Biomanipulation

How can we use our knowledge of trophic cascades to our benefit?

The removal of a top predator has cascading effects on the environment. The cascade effect often leaves ecosystems barren of vegetation. I wanted to look at some ways we can use the knowledge of the trophic cascade mechanism to restore ecosystems. In my previous post, Monbiot (2013) introduces rewilding. But today, I want to present a new method of utilising trophic cascades to re-establish ecosystems to their previous health. Biomanipulation is the process of ‘manipulating’ the ‘biology’ of an ecosystem (Carpenter 2014). The aim of Biomanipulation is to eliminate or reduce the presence of harmful phytoplankton (microscopic plants). The presence of harmful phytoplankton such as blue-green algae is most commonly caused by excess nutrients (eutrophication). Eutrophication is the process of the build-up of nutrients in aquatic systems (Carpenter 2014). Although eutrophication occurs naturally, humans accelerate the process, resulting in more damage. Eutrophication has negative impacts on aquatic systems because the excessive nutrients disturb the ecosystem dynamics (Riedel-Lehrke 1997). Excess nutrients decrease the population of large fish  causing a cascade that finally results in an abundance of algae (image 1).  

Image 1: Trophic cascade in an aquatic ecosystem caused by eutrophication (Missouri Department of Natural Resources 2005)

 Too much algae reduces the level of dissolved oxygen in water systems. Obviously this is not good for fish or other organisms relying on the aquatic ecosystem (image 2).

Image 2 Fish die due to lack of oxygen in water (Archer 2013)

To restore these ecosystems back to their previous health, trophic cascades can be used. By introducing more fish to the ecosystem, or protecting the current fish populations the balance between trophic levels can be restored (Riedel-Lehrke 1997). This use of biomanipulation in aquatic ecosystems also effect the abundance of aquatic vegetation, which effects sediment stability and indeed nutrient cycling.

It is important to study and understand natural processes such as trophic cascades that might be used to maintain the dynamics in ecosystem. With this knowledge we can find ways to restore ecosystems damaged by human interference.  

Image sources

Missouri Department of Natural Resources 2005, US Environmental Protection Agency, Missouri, viewed 30 April 2014, <http://www.lmvp.org/>

Archer 2013, University of Michigan, viewed 30 April 2014, <http://sustainability.umich.edu/>

Other sources

Carpenter, S 2014, Encyclopaedia of Britannica, viewed 25 April 2014, <http://www.britannica.com/EBchecked/topic/1669736/trophic-cascade/288348/Biomanipulation-in-lakes>

Riedel-Lehrke, M 1997, ‘Biomanipulation: food web management of lake ecosystems’, Student Online Journal, vol. 2, no. 2, pp. 1-4.  

Rewilding

The knowledge on trophic cascades can be used to restore ecosystems. 

In one of my previous posts I showed a video describing the trophic cascade that occurred in the Yellowstone National Park. This video was narrated by George Monbiot. Monbiot is an environmental and political activist. He has recently become interested in rewilding ecosystems. Rewilding is the “mass restoration of ecosystems”(Monbiot 2013). My past posts have described the cascading effects that occur when predators are removed from an ecosystem. This knowledge “make(s)...a powerful case for the reintroduction of missing species” (Monbiot 2013), and so can be used for restoring ecosystems back to their original health. According to Monbiot (2013), rewilding is bringing back lost plants and animals, then basically letting nature do its work. He explains in more detail in the video below. Enjoy

If anybody wants to know about something in particular on trophic cascades, please leave a comment below.

References

Monbiot, G 2013, For more wonder, rewild the world, TEDTalks.

Fish are friends, not food

Today there are countless threatened species. Many of these are top predators, the removals of which have the potential to trigger detrimental trophic cascades. One top predator that is threatened by human pressures is the shark.

 

Great White Shark (Melissa Smith 2013)

DID YOU KNOW Sharks are 200 million years older than dinosaurs and the largest known shark was 20 metres long (Defenders of Wildlife 2013).

Sharks are beautifully aerodynamic creatures, designed for stealth and grace in the water. Their stealth, sense of smell and razor sharp teeth are the reasons they rule the oceans, as a top predator, around the world (Defenders of Wildlife 2013).

Nevertheless, while many sharks eat marine animals such as fish and seals, many more feed on crustaceans, molluscs and plankton. Unfortunately, all sharks have copped a bad reputation, as a result of media sensationalism and ignorance.

 

Finding Nemo (Finding Nemo 2003)

 It is the human-created stereotypes that have planted the immediate fear for sharks. But the truth is, most sharks are harmless to us. 

Indeed, Bruce, Anchor and Chum from Nemo are a better representation of the average shark: " I am a nice shark, not a mindless eating machine...", well said...  

In Western Australia, sharks are now being culled as a result of humans’ fear. The culling of sharks in these waters is random and uncontrolled, which means any shark can be caught and killed, whether or not they are a threat to humans. Remember, not all sharks attack people. 

Sharks are also being caught for their fins. This practise is a major contributor to overfishing, as well as being cruel and wasteful (sharks are thrown back into the water once the fins are removed).

