Zooxanthellae and their Symbiotic Relationship with Marine Corals - microbewiki
Tiny plant-like organisms called zooxanthellae live in the tissues of many Close-up photograph of translucent coral polyps, showing the symbiotic algae living. The corals and algae have a mutualistic relationship. The coral The relationship between the algae and coral polyp facilitates a tight recycling of nutrients in. Zooxanthellae are the symbiotic algae that live within the hard or stony corals in by opening the polyp and exposing more or less algae to the light as needed.
More about coral reef ecosystems can be found in our Coral Reefs featured story. Bleached Corals, Pacific Ocean Credit: Wolcott Henry When the reef is under stress from high temperatures, pollution, or other threats, the zooxanthellae abandon their coral hosts in a process called "bleaching. When they die, just the white skeleton is left behind as if it had been bleached. Bleaching spells trouble for coral reefs.
The reef suffered a mass bleaching event in the summer ofwhen water temperatures were unusually high. Bleached corals have lowered defenses against disease, so often will suffer further damage and death as disease moves in after a bleaching event.
In this photo, healthy brown coral gives way to the frontlines of disease.
Amanda Feuerstein It can be hard for coral to recover for a bleaching event. The best bet is the some healthy tissue still remains deep in the skeleton and, if conditions improve, this coral can grow and recover, spreading to the rest of the skeleton.
The corals pictured here are still in recovery after a mass bleaching in Panama in the summer of In a paper discussing the effects Hurricane Flora had on coral reefs in Jamaica, it was found that some zooxanthellae did in fact reinhabit the coral after some time, thus making part of the reef salvageable after the natural disaster Interestingly, however, it was found that perhaps the differentiation of lipids in the Symbiodinium could cause varying sensitivity to thermal stress.
In one study it was found that more disorganized stacking in the thylakoid membrane resulted from the Symbiodinium being exposed to high temperatures. This showed that the composition of the lipids might be important to understanding the temperature range of the algae Besides the direct loss of zooxanthellae, coral bleaching can occur in other ways.
UV and visible light have both been shown to have a role in coral bleaching, along with subaerial exposure, which causes an inconsistent environment for the coral.
What Is Coral? A Coral Polyp and Zooxanthellae | Smithsonian Ocean
Furthermore, sedimentation has been thought to induce coral bleaching, along with dilution of waters or an influx of inorganic ingredients into the ecosystem. Also, pollution and pathogens are understandably a cause for coral bleaching to occur 5.
Some of the symbiotic organisms do have a defense against the UV light, however. Mycosporine-like amino acids MAAs can uptake the UV light and do not require extra reactions to do so. The MAAs can also uptake radicals, but are not found in every clade of Symbiodinium A study in showed that two of the three clades observed did not produce these MAAs, and the one clade that did had an increase of them during the middle of the day. This implies that some species of the Symbiodinium have adapted to the UV radiation, while some still have not, and perhaps in the future the algae with the ability to survive will attach to the majority of the coral so UV radiation will no longer be a threat to reefs.
Global Warming Figure 4. It is expected that if the ocean warms just one to two degrees, the locations that are between twenty and thirty degrees North will then fall within the range of lethality for most coral species. Some may be able to adapt, but typically the photosynthesis pathways are hindered at temperatures rising above thirty degrees Celsius.
Thus, temperature shocks resulting from global warming results in zooxanthellae adhesion dysfunction, so they detach and are expelled from the coral 5. In a study fromit was shown that the Symbiodinium density significantly decreased after twenty-seven days of heat stress In other words, different zooxanthellae are sensitive to different temperatures, and coral can expel the old algae in hopes that the less sensitive algae will have survived and become a new symbiont.
This is an idea among scientists because zooxanthellae species diversity is very widely spread Figure 5. Horizontal gene transfer and many genetic lineages make up the Symbiodinium species, causing disparity among the clades. So although there are many Symbiodinium-like species, this idea of clade shuffling seems slightly implausible, because it usually is a matter of Another study focused on the classification of zooxanthellae They isolated compounds that were later identified as toxins that were unique from other dinoflagellates.
The discovery and research into these compounds also supported that the molecules were from the algae and not a result of the host, but it seemed that variation to the host and environment caused the production of different algal metabolites.
Many other toxins and compounds were isolated in this study and added significantly to the fact that the metabolism and taxon of zooxanthellae are extremely diverse.
Furthermore, it has been shown that specific Symbiodinium are more tolerant to heat and stress, and perhaps corals adopting these specific algae will be able to survive the temperature changes from global warming and natural disasters Another study found that following bleaching, corals had clade shuffled from C2 to D, because D has a higher densities and photochemical efficiency, resulting in higher thermal tolerance The coral polyps do cellular respiration, thus producing carbon dioxide and water as byproducts.
The zooxanthellae then take up these byproducts to carry out photosynthesis. The products of photosynthesis include sugars, lipids, and oxygen, which the coral polyps thus uptake for growth and cellular respiration, and the cycle continues.
The Symbiotic Relationship between Zooxanthellae and Coral by Brianna Velasquez on Prezi
The photosynthesis byproducts are more specifically used to make proteins and carbohydrates in order to produce calcium carbonate for the coral to grow. Furthermore, the oxygen is used by the coral to help remove wastes. This recycling of nutrients in between these symbionts is extremely efficient, resulting in the ability to live in nutrient poor waters. About ninety percent of the material produced by photosynthesis is thought to be used by the coral 6.
In terms of disease, the zooxanthellae is commonly the point of attack, rather than the coral itself. For example, the Montastrae species, which causes Yellow Band Disease, affects the zooxanthellae directly rather than the coral 7. Scientists found that a coral, Acropora, lacked an enzyme needed for cysteine biosynthesis. It thus needed Symbiodinium for the production of this amino acid. The genome size for the zooxanthellae algae is about 1, Mbp while the coral is approximately Mbp: Sure enough, other studies have shown phosphate-linked relationships between these two species.
Zooxanthellae extracted from the Acropora coral had two acid phosphatases P-1 and P The activity of these enzymes shows that perhaps their role is involved in the mobilization of a phosphate storage compound. The exact role of these enzymes is unknown, but it seems that the symbiotic relationship between coral and zooxanthellae is phosphate limited But together, the coral and zooxanthellae can synthesize twenty amino acids 17 Figure 6.
There is also a relationship between the amount of time the tentacles of the coral spend expanded or contracted and the amount of zooxanthellae present on the coral. In general, there was lower photosynthetic efficiency in the zooxanthellae coral species that has their tentacles expanded only at night than the species with their tentacles constantly expanded. Also, the zooxanthellae density was higher in the continuously expanded tentacle species.
These differences were found only in the light however, because when the species were placed in the dark no differences were found.
Thus the light has a relationship with the coral and zooxanthellae, which was assumed because zooxanthellae are photosynthetic organisms.
Conclusively, the species with continuously expanded tentacles have dense populations or small tentacles. The findings suggest that small tentacles do not shade the zooxanthellae, thus they are all visible to the light, and that dense populations are necessary to harvest the light. So the species with these proactive properties expand continuously to collect all the light, while the species with few zooxanthellae only expand at night Another study related the exposure of the coral to oxygen as a means for oxygen radical accumulation in its tissues The O2 concentrations were found to increase by a pH of about 1.
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.
Zooxanthellae and their Symbiotic Relationship with Marine Corals
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