Biology of Humans 6th Edition by Judith Goodenough,Betty McGuire

Exercise 10

Coral reefs are complex ecosystems with a staggering diversity of vertebrate and invertebrate species. The corals themselves are immobile colonial organisms consisting of hundreds to thousands of tiny individual animals called polyps that secrete external skeletons of calcium carbonate. The hard skeletons form the foundation of the reef. The tissues of the polyps usually contain photosynthetic algae that provide food for the polyps and are, in turn, protected by the corals' skeletons. Corals feed at night, capturing prey varying in size from zooplankton (microscopic animals) to small fish.
Global climate change is one of the threats causing worldwide declines in coral reefs. Elevated water temperatures cause corals to bleach-a phenomenon in which the colorful photosynthetic algae leave the coral, creating white regions in the reef and depriving the coral of nutrients. Bleaching often kills coral. As we saw in the previous chapter, elevated atmospheric carbon dioxide concentration increases the amount of carbon dioxide that dissolves in the water and forms carbonic acid. The acidification of the ocean makes it difficult for corals to obtain the calcium carbonate they need to form their skeletons. Some people are growing corals in underwater gardens and "replanting" them in damaged coral reefs. The following is an excerpt from a press release issued by the University of Miami in reference to a study1 showing that staghorn coral can withstand the pressure of overheating and acidic water if they have dietary supplements. You can read the entire press release here: "Rosenstiel School of Marine and Atmospheric Science. Study Shows Dietary Supplements Are Good For Coral Health," press release, May 4, 2015, at: www.rsmas.miami.edu/news-events/press-releases/2015/ study-shows-dietary-supplements-are-good-for-coral-health "The research team separated eight genetically diverse colonies of Staghorn coral, Acropora cervicornis, into two groups-fed or unfed-and exposed them to elevated temperatures (30°C), a level just below the mean bleaching threshold in the Florida Keys, increased carbon dioxide concentrations (800 ppm), the CO₂ levels predicted for 2065, or both (30°C/800 ppm), for eight weeks. The 'fed' group was given a supplemental diet of dried zooplankton powder twice a week. "The researchers then analyzed the feeding rate of both groups by measured the amount of prey, a live rotifer species Brachionus plicatilis, each coral captured per hour and lipid content, an indicator of energy storage. "They found that the fed corals were able to maintain normal growth rates at both elevated temperature and elevated CO₂, while unfed corals experienced significant decreases in growth compared to their fed counterparts. The results revealed that temperature, CO₂ and feeding each had significant effects on the coral's growth rate.... "[Staghorn coral] was able to increase its feeding rate and stored energy reserves when exposed to high CO₂ conditions at 26°C or 30°C and mitigate reductions in calcification that caused significant decreases in growth rate in unfed corals." The author concludes, "This has implications for how we care for and where we out-plant Staghorn corals back onto reefs to give them the best chance for resilience possible in the future."
Use at least three reliable sources to find other factors threatening coral reefs. For each factor you find, describe a study supporting the hypothesis that it is a possible cause of coral reef decline. Cite your sources.