Good day Explorers! Guess what?

 

 

 

 

 

Did you get my pun from my previous post? 😀 😀 Okay, back to the topic…

In today’s feature, we are going to shed some light on another coral reef destructor – the crown of thorns starfish! Their biggest “handiwork” can be seen in the Great Barrier Reef. (Scientists call them COTS)

Fun fact: this handsy little guy can have up to 21 arms!! 

How are they killing the reef?

As mentioned last week, sea temperature rise as a result of human activities can be detrimental for marine ecosystems particularly for coral reefs. Coral bleaching is already one of the most obvious effects of ocean acidification – where corals lose their symbiotic algae. The great barrier reef (GBR) has already lost over 50% of coral cover by 2012. 

The crown of thorns starfish are unfortunately adding to this problem. You see, their favourite food is hard coral! A previous impact assessment done in 2012 at the GBR considered 3 factors for coral habitat loss (storms, bleaching and COTS) and discovered that COTS predation accounted for almost half (42%) of coral loss (De’ath et al. 2012). 

Why are there so many of them?

A 2013 experimental study on the critter’s thermal resistance found that optimal development of COTS embryos occured between temperatures of 25.6 and 31.6 deg C. Average sea temperatures at that time of the year ranged between 25 to 30 deg C (Lamare et al., 2013). Conditions were perfect for a bloom of crown of thorns starfish. 

You must be wondering, where are the predators? Wouldn’t they be prey to some bigger animal? You’re right, they do have a few natural predators. However, their primary predator – the Giant Triton Snail are sought after by humans for their valuable shells, causing a decline in their population. Another human hand in the ocean. 

What does this all mean?

 Our Earth is a closed looped system in which whatever energy is created has to be stored somewhere, the pollutants are crossing boundaries (air to water). As mentioned in this article, carbon dioxide (CO2) released from vehicle exhausts, hundreds of factories around the world, and a small percentage coming from trees is entering our ocean. We cannot see this happening since CO2 is odourless and colourless, but what we can see are the effects of this process. And the crown of thorns apocalypse is just one of the examples.

At the end of the day, all life on Earth are interconnected in a massive, complex web. No matter how deep into the concrete jungle we live in, our (everyday) actions will have an impact on our natural spaces. In this case study alone, we see how anthropogenic emissions (CO2) and overfishing have contributed to the starfish apocalypse, an event that is unnatural and is evident of an imbalance in the food chain.

Thankfully, there are efforts to combat this problem, which will be a featurette on Stories of Hope so stay tuned to find out more! 

Sea you next time, in the mean time…

Stay Safe on the high seas 😉 

References
De’ath G, Fabricius KE, Sweatman H, Puotinen M (2012) The 27-year decline of coral cover on the Great Barrier Reef and its causes. Proc Natl Acad Sci USA 109:17995–17999

Lamare, M., Pecorino, D., Hardy, N. et al. The thermal tolerance of crown-of-thorns (Acanthaster planci) embryos and bipinnaria larvae: implications for spatial and temporal variation in adult populations. Coral Reefs 33, 207–219 (2014). https://doi-org.libproxy1.nus.edu.sg/10.1007/s00338-013-1112-3