What Is Coral? A Coral Polyp and Zooxanthellae | Smithsonian Ocean
Polyps are live coral tissue extensions that cover the calcium Besides the direct loss of zooxanthellae, coral bleaching can occur in other ways. The symbiotic relationship between zooxanthellae and marine coral is. What are corals? Corals themselves are animals. But tropical reef-building corals have tiny plant-like organisms living in their tissue. The corals couldn't survive. Teacher Tip: In this portion of the lesson, you will be drawing the coral polyp anatomy on the board while . Coral Symbiosis: Coral Polyp and Zooxanthellae.
Nutrient exchange within the symbiosis As long as the symbiosis between zooxanthellae and corals is intact, both partners benefit from an intricate exchange of nutrients. The coral cells provide the zooxanthellae with inorganic carbon and nitrogen carbon dioxide, ammoniumproduced by the breakdown of organic compounds obtained from the zooxanthellae glycerol, glucose, amino acids, lipids and the surrounding water plankton, detritus, dissolved organic matter.
The zooxanthellae, in turn, use inorganic compounds obtained from the coral and seawater carbon dioxide, bicarbonate, ammonium, nitrate, hydrogen phosphate to produce organic molecules through the process of photosynthesis. A major part of these organic molecules, now called photosynthates, is then transferred back to the host.
This nutrient exchange between corals and zooxanthellae allows them to use the scarcely available nutrients in the ocean efficiently. The translocation of energy-rich compounds from zooxanthellae to their host has allowed corals to build vast reefs, through the secretion of calcium carbonate skeletons.
It is clear that zooxanthellae do not simply transfer any excess substances to their coral host. The release of photosynthates from the zooxanthellae is cleverly induced by the coral with a so-called "host release factor", or HRF. This HRF is a substance produced by the coral, possibly a cocktail of specific amino acids, which triggers the release of nutritious glycerol and glucose by the zooxanthellae Gates et al.
Indeed, when a drop of coral tissue slurry is added to a Symbiodinium culture, it will quickly induce nutrient release by the dinoflagellates Trench However, Davy et al. This is because corals require additional protein and lipid to grow tissue and the organic matrix, a proteinaceous "scaffold" that provides sites for calcium carbonate crystals to precipitate.
Providing corals with a daily batch of zooplankton, such as copepods or brine shrimp nauplii, not only provides them with nourishment; the slight increase in inorganic nutrients will also feed the zooxanthellae. In addition, the cycling of nutrients within the symbiosis is stimulated. Some aquaria are so devoid of nutrients, owing to the use of heavy filtration combined with scarce feeding, that the zooxanthellae stop growing and die.
Overview of the nutrient exchange between a single coral and zooxanthella cell. In addition, it receives organic molecules from the zooxanthellae, such as glycerol. The coral cell breaks these down to ammonium and carbon dioxide, which are subsequently absorbed by the zooxanthella. A major part of these compounds is again exuded into the coral host cell.
This cycling of nutrients between coral host cells and their symbiotic zooxanthellae allows corals to grow in nutrient-poor environments. How to study zooxanthellae: To extract zooxanthellae, and thus valuable information from the coral, some equipment is required. The first step during isolation is weighing the coral, use the so-called buoyant weighing method. This is most accurate, as weighing above water would obscure the coral's real air weight as a small layer of seawater would be attached to the coral.
Zooxanthellae and their Symbiotic Relationship with Marine Corals - microbewiki
As each coral was weighed before and after it was glued onto a PVC plate, the net weight of the coral can be calculated when it is weighed again at any point in time, by simply subtracting the weight of the plate and epoxy resin. When the buoyant weight of the coral is known, the next step is removing tissue from the skeleton. With a fine jet of air, this is done easily. Small coral fragments about 0. Depending on the coral's morphology, the air jet is applied from 1 to 3 minutes, effectively removing all tissue.
When the coral skeleton is completely bare, it is removed from the tube. The skeleton can be used itself for other types of analyses, such as determining the proteins that make up the organic matrix. After the tissue has been separated from the skeleton, artificial seawater is added, and the tube is shaken until a tissue suspension is obtained. With a centrifuge, coral tissue and zooxanthellae are then separated.
The zooxanthellae are heavier and will sink to the bottom of the tube, creating a brownish pellet. The coral tissue forms a slightly opaque solution above the pellet, called a supernatant.
This supernatant can be removed with a pipette, or poured, and the zooxanthellae pellet can be resuspended in seawater. Both fractions can be analyzed for enzymatic activity, protein content, or even DNA.
The zooxanthellae fraction can also be used to establish live cultures of free-living dinoflagellates for research. To obtain the zooxanthellae density in the coral, a small volume from the zooxanthellae suspension is applied on a haemocytometer with a pipette.
A haemocytometer is a small chamber which contains a counting grid, and is also used to count bacteria, algae and blood cells. Under a microscope, the amount of zooxanthellae per unit of sample volume is then determined. Because the total sample volume is known, the total amount of zooxanthellae isolated from a piece of coral can be calculated. By dividing this number by the weight or surface area of the coral, the zooxanthellae density is obtained. Thus causes an increase of oxygen radicals in the coral tissues from the molecular oxygen, and the radicals can destroy cells.
This study found that the anemones with higher chlorophyll, and thus higher Symbiodinium, actually adjusted their protein expression so the fluctuating oxygen concentrations would not be destructive.
This is just another example of how the coral changes its innate reactions to adjust for its symbiotic algae Figure 7. Movement Furthermore, it was found that the temperate symbiotic sea anemone, Anthropluera balli, incorporates a maternal inheritance of the zooxanthellae because the anemone live in locations of low zooxanthellae algae.
