Cromarty Seascape

The Native Oyster: A Species of Cultural & Ecological Significance

Densities of the native oysters were once so great that they formed large reefs along Europe’s coastlines. In Scotland, this common bivalve mollusc would have been an integral part of people’s diet. During the 18th century, it was estimated that the oyster reef at the Firth of Forth would produce around 30 millions oysters per year! As an important source of food, oysters were cultivated and fished for thousands of years with records going back to Roman times.

More than just being culturally significant, native oysters can be ecologically valuable when they exist in healthy numbers. Forming living ‘biogenic’ reefs, they provide food and shelter for other marine wildlife. Crevices in the reef make ideal spaces for other organisms such as fish to seek shelter and reproduce. Native oysters also act as biofilters helping to improve water clarity. They filter particles from the water column which assists important light-dependent species like seagrasses. In turn, seagrasses provide ecosystem services such as oxygen production and nutrient cycling. Furthermore, where native oyster populations bounce back, there could be a positive impact on local fisheries. As a habitat for fish and the species they feed on, oyster reefs are capable of creating a ‘spill-over’ effect that could see local economies and livelihoods benefit.

Our Nursery Proposal

Because of their clear benefits to the ecosystems in which they are supposed to be present, we are working to establish a native oyster nursery in the Cromarty Firth and explore whether they could be successfully reintroduced. However, the project is not without its challenges. There have been supply issues throughout the UK for young native oysters known as ‘seed’, and there are also diseases & invasive non-native species impacting the species that need to be considered with biosecurity measures put in place.

Knowledge Gaps Within the Project Area

Volunteer mapping studies undertaken by Moray Ocean Community in 2023 with our support have identified some intertidal seagrass beds in the Inner Moray Firth that have not been formally mapped for an extended period of time. From comparison between a survey carried out by Fox, Yost and Gilbert (1986) and our data, preliminary results show that there could have been losses in the past 37 years (see Figure 1). There has been limited survey work in the area since then, with the majority of publicly available records from 2008 or earlier.

Part of the challenge when it comes to promoting the recovery of seagrass meadows is that they suffer from cumulative impacts, and it can be difficult to identify why losses are happening where they occur. This is why having groups of people from our local area invested in and taking ownership of their local seagrasses is paramount, because there’s nothing quite like local knowledge! Connecting with other local people with various interests has been extremely helpful, particularly those like local shellfish farmers and others with family ties here spanning decades.

In 2024 alongside other sampling work, we are on a mission to identify and map seagrass meadows within approximately 1151 ha of potentially suitable intertidal habitat. To do this, we will be using a combination of ground truthing with drone mapping, and we are also exploring whether satellite data might come in useful. We plan to use this information to see whether it might be beneficial to reinforce the seagrass beds already present through active or passive restoration. Active being through planting, and passive being through the removal or reduction of pressures to promote recovery.

Evidence Sharing

Currently, there is a knowledge gap on native oysters and seagrasses in the project’s area. We intend to help address this by gathering data on species presence/absence, habitat mapping and other survey work. We share our findings directly with Scotland’s nature agency, NatureScot.

We thank Mossy Earth members and everyone else involved in the effort to turn the tide for this section of Scotland's coastline.