Return of the natives
Oysters and oyster restoration projects are in the news, says Nicki Holmyard.
Wilder Humber, an ambitious five-year conservation programme to restore marine habitats and species throughout the Humber estuary, will see more than £2.5m invested to enable the planting of saltmarsh and seagrass to provide nutrient-rich habitats ideal for wading birds, plus the introduction of half a million native oysters (Ostrea edulis) to create a biogenic reef.
The project is a partnership between Lincolnshire Wildlife Trust, Yorkshire Wildlife Trust, and international green energy leader Ørsted.
According to Wilder Humber, 95% of native oyster reefs have disappeared from the estuary since the early 1900s, due to overfishing, poor water quality and disease. Records suggest that one historic oyster reef spanned over 300 acres, but today, native oysters are fragmented and isolated which hinders their natural recovery.
Spat on shell
The native oyster is known as a particularly vulnerable species. It is characterised by a slow growth rate and sporadic recruitment success, resulting in a large variation in the number of oysters surviving to maturity year to year.
It is hoped that by creating a reef through the introduction of native oyster larvae, the restoration project will provide a critical habitat for commercial fish species, protection from coastal erosion, a reduction in nitrogen levels, and an overall improvement of the water quality in the estuary through the filtering action of the animals.
Oysters are being provided by the Oyster Restoration Company, which will trial a remote setting method for the first time on a restoration project in the UK, in collaboration with The Nature Conservancy. Remote setting is a technique for setting oyster spat from larvae in the field, rather than placing juvenile and adult oysters directly onto the seabed. It is common practice in commercial Pacific oyster Magallana gigas hatcheries.
Natural oyster spat settlement on shell
At the company’s hatchery in Aultbea, Scotland, adult oysters will be induced to spawn, resulting in the production of millions of larvae. The next step is to transport the larvae to Spurn Point National Nature Reserve in Yorkshire, where they will be put into tanks filled with scallop shells. Over three days, the larvae will undergo metamorphosis and attach themselves permanently to the shells.
The oysters will then be monitored at a nursery until they are ready to be released into the Humber estuary to grow into adult oysters.
It is anticipated that if successful, this project could point the way for future native oyster restoration efforts in the UK and Europe.
“This innovative approach allows us to produce oyster larvae closer to their eventual home, minimising stress and improving survival rates,” Dr Nik Sachlikidis, CEO of The Oyster Restoration Company, explains.
Dr Nik Sachlikidis
Oyster restoration in Essex
As oyster restoration projects gather momentum across the globe, there is need for a greater volume of cultch, the material laid down for oyster spat to settle onto. Lack of availability of suitable seabed substrate is one of the biggest barriers to oyster restoration and holds back the UK’s capability to build new oyster reefs.
Shells are the ideal substrate, whether scallops or oysters, but unfortunately, a great deal of the most suitable material has been lost from the marine environment. However, the Blue Marine Foundation (also known as “Blue Marine”) has just set up a “Shell to Shore” circular oyster recycling scheme that aims to address this challenge.
Shell to Shore’s solution is to collect waste oyster shells from restaurants in London and make them available for use as cultch to native oyster restoration projects, initially in Essex, then to others in the wider UK. A secondary benefit of this project is that it will reduce the amount of shell waste going needlessly to landfill.
The self-funding project will be trialled this autumn with seafood restaurants in London. This follows a scoping study to determine project feasibility, restaurant interest and likely shell volumes. Matt Uttley, Blue Marine’s Restoration Project Manager, says that responses have been “extremely positive.”
Barge loaded with scallop shells
Seafood wholesaler Wright Brothers, which supplies more than 200 restaurants in London, will arrange to supply the oysters and uplift the shells, which restaurants will collect in sealable barrels.
Once full, the barrels will be transported to Wright Brothers’ holding facility at Billingsgate Market, for onward transport to Essex Native Oyster Restoration Initiative (ENORI), in conjunction with Essex Wildlife Trust.
“To prevent any risk of transferring a disease or invasive species back into the marine environment, the shells have to be weathered in the open air for a minimum of six months and ideally 12,” Uttley advises.
This practice has been used by ENORI since 2019, using shells purchased from large scale food processors. The move to using shells recycled from restaurants will significantly reduce the cost of the restoration project.
Shell recycling initiatives are commonplace in the USA and Australia, in, for example, the Billion Oyster Project. Shell to Shore has borrowed its protocol for curing the oysters, which so far, has ensured that all bacteria and non-native species are eliminated.
