Category Archives: Interesting new research!

A place to plug any interesting new scientific research I found out there (mainly marine ecology related)…as well as my own articles!

Shark Bay: a pristine template for marine ecosystems worldwide

Here in Western Australia, we are lucky to be in the global centre of seagrass diversity.  As such, we have a coastline dominated by many different species of seagrasses – from large, temperate seagrasses like Posidonia australis to small, tropical species like Halodule uninervis. Seagrasses form the foundation of coastal ecosystems, and support much of the diverse marine animal life we also have off the coast of WA.

In Western Australia, Shark Bay is the epicentre of seagrass diversity.  In fact, Shark Bay contains 12 off the 65 (ish!) species of seagrasses found globally, and some locations have as many as nine different species growing side by side!  Pretty impressive stuff.  Some of the smaller tropical seagrasses are eaten by critically-endangered megagrazers like turtles and dugongs; amazingly 1 in every 8 dugongs in the world lives in Shark Bay!  And the seagrasses of Shark Bay also indirectly support an amazing food web that includes dolphins, sea snakes, and tiger sharks!  Again, pretty impressive!  On top of all this, the seagrasses of Shark Bay also give provide more unique benefits to the ecosystem.  For example, the presence of Amphibolis antarctica Posidonia australis (the two big seagrasses in Shark Bay that cover a large area) increase sedimentation rates, and have led to the build up of shallow areas across the middle of Shark Bay called the Faure Sill.  The Faure Sill restricts water circulation in Shark Bay and contributes to the really strong salinity gradient we see in the Bay, which reaches up to 65 parts per thousand in Hamelin Pool – that’s twice as salty as normal seawater.  This hypersalinity has allowed stromatolites to flourish in the southern reaches of Shark Bay, Stromatolites are really important as they provide an excellent example of Earth’s early organisms were like, and contribute to the World Heritage Status of the Bay.  But without the seagrasses we may not even have had the stromatolites in Shark Bay in the first place!

Posidonia australis, commonly known as strapweed, is an important seagrass species found in Shark Bay and along much of the temperate Australian coastline.

Posidonia australis, commonly known as strapweed, is an important seagrass species found in Shark Bay and along much of the temperate Australian coastline.

Shark Bay is also extremely important in terms of restoration of other globally important marine embayments.  Shark Bay is fortunate enough to be relatively isolated from areas of high human population densities.  As a result, there has been little human influence on Shark Bay, and we can consider it to be a relatively pristine ecosystem.  However, other coastal ecosystems around the world haven’t been so lucky, and there is a long history of degradation of these systems due to human activities such as pollution, coastal development and pollution.    This degradation has resulted in distinct changes to the ecology of many organisms living in these ecosystems, leading to public calls for restoration of the systems.  However, there is often a lack of data before human impacts, leading to the questions ‘How did this ecosystem function before human disturbance?’ and ‘What aims should we put in place for restoration of the ecosystem?’.  This is where Shark Bay comes in; we can learn lots about what impacted ecosystems should be like from pristine ecosystems, especially in terms of interactions between species.

 

Shark Bay World Heritage Site, Stromatolites, microbial

Stromatolites may not look like more than rocks, but they are really important as they show us what early life on Earth was like! Shark Bay has some of the most extensive stromatolite communities, contributing to it’s World Heritage Status.

I was recently part of a collaborative project involving UWA and Florida International University that investigated the similarities and differences between Shark Bay and Florida Bay.  This formed the introductory article for a special issue in the journal Marine and Freshwater Research exploring sub-tropical marine embayments.  Despite the two Bays sharing many similarities, far more research has been conducted in Florida Bay, primarily due to the close proximity of the Bay to areas of high human populations.  Degradation of Florida Bay has been recognised in many different aspects of the ecosystem – from seagrasses to fish populations.  There are numerous restoration and monitoring projects occurring in Florida Bay, but the previous questions still arise – what should these projects aim to acheive.  We conclude that using Shark Bay can be used as a template for the types of function a healthy ecosystem would display, we can make more informed management decisions for Florida Bay.  This principle could also be applied to other degraded, sub-tropical embayments worldwide.  Collaborations between different research institutions in different ecosystems should increase scientific knowledge in pristine ecosystems, while leading to more informed management policies in degraded ecosystems!

Admittedly, I have lots of interest in Shark Bay itself (the bulk of my research for my PhD is centred in Shark Bay!), but hopefully this little post will allow people to see the local, regional, national, and international importance of this iconic, World Heritage Site!

