Cell Biology of Coral Symbiosis: Foundational Study Shows Melanin Can Inform Solutions to the Coral Reef Crisis!
The largest barrier reef in the Western Hemisphere boasts a mosaic of marine and coastal habitats. Stretching for 625 miles along the coast of Honduras, Guatemala, Belize and Mexico, the Mesoamerican Reef (MAR) is the largest barrier reef in the Western Hemisphere.
Corals like humans also produce a substance called melanin to trap harmful bacteria and other microorganisms. Melanin in corals is made by specific enzymes called phenoloxidases (PO). An increase in the activity of PO can tell us if the coral has started to respond to the presence of harmful bacteria! The coral reefs off the Caribbean coast of Honduras are part of the larger Mesoamerican Reef system—the second largest barrier reef system in the world. Black Coral Inc works deeply with coastal municipalities, the fishing industry, national government, and scientists throughout Honduras to protect these vital reefs. All black corals have a skeleton made of protein and chitin (the same material as an insect skeleton). In addition, black corals do not have symbiotic algae associated with them, and they do not require light which enables them to extend into depths where light is not present.
A recent study argues that effective marine conservation is impossible without the people who depend on oceans the most: Indigenous and local communities. Black Coral Inc focuses on people in many communities from Boston to Bonaire who are seeking to protect their natural resources from climate destruction. However, conservation efforts often fall short on addressing the rights and priorities of these groups. Most shallow water corals rely on symbiotic algae called zooxanthellae to convert sunlight into energy. Black corals instead eat floating particles in the water.
Black corals grow vertically and then branch to maximize their ability to obtain food. Species that live in the deep sea have had to evolve in interesting ways to survive where there are so little nutrients and hard seafloor is scarce. For example, some grow to form wind tunnels, which funnel nutrients into their outstretched polyps. Others modify how they attach to the seafloor by growing a hook to anchor themselves in soft sediment. Most coral and algae depend on each other to survive. Unlike Black Corals these have a symbiotic relationship with microscopic algae called zooxanthellae that live in their tissues. These algae are the coral’s primary food source and give them their color Stressed bleached Coral.Coral is left bleached and vulnerable. Without the algae, the coral loses its major source of food, turns white or very pale, and is more susceptible to disease.
Not all coral species are equally susceptible to bleaching. In response to elevated sea temperatures, some corals may bleach, while other coral species in the same location may not. Some corals are able to acclimatize to local temperature increases over time. In general, coral species that are more resistant to bleaching can be characterized by massive growth forms, thick or less-integrated tissues and slow growth rates.
Although found at all depths, black corals can be a dominant feature of The Honduras's and Hawaii's unique deep coral reef environments. Despite its name, Black Coral isn't necessarily black. The color ranges from dark brown to practically black. Unlike shallow-water corals, most black corals (including the yellow cup black coral) do not develop symbiotic relationships with algae that provide them energy. Black corals grow extremely slowly, so any excessive harvest can quickly drive populations down. For that reason, all black corals are offered some level of legal protection wherever they live. Also they may hold the key to the survival of other corals.
Increased ocean warming is causing detrimental impacts to tropical corals worldwide. Compounding the effects of heat stress, incidences of tropical coral disease have risen concurrently. While tropical coral responses to these impacts are well studied, temperate coral responses remain largely unknown. The present study focused on the immune response of the temperate coral Astrangia poculata to increased temperature and disease. Symbiotic and aposymbiotic A. poculata were collected from Narragansett Bay, Rhode Island (USA) in summer and winter seasons and exposed to control (18°C) versus elevated temperatures (26°C) in the presence of an immune stimulant (i.e. lipopolysaccharide) for a 12 h period. Prophenoloxidase (PPO) and melanin concentrations from the melanin-synthesis pathway were assessed via spectrophotometry to examine immune responses. While PPO measurements were higher on average in symbiotic corals compared with aposymbiotic corals, temperature and season did not significantly affect this metric. Melanin was significantly higher in symbiotic compared to aposymbiotic corals, implying that symbiotic state may be important for melanin-synthesis response. Conversely, melanin as an immune response may be of less importance in aposymbiotic A. poculata due to the potential capacity of other immune responses in this species.
