Catalina A Musrri from the University of Sydney and Georgina Wood from Flinders University discuss the importance of underwater rainforests and how to conserve them.
A version of this article was originally published by The Conversation (CC BY-ND 4.0)
Australia’s Great Southern Reef is not made of coral but of seaweed. The kelp forests on these reefs stretch more than 8,000km around southern Australia.
Among the swaying leaves live seadragons, rock lobsters, giant cuttlefish and southern blue devils. The ocean is home to more than 1,500 marine species and contributes billions to the economy each year.
But these amazing cold water forests are facing the threat of degradation. The oceans are getting warmer, pushing marine life out of their habitat. Much of this damage is caused by sudden ocean heat waves, when temperatures rise and remain high for a period of time. Heat waves have caused the decline of seaweed forests across the country.
To protect these underwater forests, we need to preserve their genetic diversity. We led the first attempt to cryopreserve (freeze and store reproductive material at very low temperatures) an important Australian seaweed, crayweed, and found that the concept shows promise, although techniques need to be perfected.
Why are seaweeds important?
Most of us encounter seaweed as a smelly mass that appears when walking along the beach. But underwater, these large algae (not plants) form beautiful forests that move in the water – some are 30 meters long.
Seaweed forests are among the most productive ecosystems on Earth. Like terrestrial forests, they provide habitat, shelter and food for many creatures. They support important fisheries such as lobster and abalone.
When local people are wiped out, they take something important – genetic diversity. Species with higher genetic diversity can better adapt to change. Some people will be able to tolerate heat better, for example. But when these populations disappear, their unique genes go with them.
In 2011, extreme ocean temperatures in western Australia led to two common types of seaweed losing an estimated 30pc to 65pc of their genetic diversity. This loss may mean negative results in response to increasing threats.
Think crayweed
Blue crayweed (Phyllospora comosa) once formed extensive underwater forests off the coast of Sydney. Many of them disappeared in the 1980s, probably due to sewage pollution. But the crayweed didn’t come back even after pollution levels dropped.
For the past 14 years, scientists and divers have been replanting these species around Sydney through Operation Crayweed. Their work has led to the return of livelihoods, including Australia’s first forest named after seaweed – the Yanggaa forest on Coogee Beach.
But the recovery may not be enough in a rapidly warming sea. Our research shows that different crayweed species have different genetic variants – and some individuals seem to be better equipped to tolerate the heat. It may make sense to plant bacteria (seaweed) for these people in vulnerable areas to increase their chances of survival.
For seed banks, biobanks and cryopreservation
For decades, thousands of land-based plant species have been conserved through genetic diversity in seed banks. The stored seed is dormant but still alive. If they are planted in the right place, they will grow.
Some types of kelp can also be kept alive in biobanks – not as seeds, but in microscopic form (gametophytes) that can be kept alive in laboratories for years. Current kelp collections support research, aquaculture and restoration programs around the world, including in Australia.
These banks are important. But they will not be enough. Most of the marine species that inhabit the Great Southern Reef are known as fucoids. Unlike true kelp, fucoids do not have this invisible life stage; they release sperm and eggs directly into the seawater where they fertilize and form bacteria. This makes species such as crayweed, bull kelp (Durvillaea potatorum), Cystophora sp again Scytothalia dorycarpa more challenging to save.
It is possible to bank species that rely on sexual reproduction, such as humans, cows, corals and fucoids. Assisted reproduction methods such as IVF rely on cryopreservation: keeping reproductive material, tissues or early life stages at very low temperatures (around -196°C) to keep them viable for future use.
Our latest study tested whether frozen crayweed sperm and bacteria are active after thawing. We found that the sperm did fine, but the bacteria didn’t (yet). Our ultimate goal is to develop proven methods that can work across a wide range of Australian seaweed species.
Conserving the genetic diversity of seaweed species can mean that these genes can be pulled for restoration. This buys valuable time and keeps the door open to new approaches such as assisted gene flow, where people from better-adapted populations are used to help the vulnerable cope with warmer climates.
Time for seaweed biobanks?
Australia already has an impressive collection of algal cultures and is a world leader in coral cryobanking.
However, it will take real work to develop ways to conserve forest-forming seaweed species that rely on sexual reproduction. We need to learn which populations contain the most unique or threatened genetic diversity, understand which are most vulnerable to climate change, and develop mitigation and recovery strategies.
The choice of which species and communities should be made together with indigenous custodians, governments, conservation organizations and local communities.
Cryobanking does not solve climate change or replace the need to protect the environment. It is a biodiversity insurance policy. Much has been lost. Preserving the remaining genetic diversity of our kelp forests may be critical to the survival of the Great Southern Reef.
By Catalina A Musrri and Georgina Wood
Catalina A Musrri from the University of Sydney has recently completed her PhD in marine vegetation restoration in the context of climate change. He is interested in the impacts of climate change and other environmental activities, such as pollution and overfishing, on coastal ecosystems.
Georgina Wood is an Australian Research Council Fellow at Flinders University and a research consultant at the University of Western Australia whose research focuses on adaptation to climate change, particularly the temperate kelp forest ecosystem..
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