A coral disease called growth anomalies (GAs) is represented here in the coral species Porites Compressa, a reef-building species found off the coast of Hawaii. GAs are a tumor-like disease that can cause tumor-like protrusions that affect both the coral skeleton and its soft tissues. Photo credit: E. Andersson / NIST
Coral reefs are a popular diving spot and are among the most diverse ecosystems in the world. For example, the Hawaiian coral reefs known as the “rainforests of the sea” are home to over 7,000 species of marine animals, fish, birds and plants. However, coral reefs face serious threats, including a number of diseases that have been linked to human activity.
To understand the link between human activity and a type of tumor-like disease called growth abnormalities (GAs), researchers from the National Institute of Standards and Technology (NIST) worked with the US Geological Survey (USGS) and the National Oceanic and Atmospheric Administration (NOAA) a new molecular profiling method to identify 18 small molecules that will help them better understand the series of molecular reactions that lead to disease.
GAs affect both the coral skeleton and its soft tissues. Scientists do not know the cause of the disease or how it spreads, but believe that there is a strong correlation between GA prevalence in coral colonies and nearby population density.
Almost all types of coral are made up of hundreds to millions of individual soft body animals called polyps. The polyps secrete calcium carbonate to form a tough skeleton that lays the foundation for the coral colony. GAs affect corals by irregular and accelerated growth of their skeleton, making it less dense and filled with holes. This leads to a tumor-like mass in the skeleton of a coral colony with fewer polyps and reduced reproductive capacity.
Shallow water corals get food like carbohydrates and oxygen as a by-product of photosynthesis from the symbiotic relationship they have with zooxanthellae, photosynthetic algae that live in coral tissue. GAs can result in fewer symbiotic zooxanthellae and therefore less energy from photosynthesis being absorbed.
Although GAs do not usually directly lead to coral death, they affect the overall health of coral colonies and can pose an ecological threat to coral populations. To analyze the disease, the NIST researchers selected the coral species Porites Compressa as the target sample.
Known as the “finger” or “hump coral,” this species of coral is a member of the hard coral family, which is “one of the most important reef-building species in Hawaii,” said NIST chemist Tracey Schock. “You are laying the foundation stone for the coral reef.”
P. Compressa is found in shallow lagoons off the Hawaiian Islands, and the researchers obtained their coral samples from Kaneohe Bay on Oahu. The bay has been widely studied as a site affected by human activities such as sewage discharge and metal pollution. GAs have already been observed there in the coral species.
To analyze and study GAs in P. Compressa, researchers turned to the field of metabolomics, that is, the study of small molecules as they make up living organisms found in tissues, blood, or urine. These small molecules, known as metabolites, are the intermediate and end products of an interconnected series of biochemical reactions known as molecular pathways in an organism.
Some examples of such small molecules include sugars such as glucose, amino acids, lipids, and fatty acids. Their production can be influenced by genetic and environmental factors and can help researchers better understand the biochemical activity of tissues or cells. In this case, chemical analysis of metabolites provides important information that will help researchers understand the physiology of the disease.
Two different field recordings of the coral species Porites Compressa, a reef-building coral off the coast of Hawaii. The corals are affected by growth abnormalities (GAs), a disease that can cause tumor-like protrusions that affect both the coral skeleton and its soft tissues. The GAs are the “larger protrusions” of the corals. Photo credit: R. Day / NIST
For their study, the researchers examined a coral colony that had both healthy and diseased tissue. They divided up their samples in order to be able to assess the healthy and the diseased coral separately. They also had a separate adjacent sample that was free of diseased tissue.
The samples were frozen in liquid nitrogen and then freeze-dried for convenient sample processing while maintaining metabolic integrity. Then the researchers separated the diseased parts from the healthy colony with a hammer and stainless steel chisel and collected the tissue from the skeleton with a brush. In one of the final steps in sample preparation, they chemically extracted the metabolites from the coral tissue using a combination of methanol, water, and chloroform.
“The method is new to coral studies,” said Schock. “In metabolomics, it is critical to maintain the state of all metabolites in a sample at the time of collection. This requires stopping all biochemical activities with liquid nitrogen and maintaining this state until the metabolome is chemically extracted. The complexity of a coral structure requires strict collection and processing protocols. “
The researchers then performed a metabolomic analysis of the coral samples using a reproducible profiling technique known as proton nuclear magnetic resonance (1H NMR).
The 1H-NMR technique exposes the coral extract to electromagnetic fields and measures the high-frequency signals released by the hydrogen atoms in the sample. The different types of metabolites are revealed by their unique signals that inform about their chemical environment. NMR recognizes all signals from the magnetic cores within a sample, making it an unbiased “all-in-one” technique. Two-dimensional NMR experiments, which can identify both hydrogen atoms (1H) and their directly attached carbon atoms (13C), provide more chemical information and give confidence in the accuracy of the identity of the various metabolites in a sample.
The study identified 18 different metabolites and a new morphological form of GA in P. Compressa. The researchers found that GA tumors have different metabolite profiles compared to healthy areas of the same coral colony, and identified specific metabolites and metabolic pathways that may be important for these profile differences. They also discovered that the loss of internal pH regulation appears to be responsible for the hollow skeletons that are characteristic of GAs.
“Not only did we characterize new aspects of GA physiology, we also discovered candidate pathways that provide a clear path for future research aimed at further understanding GA formation and coral metabolism in general,” said Schock.
As studies of this type pile up, researchers envision a database that could bring together information on coral metabolites from multiple coral species in one place accessible to all scientists.
Working with other researchers in different fields could improve our understanding of the biological effects of this disease on coral colonies. “We will learn which species are tolerant and which are stress-sensitive, and the physiological adaptations or mechanisms of both species will be important to conservation efforts,” said Schock.
For now, the researchers hope that these results will be helpful to other scientists in the analysis of coral species and ultimately benefit the coral reefs themselves and possibly help to better preserve them.
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More information:
Erik R. Andersson et al., Identification of Metabolic Changes Associated with Coral Growth Anomalies Using 1H NMR Metabolomics, Coral Reefs (2021). DOI: 10.1007 / s00338-021-02125-7 Provided by the National Institute of Standards and Technology
Quote: Understanding the Molecular Basis of Coral Disease (2021, July 9), accessed July 9, 2021 from https://phys.org/news/2021-07-molecular-underpinnings-disease-affecting-corals.html
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