Nutrients and Coral Reefs

Figure 1:

Coral reefs are some of the most beautiful and one of the most complex ecosystems in the ocean. Coral reefs are made up of a wide variety of different organisms such as marine life, algae, and plant life. Due to all the biodiversity that is present in the reefs, the amount of nutrients that is present in the reefs is abundant. Coral reefs are so successful in containing biodiversity because they “tightly recycle nutrients, and all the plants and animals live in symbiosis.” However according to the article, some of the nutrients are limited in amount but also abundant in amount. So how can something that is so essential to life be limited but also be successful at the same time? I think coral reefs are so successful in being able to provide nutrients in order for it to strive because it has many different ways of gaining the nutrients it needs.

One way that coral reefs are able to gain carbon is through the symbiotic relationship between coral and the algae (zooxanthellae). The algae live inside the host coral, and garn its energy from the sun and are able to “fix carbon” through the process of photosynthesis. Thus, the algae provide energy for their host and in return gain nitrogen and phosphorus waste from its host. The nitrogen and phosphorus waste fertilize the algae, causing more algae to grow at a rapid pace. Meaning that more fixed carbon and more nitrogen and phosphorus waste. However, coral reefs significantly lack in the amount of fixed nitrogen. The algae to host relationship is symbiotic which allows those organisms not to lose fixed nitrogen but within the coral reef, fixed nitrogen is passed back and forth between plants and animals through the process of ingestion. Which means that if there is a lack of plants or a lack of animals many organisms would become deprived of fixed nitrogen which is essential in creating proteins and nucleic acid. Due to the lack of fixed nitrogen available, corals have to garn energy from a different source. Through the process of ingestion, corals ingest zooplankton or bacteria that come in contact with their mucus layer. Corals can also uptake fixed nitrogen when the water is low in ambient levels. These types of foods are not consistently available so the easiest form of fixed nitrogen that is available is in the form of ammonia. The ammonia becomes available to the corals because fish in the area are constantly excreting ammonia.

Another way that coral reefs gain nutrients is through a relationship called the mangrove-seagrass-coral reef. The mangroves which are located at the shoreline in which they provide many organisms with shelter and because of that they are very nutrient rich. At the mangroves a lot of denitrification takes place. The same happens with segrass. Although the process of denitrification occurs, seagrass provides shelter for many of the terrestrial animals that provide nutrients for the coral reefs. Due to the shelter they provide, fish are able to survive and provide coral reefs with solid nutrients rather than liquid nutrients through its feces.

Figure 2

With all this nutrients coming in, when is there to much nutrients and what are some of the side-affects. According to Olivieri, “With excess nutrients the zooxanthellae population grows uncontrolled and the balance of the nitrogen-carbon fluxes between the coral host and zooxanthellae is disrupted, resulting in a reduction of calcification and weakening of the coral calcareous skeleton.” (Olivieri, 1997).  In 1994, Hoegh-Guldberg conducted a study based on the population dynamics of symbiotic zooxanthellae in an area that was exposed to high levels of ammonia. He found that, “The calculated growth rates of zooxanthellae exposed to 20 µM or 50 µM NH4Cl were higher than those representative of zooxanthellae living in control corals.” (Hoegh-Guldberg, 1994). This supports his theory that the population of the zooxanthllae can become toxic when the amount of NH4CL in the sea water reaches 50 µM NH4Cl. If the amount of nutrients becomes too toxic for the ecosystem, all the nutrient cycles would be affected and many organisms that serve important roles in the cycles will begin to die out and eventually the coral reefs will begin to die themselves.

I think that coral reefs are successful in maintaining a nutrient efficient ecosystem because they are able to keep levels from becoming toxic even when there are loads of nutrients coming in from different sources. I think that we as humans also help keep them successful through the process of fishing.

Sources:

Fig. 1: http://www.noaa.gov/features/economic_0708/coralreefs.html

Fig. 2: http://www.fao.org/docrep/003/t0708e/t0708e03.htm

http://www.fisherycrisis.com/coral3.html

Hoegh-Guldberg, 1994

Olivier 1997