The second research article I have decided to discuss is one I had the pleasure to be involved with! In fact, it was the first paper I was a co-author on, after linking up with the Department of Environment and Conservation through an ANNiMS internship program. The paper was recently published in the journal Coral Reefs, and can be found here!
We know that predation events structure communities in many ecosystems, but this effect could be particularly important in coral reefs. Juvenile reef fish that are newly settled on a coral reef patch can be extremely vulnerable to predation attacks. However, we know very little about predation on juvenile coral reef fish in all but a few ecosystems worldwide. Given the lack of empirical data in most marine systems, we tried to find out which fish was responsible for the predation encountered at Ningaloo Reef in Western Australia (as a side note, Ningaloo Reef is a beautiful place – recently granted World Heritage Status – that everyone should visit if they get the chance… but I will be writing about it a bit later on in more detail!)
To do this, we “fertilised” some coral patches with juvenile reef fish while leaving others untouched (i.e. no juvenile reef fish), and filmed what happened over the course of the day! We even used special lights to allow us to see what was happening during the first couple of hours of darkness! We ended up with 199 hours of video recordings, where we identified all fish within 30cm of the patch, measured how long they spent within the vicinity and whether or not they tried to eat one of the juveniles!
We discovered that, unlike most other locations, predation of juvenile reef fish at Ningaloo Reef is concentrated during mid-afternoon times, instead of the normal dusk/dawn periods. We also found an unexpected candidate for the top predator of juvenile fish at Ningaloo Reef…..the moon wrasse (Thalassoma lunare). In fact, of all the predatory strikes we seen on the videos, the moon wrasse was responsible for over 75% of them! The interest of the moon wrasse towards the juvenile fish was highlighted by them spending significantly longer around the patches ‘fertilized’ with juvenile fish compared with control patches with no juveniles.
The really cool thing about this research is that it displays just how unique Ningaloo Reef is. Firstly, predation of juvenile fish primarily occurred during the middle of the day, contrary to what we see in most other coral reef environments – a rise in predation during dawn and dusk. And on top of this, the moon wrasse hasn’t been identified as a major predator of juvenile fish in other ecosystems. However, in Ningaloo Reef, they appear to be responsible for a large proportion of juvenile fish predation, at least in corymbose coral patches where their slender body shape is ideal for hunting!
Holmes, T., Wilson, S., Vanderklift, M., Babcock, R., & Fraser, M.W. (2012). The role of Thalassoma lunare as a predator of juvenile fish on a sub-tropical coral reef Coral Reefs, 31 (4), 1113-1123 DOI: 10.1007/s00338-012-0934-8