In addition, differences in resource allocation to immune investment as a result of symbiosis is plausible given melanin production observed within the present study. However, thermal stressors may reduce the overall influence of symbiosis on melanin production. Future studies should build upon these results to further understand the entirety of innate immunity responses in temperate coral species.
"Coral reefs are faced with almost complete destruction by the end of the century due to global warming unless humanity can cap global temperature rise. There is now a race to develop a diverse set of solutions to save coral reefs. In this perspective, a case is made for understanding the cell biology of coral-dinoflagellate symbiosis to help inform development of solutions for saving reefs. Laboratory model systems for the study of coral symbiosis, including the sea anemone Exaiptasia pallida, are featured as valuable tools in the fight to save corals. The roles of host innate immunity and inter-partner nutrient dynamics in the onset, ongoing maintenance, and dysregulation of symbiosis are reviewed and discussed. Key innate immune genes and pathways, such as glycan-lectin interactions, the sphingosine rheostat, and the cytokine transforming growth factor beta are shown to modulate a host immune response in the symbiotic state. An upset in the homeostatic inorganic nutrient balance during heat stress and high exogenous nutrient availability is credited with driving the partnership toward dysregulation and coral bleaching."(Virginia M Weis 2019)
Humanity's survival like the coral reefs are highly dependent on a mechanism to manage sunlight and repair damaged DNA. No melanin means no future Sunlight--especially the ultraviolet (UV) part of the light spectrum--is naturally a photocarcinogen. It can penetrate keratinocytes, damage the DNA, and lead some cells to possibly be transformed into cancer cells, such as a deadly melanoma. The cumulative effect on the human species of sun-damaged DNA over time is not trivial. Humanity's survival is highly dependent on a mechanism to manage sunlight and repair damaged DNA. People produce a complex compound called melanin that dissipates the damaging effect of UV light as heat and helps prevent skin cancers in other ways.
The transfer of melanosomes from melanocytes to skin cells is unique in human biology, requiring a whole organelle specific to one cell type to be transferred to a completely different type of cell. How? The melanocyte will form long arms that will extend up between the skin cells. Growing inside are microtubules (so small that 3,000 could fit in the diameter of a human hair), which act like railroad tracks to shuttle melanosomes. Tiny protein motors made for the microtubules pull the melanosomes outward. Under the direction of at least two more genes and controlled by four carrier proteins, the melanosome is put into a transfer vesicle at the tip of the arm. This tip fits into a special invaginated spot on a skin cell, and then the melanosome is injected into it. Skin cells will convey melanosomes to the sunward side of their nuclei. As illustrated in human skin, raw energy from the sun must be managed by preexisting complex biological systems or else it kills life.
This fact of nature still reigns over all evolutionary speculations. In 2024 about 200,000 cases of melanoma will be diagnosed in the UUSA alone, with an estimated 3.4 million reported and unreported new cases of mostly curable basal cell and squamous cell skin cancer--predominantly in lighter-skinned people globally. Melanin certainly provides a measure of natural protection, but nobody is immune from skin cancer, regardless of skin color and all need to be aware of skin care and protections. When people overexpose or fail to protect their skin, or have a defect in the pigment-making process, the sun's UV energy can eventually overwhelm skin's protective and repair mechanisms with deadly results as well as cause infertility and shorter lifespans in Caucasian children according to a recent Norwegian study.
According to data compiled by the American Cancer Society and the American Society of Clinical Oncologists, an estimated 3.5 million Americans will be diagnosed with skin cancer in 2023. Skin cancer is the most diagnosed cancer in the U.S. and is among the few preventable cancers. However, incidence rates continue to rise. “The rates are only going up,” says Dr. Vernon Sondak, chair of Moffitt Cancer Center’s Department of Cutaneous Oncology. “If nothing changes, by 2040, melanoma will be the second most common major form of cancer in the U.S. and the first among males.”Climate change global warming only increases the number of cases annually.
The majority of those diagnosed will develop basal cell or squamous cell carcinoma while the other 99,780 will develop melanoma, the most dangerous and deadly type of skin cancer. While melanoma accounts for only about 1% of all skin cancers in the U.S., it is the deadliest form of the disease. The reports estimate that over 7,650 deaths from melanoma occurred in 2022 and over 65% were white men.
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