It was found that the spawned ova consistently contained zooxanthellae, and were released into the ocean water to become fertilized and grow. The zooxanthellae was clearly integrated into the life cycle of this particular sea anemone, and was found to localize at one end of the embryo to become integrated within the endoderm, which as mentioned above is where the zooxanthellae live within coral This study brings arise the question of how zooxanthellae disperse among the coral.
Another study discovered that the zooxanthellae can be released by the host in ways such as predation, extrusion, spontaneously, osmotically, or as we know, due to temperature or stress. This particular study proposes another way for zooxanthellae to disperse, through the feces of their predators. Interestingly, photosynthetic rates from the unharmed species were very similar to the rates from the fecal zooxanthellae that made their way through a digestive tract.
Furthermore, the zooxanthellae reinfected sea anemones after their travel through the digestive tract of their predator. This finding showed that predation is an important means by which the zooxanthellae are dispersed among a coral reef History The relationship between Symbiodinium and coral has been known for about fifty years.
One of the first studies found that certain dinoflagellates fixed labeled carbon from CO2 and moved it to their host sea anemone after forty-eight hours. This study also showed that Symbiodinium produced higher amounts of carbohydrates when living inside a host rather than free living After this symbiotic relationship was discovered, other studies delved further into how the algae and coral used the nutrients they acquired from the other.
One study found specifically that the algae fixed the carbon primarily as glycerol, which was then taken up by the coral tissue as proteins and lipids It was also discovered that the other organic acids produced by the Symbiodinium were different biochemically, even though they looked the same This information was the beginning of other scientists discovering the increasingly wide variety in the taxon of dinoflagellates.
It is not entirely sure how the coral does this, but some studies have hypothesized. Other studies suggest that the host coral produces compounds that act as host release factors, and that these factors can control the metabolite production in the Symbiodinium Energy Storage Not only are nutrients shared between the two species, but energy and energy production is integrated as well. The Symbiodinium produced these lipids, using acetate from the coral and extra ATP, and excreted them back to their host.
These lipids are mostly wax esters and triglycerides A figure showing the decline in zooxanthellae over a starvation period http: It was further shown that the retention of this ammonium by the coral was related to the Symbiodinium because the algae uptakes most of the ammonium itself The algae were also more efficient with its use of a nitrogen source because it can use nitrite.
A study used tagged enzymes involved in the use of different forms of nitrogen, and concluded that the algae do indeed utilize nitrates. They also found that the algae densities increase with the nitrate concentration, although further details of this relationship with the coral are not known It is also interesting to note that the MAA concentration, which usually increases with UV exposure, also increased at high ammonium concentrations This study was done in red algae, Porphyra, but still may provide information regarding the zooxanthellae and its symbiotic relationship with corals Figure 8.
Human Threat Figure 9. Some fishing practices involve blowing up reefs with explosives to stun the fish so the fisherman can catch them easily Figure 9. Another fishing practice that is particularly detrimental is fishing with cyanide. Divers pour cyanide, a poison, on the reefs to stun the fish. The divers also directly rip coral off the reef to catch the hiding and sick fish. These practices of fishing are completely destroying the reefs and environment.
Also, as we saw above, some fish that are predators of the zooxanthellae actually disperse the algae in their feces.
Due to overfishing, this dispersion technique may no longer be available, thus diminishing the diversity of zooxanthellae, and therefore coral, around the oceans. Also, coral is very delicate, and divers merely touching the coral can damage years of growth.
It is also thought that the oils from a human can be harmful towards the coral and algae living within or on it; tourism perhaps has been degrading coral for years. Conclusion Zooxanthellae and coral have clearly been shown to have a close-knit symbiotic relationship. The most prominent research topic is the discussion regarding coral bleaching.
The zooxanthellae are expelled from the coral in stress situations, most recently due to the rising ocean water temperatures. The enzyme, nutrient, and molecule cycling between the algae and the coral are extremely co-dependent, and the loss the algae clearly results in coral bleaching and death.
The organisms protect each other, whether from UV radiation or predation, although it seems humans can surpass all natural protection and destroy the coral by merely overfishing or stepping on it. The loss of the coral has a large global impact because it is a home for a large number of fish and other marine creatures.
Zooxanthellae and their Symbiotic Relationship with Marine Corals
We are learning that it is necessary to be aware of not only the coral itself, but of the organisms that live in the reefs or within the coral. For Part 2, prepare 1 plate of materials per student. Each plate should include: What could coral be? Students are often split in their ideas about this question.
Some students might firmly believe a coral is a plant or an animal, and some students might be totally unsure.
- Smithsonian Ocean
- Feature Article: Zooxanthellae: Biology and Isolation for Scientific Study
Have a few students share their ideas. Be sure to keep the question on the board for the remainder of the lesson. Tell students that coral is definitely a living thing, and that the goal of this lesson is for students to discover what type of organism coral is. They can talk in pairs or write their ideas individually. Ask students to share some of the big differences between plants and animals.
Create a table on the board to keep track of the key differences between plants and animals. Fill in the table as students share their ideas. After reviewing the table, tell students that coral is definitely a living thing, and that they will get to discover what type of living thing coral is during the next part of the lesson.
Explain that they are going to make a simple representation of coral polyp using everyday materials. By building this representation of a polyp, they will be able to figure out whether a coral polyp is a plant, an animal, or something else. Build a Coral Polyp 45 min Teacher Tip: In this portion of the lesson, you will be drawing the coral polyp anatomy on the board while your students build their edible polyp.
Before starting the hands-on building, be sure to set expectations so students do not consume any of their building materials. You can reassure students that they will get a chance to consume their coral polyps at the end of the lesson.
Begin the lesson by reminding students of the ideas that they discussed in Part 1. Remind students of the focus question and the goal of the activity.