The Plight of British Oyster Beds
Ben - Also this week, a conference at St Catharine's College, here in Cambridge, hoped to shed some light on the plight of British oyster beds. Despite being a long way from the coast, oysters were once an important trade in Cambridge, especially at the Stourbridge Fair - dredging the river Cam turns up lots of old oyster shells, worn smooth by the passage of time and water. But as well as an important commercial species, oysters played an important ecological role. To find out more about British oysters, I met Dr Philine zu Ermgassen on the banks of the Cam...
Philine - Native oysters used to be a really dominant ecosystem in coastal waters all around the temperate climate of the world actually, so in the US and around Europe. But in the mid-1800s, they suffered enormous fishing and enormous over exploitation just through huge demands and the increase in technology associated with that fishery. So they went through a huge population crash. They're just a fraction of their former populations and fundamentally, that habitat has disappeared for many of our coasts.
Ben - What are the threats that the oyster beds are facing? Is it purely over fishing or are there invasive species, disease, those sorts of problems as well?
Philine - The beds have suffered from over exploitation, but the peak exploitation was really towards the end of the 1800s. Since then, they've never really recovered and that's as a result of numerous factors including invasive species, the introduction of a disease in the '80s which really has a high mortality on the native beds, as well as pollution.
It's clear, we know now by looking at the oysters, that they provide a whole range of services which we definitely aren't getting anymore. Things like water filtration, they are filter feeders, so they clear the water column, making the water more transparent which is great for bottom rooting vegetation. They also help denitrify the water by concentrating these sediments full of nitrates which then bacteria work on to convert those nitrates that are very active biologically to nitrogen which is inert and can escape into the atmosphere. They also create fantastic structure which fish love as a habitat, particularly when they're small, they can hide between the oysters and suffer from a lower rate of predation as a result.
Ben - So, what would a typical healthy oyster bed look like?
Philine - There are very few examples remaining, but a typical healthy oyster bed would be made up predominantly of oysters. They'd be lying on the dead shells from previous generations of oysters, and they'd be at a relatively high density - probably, over 50 oysters per metre squared.
Ben - And what are the oyster beds that we do see now? What do they look like?
Philine - The oyster beds that we see today are defined by OSPAR, which is an international convention, as being more than 5 oysters per metre squared and they are really not habitat building. When we do find them they tend to be individuals scattered across the ground. They're not really building any habitat whatsoever anymore. They're really sitting on the sediments.
Ben - What do we think might be the impact if we do actually lose these oyster beds completely?
Philine - Again, we don't really know because we don't have very good baseline data and there aren't many good examples out there. What we do know is they have been lost completely from the Wadden Sea in the Netherlands and associated with that loss of habitat, there has been a loss of several associated species. It's clear that if we get these habitats back, we really hope that we can start to see a bolster of the populations that were previously associated with them. As yet, we can identify those species, we need a bit more science.
Ben - What now do we think we can start doing to try and get back to that position and to give ourselves healthy oyster beds again?
Philine - Oyster restoration has been really successful in the United States. They've invested a lot of money into restoration and they have huge public support for putting reefs back in water where they previously were found and now are non-existent. It's huge investment, but also, the public have really got behind it. We're not really seeing that yet in the United Kingdom. It would be great to see more support for the native oyster. Hopefully, as people realise the real value of the habitat that we've lost, we'll begin to see that motivation reappear in our communities. But certainly, in coastal communities still today, there is a great love of the oyster. There's a lot of cultural value associated with having that fishery and with knowing they're out there providing all these services.
Ben - What's going to be the next stage? How do we actually take this forward to come up with a more comprehensive, and a more joined up plan to make sure that we can protect these environments?
Philine - At the moment, really the key players in oyster restoration are the fishermen themselves. The fishermen have a great understanding of this habitat and of the species, and a fantastic cultural connection with them, and they're really the best advocates for restoration that we have. They're really pushing for restoration in the United Kingdom primarily so they can restart an active fishery on the basis of a native oyster and not just the non-native. I think that's definitely the place to start. Ideally, we'd love to see that grow into habitat restoration where restoration is taken purely for the habitat's sake and for all those services.
Ben - Does this mean that as a consumer, we should be asking for English oysters in order to encourage those fishermen to make sure they bring us the right things?
Philine - Absolutely. We should be eating more native oysters. It is a big concern that if we start to produce more, the culture associated with eating oysters more commonly has declined and that there won't be a demand. We'd love to be able to support our local fishermen in investing in this restoration to produce more native oysters.