Seaweeds may not be the most glamorous of sea creatures, but they’re AMONG the most important, providing critical food and habitat that supports hundreds of species. Just like trees on the land, seaweeds form vast underwater forests that underpin coastal food webs, all while quietly capturing atmospheric carbon and producing precious oxygen.

Alarmingly, temperate seaweed forests are in decline, due to multiple human activities. This is bad news for anyone who enjoys eating seafood, diving or fishing, because if seaweed forests disappear, all the critters that depend on them will disappear too and we’ll have no crays or abalone to see, catch or eat.

‘Crayweed’ forms dense forests on shallow reefs all the way from Port Macquarie to Tasmania. Crayweed (scientific name Phyllospora comosa) used to also be very abundant along the Sydney coastline, but sometime during the 1980s it disappeared completely from the metropolitan area between Palm Beach and Cronulla. The high volumes of poorly treated sewage that were pumped directly onto Sydney’s beaches and bays before the 1990s likely caused this decline. The problem is that although water quality in Sydney has improved dramatically since the establishment of deep ocean sewage outfalls, the crayweed forests have not returned. 

Crayweed provides food and habitat to a huge diversity of fish and invertebrates, including economically important abalone and crayfish. Other species of seaweed do not play the same role in Sydney’s marine environment, so losing crayweed is bad news for our local marine biodiversity.

Scientists at OPERATION CRAYWEED have already developed a successful method to create crayweed forests on reefs where they were once dominant, by transplanting healthy, fertile adults from existing populations and attaching them to deforested rocks using BIODEGRADABLE mesh drilled into the bottom. There, they survive, they thrive and they start having sex – a lot of sex. 

Crayweed can either be male or female and their sexually produced babies attach permanently to the reef, forming the basis of a new, self-sustaining population, which expands from the initially restored patch. We now find adult crayweed (offspring from the original crayweed restoration experiment) hundreds of metres from the original patch

So by creating patches of transplanted crayweed onto a reef, we can, in the long term, restore forests of this essential species in an entire site.

The idea here, of course, is that by restorating crayweed we’re also restoring its associated community, and thereby increasing the chances of finding crayfish, abalone and a huge diversity of other fish and invertebrates at restored sites, which is good news for snorkelers, fishers, beach goers and seafood lovers.

We are very grateful to the NSW Environmental Trust and the Recreational Fishing Trust , who funded the research that led to the development of these restoration methods.

Crayweed (Phyllospora comosa) is a big brown species (in the group Fucales) that used to dominate the Sydney coastline. The loss of crayweed across 70 km of its range went unnoticed and unreported in the scientific literature until 2008, when our team (Coleman et al. 2008) published an article describing a conspicuous gap in the distribution of crayweed in south-eastern Australia, matching the extent of the Sydney metropolitan area.

Our research has shown that crayweed supports unique biodiversity, including commercially important species like lobster and abalone (Marzinelli et al. 2014), specific assemblages of epifauna (Marzinelli et al. 2015) and microbial communities (Campbell et al. 2015) that are not associated with other co-occurring species of macroalgae. It also contributes to detritus in soft sediment habitats (Bishop et al. 2010), which underpins food webs of key fish species including mulloway and bream.

The local disappearance of crayweed from the most urbanised stretch of coastline on the Australian continent was linked to the high volumes of poorly treated sewage that used to flow onto Sydney’s shores before the construction of deep ocean outfalls in the 1990s. These outfalls and improvements in wastewater treatment practises have vastly increased water quality around Sydney since the 1980s (Scanes & Philip, 1995) but despite this, crayweed has failed to recover.

In our initial pilot experiments, we tested the hypothesis that today’s water quality along Sydney’s coastline is suitable for the survival of crayweed transplants. We transplanted crayweed from extant populations to the north and south of Sydney, back onto Sydney reefs with suitable control treatments, and we found that the transplanted crayweed not only survived similarly well to those in natural populations, but they reproduced more and had more babies (Campbell et al. 2014). Moreover, by restoring crayweed we also restored unique creatures associated with it, which are key components of biodiversity (Marzinelli et al. 2015).

Thus, by restoring seaweed populations, we have the potential to enhance coastal biodiversity, improving the ecological and economical value of marine environments around Sydney.

•  Crayweed = “Phyllospora comosa” = “Phyllospora” = “P. comosa”

• Crayweed was once dominant on reefs in Sydney, but disappeared completely from the coastline adjacent to the metropolitan area during the late 1970s and early 1980s (Coleman et al. 2008).

• Its disappearance coincided with high volumes of poorly treated sewage waste that was (until the late 1980s and early 1990s) released directly onto Sydney’s beaches and bays (Coleman et al. 2008).

•  Water quality has improved dramatically since that time, due largely to the construction of deep water sewage outfalls (Scanes & Phillip 1995; Sydney Water Report 2007), but crayweed has failed to recover in Sydney (Coleman et al. 2008).

• Crayweed supports a unique component of coastal biodiversity, which is not supported by any other extant seaweed species. Therefore, once it’s lost from an ecosystem, many other organisms and ecosystem services are also lost.

• Crayweed supports much higher abundances of abalone (7-10 times) than other seaweed species in the region (e.g. Ecklonia radiata) or barrens habitat (Marzinelli et al. 2014).

• Crayweed also contributes uniquely to detrital food webs (Bishop et al. 2010), which support recreationally and commercially important fish species, including Bream and Mulloway.

• Crayweed has a specific diversity of microbes on its surface, compared to other seaweed species (Campbell et al. 2015).

•  In our first attempt to restore this seaweed (initial experiment run between February 2011 – May 2011 and repeat experiment set-up in August 2011), survival rates of transplanted crayweed were similar to those in undisturbed, remnant populations (~70%; Campbell et al. 2014).

• Rates of reproduction and the resulting numbers of babies (“recruits”) was very high – around 100/0.1 m2 (ten times higher), 6 and 12 months after transplantation (Campbell et al. 2014).

• By late 2015, none of the originally transplanted, fertile adults remained (through natural loss and mortality.). However, many of the ‘babies’ produced by our transplants remain, firmly attached to the rock and have now become reproductive adults in their own right. We now find dozens of these new plants at our sites, tens or even  hundreds of metres from the originally restored patch, indicating that this method can successfully restore self-sustaining populations of crayweed at places where it was once dominant but has been missing for decades.