We Found Love in a Salty Place

By Sammy Harding

Coral & Zooxanthellae

The first romance we want to highlight today is that between most reef-building corals and a photosynthetic algae that lives inside of them called zooxanthellae! Zooxanthellae live within the gastrodermis cells of each coral polyp of a coral colony, as seen in the picture above. The relationship between the two is called a Mutualistic Symbiotic Relationship — meaning both organisms involved are benefiting. The zooxanthellae are being housed and protected by the corals while they photosynthesize and provide the coral with nutrients and food. Additionally, corals are typically transparent in color but gain their color from the algae living within them as a byproduct of this relationship. It seems like these two have quite a healthy relationship… unless the coral becomes stressed. If water temperatures were to rise significantly, corals will “break up” with zooxanthellae and expel them into the water, an event called coral bleaching. Talk about getting dumped! Luckily, as long as conditions are able to return to normal within a certain amount of time, the zooxanthellae will return to their polyps and “get back together” with the coral.

Close-up picture of a coral colony and individual coral polyps

Butterfly Fish

One of the most romantic relationships we will feature today is the endless love between two butterfly fish. Butterfly fish are monogamous in nature, meaning they tend to mate with a single partner and remain in those pairs. Some species of butterfly fish maintain long relationships (up to 10 years!) and can actually tell the difference between their mate and another butterfly fish entering their feeding territories. You will often see butterfly fish darting around in their buddy pairs as they roam along the reef and graze on coral and other invertebrates. Next time you are out swimming at the reef, see if you can spot a pair of these sweethearts.

These butterflyfish have the same Valentine year after year!

White Mangroves & Sugar Ants

Another great example of a mutualistic symbiotic relationship is the white mangrove and their love interest, a species of sugar ant. On the petioles of white mangrove leaves, there are two nodes that contain extrafloral nectaries or simply put, nectar! White mangroves evolved to have two nodes at the base of their stem on their leaves called “leaf petioles” that contain extrafloral nectaries or simply, nectar. The ants are naturally attracted to the nectar and are able to use this as a food source in addition to making the white mangrove their home. In turn, the ants attack smaller predators to the mangroves such as caterpillars or other bugs and keep it safe from insect harm. 

White mangroves have nectaries at the base of their leaf that attract sugar ants!

Here at MarineLab, we are wishing you a sweet and salty Valentine’s Day!