Artificial Reefs

Now for another type of hybrid coastal defence - artificial reefs. Artificial reefs can be made out of anything from concrete, to old tyres, to intentionally sunken boats (NOAA). And they have loads of exciting and useful benefits ranging from providing new habitats to marine life, supporting beach nourishment programmes, reducing wave energy reaching the shore, or even creating great waves for surfers (Corbett et al, 2007). Interestingly, artificial reefs were first created as a way stock enhancement in an area to improve fishing (Chuang et al, 2008).

I had to use this one because Nemo (or his dad) is in the bottom right corner (NileConstructionInc)

Ferrario et al (2014) looked at lots of studies on the efficacy of reefs in terms of protecting the coast. They found that the reef crests dissipated on average 86% of wave energy heading for the shore, and that the reef flats, which are closer to the shore could deal with 65% of the remaining energy. In total, a complete reef system can dissipate on average 97% of the wave energy that would otherwise reach shore. On top of this research has shown that in areas such as Tuvalu where the natural coral reef has been mined, become degraded, or cannot keep up with rising sea level the amount spent on new artificial barriers increases (Ferrario et al, 2014).


Clearly natural reefs are really important, artificial reefs are attempt to try and replicate these benefits. While they don't actively protect the coast from higher sea level, by minimising wave energy reaching the beach they reduce coastal erosion and protect active sea level defences such as sea walls. In this respect they can be quite successful, and are likely to become increasingly common as the oceans become stormier with a warming climate (Moschella et al, 2005).


However, as with all things they have to be thought through carefully - in Florida an attempt to build an artificial reef from tyres as a way of increasing biodiversity has turned into an environmental nightmare. The tyres quickly became loose and currents moved them around so they build up against the natural reef system causing death and destruction for marine life (USAToday).



How not to make an artificial reef - Osbourne reef today (Source:ProjectBaseline)



So essentially - I think artificial reefs are great but natural reefs are way way better. In any case, forgetting about their other benefits, in terms of sea level rise they are short term responses for protecting other defences and reducing erosion. I do also wonder a bit if some artificial reefs are a form of pollution - whether it be concrete, tyres, or old boats, none of these things are meant to be on the sea floor - and their presence can't be great for marine biodiversity in the long term - new coral reefs will never be able to grow underneath, and apart from anything else we are really going to confuse the geologists of the future...