Hey hey hey welcome back. 

As we already know, zooxanthellae are little algal bodies that live in symbiosis with coral. They live in a mutualistic relationship, which means both organisms benefit. If you have any question about that, look at my last blog post. 

We’re going to talk about something a little dark this week…. coral bleaching. 

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So first off, lets define what coral bleaching is. The actual mechanism of coral bleaching is when the coral “spits out” its zooxanthellae partner. This happens when sea temperatures change drastically, warm or cold, which as we know is inevitable. When sea temperatures change drastically, the zooxanthellae starts creating oxygen free radicals in its photosynthesis process. This in turns hurts the coral, so it rids itself of the zooxanthellae. This doesn’t happen simultaneously. The zooxanthellae is spit out one by one, but eventually all are gone. This leaves the coral “bleached” because the zooxanthellae is what gives the coral its vibrant color. Once the coral begins a bleaching event, if it has spit out enough of the zooxanthellae, it will eventually die. Some corals can feed themselves, but because nutrients greatly comes from the zooxanthellae, mortality comes quickly after full bleaching events. 

You may be asking, why do I care? 

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Long story short, YOU SHOULD CARE A LOT. 

Coral reefs are detrimentally important to the ocean and it’s balanced ecosystem. Coral reefs provide shelter and habitat to many fish. They only inhabit 1% of the ocean floor, but are homes to over 25% of the marine life. I took a class in the Florida Keys over spring break, and seeing the corals alive and well was something to behold. So many fish call the coral reef home. What happens when that coral bleaches? No home for the fish anymore. Another reason that coral reefs are necessary is their ability to assist in carbon and nitrogen fixing. If you didn’t know nitrogen and carbon isn’t just ready and available for us to use (us in this case being the fish). Also when you think about the symbiotic relationship, the zooxanthellae is a very important player is cycling nutrients through the coral but also the ocean as a whole. Coral also acts as an important source of food for many organisms. One in particular, is the parrotfish. The parrotfish is a funny looking fellow. 

He has a little beak that scrapes off pieces of the living coral, digests the zooxanthellae, and poops out the coral skeleton which becomes sand. If a coral bleaches, the parrotfish no longer has food. If the parrotfish goes extinct, than things that eat it like the moray eel and the reef shark no longer have that as a food option. Coral bleaching leads to major disruptions in the oceanic food chain. The ocean as we know it relies on these coral reef populations. 

Here is some scary numbers for you: Coral bleaching is five times more frequent now than it was 40 years ago. This can be seen following global warming trends. After significant warming weeks, coral bleaching reaches a dangerous level. Pictured below is coral bleaching risks for the year 2016. 2016 was the last major coral bleaching event. 

So yeah lets save the planet and stuff. This is kind of getting a little scary.

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Welcome back to another thrilling week of knowledge

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Symbiodinium, or zooxanthellae, live a life that consists of two stages: one being more common than the other. The first stage of life is characterized by a small, oblong, body equipped with 2 flagella. This stage occurs before the zooxanthellae has found their home in a coral. The flagella is necessary for mobility in their journey through the big blue. This is called the motile mastigote stage. The most common stage is referred to as the coccoid stage. This is characterized by a spherical body that lacks flagella. This is the stage found dwelling in symbioses within the coral. 

The grey arrows in the image above depict lab-observed actions. The red arrows depict inferences made. Symbiodinium reproduces asexually via fission. This happens through the mechanism of meiosis and daughter cells are identical to mother cells. The rate of meiosis depends on available nutrients and conditions. There are two possible outcomes that occur after this split. The motile phase could be spit out of the coral and find a new coral to inhabit or the motile phase could quickly transition to the coccoid phase to remain in the same coral. Reproduction has been created in a lab setting, but in the wild a coral is needed for reproduction to begin. The coccoid stage must be present for reproduction to happen. 

A new question comes to mind after learning this. How does the coral get its symbiodinium? 

This is legitimately a “chicken or the egg” scenario. 

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The coral can either swallow a zooxanthellae and have it enter its tissue OR maintain the mother and daughter cells that are reproducing inside its tissues already. It is thought that corals regularly spit out, swallow, and hold onto their symbiodinium to maintain a good number present in its tissues. 

