Fisheries are a major contributor to the economies of Europe’s Member States and have a central role in societal wellbeing [1]. In the UK and Portugal, fisheries contributed £770 million (2012) and €250 million (2010) to gross domestic product (GDP), with landings continuing to increase year-on-year [2, 3]. Shellfish fisheries are an especially important subsector. For example, in the UK shellfisheries make the largest contribution (39%) of all fishing sectors [3] to GDP. Threats to the viability of this sector have the potential to have wide-ranging and catastrophic impacts to the economy and society [4].

 

The 2014 Marine Climate Change Impacts Partnership identified shellfish fisheries as especially vulnerable to climate change and ocean acidification (OA herein) and highlighted these relationships as a research priority [5]. In the United States, OA has decimated populations of the commercially important Olympia oyster [6, 7] placing the industry on the brink of collapse and may be an indication of what is to come in Europe. While such severe impacts have yet to be seen in Europe, identifying the mechanisms and extent to which OA could impact commercially valuable shellfish and the timescale for any impacts will play a crucial role in future industry and food security planning, and assessment of the sustainability of ecosystem services [4]. 

 

Impacts of climate change, such as increases in water temperature and OA can impact shellfish species in several ways, including reproductive success [e.g. fertilization 8], larval morphology [e.g. 9, 10] and juvenile growth [e.g. 6, 11]. Impacts can “carry-over” from one life-history stage to the next [6] and across generations [12] and may play an important role in the persistence of adults of shellfish species and the long-term viability of local and regional populations [13]. While “carry-over” effects of climate change can clearly impact individual life-history stages, how these impacts are manifested across all life-history stages and impact longer-term persistence remains unknown. 

 

The use of non-native species in commercial aquaculture has become a widespread practice in Europe and worldwide [14]. For example, the culture of reproductively sterile (triploid) Pacific oysters, Crassostrea gigas, has become widespread in France, the UK and Ireland in order to exploit commercially preferential characteristics such as faster growth and development. Despite control measures being implemented, wild (feral) populations have become established in many areas [e.g. 15, 16, 17], to the detriment of native communities in the form of loss of regional native biota [18-20] and leading to fundamental changes in ecosystem functioning [21-23]. Given that non-native and native shellfish species often occupy the same ecological niche (e.g. C. gigas and the European oyster, Ostrea edulis), climate change impacts affecting the performance (competitive ability) of native and non-native species may change the likelihood of invasion success in the future. 

In this proposal, the carry-over effects of climate change impacts (temperature and OA) on the growth, development and performance of three commercially important species in Europe, namely the Pacific oyster, Crassostrea gigas, the European oyster, Ostrea edulis, and the European clam Ruditapes decussatus will be assessed. The candidate will address 3 key questions: 

 

Q1). Test effect of ocean acidification and warming on: (1) shellfish larval growth, development time and mortality, and (2) post-settlement growth and mortality (carry-over effects from larval stages). Following aquaculture training from the supervisor at PU, the candidate will collect from the field and maintain adults of the 2 commercial oyster species in the lab and culture larvae of each species. Adults will be maintained in the existing ‘climate’ mesocosms at PU, with conditions reflective of current (prevailing) and predicted future temperature and pH conditions [24]. Future climate scenarios will include conditions predicted for 2050 and 2100. Changes in development time, hatching success, larval survival, feeding rate and settlement rates will be evaluated to test the effect of different conditions on each species.

 

Q2a). Current Climate: Recruitment success of habitat-forming and commercially important molluscs under competitive pressure. Using the larvae cultured under contemporary climate conditions from Q1, individuals will be established on recruitment plates at a range of settlement densities and in combination with other species. Settlement densities will be manipulated by way of removing individuals from plates [e.g. 25] to simulate changes in propagule pressure [26, 27]. Four settlement densities will be established: (i) ambient (maximum), (ii) 50% of ambient, (iii) 25% of ambient, and (iv) 0% settlement, and all combinations tested in an orthogonal design resulting in a total of 16* treatments (Fig. 1). Recruitment plates will be established in the lab under current climate conditions and in the field at multiple locations in areas where both species already occur. Plates will be photographed every two weeks and the size, density of living and dead recruits monitored over time (~6 months). Growth rates will be calculated using image analysis software (Image J) and survivorship in relation to recruit proximity to one another examined. 

