Tag Archives: Marine Biology

Predation of juvenile reef fish in coral patches at Ningaloo Reef

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!

Chromis sp. on a coral patch in Ningaloo Reef

The little juvenile fish we used to fertilize our coral patches…so who eat’s them, and when!?

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!

ResearchBlogging.org

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

Marine Ecology or Marine Biology….what’s the difference!?!?!?

A few of you may be wondering why the blog is called ‘Confessions of a Marine Ecologist” and not ‘Confessions of a Marine Biologist”.  After all, if you ask a group of school kids what they want to be when they grow up, more than a handful would happily answer “marine biologist”, but I would happily put money on none answering “a marine ecologist”!  Even when I decided I wanted to study life in the ocean, I searched for courses on marine biology, not marine ecology!  And I myself often wondered why people I was introduced to describe themselves as ‘marine ecologists’ instead of ‘marine biologists’.  So what’s the difference?  And, more importantly, why do I feel the need to describe myself as a marine ecologist that will almost definitely get me less traffic and fewer looks of admiration from non-scientists (incidentally, these looks of admiration are quickly replaced by confusion when you explain to people that you work on seagrass instead of dolphins or turtles!)

Coral Reef Community at Ningaloo Reef, Western Australia

Why do we find marine organisms in some places but not others? This question is at the heart of all marine ecology!

Let’s start at the difference between the two.  Marine biology is the study of life in the oceans.  The mention of marine biology invokes thoughts of dolphins, turtles, and maybe even some pretty coral-reef fish from Finding Nemo!  However, marine biology is a whole lot more than that, investigating all life in the ocean, from the phytoplankton (very small) to the blue whales (very big).  In short, marine biologists concentrate on studying their chosen species, answering questions like “What type of fish is that?”, “How do the bodies of whales cope with extreme depths?”, and “How do sharks sense their environment?”.  All in all, some pretty cool stuff in my opinion!

So what makes us fully fledged marine ecologist different from our biologist counterparts?  Well, I think that marine ecology is even cooler than marine biology because as marine ecologists we link what we know about the biology of a given species with other plants/animals and the environment as well.  This allows questions to be explored like :”Why do ecosystems that are so depleted in nutrients (like the Great Barrier Reef) have such high biodiversity and productivity?”, “What will happen to the local seagrass and fish population if we build a new jetty here?”, and “How does the presence of keystone predators (like sharks) effect not only turtle and dugong numbers, but the type of plants we see on the seafloor?”.  Nature is extremely complex, and I believe that we can only  gain a limited understanding of how nature works by simply looking at individual species in isolation.  This is where marine ecology comes in….we attempt to understand how species interact with one another and their environment (things like temperature, nutrient/food availability, light……even human-related disturbances).  When we consider that we live in a world where climatic conditions are changing at an unprecedented rate, we need marine ecology to help make predictions about how marine species will respond to such environmental changes, and how best to mitigate against any potential losses.

If we were splitting hairs, ecology is technically a form of biology, but I felt the need to write this post given how passionately I see some researchers stating that they are in one camp or another. Most importantly, we need to have marine biologists and ecologists to help us understand marine organisms and how they interact with the environment and each other.  But as an ecologist (albeit a biased one!) what gets me excited isn’t just finding out how the amazing plants and animals we find in the ocean work, but how they interact with each other and their environment, explaining why we see certain species in some places and not others!

So hopefully this little rant has shed some light on the importance of us marine ecologists!  Though I’m still not holding my breath for any school kids to profess a desire to become a marine ecologists any time soon!