If you take a close look at the coral reef ecosystem. you’ll notice that there is a fight for the survival of organisms that live on the reef.
In the fighting ring are corals versus other corals, corals versus plants, corals versus fish, fish versus fish and so much more.
Today, we’re going to talk about these interactions and explain a few of the ways organisms survive on the coral reef.
You can watch the video below or keep reading…
In a previous post, I explained that corals need several different things to survive. Among those things are sunlight and sufficient space to grow. But this requirement is not unique to corals because many reef organisms need these things as well.
This common requirement sets the stage for a fierce underwater competition among all the different types of organisms on the reef.
Generally, the branching corals grow faster than the slow growing encrusting or massive corals.
This could pose a threat to the slow-growing corals because the branching corals could potentially use up all of the available resources, leaving none for the slower-growing corals.
But this isn’t always the case. Slow-growing corals have a secret weapon located within their body cavity – it’s called “mesenterial filaments”! The mesenterial filaments are used to attack fast growing coral competitors. This gives the slow-growing corals a chance to obtain important survival resources for themselves before it is used up by the fast growing corals.
This attack on the faster growing corals does not damage the entire colony of polyps however. The undamaged polyps of the faster-growing coral can attack back using their long sweeper tentacles. These tentacles have stinging cells on them called cnidocytes.
Cnidocytes contain stinging cells or nematocysts that inject venom and can kill the polyps of the slower-growing corals.
In most cases, the faster-growing corals tend to prefer the upper shallower areas of the reef and the massive slow-growing corals prefer the deeper areas. This difference in habitat preference offers one way for both species to get the necessary resources needed and survive.
Competition however, is not exclusive to coral-coral interactions. Corals must also compete with other reef organisms like sponges, soft corals, and even algae plants!
But how could a plant such as algae compete with an animal such as a coral polyp?
Well, algae competes with corals for growing space. If given the opportunity, algae will also grow on top of corals. use the corals as a foundation on which to grow.
In a previous video, I mentioned that corals have microscopic plants called zooxanthellae living within their polyps and like all plants the zooxanthellae need sunlight for photosynthesis and its survival.
If algae grows on top of the coral, it can block sunlight for the zooxanthellae. Left unchecked, the algae can cover the entire reef and stop/prevent the corals from receiving sunlight
However, the algae population is kept under control by herbivores such as the long-spined sea urchin. Sea urchins will eat the algae and prevent overgrowth.
Herbivory is most prominent in the shallow fore reef areas and this is because the temperatures are warmer and there is more sunlight in that region where plants can grow, unlike in the deeper areas.
If by chance, there were a decrease in the herbivore population, it can cause extreme algae growth and death of the coral.
ANOTHER way algae populations are kept in check is by the Damselfish. The damselfish will weed out unwanted algae species to allow only certain species to grow. They’re kind of like like little farmers – who farm algae.
Some fish such as the parrotfish will feed directly on the coral polyps or its mucus and cause stunted or delayed coral growth. After a meal of feeding on the corals, parrot fish would pass the coral skeletons through their digestive tract and let it out in the form of sand particles on the reef.
These coral-eating organisms are called corallivores, and while they do affect which corals can grow and the rate of growth, they hardly ever destroy an entire coral colony.
So, to recap
- There is competition which takes place between different kinds of organisms on the reef.
- Resources like space, sunlight and food are in demand on the reef and because of this
- There are many different survival tactics that are used including body weapons such as mesenterial filaments and stinging cells.
- In the process of survival some organisms will indirectly help the reef such as the long spined spiny sea urchins
- And finally, survival on the reef is not a matter of luck, but the result of various defense mechanisms used by the organisms on the reef.
That’s it for today and until next time, keep exploring!
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