Underwater deforestation

26 05 2009
© C. Connell

© S. Connell

I’ve been meaning to blog on this for a while, but am only now getting around to it.

Now, it’s not bulldozers razing our underwater forests – it’s our own filth. Yes, we do indeed have underwater forests, and they are possibly the most important set of species from a biodiversity perspective in temperate coastal waters around the world. I’m talking about kelp. I’ve posted previously about the importance of kelp and how climate change poses a threat to these habitat-forming species that support a wealth of invertebrates and fish. In fact, kelp forests are analogous to coral reefs in the tropics for their role in supporting other biodiversity.

The paper I’m highlighting for the ConservationBytes.com Potential list is by a colleague of mine at the University of Adelaide, Associate Professor Sean Connell, and his collaborators entitled “Recovering a lost baseline: missing kelp forests from a metropolitan coast“. This paper is interesting, novel and applied for several reasons.

First, it sets out some convincing evidence that the Adelaide coastline has experienced a fairly hefty loss of canopy-forming kelp (mainly species like Ecklonia radiata and Cystophora spp.) since urbanisation (up to 70 % !). Now, this might not seem too surprising – we humans have a horrible track record for damaging, exploiting or maltreating biodiversity – but it’s actually a little unexpected given that Adelaide is one of Australia’s smaller major cities, and certainly a tiny city from a global perspective. There hasn’t been any real kelp harvesting around Adelaide, or coastal overfishing that could lead to trophic cascades causing loss through herbivory. Connell and colleagues pretty much are able to isolate the main culprits: sedimentation and nutrient loading (eutrophication) from urban run-off.

Second, one might expect this to be strange because other places around the world don’t have the same kind of response. The paper points out that in the coastal waters of South Australia, the normal situation is characterised by low nutrient concentrations in the water (what we term ‘oligotrophic’) compared to other places like New South Wales. Thus, when you add even a little bit extra to a system not used to it, these losses of canopy-forming kelp ensue. So understanding the underlying context of an ecosystem will tell you how much it can be stressed before all hell breaks loose.

Finally, the paper makes some very strong arguments for why good marine data are required to make long-term plans for conservation – there simply isn’t enough investment in basic marine research to ensure that we can plan responsibly for the future (see also previous post on this topic).

A great paper that uses a combination of biogeography, time series and chemistry to inform about a major marine conservation problem.

CJA Bradshaw

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