The importance of kelp forests
Kelp are big brown seaweeds that grow up from the seabed, forming graceful forests of waving blades that provide a protective habitat for vast numbers of marine species.
In Australia there are only four types of true kelp, but the terms ‘kelp’ or ‘kelp forests’ are also sometimes given to similar-looking large brown seaweeds which also form rich habitats.
“People call them kelp ‘forests’ because in some sense they’re the underwater trees,” says Professor Peter Steinberg, marine scientist at the University of New South Wales and one of the principal research scientists involved with Explore the Seafloor.
These forests are rich in ocean life – invertebrates ranging from worms to crabs to sea urchins to abalone can be found amongst the kelp. They also protect many fish species, such as little wrasses, blue groupers, blackfish and Port Jackson sharks. For some fish, the kelp forests are a nursery habitat while others go there to mate.
“You get cuttlefish that come into the kelp forests to breed and they’re actually remarkably brazen,” says Steinberg, “They’ll sit there and look at you and change colours.”
Kelp provide habitat for commercially important species, such as abalone and crayfish and also for some of the fish popular for recreational fishers, such as wrasses.
Even the kelp that is ripped from the ocean floor and tossed up on the beach after a big storm is important – both commercially and environmentally. Kelp harvested from beaches is used in fertilisers and personal care products – you probably use it every time you wash your hair. It’s also a major food source for beach and estuarine ecosystems.
“A lot of that kelp gets torn off in storms ends up in sandy bays and estuaries and it’s a major food source in some of those estuaries,” says Steinberg .
Kelp forests are also highly prized for their beauty. Most people prefer to dive over the biologically rich environment of a healthy kelp forest rather than over bare rock.
“The estimate of the economic value of kelp beds, Australia-wide, is in the billions of dollars,” says Steinberg.
Climate change and other threats
Like much of the natural world, kelp forests are under threat from a number of factors.
Some kelp forests are being decimated by the invasive sea urchin – Centrostephanus rodgersii.
They’re also being affected by pollution, nutrient overload and coastal development.
Adding to these impacts are the effects of climate change. Unfortunately, Australia’s kelp forests are literally in a global hot spot – parts of the oceans around southern Australia are warming at up to four times the global average.
Scientists aren’t sure how the kelp forests, which prefer cooler water, will respond to these changing ocean conditions.
Kelp forests could shift southwards or they could move into deeper waters as water temperature rises, though light levels at depth may become limiting for kelp photosynthesis.
“The hypothesis is that warming of the coast will either drive kelp further south or deeper,” says Steinberg.
While there is some evidence currently that kelp may be retracting towards the south pole there’s not enough data available on kelp populations to be entirely sure. This is why setting a baseline is vitally important.
“One of the challenging things about climate change research is that the timescale in which things happen is decades,” says Steinberg, “ We’re in the stage in the project where we’re setting the baseline for future work.”
In addition to the long term average changes to water temperature there’s also the potential impacts of extreme warming events – such as the warming event that occurred off the coast of Perth, WA in 2011.
This event saw water temperature warm by 2-4 degrees C for a couple of months as a result of change in oceanographic conditions. One of the brown seaweed species that forms seaweed beds off the coast retracted its distribution southwards as a result of the warming event. It hasn’t yet returned.
Phase shifts of this sort can happen in ecosystems. When it happens to kelp forests they tend to end up as barren or deforested areas where most of the biological structure has been lost.
“Mostly what you get is relatively bare rock or rock covered by small crusts of algae or turfing algae, which is a few centimetres high. So if you snorkel, you’ll see areas with lots of sea urchins and no kelp.”
It’s possible that kelp forests will respond to warming water by moving from shallower waters into deeper waters. Scientists aren’t currently sure of exactly how far down kelp can live – but the new data collected by AUVs (automated underwater vehicles) provides insight into a world that was previously impenetrable by scuba divers.
Managing the problem
Understanding the distribution of kelp beds around southern Australia is an important first step in managing the impacts of climate change.
However, climate change is not the only stressor that kelp beds are being exposed to – there are local events like fishing, coastal development and pollution.
“All those things interact,” says Steinberg, “so we need to understand multiple stressors in order to manage ecosystem impacts. “
Information is certainly important in making economic management decisions.
But there’s also the importance of maintaining kelp forests simply because they are a beautiful natural habitat that supports a huge variety of marine life.
“Do we care about the maintenance of the natural habitat?” asks Steinberg, “A lot of people do. I think it’s important to try to maintain the natural world.”
By Kylie Andrews