Coral Reef Symbiotic Relationships

Most reef-building corals contain photosynthetic algae, termed zooxanthellae, that live in their tissues. The corals and algae have a mutualistic association. The coral provides the algae a environment and compound

Corals dislike warm water about as much as acidity. When oceans get typically warm, corals can eject the algae that symbiotically live in their skeletons, providing food in exchange for shelter. The ejection process is called bleaching, named by the white skeleton left behind when the coral gets sick and, in some cases, dies.

Corals are tiny immobile animals that live in colonies, where each cluster is called a polyp. Different species build structures of various sizes and shapes, such as brain or fan coral, creating a diverse and complex ecosystem (EPA 2000). Nearly all reef-dwelling corals have a symbiotic (mutually beneficial) relationship with the algae, which live inside the coral polyps and perform photosynthesis, a process that produces food that is shared with the coral (Fagoonee 1999). In addition, the algae share its

Elevated sea temperatures caused by climate change and extra-bright sunlight can result in coral bleaching. As the water gets warmer, corals will expel the algae known as zooxanthellae that lives in their tissues causing the coral to turn completely white. When temperatures drop, the corals can recover, but they might be vulnerable to disease and when

Coral reefs exist all over the world and are generally known as being one of the most diverse, intricate and beautiful of all existing marine habitats. They have many varying structures which are developed by algae and are symbiotic with various reef building corals which are referred to as, zooxanthellae (algae). There are many other factors such as, coralline algae, sponges and other various organisms that are combined with a number of cementation processes which also contribute to reef growth, (CORAL REEFS, 2015).

Coral bleaching is normally characterized by the expulsion of the zooxanthellae algae, loss of algal pigmentation, or both. Coral bleaching events have had serious effects on corals and reefs worldwide. What is crucial to the understanding of zooxanthellae expulsion and bleaching is how the density of zooxanthellae within the coral is changing, if at all, under the prevailing range of environmental conditions (Gates and Edmunds, 1999). Over the last twenty years, there has been a dramatic increase in both the frequency and intensity of coral bleaching events. Sixty major bleaching events have been reported between 1960 and 1979, whereas only nine were reported prior to 1979 (Huppert and Stone, 1998). Given the dependence of the coral on this symbiotic algae, it is important to determine the cause of these bleaching events. According to Helvarg (2000, p.12):

Since early 1998, climate change has been demonstrating its effects in increasing the ocean 's temperature (West & Salm, 2003). Warm water stress corals causing the phenomenon known as coral bleaching, by which expulsion of colourful symbiotic algae the zooxanthellae, vital for

The bleaching of coral reefs is when warm water forces algae to leave the reef. Once the algae disappear, the coral goes from a vibrant color to a pale white. As one marine biologist said, “You go from a vibrant, three-dimensional structure teeming with life, teeming with color, to a flat pavement...” This bleaching makes the coral more vulnerable to diseases and a greater risk of death. The biggest bleaching events to have occurred in

Although bleaching can be found in animals, it is most notable in corals. These species have a symbiotic relationship with the yellow-brown colored zooxanthellae from the genus Symbiodinium (Douglas ). Figure 3 shows the

According to the latest research of scientist team led by the University of New South Wales (UNSW), tropical corals cannot survive without the Symbiodinium algae that live inside them. These photosynthetic organisms supply the corals with all their food, more than 90 percent. UNSW specialists say that increased water temperatures stress the algae, provoking them to produce an excess of toxic substances, which called reactive oxygen species. As a result of intoxication, damage both the algae and the corals.

Coral reefs are threatened by global warming. They can only live in waters between 18 C and 30 C. Therefore, with the increase in temperature of the surrounding water, there has been an unprecedented increase in the number of coral bleaching events during the past 2 decades (which have had some of the warmest years in history). When ocean temperatures get too high, coral polyps lose the symbiotic algae inside them, causing them to turn white, or "bleach," and eventually die.

Coral bleaching occurs when the microscopic plants (zooxanthellae) are expelled by rising ocean temperature. When there are no microscopic plants such as zooxanthellae, the coral turns white and die. The studies show that throughout the worlds ocean, from the Florida Keys to the Great Barrier Reef of the Australia have been evidence of unique coral bleaching caused by the rising of ocean temperature. In the early 1980s the coral bleaching event has increased because of rapid increase of sea water temperature. Esther et al., investigates growth of Oculina patagonica at multiple environmental conditions in the western Mediterranean Sea. The Oculina patagonia is stony coral specie which is found mostly in the Gulf of Mexico and Caribbean. The coral was basically Atlantic origin which was transferred to Mediterranean Sea.

Currently due to CO2 emissions changing the waters pH and climate, change warming up the water coral bleaching is occurring. This is when zooxanthellae are release from the symbiotic relationship with coral leading to the death of the coral.

Coral reefs contain symbiotic algae called zooxanthellae which gives the coral its healthy brownish color. The algae "utilizes sunlight and the coral animal's respired CO2 to produce energy rich compounds that feed the coral host" (AIMS, 2003). When stress factors such as "heat, solar radiation, pollution, reduced salinity and changes in oxygenation" occur around the coral, bleaching can begin (Dennis). When bleaching occurs, the algae, which create nutrients for the coral to feed from, is released due to stresses to the reef. Thus the coral starves and its white calcium carbonate skeleton of the coral becomes visible (AIMS, 2003). But one of the main stresses that contributes to the lifeless white appearance of the coral is the warmer temperatures of the sea surface water.

      Coral reefs are continuously being both built up and decomposed, so different parts of a reef are in varying stages of succession (Richmond, 1993). Coral reefs are very fragile, because reef-building organisms cannot thrive if the surrounding water changes significantly. Coral reefs require very specific conditions in order to grow: a solid structure for the base; warm and consistent water temperatures (averaging between 20 and 30 degrees Celsius); stable salinity; moderate wave action; and clear water that is low in nutrients and plankton. The water on a healthy coral reef is clear because there are very few nutrients, so plankton that would cloud the water are few. In general corals grow slowly, but they are extremely efficient at living and reproducing in these conditions (American Zoologist, pg 524-536).