New Orleans
Oyster restoration and chance encounters at New Orleans conference
THE recent triennial meeting held in New Orleans was a coalition of the National Shellfisheries Association (NSA), the World Aquaculture Society, and the fish culture section of the American Fisheries Society and the National Aquaculture Association. The first person I met on arrival at the conference venue was Sandra Shumway, the main organiser of the event, and I remarked to her that I was surprised how cold it was in New Orleans, where the Scottish winter garb I had travelled in was just perfect.
‘You think this is cold?’ she replied. ‘When I left home this morning it was 15 degrees.’
That sounded quite balmy to me for a split second – then it served as a reminder to get back to thinking in Fahrenheit in the US.
I was glad I had arrived early. It helped with the jet lag, but in such a huge programme, with 15 parallel sessions, one had to plan ahead carefully.
With sessions on mussels running concurrently with those on oysters, and mollusc health and disease sessions clashing with shellfish restoration, it was not an easy choice, and some of the most interesting talks turned out to be chance encounters.
The session I had been invited to, and the reason for my attendance, Ostrea spp biology, ecology and physiology: is this genus a tractable prospect for restoration , was organised by Zoë Holbrook, PhD student at the University of Southampton.
Zoë’s attendance owed a great deal to her winning free registration while at the Montpellier EAS conference last October.
From this one piece of fortune she was invited by Jay Parsons, co-programme chair for Aquaculture 2019, to chair a session, and she organised quite a number of European Ostrea specialists to join the conference.
With aquaculture of the native European flat oyster established on both the east and west coasts of the US, there was the potential for useful discussion.
But the additional value of this group travelling to America was for the opportunity to hear at first-hand about a variety of oyster restoration projects in the States.
These mainly deal with restoration of their native species, Crassostrea virginica, which is now farmed increasingly. Certainly, the availability of oyster seed provided for restoration projects stimulated aquaculture of the species in some states, but hearing of the progress and benefits can only be helpful and encouraging for those working on O. edulis.
After an introductory talk at the session from me to argue the importance of re-establishing oyster reefs, which were probably all destroyed in the mid-19th century, it was interesting to hear the echoes in the talks from US speakers.
They still carry out the practices as described in the Royal Commission on Sea Fisheries of 1866 (my talk really delved into the history of oyster fisheries management in the British Isles), but they have some reefs to provide spat, and now know and understand that preserving these reefs is essential.
At the time of the Royal Commission, both the commissioners and the fishermen only knew that the oyster fisheries were in trouble.
But they did not connect that with the fact that deep banks of oysters had been discovered in the English Channel and on the east coast that they had systematically been harvesting (destroying) in the years leading up to the commission’s opening.
So, for the most part, UK and some mainland European restoration is working from a very much more impoverished starting point than the US.
Yet the talks in the session were optimistic and upbeat, with Joanne Preston on the establishment of the UK and Ireland oyster network, and Aad Smaal and Luca van Duren on two separate approaches in the Netherlands, where there is real progress to utilise protected areas around wind farms.
Similarly, different approaches were presented from the UK, with the PhD projects of Zoë Holbrook investigating performance of oysters growing in raised cages, and Luke Helmer of culturing broodstock in suspended cages, both in the Solent.
Not all of Europe presents bad news on the native oyster either. Sweden, as reported by Åsa Strand, in fact has comparatively healthy populations, possibly due to the fact that they have a total ban on dredging in inshore waters.
But, on the other hand, they have huge settlement of the non-native Crassostrea gigas that they cannot control, since dredging is not permitted in inshore waters!
Alison Debney reported on yet another approach, in which her project is working with fishermen in the West Mersea area in Essex with the aim of restoring ‘natural populations’ or ‘rewilding’ oyster habitats, and had succeeded in getting a 284km2 marine conservation zone or MPA to recover both
Microplastics featured heavily but, for once, there appeared to be a positive side”
native oysters and native oyster habitat.
While the positive side of all this was knowing that there is such a concerted effort underway in Europe towards the recovery of this important habitat forming species, there was less upbeat news from the other side of the world.
Zoë Hilton, from the Cawthron Institute in New Zealand, speaking of the NZ native, Ostrea chilensis, told a tale of woe.
This species is not nearly as fecund as other oysters, only producing 50k to 250k eggs, but also has the novel characteristic of its larvae settling almost immediately after release from the mother oyster. They get 98 per cent settlement within minutes.
There were parallels with the UK situation historically since they have also been under threat since the 1860s. The fishery, however, continues in the Foveaux Strait, albeit with larger dredges, and reefs have been substantially broken up.
The parasite, Bonamia exitiosa, has been a presence for some time but then Bonamia ostreae arrived in 2015 and all farms dealing with this species have been closed, with the aim of preserving the wild stock (and fishery).
This is a very difficult situation which has yet to be resolved but it very much highlights the real conundrums disease presents in restoration projects.
One of the chance encounters mentioned earlier, made possible in such a huge conference, was a session on interactions between aquatic animals and contaminants of emerging concern.
Microplastics featured heavily but, for once, there appeared to be a positive side. Microplastics are defined as being of size 5mm to 0.1μm.
Prof Evan Ward (University of Connecticut) said that for all the large amount of publicity, concentrations documented so far in animals are low to moderate, with bivalves having from 0-9 particles per individual.
Lugworm figures were 1-3/g, and for fish 0-10 particles/individual but this is expected to increase and there have been adverse effects found on feeding, digestion, energy reserves and cell biochemistry.
As part of their studies they had asked the question: are bivalves a good indicator species? On the face of it, being ubiquitous, sedentary, and interactive with their environment, they should provide a good baseline of environmental levels.
They investigated this and found that, in fact, the oyster was pretty good at not taking in the microparticles.
There was some superb video film of different size particles being transported across the gills, with different sizes going at dramatically different speeds and then being ejected in the pseudofaeces.
Not all particles were ejected this way, but a very high proportion were ejected from the body in less than three hours in the faeces- the larger the particles, the greater the speed of rejection.
In the case of microfibers, however, there was no trend in relation to size in either oysters or mussels but more than 50 per cent were rejected.
So the final results seem to be that very few microplastics are actually ingested into bivalves and, no, they are not a good indicator species for this purpose.
The overall tenor of the papers presented seems to be that the bivalve could protect itself pretty well from accumulating microplastics.
Ward concluded the final discussions by saying we are more likely to breathe in microplastics than eat them!