Bamboo shark, strapweed, Shark Bay

Seagrasses in Shark Bay support a huge variety of animals! Here, a bamboo shark chills out in a Posidonia australis patch. I wonder if the starfish is happy about that!

ResearchBlogging.org
Kendrick, G.A., Fourqurean, J.W., Fraser, M.W., Heithaus, M.R., Jackson, G., Friedman, K., & Hallac, D. (2012). Science behind management of Shark Bay and Florida Bay, two P-limited subtropical systems with different climatology and human pressures Marine and Freshwater Research, 63, 941-951 DOI: 10.1071/MF12280

 

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Impacts of climate change on marine communities, seagrass dieback, and a trip to the Abrolhos Islands!

You may have noticed a lack of posts over the last few weeks.  No holiday for me though, here’s a quick taste of some of the other stuff I’ve been up to!

Impact of climate change on marine coastal ecosystems – A masterclass with Nuria Marbá
I was lucky enough to be invited along to present some research at a masterclass at the Institute of Advanced Studies led by Nuria Marbá in late March.  Nuria is a highly respected marine ecologist, and is mainly focussing on researching how coastal communities will respond to climate related stressors such as increased sea surface temperature.  Nuria gave a fantastic talk on the responses of a variety of different coastal ecosystems to projected future warming; from seagrass meadows in the Mediterranean to seaweed communities off the coast of Greenland.   In particular, the seagrass Posidonia oceanica – the real foundation species of the Mediterranean Sea – is at real risk from a combination of increased temperatures and future human activity.  P. oceanica has historically been able to resist disturbance events through extremely long life spans – a study led by Sophie Arnaud-Hound in 2012 suggest that some clones are thousands of years old!!!  However, this long life span is coupled with extremely slow recovery, and it is the really fast rate of expected change in temperature that is expected to cause the P. oceanica meadows to really struggle.  Above average temperatures in the Mediterranean in the last decade has already resulted in significant shoot mortality (Marba and Duarte 2010 Global Change Biology), and the predictions for seagrass response to future warming events look even scarier – with the present consensus being a “functional extinction of P. oceanica meadows by the middle of the century (2049±10), even under relatively mild greenhouse-emissions scenario” (Jorda et al. 2012 Nature Climate Change).  This is all pretty sobering stuff considering that P. oceanica forms the basis of key ecosystems in the Mediterranean Sea.

Closer to home, I presented some initial research that was conducted looking at the effect of the 2011 Marine Heatwave on seagrass populations in Shark Bay.  We travelled up to Shark Bay in March 2011 (right in the middle of the heatwave) as part of a separate research project, and noticed two striking features – water temperatures were far higher than normal, and the dominant seagrass Amphibolis antarctica (wire weed) had experienced severe defoliation (leaf loss) in certain parts of Shark Bay.  Closer analysis showed that the areas worst affected were adjacent to the recently flooded Wooramel River, so we hypothesis that a combination of elevated temperatures and decreased light availability may be leading to the loss of leaves.  Effectively, we believe that the increased temperature increases respiratory demand (the seagrasses get ‘hungrier’ for light) whilst the decreased light availability stops that demand being met.  We are re-visiting previous study sites where defoliation was noticed in an attempt to measure the recovery of the seagrasses; so I’ll keep you posted!

Defoliation in Shark Bay seagrass meadows

A healthy Amphibolis antarctica meadow (left) and a defoliated meadow in Shark Bay (right). We believe a combination of low light availability and elevated tempertaures has led to this loss of leaf material.

Other workshop presentations included a discussion on the impacts of the same marine heatwave on marine communities (in particular, macro algae) up and down the West Australian coastline by Thomas Wernberg, carbon sequestration impliactions from Oscar Serrano-Gras, and a discussion of the effects of warming on feedback in algal assemblages from Scott Bennett.  All in all, a fantastic workshop that will hopefully have positive benefits for the management of marine communities in the face of continued warming of our oceans.

A trip to the Houtmans Abrolhos!
For one week at the start of April I was lucky enough to help out Luke Thomas with his research into coral resilience at the beautiful Houtman Abrolhos.  The Houtman Abrolhos is a chain of small islands located 80km off the coast of Geraldton, Western Australia.  They are really special as they are the highest latitude true coral reef in the Southern Hemisphere.  As such, they may represent an important site that could potentially act as a refuge or a stepping stone for some coral species to move south as temperatures increase.

Acropora research at the Abrolhos Islands

Luke taking samples to investigate coral resilience at the Houtman Abrolhos.

