What factors govern the success of algae as "tenants" of their coral hosts, both under optimum conditions and when ocean temperatures rise? A team of experts led by Victoria University of Wellington that includes Carnegie's Arthur Grossman investigates this.
Corals are marine invertebrates that build large exoskeletons from which colorful reefs are built. But this reef construction is only possible because of a mutually beneficial relationship between corals and several species of unicellular algae called dinoflagellates that live inside the cells of coral polyps.
These algae are photosynthetic, which means that, like plants, they can convert the Sun's energy into chemical energy in the form of food. Many of the nutrients derived from photosynthesis, synthesized by an algae, serve as food for the coralline host, while the host, in turn, supplies the alga with essential inorganic nutrients, including carbon dioxide, nitrogen in the form of ammonium and phosphate. However, ocean warming due to climate change is causing many corals to lose their native algae renters – along with the nutrients they provide – a phenomenon called whitening. If the bleached coral is not recolonized with new algae renters, it may die.
Some species of dinoflagellate algae form these symbiotic relationships with multiple types of coral, others are more specific.
"We are interested in understanding the cellular processes that maintain these preferential relationships," Grossman said. "We also want to know if it is possible that non-preferential, more heat-resistant algae can revive bleached coral communities, even if the relationship is less efficient."
Other organisms, such as sea anemones, are part of the same phylum as the coral, called cnidaria; they also host algae, but are easier to study. In this article – published by The ISME Journal– researchers analyzed the differences in cell function that occurred when a type of anemone called Exaiptasia pallida was populated by two different genera of dinoflagellate algae – one native and highly susceptible to thermal bleaching and the other, which is not native but more calorific. resistant.
"In this study, we hope to elucidate the proteins that work to improve the nutrient exchange between the anemone and its native algae and why the anemone's success is compromised when it hosts non-native heat-resistant algae," said Grossman.
The team found that anemones colonized by native algae expressed high levels of proteins associated with nitrogen metabolism and organic lipids – nutrients that can be efficiently synthesized as a consequence of algal photosynthetic activity. These anemones also synthesized a protein called NPC2-d, which is considered the key to the cnidarian's ability to absorb algae and recognize it as a symbiotic partner.
In contrast, anemones with the non-native tenant expressed stress-associated proteins, which probably reflects a less optimized integration of the metabolism of the two organisms.
"Our findings open the door to future studies to identify the key proteins and cellular mechanisms involved in maintaining a robust relationship between algae and its host cnidarian and the ways in which organism metabolism is integrated," concluded Grossman.
Are algae that are "poor providers" able to help corals come back after bleaching?
Ashley E. Sproles et al., Proteomics quantifies protein expression changes in a cnidarian model colonized by a thermotolerant but sub-optimal symbiont, The ISME Journal (2019) DOI: 10.1038 / s41396-019-0437-5
Investigating "marriage" of corals and algae at the cellular level (2019, June 19)
recovered on June 19, 2019
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