Mangrove Forests in Australia Tend to Grow According to A Roughly 18-Year Lunar Cycle, a New Study Finds.

Mangrove forests are formations of specific plants and are generally found growing and developing in protected coastal areas in the tropics and subtropics. The word mangrove itself comes from a combination of Portuguese, namely mangue, and English, namely grove (MACNAE 1968). In Portuguese, the word mangrove is used for individual plant species, and the word mangal is used for forest communities consisting of individual mangrove species. Whereas in English, the word mangrove is used both for communities of trees or grasses that grow in coastal areas and for individuals of other plant species that grow associated with them. Various terms are used to describe mangrove forests, including coastal woodland, mangal, and tidal forest (MACNAE 1968; WALSH 1974). A mangrove forest is an area that absorbs greenhouse gases, especially CO2, until it reaches a level of balance. Mangrove forests are very important carbon sinks because mangrove forests are one of the groups that can regulate greenhouse emissions. With a decrease in the area of mangrove forests, the carbon storage capacity will also decrease (Soemarwoto, 1998).

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In the summer of 2015, 40 million mangrove trees died of thirst. The mass extinction, the largest in the world on record, wiped out the rich mangroves along 1,000 kilometers of coastline in the Gulf of Carpentaria, Australia. The question is why? Last month, scientists discovered why: A strong El Ni?o caused a temporary drop in sea levels. It keeps mangroves, which rely on tides to cover their roots, high and dry during the unusually dry early monsoon season. The case has been closed. Or is that so? While the evidence clearly hints at El Ni?o, we find that this climate cycle has a very big accomplice: the moon. The expansion and contraction of mangrove cover over the past 40 years and found clear evidence that oscillations in the moon's orbit are having an impact. Our mapping also shows that mangroves across the continent are expanding and their canopies are becoming denser, most likely due to higher carbon dioxide levels. Although spectacular, the Carpentaria Bay mangrove die-off event was completely natural.

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What clues indicate the role of the moon?

During an El Ni?o cycle, like in 2015, sea levels around Australia and other Western Pacific nations fall. But this climate cycle affects the entire Indo-Australian region. If El Ni?o is the main cause, mangroves elsewhere should also be affected. But the dieback of these tidal shrubs and trees is largely confined to the Gulf of Carpentaria. High-tide coasts have higher mortality rates. In contrast, mangroves continue to thrive on the tidal fringes of estuaries, deep in floodplains, where climate influences should be most pronounced.

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That's where the moon comes in, specifically "moon wobble." In 1728, astronomers determined that the plane in which the Moon orbits the Earth is not fixed. Instead, it bounces up and down, kind of like a spinning coin, as it slows down. The extent and distribution of Australian mangroves over the past 40 years have shown clear signs of lunar tremors. This 18.6-year orbital cycle turned out to be the main reason why the mangrove canopy expanded and contracted over much of coastal Australia and explained the pattern of mangrove mortality in the Gulf of Carpentaria.

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You might wonder why oscillations have such a big impact on the life and death of mangroves. The high tide changes its wobble and changes the way the moon's gravity pulls on the world's oceans, so a period of very high tides is followed by a very low tide after 9.3 years. Research by NASA scientists suggests this cycle could lead to major coastal flooding in the early 2030s when extreme tides collide with accelerating sea level rise. In April 2016, the authors examined dead mangroves in northern Queensland. The mangrove cycle on the Moon can be clearly seen from above. When we mapped the change in the dense mangrove forests of North West Australia and Western Australia, we saw a distinct peak in the closed canopy, where the leaves and branches of the mangroves thickened to cover more than 80% of the surface, consistent with this stage. The climax coincides with the moon. cycle. When tides are at their peak, water floods the mangroves and carries nutrients, accelerating growth. This period could potentially affect the amount of blue carbon that a mangrove forest stores over thousands of square kilometers.

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But when the sea recedes, the mangroves don't get the water they need. In 2015-2016, lunar sway reduced tidal amplitudes in the Gulf of Carpentaria enough to reduce tides by about 40 centimeters. Mangrove deaths in 1998 and before 1982 also coincided with this nadir. In 2015, under the influence of El Ni?o, the tides on Australia's north coast continued to decline, bringing seawater into the eastern Pacific. The massive die-off of mangroves is due to overlapping lunar and climate cycles in the Gulf of Carpentaria. One of the challenges we face is distinguishing between El Ni?o and lunar wobble effects, as they tend to occur at the same time period in the western Pacific. Some scientists even believe that the wobble of the moon could lead to a strong El Ni?o event.

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To describe these two reasons, we rely on the characteristics of the moon's motion and the characteristics of the coast. The time of the moon's oscillation in the period of inverse tide and tide range between coastlines with two daily tides (semidiurnal tides) and those receiving one daily tide (diurnal tides).

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Carpentaria Bay is one of the few coasts in Australia with low tides during the day. Most other beaches experience high tide twice a day. Taken together, this means that in 2015, tides were higher than usual on half-day coasts, and lower than usual on sparse coasts such as bays. This explains why, in the summer of 2015/16, the mangroves on the half-day coast near the Gulf of Carpentaria were spared. The northern shore near the bay is in the high water and productive phase of the 18.6-year cycle and is therefore unaffected by El Ni?o. In the day and night bays of Carpentaria, the retreating phase of the moon's wobble cycle is combined with El Ni?o. Lower sea levels and lower tidal ranges are marginalizing mangroves.

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Interestingly, despite the El Ni?o, mangroves continued to grow near the headwaters of the Gulf River, as the effects of the moon's wobble were less pronounced upstream. This is good news for mangroves. We now know that short-term natural climate cycles, such as El Nino, may not cause widespread mangrove mortality on their own. And we can anticipate moments of danger when it coincides with low tide caused by the moon's wobble. While mangroves still face an uncertain future in adapting to the world of the high seas, we can attribute the 2015 mass deaths to "natural causes".

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References

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Bouillon, S., A.V. Borges, E. Casta?eda-Moya, K. Diele, T. Dittmar, N.C. Duke, E. Kristensen, S.Y. Lee, C. Marchand, J.J. Middelburget al. 2008.Mangrove production and carbon sinks: a revision of global budget estimates. Global Biochem Cy. 22:

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Controlled by the moon! Researchers find that mangroves expand and contract as per lunar pull. (n.d.). Retrieved October 14, 2022, from https://www.timesnownews.com/technology-science/controlled-by-the-moon-researchers-find-that-mangroves-expand-and-contract-as-per-lunar-pull-article-94478180

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MacNAE, W. 1968. A general account of the fauna and flora of mangrove swamps and forests in the Indo-West Pacific Region. Adv. Mar. Biol. 6: 73-270.

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Mangroves grow in sync with the moon’s orbit | Science News. (n.d.). Retrieved October 14, 2022, from https://www.sciencenews.org/article/mangrove-forest-grow-moon-orbit-lunar-cycle

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Neil Saintilan et al, The lunar nodal cycle controls mangrove canopy cover on the??Australian continent, Science Advances (2022). DOI: 10.1126/sciadv.abo6602

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NOOR, Y. R., M. KHAZALI dan I. N. N. SIJRYADIPURA 1999. Panduan pengenalan mangrove di Indonesia. PKA/WI-IP, Bogor: 220 hall.

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Soemarwoto, O. 1998. Ekologi lingkungan hidup dan pembangunan. Djambatan. Bandung.