Hammerhead sinking to ocean floor after being de-finned (Western Australians for Shark Conservation 2014)

Aside from the direct action being taken against sharks, there are indirect effects that are contributing to the rapid decline of sharks worldwide. Climate change, pollution and habitat destruction are some examples (Save Our Seas Foundation 2014).

But what does this all mean? What are the consequences?

Because they are slow in developing, and have low reproductive rates, sharks are slow to recover from rapidly changing environments or external pressures. A decrease in shark populations lead to  trophic cascades. This has been seen on several occasions. Off the coast of North Carolina, USA, shark populations were severely depleted due to human pressures. In a healthy ecosystem, the sharks preyed upon Cownose rays, which in turn fed on scallops. The coastal human population also relied on the scallops. Once the shark numbers faded, there was an excess of rays, which severely damaged the local scallop community. Not only did the removal of this shark population lead to a unhealthy ecosystem, the livelihoods of the people who relied on the scallop population were negatively impacted (Save Our Seas Foundation 2014). 

It is clear that sharks are important for the health of our oceans and for our own wellbeing. We must prevent the decline of shark populations by stopping culling, shark finning and by preserving their habitats and reducing pollution.

Sign the petition to end shark culling here: http://www.marineconservation.org.au/petitions.php/9/save-wa-sharks-stop-the-cull

Sources

Defenders of Wildlife 2013, Defenders of Wildlife, Washington, DC, viewed 8 April 2014, <http://www.defenders.org/sharks/basic-facts>

Save Our Seas Foundation 2014, Save Our Seas Foundation, Switzerland, viewed 8 April 2014, <http://saveourseas.com/threats/predatorloss#3>

Humans as ecosystem engineers

Humans as ecosystem engineers (Engineers Australia 2013)

While writing my last blog, I was introduced to many ecosystem engineers. Indeed, there are many ecosystem engineers out there. Some examples, aside from beavers, include prairie dogs, earthworms, zebra mussels, coral, lianas and humans. A human as an ecosystem engineer was a thought-provoking concept for me.  It is true that humans have huge impacts on ecosystems. But, for the most part, these impacts are negative. So identifying humans as a sort of engineer of life was difficult.

Ecosystem engineers impact their surroundings. But there are always negative impacts that come with the positive impacts. Beavers have a more positive than negative impact. While humans have a more negative impact.

What are humans’ skills as an ecosystem engineer? We have the ability to figure out how we can use any niche for our own benefit. Most of the time this involves exploiting ecosystems. We clear land to build shelter and farmland, we pollute and we change the structure and functions of ecosystems.

Our actions are indeed changing the environment. However it is changing the environment in an unsustainable way. We are changing the composition of the air we breathe, our actions are influencing the temperature and the weather, we are mixing species together in a jumble, paving surfaces and generally modifying our surroundings at will (Woolley-Barker 2012), without thinking about the consequences.  

However, we cannot forget that we are part of the web of life. We utilise other animals and plants for our benefit, but other animals and plants utilise us in the same way. There are some organisms that benefit from the way that we live. Rats, cockroaches, pigeons, dogs and mosquitoes are just few organisms that thrive off us (Pottage 2003).

Perhaps many more will adapt to our own way of life. Indeed, Woolley-Barker (2012) suggests that plastic-eating bacterial communities may arise, or photosynthesising plants may figure out what to do with the excess carbon in the atmosphere. But on the whole, I believe that humans must find a way of making conditions conductive of life, rather than crushing life beneath out feet. It is time to find a way to sustain a diverse web of life, and provide opportunities that were not there before, like other ecosystem engineers (Woolley-Barker 2012).  

As ecosystem engineers, we are keystone species. But what would be the consequences of removing us from the planet? Would there be a trophic cascade? I think that there would be a trophic cascade, but it would be more progressive and less disruptive than a trophic cascade induced by other species. Because we have created such long-term structures and long-term pollutants, it would take a long time for the evidence of humans to be eradicated. (For interesting facts on our lasting impact after we are gone see: http://www.worldwithoutus.com/did_you_know.html)

Many species will boom that had been hunted or somehow diminished by humans, forests would take over our cities. There would be a general change of species composition, most likely increasing biodiversity. I suppose it makes sense that as an ecosystem engineer with more negative effects than positive, the effects of removing us would be more positive. It is interesting to consider our effects on the planet, and also a motivation to lead a less damaging life.  

Image source

Engineers Australia 2013, ‘Humans as engineers’, Image, Engineers Australia, 2 April 2014 < https://www.engineersaustralia.org.au/tasmania-division/discover-engineering-tasmania>

Sources

Pottage, J 2003, Swarthmore College Environmental Studies, 2 April 2014, <http://fubini.swarthmore.edu/~ENVS2/S2003/jpottag1/Jpottag1essay1.HTML>

Woolley-Barker, T 2012, Blogspot, 2 April 2014, <http://bioinspiredink.blogspot.com.au/2012/07/the-ecosystem-engineer.html>