Monthly Archives: August 2013

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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