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Under Siege: The Imperiled State of Coral Reefs and Marine Biodiversity

Coral reefs host the most ecosystem biodiversity and are the backbone of marine life and even some lower-income countries. But will coral survive the oceans' warming? The short answer is no, but don't fret—corals are nowhere near gone.


The Great Barrier Reef

Map of The Great Barrier Reef

Over the last 50 or so years, almost everybody's concerns regarding the oceans have been about coral. Many people are concerned about ocean warming and its effects on coral reefs. In the southwestern part of the Pacific Ocean lies the coral sea, the home of the largest coral reef in the world: The Great Barrier Reef. The Great Barrier Reef hosts thousands of different species of marine life and is essential to their survival. The Great Barrier Reef is very big, about 133,000 square miles, but technically does not reach out to Fiji, Tonga, The Solomon Islands, Palau, or Indonesia, but many coral species found off the coast of those countries can be traced back to The Great Barrier Reef. Corals are a vital piece to many countries' economies, especially Palau, Tonga, and eastern Indonesia. But, I digress; let's get back to the "problem:" ocean warming; the Coral Sea is warming up right now; it is 83.5Fº right off the coast of Cairns, Australia, which is almost due west of the middle of the Coral Sea. But, the Great Barrier Reef is not at the surface of the water, it averages 98ft below the surface, with some areas dropping off suddenly, and with every 100ft that you descend in water, the temperature drops about 1.45Fº. So the Great Barrier Reef sits around 82Fº daily.

But the real problem is much deeper than ocean warming.

Coral Fortress: Understanding Coral

LPS left, SPS right

Many people think that corals are super fragile and will die with even the slightest changes because that is what they have been told. But that is not true; with experience keeping corals myself, coral is not super fragile, it is actually pretty resilient. Some corals are more fragile than others, large polyp stony (LPS) corals tend to be the least fragile corals, then comes, small polyp stony corals (SPS), but perhaps the most fragile corals are non-photosynthetic (NPS); there isn't a clear-cut line as to which is the hardiest and which is the most fragile as some LPS corals are more fragile than some SPS and some SPS is more fragile than NPS. Most of the coral on the Great Barrier Reef is Staghorn coral, scientifically known as Acropora, which is what I know it as, this coral belongs to the SPS family; it looks like a tree with no leaves and has short polyps hanging off each branch. This coral comes in many different colors and, like every other coral, will infinitely grow given the right conditions, but the caveat of this coral is that it is on the more fragile end of SPS corals. I kept a few fragments of Acropora coral in my tank at home, and I can tell you for certain that they are sensitive, not to water temps, but pH changes. When I kept these corals, I changed the temperature of my tank based on the temperature of my house because the surrounding air can raise or lower the tank's temperature, but I always tried to keep it between 78-82Fº. Every time I did this, no matter if I went up or down in temperature, the coral would release its algae that gives it color, zooxanthellae. Coral releasing zooxanthellae isn't typically a good sign, so you have to make sure to keep water parameters in check following your changes, but every time, without fail, my Acropora's would recover within a few days and shine bright as ever.


Dear Plastics, You Suck.

While I never kept NPS corals, I did keep lots of LPS and some SPS. What I can tell you is that they both absolutely hate plastics in the water. Plastics are the bane of just about anything that has to do with water; they are one of the worst things that can touch water. I always made an effort to try and keep plastics out of my tank, but sometimes it is just unavoidable, as it will forever be in our waters, in the form of microplastics, no matter how much you filter it. Plastics are nasty with water due to how they are made; plastics are made using tons of chemicals. Putting plastics in the water causes the plastics to release chemicals from manufacturing, lowering water pH. The other problem with plastics is that they freely move around in the ocean and get caught on corals, essentially stopping their growth, barring someone removing the snagged plastic. Plastics getting caught on corals also means that the coral can no longer use its polyps to snag food out of the water column, which is essential for coral survival, essentially sentencing part of, or the entire piece of coral to death.


The Real Problem

The bigger problem than plastics is global warming, specifically the release of carbon dioxide into the atmosphere. When carbon dioxide gets absorbed by our oceans, it forms carbonic acid (H2CO3), a weak acid that breaks or "dissociates" into hydrogen ions (H+) and bicarbonate ions (HCO3-), per NOAA. The Coral Sea sits at 8.1pH, nearly perfect for coral survival, but it hasn't always been this way. Coral was living in 8.2pH waters, all the way up until about 200 years ago, when the Industrial Revolution started. The industrial revolution was a massive contributor in releasing carbon dioxide into the atmosphere, which the oceans absorb about 30% of; over time, the ocean's pH has slowly dropped about .1pH. It doesn't seem like a lot, does it? But remember, the pH scale is logarithmic, so this .1pH drop is actually an almost 30% increase in acidity. While the slightly lower pH still falls into the ideal range for corals (8-8.4pH), the corals still are not used to the relatively new water parameters as they lived in higher pH waters for thousands of years prior. The new lower pH does not threaten coral right now, but if humans keep adding carbon dioxide to the atmosphere, the oceans will continue to become more acidic. This is a problem because not only corals but also any other animals that make hard shells or skeletons using calcium carbonate will not be able to form their shells or skeletons because they rely on alkaline waters to form and maintain them, as acidic waters will dissolve their shells or skeletons.


Ocean Acidification Impacts on Fish and Algae

Changes in ocean chemistry not only affect calcifying organisms but also affect fish and algae. Clownfish (yes, this would be Nemo) rely on alkaline water to detect looming predators, so obviously, the more acidic the waters, the harder it becomes for the clowns to use their abilities to the fullest. Clownfish in the wild typically host anemones, a vital piece of keeping nitrogen in ocean water. But when clownfish are not around because they are getting hunted down by bigger fish, they cannot host the anemones, and the anemones struggle. Anemones are probably one of the weirdest organisms in the ocean as they are like a stinging coral that can walk around. They will walk around until they find a crustacean to latch onto and protect, but sometimes they will latch onto rocks, and during this whole process, the clownfish is hosting the anemone. It is quite a cool process, and when the anemone has settled, the crustacean, anemone, and clownfish(s) are like one big team. But back to the point, the oceans need nitrogen, an already scarce nutrient.


Algae are also essential to the oceans, but not all algae are good algae, as some types are very invasive and will quickly overrun an entire ecosystem and kill it. Algae is formed by CO2, and excess amounts of CO2 mean more algae growth, which can be bad. Obviously, with humans adding CO2 to the environment, algae is growing at a rapid rate, but it can usually be kept under control by ocean currents breaking it up or marine organisms snacking on it.


Outlook For The Future

Current estimations by the NOAA predict that our ocean's pH will drop to 7.8pH by the end of the century if we continue with business-as-usual emissions, and a 7.8pH will kill coral. The last time the oceans were down to 7.8pH was during the middle Miocene, 14-17 million years ago. During this time, the oceans were several degrees warmer than todays, and the world was going through a major extinction event. If this is the case, obviously, many animals and people will suffer, as much of the world relies on food from the ocean for protein. Some people will also suffer financially as most of their income comes from the ocean because they sell coral, or fish and sell their catches. For now, the ocean isn't too threatened as many ocean organisms can be purchased at a consumer level, but we do need to make an effort to lower our carbon emissions to keep these organisms around.



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FANTASTIC article about coral reefs and marine biodiversity. VERY informative with A LOT of great information!!!

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