Are you getting hungry? I think its time to talk about food. 

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So what does a little zooxanthellae eat? Zooxanthellae are actually photoautotrophs. This means that they preform photosynthesis for energy and food. The coral provides the zooxanthellae with carbon dioxide and water to do so. The zooxanthellae then does photosynthesis and provides the coral with sugars, lipids, and oxygen. 

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That looks like the end of it for this week! Comment if you have any questions.

Welcome back to our coral adventure!

As mentioned in the previous blog post, zooxanthellae are small single celled algal bodies that live in symbioses with cnidarian species. The specific symbiont we will be looking at is one that resides inside the Coral and its polyps. Whenever you hear the word algae, you probably think something that looks like this:

And you wouldn’t be completely wrong! Maybe you’ve experienced the little icky green film that forms on your grandma’s pool. Zooxanthellae that live in coral just exist in a much smaller scale. Zooxanthellae can range anywhere from 5-12 micrometers in size. 

Symbiodinium, commonly known as zooxanthellae, is a type of dinoflagellate that lives in correlation with a coral. They live inside the coral tissue and preform photosynthesis to provide the coral with oxygen and nutrients. In return, the coral provides protection, carbon dioxide, and a home for the zooxanthellae. 

What does the zooxanthellae look like? There are two different life forms that the zooxanthellae displays: one of them more common than the other. There is the motile masticate phase and the stationary phase. The motile phase is before the zooxanthellae finds its little coral soulmate to live with. This phase is characterized as an algal body with a flagella wrapped around its middle and continues into free space to help with motility. The stationary phase loses the flagellum and resides inside the coral tissue.

Pictured below is both the motile phase and the stationary phase.

There are different species of zooxanthellae and each species is specific to the coral they inhabit. Each different kind of species is called a clade. There are 9 different clade’s named via alphabetic order (clade A through I). Each clade has their own specific genome. Extensive research has not been done on the specific genomes of each clade, but we do know that the genomes help with temperature resistance.  The general size of the genomes of dinoflagellates is ridiculously large in variation, ranging anywhere from ∼3–245 giga base pairs.  Dinoflagellate nuclear DNA is extensively methylated. “Previous studies showed that 12–70% of thymine is replaced by 5-hydroxymethyluracil and varying levels of methylation occur to cytosine”. (https://www.sciencedirect.com/science/article/pii/S0923250811000684).                                                                                                        

 As you can see pictured above, all clades except for clade H are represented in phylum Cnidaria. 

The cellular structure of the symbiodinium is simple yet adequate. The cells contain a nucleus that holds super coiled DNA, chloroplasts containing pigments such as pigments a and c, a strange structure called the accumulation body whose contents are unknown, and a cell wall filled with glycosidic proteins. Chloroplasts preforms the photosynthesis so important for this relationship.

Thanks for coming on this zooxanthellae journey!

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On Tuesday March 26th, I went to the Georgia Aquarium. I like to consider this one of my happy places. I love seeing the majestic whale sharks, the funny beluga whales with their knees, and the fluffier than life otters. When I heard that this was an option for a site visit, I jumped at the opportunity. Another reason I chose this site is because I just recently went on a spring break class trip to Key Largo. I wanted to test my fish identification skills. All of this considered, I decided the aquarium would be perfect.The day I went was very crowded. It was the middle of spring break, so small children were bouncing off the walls. Regardless, I still let myself have a good time. If you have never been, the aquarium is split up into different ecosystems. The coral in question was found in the Tropical Diver section. 

Now lets talk about our microbe. I have taken marine biology, so I already knew a little bit about the zooxanthellae and their role in their coral friends. I think any level of symbioses in nature is very fascinating. Two organisms that have evolved to solely rely on each other is mind blowing to me. Also, on my class trip to the Keys, we visited a coral nursery and I saw tons of coral in their natural habitat. I have a new found love for them and a new fire for saving them. I couldn’t “see” the zooxanthellae, but I saw the particular coral they were living amongst. 

Pictured above is the orange cup coral. Zooxanthellae is phylum dinoflagellate and species Symbiodinium.