• 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.
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