 

Figure 1. Treatment and density combinations of two oyster species used in experiments. *Non-existent treatment shown (red box) for completeness. Species A = Crassostrea gigas, Species B = Ostrea edulis.

 

Q2b). Future Climate: Will high CO2-world scenarios alter the competitive performance of native and invasive species? The same design as outlined in Q2a will be used to test the effect of future climate scenarios on species performance, but using larvae cultured under future climate scenarios (see Q1). Recruitment plates in the lab will be maintained under future climate conditions, whereas field-based recruits will experience current climate conditions. As per Q2a, plates will be photographed every two weeks and the size, density of living and dead recruits monitored over time (~6 months). Growth rates will be calculated using image analysis software (Image J) and survivorship in relation to recruit proximity to one another examined. Results from Q2a and Q2b will be compared.

 

Q3). The use of seagrass natural stands as mitigators of OA effects on commercial shellfish. Most natural European clam and oyster beds occur in coastal lagoons or sheltered estuaries, whose shallow waters and intertidal areas are often dominated by seagrasses [28]. These plants structure the habitat and provide a number of ecosystem services, of which carbon sequestration is one of the most relevant [29]. It has been recently demonstrated that the seagrass photosynthetic metabolism has the capacity to modify the seawater pH within their canopy and adjacent areas [30]. It is therefore hypothesised that seagrasses may provide refugia for calcifiers like oysters and clams, by increasing pH and the calcium carbonate saturation state. In Ria Formosa, a mesotidal coastal lagoon in southern Portugal, intertidal and shallow subtidal seagrass meadows are often adjacent to commercial clam and oyster farms. Using a combination of field and manipulative mesocosms experiments, the candidate will evaluate the influence of seagrass metabolism in the pH and carbonate chemistry of adjacent clam and oyster beds and explore the ratios of biomass and areal extent of seagrass/bivalves to determine the area of seagrass required to mitigate and/or offset the effects of OA on the growth and calcification of given clam and oyster beds.

 

References:

 

 

 

Each question will form the basis of a data chapter in the PhD thesis. The candidate will structure their thesis around 3 scientific papers (the data chapters), with an introductory review section (with an aim for submission as a review paper) and a discussion section to give a closing coherent synthesis of the work outputs and suggestions for future work. The thesis will therefore go beyond the MARES objective of a single paper from this work. Target journals will include Nature Climate Change, Global Change Biology and Ecology.  

The student will attend at least 2 leading international conferences over the course of the project, specifically the International Temperature Reef Symposium (University of Florence, 2016) and the Ecological Society of America Annual Meeting (2017, USA, location yet to be announced) giving them and their work exposure to the international scientific community. 

This work will contribute to the burgeoning literature on climate change and ocean acidification [31, 32], and is of global relevance and concern. The research will show scientific leadership by demonstrating cutting-edge approaches that couple multiple life-history stages. The research will contribute to a global assessment of the generality of key ecological processes responsible for the structuring of marine communities.  

The collaboration between PU and UA supervisors will enable the candidate to benefit from their extensive experience in undertaking ecological experiments in the areas outlined in this proposal and existing collaborations. Further, the PhD project will have direct relevance to real world examples and case studies. For example, the outcomes are expected to provide a scientific basis for environmental policy and decision-making in relation to continued use of invasive species in aquaculture. The candidate will engage with relevant international and national management bodies (e.g. European Environment Agency; Cefas) following introductions by the supervisors. The outcomes are expected to support resource managers in the sustainable management of ecological resources and continued provision of ecosystem goods and services [33] e.g. providing guidance for good practice in the culture of commercial shellfish species (e.g. invasive species monitoring and control) supporting biodiversity protection.