Coral reefs and dinoflagellates form a symbiotic relationship

When corals met algae: Symbiotic relationship crucial to reef survival dates to the Triassic

coral reefs and dinoflagellates form a symbiotic relationship

The relationship between cnidarians and dinoflagellate algae is termed as " symbiotic", because After many years of this process, coral reefs are formed ( ). Most reef-building corals contain photosynthetic algae, called zooxanthellae, that live in their tissues. The corals and algae have a mutualistic relationship. Many microbes form symbiotic relationships with plants and animals. The dinoflagellates symbiotes of coral conduct photosynthesis and Most tropical corals exist in colonies and many colonies together form a reef.

This relationship keeps the nutrients recycling within the coral rather than drifting away in ocean currents and can greatly increase the coral's food supply. Symbiosis also helps build reefs—corals that host algae can deposit calcium carbonate, the hard skeleton that forms the reefs, up to 10 times faster than non-symbiotic corals. Finding out when symbiosis began has been difficult because dinoflagellates have no hard or bony parts that fossilize.

coral reefs and dinoflagellates form a symbiotic relationship

Instead, the researchers looked for three types of signatures in the coral fossils that indicate the past presence of algae: Their analysis revealed regularly spaced patterns of growth consistent with the symbiotic corals' reliance on algal photosynthesis, which only takes place during daylight. Frankowiak and Anne Gothmann, who earned her Ph. The third approach, determining the forms of nitrogen—which derive in part from the ammonium the corals had excreted—was conducted by Xingchen Tony Wang, who earned his doctoral degree in geosciences from Princeton in and is now a postdoctoral research fellow working with Sigman.

This polished fossil slab used in the study dates to more than million years ago and contains well-preserved symbiotic corals. The fossils were collected in a mountainous region in Antalya, Turkey, and originated in the Tethys Sea, a shallow sunlit body of water that existed when the Earth's continents were one solid land mass called Pangea.

When corals met algae: Symbiotic relationship crucial to reef survival dates to the Triassic

Jaroslaw Stolarski, Polish Academy of Sciences The nitrogen atoms, which are trapped in the fossil's calcium-carbonate matrix, come in two forms, or isotopes, that vary only by how many neutrons they have: By studying modern corals, researchers knew that symbiotic corals contain a lower ratio of 15N to 14N compared to non-symbiotic corals.

The team found that the fossilized corals also had a low 15N-toN ratio, indicating they were symbiotic. We were able to link the environmental conditions from million years ago to the evolution of corals. Also, traits were probably passed from microalgae to microalgae by the means of horizantal gene transfer. Re characterization of the Host-Symbiont Relationship The role of organisms in symbiotic relationship may be difficult to determine due to the intertwined evolutionary history of the two species.

The widely held view in the field concerning coral and their microalgal symbionts is that the relationship between the two organisms can be characterized as a purely symbiotic relationship. This characterization is due to the dependence of the two species upon each other for nutrients. However, there are emerging schools of thought which differ from the general consensus. Wooldridge argues that the recent crisis of coral bleaching and habitat degradation caused by pollution and climate change has led researchers to see this relationship in a new light.

When coral bleaching occurs, a "mass exodus" of the microalgal symbionts from the dying corals has been observed, which is not expected with purely symbiotic relationships 8 The authors of this paper suggest that the relationship should not be characterized as symbiosis, but as mediated parasitism exerted by the coral on algae.

Instead of coexisting with the microalgae, the coral "farms" it for its own benefit. It has long been assumed that neither corals or their microalgal symbionts could survive in nutrient poor tropical waters, leading researchers to believe that the relationship was symbiotic.

coral reefs and dinoflagellates form a symbiotic relationship

However, it has been found that microalgae are capable of surviving outside of their coral hosts. When the microalgal symbionts colonize the internal tissue of the coral, they shift from a motile phase to a non-motile phase. This change has negative implications for their reproductive success, and leaves them essentially "trapped" in the coral host.

On the other hand, there do not appear to be any costs for corals in relationships with microalgal symbionts. These unequal benefits for the two parties beg the question: Is the relationship actually symbiotic? Wooldridge would assert that is it not; rather,corals exert a controlled parasitism on their microalgal symbionts.

As climate change continues, and the earth's temperature increases, the acidity of the oceans is also increasing.

Microalgal symbionts: The coral-dinoflagellate relationship - microbewiki

This increase in acidity is causing the calcium carbonate structures of corals and other marine organism to become compromised, affecting survival. Coral reefs depend on a delicate balance of conditions to thrive and coral bleaching can push reefs to the edge.

The decimation of coral reefs is not only harmful because of the loss of species, but also because coral reefs occupy a unique place in tropical marine ecology. Coral reefs function as ecosystem engineers, creating habitats in an otherwise barren environment. This habitat creation is a factor in the rich communities of life seen in and around coral reefs.

coral reefs and dinoflagellates form a symbiotic relationship

The evolutionary history, genetics, and cellular biology of microalgal symbionts is incredibly complex and deserving of further study. As climate change continues, it is imperative that more research is conducted to understand the causes and implications of coral bleaching, and perhaps ways to protect reefs from further damage. There has never been a more appropriate time to focus energy and resources on the questions involving tropical coral reefs and the rich ecological communities which are tied to them.

coral reefs and dinoflagellates form a symbiotic relationship

Cell biology of cnidarian-dinoflagellate symbiosis. Microbiol Mol Biol Rev 76 2: A remarkable evolutionary experiment.

Microalgal symbionts: The coral-dinoflagellate relationship

Am J Bot 91 High diversity and host specificity observed among symbiotic dinoflagellates in reef coral communities from hawaii. Coral Reefs 23 4: Muscatine L and Porter JW. Mutualistic symbioses adapted to nutrient-poor enviornments. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms.

American Museum Novitates

The Coral and the Algae