1
What are the causes and effects of ocean acidification?
INFOGRAPHICS 29.1 AND 29.2
True or False: Because the pH scale is logarithmic, even a small change in pH, like the 0.1 pH unit drop in ocean pH, represents a significant change.
TRUE
Which of the following is TRUE about ocean acidification?
Acidification results when the calcium carbonate shells of marine organisms dissolve in seawater.
Ocean pH has now dropped below a pH of 7.0.
Ocean acidification is harmful, as CO2 forms carbonic acid when dissolved in water, which eats away at existing calcium-based materials.
In a more acidic ocean, the increase in key nutrients such as nitrogen and iron stabilizes almost all marine ecosystems, counteracting the effects of global warming.
C
What is ocean acidification? Describe the causes and consequences of this phenomenon.
Ocean acidification is the lowering of pH in seawater. So far, CO2 emissions from fossil fuel burning by humans have reduced the ocean’s pH by about 0.1, which corresponds to a 30% increase in ocean water acidity. If present trends continue, the ocean’s surface waters will be about 150% more acidic in 2100 than they were in 1800.
Acidification could decrease the ability of organisms to make their shells; it could also actually cause shells to dissolve. Acidification could also alter the availability of key nutrients like nitrogen and iron, which would threaten the stability of marine ecosystems by affecting primary production—plankton biomass may have already decreased by 40% in the 20th century. Less plankton could enhance acidification (positive feedback) because less CO2 would be sequestered and more would be left behind to further acidify the water. Or there could be a negative feedback effect on climate change: Less nitrification would occur, meaning less N2O (a potent greenhouse gas) would be produced and possibly less would be released into the atmosphere.
2
What environmental conditions determine the location and makeup of marine ecosystems? Where are coral reefs found, and what is their status?
INFOGRAPHICS 29.3 AND 29.4
True or False: NOAA estimates that more than half of coral reefs worldwide are threatened by human activities or environmental changes.
TRUE
A costal area that floods during high tides but is exposed to the air at low tide is known as a(n) __________________.
Intertidal zone
Organisms that live on the ocean floor are said to live in the:
benthic zone.
abyssopelagic zone.
hadal zone.
pelagic zone.
A
The highest percentage of destroyed coral reefs are found in the________, while the___________ has the lowest percentage of destroyed coral reefs.
Arctic Ocean; Atlantic Ocean
Indian Ocean; Pacific Ocean
Caribbean Sea; Mediterranean Sea
Middle East; Asian South Pacific
B
What factors determine the identification of the different ocean zones that are recognized?
The main factor is depth. This relates both to sunlight penetration (darkness) and temperature. The distance to shore is also important. Areas close to shore receive nutrients from the nearby land and rivers that empty into estuarine regions, providing nutrients that support a more abundant and biodiverse ecological communities.
3
What are coral, and how do these animals respond to stress?What does recent research suggest about reef species’ ability to adapt to acidification?
INFOGRAPHICS 29.5 AND 29.6
True or False: Slattery’s research suggests that the species that inhabit coral reefs all have sufficient genetic diversity to allow them to adapt to current and near-future levels of acidification.
FALSE
Coral are:
algae.
animals.
plants.
protozoa.
B
Bleaching of coral:
may be adaptive if it allows the coral to take up different species of zooks.
results when coral expel their resident zooks.
occurs in the winter season, when coral are less productive.
Both a and b are correct.
All of the above are correct.
D
What are coral reefs, and where are they found? Explain the symbiotic relationship the polyp shares with its resident zooxanthellae.
Corals are tiny marine organisms that live in colonies of many individual polyps. Once established, coral reefs continue to grow by using chemical cues to attract free-floating coral larvae to attach to the top of existing coral skeletons. After attaching to a surface, the larva undergoes metamorphosis to the polyp stage and secretes a calcium carbonate skeleton. A reef thus grows from corals building on top of other corals over the course of generations.
Coral reefs are found in shallow, nutrient-poor, tropical seas, between 30° S and 30° N of the equator. Their mutualistic relationship with zooxanthellae (“zooks”)—a photosynthetic algae that lives inside and shares nutrients with the coral—enables them to live in these nutrient-poor marine waters. The zooxanthellae perform photosynthesis and provide the coral with sugars, and raise the pH a little, which helps the coral lay down its calcium carbonate skeleton. The coral provides CO2 for the zook’s photosynthesis; the zooks also use coral waste as nutrients.
4
In addition to acidification, what other threats do ocean communities face?
INFOGRAPHIC 29.7
Which of the following threats to ocean ecosystems contributes to damage in coral reef areas?
Fishing with dynamite or using toxic chemicals to capture reef fish
Overfishing
Sediment runoff from land
All of the above
D
Besides ocean acidification, what threats do coral reefs and other ocean ecosystems face? Describe the causes and consequences of these threats.
While acidification is a very big threat, oceans face many other threats, including overfishing, pollution, rising sea levels, and invasive species.
Overfishing includes taking too many fish, as well as the destruction of sea beds or killing of other nontarget species during fishing. It is the biggest threat to oceans: About 90% of top trophic level predators have already been eliminated by overexploitation. Such heavy losses disrupt the interdependent relationships needed to sustain each community. For example, without grazer fish to keep it in check, algae overgrows on coral. Pollution from sediment and high levels of nutrient runoff from agricultural areas are boosting algae production and creating algal blooms, which smother corals and block sunlight, reducing photosynthesis. Trash—from both land and sea—and petroleum from ships and boats are also polluting the marine environment at unprecedented rates.
Rising sea levels will increase the depth of ocean waters and may decrease sunlight penetration, thus reducing photosynthesis, especially in the deepening coral seas.
Invasive species pose yet another threat; more than 80% of ocean harbors around the world now host at least one invasive species. These non-natives can disrupt ecosystems and prey upon or outcompete native species, changing the makeup of the community.
5
How can we reduce the threats to coral reefs and other ocean ecosystems?
TABLE 29.1
True or False: The establishment of a marine protected area around the damaged coral reefs of the Phoenix Islands in Kiribati did little to help the reefs recover.
FALSE
Which of these strategies would most directly address the problem of ocean acidification?
Limit development in coastal areas to prevent sediment pollution.
Reduce overfishing in general and prohibit bottom trawling in particular.
Designate vulnerable areas as marine protected areas.
Reduce the use of fossil fuels.
D
What are some of the obstacles that make implementing the strategies listed in Table 29.1 challenging? Which of the strategies do you think will be most effective at protecting ocean ecosystems?
Answers will vary and depend on the importance given to the benefit of the action and the cost (and therefore likelihood) of implementing it. The designation of vulnerable areas as protected areas may be one of the most straight forward and easiest to enforce but it will only protect the area given protection (and perhaps areas very close by). Limiting development in vulnerable areas may be met with opposition since these may be economically valuable; the benefit will depend on the extent of the limitations. Prohibiting bottom trawling in vulnerable areas may be doable since it is a very specific action and would only require monitoring in those areas (but that monitoring might still be expensive to undertake). Reducing the use of fossil fuels will be hard to do until we have a replacement but it may be the only way to protect the oceans from further acidification. Reducing pollution in general requires actions on many fronts, so while doable, would require a massive effort.
What role do scientific studies like those conducted by Marc Slattery play in helping us deal with threats to ocean ecosystems?
Scientific studies help us to understand the nature, scope, causes, and seriousness of the problems faced by ocean ecosystems. This information can be used to develop effective strategies for dealing with problems that arise.
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