I have a bio-sphere, a small glass orb that I purchased from Amazon. Soil made of bio-pellets, marine water, a small group of macroalgae, and seven tiny marine shrimp are all inside. The whole ball is sealed, and the tiny ecosystem inside is said to last at least two years. The instructions for caring for the bio-sphere are minimal. It shouldn’t be in direct sunlight all the time, but it should get enough light for algae to grow. Keep it at room temperature. It’s fascinating to me, that within the nearly 12 months I’ve owned the bio-sphere, nothing within has changed. In the tiny sphere that sits on a shelf in my living room, everything stays the same every day. The tiny shrimp are doing great, and the patch of algae stays the same size. I could go on and on about the many complicated interactions going on inside the little sphere that keep it closed off from the rest of the world and still allow it to grow. Then I could write and write how these same systems apply to the health of our aquariums. In reality it boils down to one thing, the food chain.
We all know the basics of a food chain. Often though, we don’t apply knowledge of marine food chains to our aquariums. These systems complete an entire cycle of waste assimilation and animal nutrition. They are vital to every ecosystem on Earth, including the one within your aquarium.
There are bacteria and plankton in every drop of water in your aquarium. They are at the bottom of the food chain in your tank. The oxygen and biomass they are creating are the heartbeat of your tank’s ability to sustain marine life. Algae and phytoplankton take in sunlight, carbon and other nutrients, creating oxygen and food for other organisms. The microbes on the other end of this spectrum break down fish and animal waste, even dead animals, into nutrients that phytoplankton can use again. It’s the very basic foundation on which your water’s quality is built.
Marine microbes mark the beginning and end of the food chain. At the start, they make nutrients for all living things. At the end, they break down dead and decaying matter so that it can be used again. Microbes in the world’s oceans are thought to weigh about the same as 240 billion African elephants put together. It’s safe to say, depending on your aquarium’s size, that the biomass within your tank is quite considerable.
We decide an animal’s trophic level, based on how many steps away it is from a primary producer. To help you figure out what trophic level each of the animals in our aquariums belongs to, read the list below.
As humans, we like to imagine ourselves at the top of the food chain, which may or may not be true. Since we will all be fertilizing daisies at some point, bacteria, fungi, and other tiny living things may be faster than us.
Now this description is based loosely and broadly on oceanic food chains. To create an accurate picture of a reef aquarium’s food chain, you must look at its inhabitants. This will help us get a better understanding of our water ecosystem and decide how to improve it. It also helps to know that we might have to get rid of organisms or change the kinds of organisms we keep in order to make it better. A food chain (and thus ecosystem) functions best when it’s in balance. When there are too many of one kind of organism and not enough of another, it throws things off and may help an unwanted organism grow.
By making a food chain breakdown of your reef tank, you can decide how many animals to add or whether you already have too many of one species. Perhaps an aquarium is overstocked with secondary consumers, or lacks a good population of primary consumers. Balance should be present throughout the whole area, and you should pay close attention to how you grow and take care of microbes in your tank. If your aquarium only uses live rock to grow microbes, you might want to look into methods that are designed to grow microbes only, like zeolite, bio-pellets, refugiums, and so on.
The intricate connections between organisms in an ecosystem are vital for supporting all life. Energy flows through the web of producers, consumers and decomposers in a continuous cycle At the base of every food chain are photosynthetic organisms that harness the sun’s energy Further up the links are the consumers that depend on the producers, and each other, for nourishment.
To understand ecosystems and how energy moves through them, it helps to follow one chain at a time. So let’s dive underwater and trace out an example of a marine fish food chain from beginning to end.
Level 1: Phytoplankton – The Foundation
Phytoplankton are microscopic single-celled plants that drift through the ocean’s surface waters. These tiny producers are the base of most aquatic food chains. Phytoplankton use photosynthesis to convert sunlight, carbon dioxide and water into carbohydrates and oxygen. There are thousands of species of phytoplankton providing nourishment for a huge diversity of ocean life.
Some types of phytoplankton accumulate into large “blooms” that can be seen from space! They multiply rapidly when conditions are right, blooming into aggregations containing millions of cells per gallon. These blooms provide a sudden feast for plankton-eating creatures.
In our example kelp forest food chain, phytoplankton are consumed by small animals called zooplankton.
Level 2: Zooplankton – Tiny Grazers
The animal group known as zooplankton includes a vast range of species, from single-celled protozoa to larvae of jellyfish, crabs, worms, sponges and other marine creatures. Most zooplankton eat phytoplankton and other plant matter, qualifying them as primary consumers.
Some zooplankton are parasites or predators that eat other zooplankton for nourishment. But in our kelp forest food chain, tiny crustaceans like copepods and krill are the primary zooplankton. They use their little appendages to scoop up phytoplankton floating by and constantly graze on the abundant plant life.
In turn, these plentiful grazers become food for a diversity of small fish occupying the next level up the chain.
Level 3: Small Fish – Planktivores
Many small fish species filter-feed on zooplankton or pick plankton out of the water one nibble at a time. These planktivores include juvenile fish like herring, sardines and anchovies. They gobble up copepods, krill and other zooplankton in huge quantities. Schools of millions of these silvery fish migrate through coastal waters targeting dense patches of plankton.
The abundant schools of plankton-feeding fish then draw the attention of larger predators. In our food chain example, the small fish are eaten by the young of a top ocean predator – the salmon.
Level 4: Salmon Smolts – Opportunistic Feeders
After hatching in freshwater, young salmon called smolts migrate out to the ocean to feast and grow. They fill their bellies with protein-rich zooplankton, small crustaceans and the schools of small fish.
This sudden abundance of food allows the salmon to grow rapidly into adults, bulking up 10X their body weight in some species. The salmon smolts aren’t picky in their eating habits at this life stage – they will target whatever prey is readily available in large quantities as they travel the ocean.
Once fully grown, the adult salmon become prey for top ocean predators at the next food chain level.
Level 5: Large Fish – Apex Predators
Larger predatory fish hunt the adult salmon as they continue maturing and fattening up at sea. These big fish include tuna, sharks, cod and halibut that patrol deeper offshore waters. Their keen eyesight, speed and large mouths make them effective hunters of fast-moving and nutritious salmon.
The predators may travel hundreds or thousands of miles in pursuit of dense schools of salmon during the year. Their numbers and movements often shadow the cyclical migration patterns of the salmon between rich feeding grounds and spawning rivers.
In our kelp forest food chain example, feeding on the adult salmon allows these large apex fish predators to accumulate the energy needed to migrate, reproduce, and regulate prey populations.
Level 6: Scavengers – Nature’s Cleanup Crew
The carcasses of spawned-out salmon that die after spawning provide a feast for hungry scavengers. Bears, bald eagles and other coastal residents harvest the nutritious dead salmon that litter the streambeds.
In the open ocean, scavengers like hagfish and sleeper sharks consume the bodies of the large predators and salmon when they eventually die. These scavengers play an important role as decomposers to recycle nutrients back into the ecosystem.
Following the Flow
While individual species make up each link, it is energy that flows through the chain from beginning to end. Solar energy is taken up by the phytoplankton and incorporated into chemical bonds. At each transfer between predator and prey, some energy is lost as heat, requiring more to be consumed.
Tracing how energy moves step-by-step through a food chain provides insight into the complex interactions between producers, consumers and decomposers that support life on our planet.
So next time you spot salmon at the grocery store, think about the intricate cycles that brought them from ocean waters to your plate! Understanding and respecting these connections in nature allows us to manage ecosystems sustainably into the future.
