from coral excretion.
Reef development is limited by the presence of relatively high temperature, open marine salinity, available light, and low turbidity.
Coral reefs live exposed to high wave energy, but strong waves can break coral colonies and limit reef growth.
Reef development is a balance between growth and bioerosion. Coral reefs can be divided into atolls and coastal reefs.
Both atolls and coastal reefs have prominent depth zones, each of which has a different set of dominant framework-building coral species.
There are two distinct biogeographic realms, Pacific and Atlantic.
Coral reefs are diverse, but Indo-Pacific reefs are more so than in the Caribbean.
Coral reefs contain a large number of closely related species with strong phenotypic plasticity and require careful molecular and ecological study.
Coral reefs and nearby environments harbor some of the most remarkable mutualisms in the sea.
Predation is intense on coral reefs, and many species have evolved strong defenses. Corals reproduce by a wide range of mechanisms.
Most broadcast-spawning corals spawn gametes in the water column, often in synchronized multispecies mass spawning at night. This is also true of species of other taxonomic groups.
Known strong dispersal potential of coral larvae presents a conundrum. Is the great potential for long-distance dispersal realized in widespread mixed populations?
Space is limiting on coral reefs, and coral species compete for space by overgrowth, shading, and aggressive interactions.
Herbivores exert strong effects on the species composition of reefs.
Coral reefs probably have strong top-down effects exerted by resident and mobile fish predators.
Coral reefs are often subject to extensive disturbance from tropical storms. In the eastern Pacific, El Niño events are also major sources of large-scale disturbance.
Disease can devastate the dominant species of a coral reef, which can result in major changes in reef community structure.
Because corals are foundation species, death from disease and coral bleaching should have strong negative effects on dependent species.
The decline of corals in the Caribbean from disease and pollution has resulted in a general increase in the abundance of sponges.
Sponge growth and expansion on coral reefs may be affected by food supply.
Owing to strong regional disturbances and other factors, coral reefs may exist in distinctly different community regimes.
Different scenarios illustrate how coral reef dominance might shift in response to different conditions of storms, disease, warming, and overfishing.
Coral reef areas might deteriorate to a tipping point, where colonization by coral larvae and recruitment of coral reef fish might decline precipitously.
The global warming trend in recent decades is strongly associated with stress on corals, especially widespread bleaching events.
Acidification presents another threat to corals as ocean pH declines in the coming decades, but preliminary evidence suggests a homeostatic mechanism to buffer pH.