There are many types of marine ecosystems, each fascinating and complex in its own way, but… have you ever wondered how an ecosystem works?
What role does each of its members play? Or why are some ecosystems more resilient than others?
In this post, we’ll explain how a marine ecosystem works, and in our next blog post, we’ll show you the signs to recognize whether a marine ecosystem is healthy and resilient.
How does a marine ecosystem work?
An ecosystem is a community of living beings that live in a specific area and interact with each other and with the surrounding environment. Therefore, we could say that every ecosystem is made up of two main groups: physical and chemical (or abiotic) factors, such as sunlight, nutrients, oxygen, ocean currents… and biotic factors or living beings, such as animals and plants, but also fungi, algae, and microorganisms like plankton and bacteria.
Trophic webs
So how are all these elements organized? Within trophic webs, which are the network of feeding relationships established among organisms.
Depending on the role each one plays in this network, it will belong to a different trophic level:
- Primary producers are the foundation of this food chain. These are living beings that, through a process called photosynthesis, transform nutrients, solar energy, and water into food so other organisms can obtain nutrients and energy from them. In the ocean, the most abundant are plants and algae—especially microalgae called phytoplankton. Since they rely on sunlight, they’re always found within the first 100 meters (or less) of depth.
- Herbivores or primary consumers: These include all those organisms, mainly invertebrate animals like shrimp, mussels, nudibranchs… and some fish, that feed on primary producers.
- Secondary consumers: Here we find carnivorous animals such as fish, rays, seahorses, seabirds, and invertebrates like octopuses and squids.
- Tertiary consumers: These are usually the top predators, feeding on other carnivores and often reaching larger sizes. In this group, we find most marine mammals like seals and orcas, but also sharks and some rays and fish, such as barracudas, tuna, or sailfish.
- Decomposers: We can’t forget about them—especially bacteria and some fish species that break down dead organic matter, allowing the resulting nutrients to be reused by primary producers, thus closing the cycle.
Now that you know the different roles of each system member, you can understand why all of them are important—because they all depend on each other.
This is why, the more species there are in an ecosystem, the more complex the trophic web will be, and also the more stable and long-lasting the system will be, since its biodiversity provides it with resilience against changes and threats.
The different types of marine ecosystems and coral reefs
The ocean hosts many different types of marine ecosystems, but all of them function in the same way.
Among all these ecosystems (mangrove forests, reefs, estuaries, seagrass meadows, deep-sea ecosystems…), the one we know best as divers are reefs, and in tropical seas, coral reefs.
Reefs are ecosystems found at very shallow depths, made up of calcareous rocks. In the case of coral reefs, the rocks are formed by the skeletons of thousands upon thousands of polyps—tiny invertebrates that provide protection, food, and shelter for other species.
Moreover, inside corals live zooxanthellae, microscopic algae that feed these polyps by converting nutrients into food, since they are primary producers, as we learned earlier.
Corals are the foundation of these reefs, and thanks to them, a vast array of species can thrive—from the tiniest invertebrates like shrimp, cuttlefish, clams, nudibranchs… to top predators like reef sharks.
Although coral reefs are large ecosystems with many different species, they also face numerous threats due to climate change and human pressure. That’s why it’s important to know how to identify those threats and determine whether a reef is healthy—or not.
We’ll tell you all about this in our next blog post!
