About this video
This lesson explains how a cleaned and sunk ship becomes an artificial reef through ecological succession, the gradual change of an ecosystem over time. It distinguishes primary succession in new environments from secondary succession after a disturbance, using Yellowstone's 1988 wildfires as the main example. It also explains why some disturbances are part of a healthy ecosystem.
You'll be able to
- explain how a sunk ship becomes a reef through stages of succession.
- tell primary succession apart from secondary succession.
- explain why disturbances can be necessary for some ecosystems.
Key words
- Ecological succession
- The process by which an ecosystem changes and develops over time.
- Primary succession
- Succession that begins in a brand-new environment where no organisms lived before.
- Secondary succession
- Succession that restarts in an existing ecosystem after a disturbance such as a fire.
- Pioneer species
- The first organisms to colonize a new environment, such as algae and barnacles on a sunken ship.
Transcript
- [Teacher] Ships, we think of them as steadfast marine vessels, safely carrying people and cargo from place to place over the open ocean. Why then would anyone want to sink a ship on purpose? It turns out that sinking ships can be part of a very carefully planned process that can help restore marine ecosystems.
When a ship can no longer be used, like an old US Navy vessel, it can become an artificial reef underwater. First, the ship goes through a deep cleaning, where any kind of toxic substances like fuel, oil, plastic, or rubber are removed. Once it's clean, the ship is carefully sunk into a spot that might have been damaged by overfishing, storms or other disruptions.
Over time, this sunken ship transforms into new habitat for all kinds of marine organisms, including corals, algae, sponges, fish, and even sharks. But how does this happen? How does a bare metal structure turn into a reef full of life? This transformation is an example of ecological succession, which is the process by which ecosystems change and develop over time.
There are two main types of ecological succession, primary and secondary. Let's start with primary succession. This process happens in brand new environments, places where no organisms lived before. These kinds of environments include dried lava flows, bear rocks, cliffs, sand dunes, and new artificial reefs like sunken ships.
Primary succession can be a slow process. It might take decades for habitat to form or even hundreds to thousands of years. Primary succession usually follows a pattern. Life starts small and species arrive in stages over time in the new environment. So what does primary succession actually look like?
For that, let's go back to the artificial reef. After a ship is sunk, it's just bare metal and maybe some rust, but not for long. Some of the first organisms to show up are algae, soft corals and barnacles. They can attach directly to the ship's surface and start to grow.
Algae are small plant-like organisms that use sunlight to make their own food through photosynthesis. Soft corals and barnacles filter feed tiny particles out of the water to eat. These organisms are called early successional species or pioneer species, and they're the first to grow in this new environment.
Now, as these species grow, they begin to change the environment. They trap bits of sand and organic matter, and they become a food source or a shelter for other animals. Over time, other species start to arrive, small reef fish, shrimp, crabs, starfish clams, and more.
These animals either feed on the early successional species or find shelter in the growing reef habitat. Finally, years later, you get what are called late successional species. These species usually grow more slowly and need more specific conditions to survive.
These conditions might include specific kinds of shelter or a more complex food web. And in artificial reef, these species include larger corals, sponges and predators like groupers, tuna, barracuda, or even sharks. Over the course of many years, the ship goes from lifeless to supporting a few species, then many.
So through the process of ecological succession, we tend to see an increase in biodiversity or the variety of species in an ecosystem. Okay, so now we know how ecological succession happens when a new environment forms. But what if there was already an ecosystem there and something disrupted it?
In contrast to primary succession, secondary succession happens when an existing ecosystem is disturbed. This could be from a natural disruption like a hurricane or a volcanic eruption or a human cause disruption like pollution or climate change. These events can damage and harm the ecosystem.
Some organisms may die out, but some life survives. Certain plants might grow back from roots or seeds in the soil. Some animals may survive by sheltering and burrows underground. These survivors are what start the process of secondary succession. One of the clearest examples of this comes from Yellowstone National Park.
In 1988, massive wildfires, some caused by lightning, some by people, burned through nearly a third of the park, covering nearly 800,000 acres. The fires burned plants and trees, namely lodgepole pines above the soil, but left roots, seeds, and bulbs underground unharmed.
The following spring, in 1989, early successional species like grasses and wild flowers quickly grew back. Lodgepole pine sapling sprouted too. These species helped to stabilize the soil, keeping it from washing away and making it easier for other plants to grow.
Over time, larger shrubs and trees that take longer to grow began to take root again. Animals returned too, such as bison and elk as food and shelter became available. Today, much of Yellowstone looks pretty similar to how it did before the fire, but it's important to remember this.
Secondary succession doesn't always return an ecosystem to the exact same way it was before a disruption. Changes in sunlight, soil, or which species grow back first can all shift the direction of succession. The new ecosystem may be similar, but it might also support a different mix of plants and animals than it did before.
Disruptions aren't always a bad thing either. In fact, disruptions are just part of life. Some ecosystems are actually adapted to certain disruptions and even depend on them to stay healthy. Take the Lodgepole pine in Yellowstone. Their cones are sealed shut and open when exposed to heat, like the heat from a wildfire, which releases its seeds.
So fires actually very important to some ecosystems where I can clear out dead plants and allow new plants to grow. But of course, too many disruptions, especially from human activities, can make it harder for ecosystems to recover. That brings us back to the question we started with.
Why would anyone sink a ship on purpose? Well, now we know. When ships are carefully cleaned and sunk, they can become artificial reefs, creating new habitat for marine organisms. So from rested metal to reef, from wildfire to wild flowers, ecological succession is how ecosystems grow and develop over time.
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