Luke is trying to figure out the genetic connectivity of the corals in the Houtman Abrolhos with those in other locations along the West Australian coast, such as those found in Shark Bay, Ningaloo Reef, and Cygnet Bay.  This will help to determine the resilience of the coral reef communities in the Houtman Abrolhos to future changes in climate (Luke explains things much better than I do here!).  We also carried out some ecological experiments on kelp beds at the same time, so it was a full week of research!  But luckily the weather held up for us and we had some stunning dives – hopefully I’ll be able to post some more photos at a later date!

Kelp research at the Abrolhos Islands

Some fantastic visibility led to some incredible kelp dives (20m depth at this site!) Photo: Gary Kendrick

The inaugural Oceans Institute Student Conference
March also seen a landmark for the UWA Oceans Institute – the first student conference was held at the University Club at UWA.  There were a huge range of talks that showed the breadth of research at the university – everything from tracking marine plastics to studying the biology of pteropods!  And even me trying to get everyone excited about phosphorus cycling in seagrass sediments (what’s more, I was awarded joint first place for the presentation, and won a return trip to Rottnest Island – fantastic!).  One of the highlights from the conference was a talk by renowned marine ecologist Callum Roberts about the pressures facing coral reef ecosystems over the next 100 years.  He was quick to emphasise that warming temperatures aren’t the only threat, with human impacts such as overfishing and pollution likely to lead to worsen negative impacts on these reefs.  Sobering stuff.  On a brighter note, the day as a whole went well, and I think that the 2013 OI student conference will set the benchmark for many more successful conferences in years to come!  Big thanks to Liza, Eric, Renee and the rest of the organising committee!

‘Worldwide diebacks of seagrass ecosystems’: A seminar from Ole PedersenI also had the pleasure of heading along to a seminar from Ole Pedersen; a 2013 Professor-at-Large at UWA.  Ole is one of the authorities in the ecophysiology of aquatic plants (including seagrasses!) and is primarily based at the University of Copenhagen, but is over for a two week stint to do some work in Western Australia!  Ole’s seminar focussed on two potential causes of dieback of seagrass – hypoxia (lack of oxygen) and sulphide intrusion (effectively poisoning!).  Ole has played a leading role in the creation of microsensors that can be used to measure oxygen and sulphide concentrations in the field, and his research indicates the both hypoxia and sulphide intrusion could lead to further loss of seagrass communities as ocean temperatures rise!  I’m lucky enough to be helping Ole and Jens Borum (also visiting from the University of Copenhagen) out with some of their experiments into the potential responses of West Australian seagrass species to changing concentrations of carbon dioxide in the water column, so I should be able to also keep you posted on that research!

As you can see, a busy few weeks, which is why the blog has taken a bit of a back seat!  Rest assured I hope to blog more over the next few weeks!

Marbá, N., & Duarte, C. (2009). Mediterranean warming triggers seagrass (Posidonia oceanica) shoot mortality Global Change Biology, 16 (8), 2366-2375 DOI: 10.1111/j.1365-2486.2009.02130.x

Jordà, G., Marbà, N., & Duarte, C. (2012). Mediterranean seagrass vulnerable to regional climate warming Nature Climate Change, 2 (11), 821-824 DOI: 10.1038/nclimate1533

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

Biotic dispersal in seagrass seeds…..cool new paper!

Just came across a great wee paper by researchers at the Virginia Institute of Marine Science, examining dispersal of eelgrass (Zostera marina) seeds through biotic mechanisms.  Basically, they found that the seeds of this seagrass species can actually pass through the guts of marine animals like fish and turtles and still be viable to germinate, much like happens with many terrestrial plant species (think of many of the fruits that you eat!).   Another reminder of the similarities between seagrasses and terrestrial angiosperms!

Now you may be thinking…so why is this important?  Well, it turns out that from an ecological point of view this is exceptionally important, as it may allow the seagrass seeds  to travel to (and eventually colonise) otherwise bare areas that would be too far away for seeds to reach through normal dispersal mechanisms (such as transport with water currents).  To get a more detailed overview of dispersal in seagrasses as a whole, there is a great paper published in Bioscience (Robert Orth is a co-author on this paper as well, as are a few people from my research group).  This paper comes to the conclusion that dispersal of seagrass seeds over long distances (10s -100s km) through mechanisms like biotic dispersal is extremely important to the maintenance of seagrass populations!

All in all some really cool stuff that’s helping shape the way we monitor and conserve seagrass meadows, which form the basis of coastal ecosystems in many parts of the world.