IAP-24-011

Habitat restoration planning: Investigating the synergism between biochemical and acoustic cues for successful settlement of native European oysters

Once widespread and constituting an important fishery to local communities, the native flat oyster, Ostrea edulis, is now almost entirely absent from Scottish waters1. Flat oyster reefs support biodiversity, maintain environmental resilience, through wave absorption and sediment stabilisation, and filter water to improve its quality2,3. The re-establishment of self-sustaining native oyster populations is crucial in promoting healthy, productive and resilient coastal habitats and associated societal benefits4. There is currently an increasing number of restoration initiatives facilitated by local coastal communities (e.g. kilchoanestate.co.uk, Loch Gair, Seawilding) as well as national organisations (e.g. nativeoysternetwork.org, rewildingbritain.org.uk, Restoration Forth). However, the success of these efforts is currently limited by lack of research on the suitability of habitats for restoration and the fact that the Scottish coastline is characterised by a uniquely complex geomorphology, environmental variation and a wide range of substrates.
A wealth of information exists on the optimal environmental conditions (e.g. salinity and temperature) for flat oyster fitness and larvae settlement (reviewed in https://www.marlin.ac.uk/species/detail/1146). Increasing research has shown that larvae settlement is more successful on existing flat oyster reefs rather than cultches of scallops or Pacific oysters as an alternative to spat collectors5. This is because of biochemical cues such as glycoprotein within the shells6 and acoustic cues produced by a healthy reef7,8. More recently microalgal biofilm formation on a hard substrate was found to be key for the successful settlement of larvae9. Therefore, it is crucial to establish the relative importance of these three processes in larval settlement (biofilm, acoustics, substrate biochemistry) as well as their synergistic effects in establishing optimal settlement conditions.
The importance of native European oyster reef restoration is recently translating into policy such as the newly proposed European Nature Restoration law that includes binding restoration targets for specific habitats including oyster reefs and directly connects to targets of the Marine Strategy Framework Directive for promoting good marine environmental status. This is largely driven by European larger scale research projects such as Haringvliet Dream Fund Project and REEFOREST. Despite the large number of restoration initiatives in the UK and Scotland in particular, research on habitat suitability of native oysters is very limited. This project aims to fill this gap in knowledge and inform restoration initiatives in the UK of suitable combination of acoustic, biochemical and substrate cues for implementing effective flat oyster restoration.
Specifically, the project aims to combine novel coastal mesocosm experiments with in situ experiments on habitat restoration sites to establish the optimal conditions for the settlement of viable populations of native oysters. Towards this aim, the project is focusing on addressing the following questions:
1) What is the role of biofilm and its specific microbiome composition in the establishment of larvae and juvenile flat oysters?
2) What is the role of nutrient inputs via freshwater inflows in supporting biofilm formation on candidate substrates for oyster settlement?
3) How does biofilm interact with acoustic cues from healthy reefs and biochemical cues from shells to enhance larvae oyster settlement and juvenile growth.

The project will comprise of both controlled experimentations in seminatural conditions of coastal mesocosm aquaria as well as in situ field monitoring and experimentations.
Objective 1: The candidate will be monitoring, with the help of staff, equipment and boat of our CASE partner (the Kilchoan Estate), the salinity gradients in front of each of three freshwater inflows (Figure 1). Monitoring will take place during a full annual cycle on a biweekly basis and will record salinity, temperature and sea water for phosphates, nitrites, water chlorophyl and eDNA analysis. Peak larval dispersal for our mesocosm and in situ experiments will be identified using eDNA qPCR analysis using primers specifically designed by our Aquatic Ecology lab for O. edulis. Nutrient concentrations that will be of relevance for our experiments will be established via monitoring of nutrient inflows in Loch Milfort in collaboration with the UK Center for Hydrology and Ecology (UKCEH).
Objective 2: Mesocosm experiments testing of interactions between biofilm, substrate and acoustic cues. Our coastal mesocosm aquaria have been developed to closely simulate conditions in the field and they comprise of aquaria tanks (300L) situated 50m from the coast and they are continuously fed with seawater including the plankton species present (unfiltered). This allows for the immediate inflow of oyster larvae into the experimental tanks testing different treatments. We will deploy experiments during high larval dispersal season (May to September) and we will test for successful larval settlement in experimental treatments crossing different substrates (e.g. oyster shells vs rocks) and different biofilm microbiomes developed due to different nutrient supplies (Figure 1). Experiments will be conducted in the presence and absence of live reef acoustic cues and the interactions of all relevant variables (acoustics, biofilm and substrate) will be statistically tested using appropriate statistical models.
Objective 3: In situ deployment of optimal conditions for larval settlement identified by the mesocosm experiments. The combination of treatment conditions that induces the maximum larval settlement will be deployed in the field using the suitable substrate and freshwater inflow of suitable nutrient inputs. Live reef acoustic cues will be applied using underwater speakers and associated equipment.

Year 1

Systematic literature review on coastal habitat restoration using oyster beds and will preparation of a review paper on the topic. Preparation of detailed plan on field monitoring and experiments.

Year 2

Monitoring of the field sites and carrying out the field monitoring (objective 1) and the mesocosm experiments (objective 2)

Year 3

Deploying the optimal settlement conditions in situ (objective 3). Data analysis, manuscript preparation, international scientific meeting attendance

Year 3.5

Completion of manuscripts and submission of thesis.

The scholar will be based within SBOHVM and the award-winning Boyd Orr Centre for Ecosystem and Population Health. The supervisory team will support the student, directly and through specific training, to learn skills in field monitoring (SS, AMG, MB), mesocosm experimentations (SS), oyster eDNA and biofilm metabarcoding (ML), acoustic techniques (AMG), and nutrient analysis and flow cytometry techniques for periphyton biofilm (MB). Transferable skills include scientific writing and communication, data analysis using R, Generalised Linear Models and multivariate statistics. As well as selecting from a variety of postgraduate courses for PhD students based on needs, in year 1, the student will receive training on systematic literature review. In year 2, the student will develop skills in on molecular analysis, integrating different datasets on metabarcoding and environmental variables. In year 3, the student will join retreat sessions on scientific writing, organised by the SBOHVM PhD cluster, to help with manuscript preparation. Through participation in Institute seminars and national and international conferences, she/he will also develop presentation and communication skills.