Bivalve shellfish aquaculture provides many benefits to society, beyond their traditional market value. This thesis reviews and collates the evidence and valuations available on the provisioning, regulating and cultural ecosystem services provided by bivalve aquaculture species. Then focuses on a UK spatial survey of the carbon (C), nitrogen (N), and phosphorus (P) removal potential of blue mussels (Mytilus edulis). This is supported by a study at two sites to examine temporal variation in C, N and P. Finally, a UK economic assessment of the mussel industry is carried out to look at the potential value of non-food ecosystem services.
Bivalves provide provisioning services such as meat, pearls and shell. Regulating services such as nutrient remediation, estimated to remove 49,000 tonnes of nitrogen and 6,000 tonnes of phosphorus globally. There is little evidence on the cultural services of bivalve aquaculture, but these are broad ranging, although difficult to quantify. Globally, non-food bivalve aquaculture services are worth $6.47 billion ($2.95 billion–9.99 billion) per annum. However, this is likely to be an underestimate of the true value of bivalve aquaculture due to knowledge gaps in the value for several key services.
There is a need to understand factors underlying spatial variation around UK. In this thesis, differences in carbon (C), nitrogen (N) and phosphorus (P) percentage content as well as the upscaled values of whole mussels are compared. Mussels were collected at sites around the UK which had a range of annual water temperatures and high and low catchment nutrient concentrations. CHN and P analysis showed that P in tissue had a significant negative relationship with mean annual seawater temperature for both rope and bottom cultured sites. Similarly, the percentage content of P in shell had a significant negative relationship with increasing salinity. Most notable was a significant difference between rope and bottom cultured mussels. Per tonne, rope culture removed significantly more C (77.52±3.65 kg), N (8.50±0.59 kg) and P (0.95±0.07 kg) than bottom cultured (74.74 ± 0.68 kg C, 5.00±0.013 kg N and 0.43±0.01 kg P). However, bottom cultured mussels removed more C in shell (60.15±0.77 kg) than rope cultured (46.12±1.69 kg) and only C trapped in shell can be regarded as a long-term store of C.
Temporal variation was investigated at two contrasting estuaries, to assess the effects of seasonality on the removal potential of mussel aquaculture. The kg of N and P tonne-1 of mussels was highest before spawning at both sites. The period immediately after spawning, had the lowest levels of N and P, before the sites recovered over autumn and winter. Similar to previous findings, the seasonal changes observed in tissue condition followed the patterns of the reproductive cycle.
Utilising the meat to shell proportions and C, N, P results from the UK spatial survey, economic analysis of four scenarios for growth and further decline of the industry were applied. Non-food ecosystem services provided are worth the equivalent of US$20.3 million year-1 in nutrient remediation and shell as aggregate, however, should there be a decrease in trade,non-food ecosystem services could decrease to only US$4.1 million year-1. Through restoration of bottom aquaculture, the associated ecosystem services, could increase to US$37.4 million year-1. Further expansion to offshore aquaculture, could increase the value of non-food ecosystem services to US$73.7 million year-1. England is estimated to spend approximately US$3.45 billion year-1 protecting the water environment through lowering input, and mitigation of historical pollution. Whilst not the complete solution, mussel aquaculture already contributes nitrogen and phosphorus reduction through the removal of these nutrients and further work is required to compare rope offshore and intertidal mussel aquaculture in more areas.