Journal of Aquaculture & Fisheries Category: Aquaculture Type: Short Communication
Will Climate Change Endangers the Current Mussel Production in the Rias Baixas (Galicia, Spain)?
- André Filipe Silva1, Magda Catarina Sousa1, Cristina Bernardes2, João Miguel Dias3*
- 1 Departamento De Fisica, Universidade De Aveiro, Aveiro, Portugal
- 2 Departamento De Geociencias, CESAM, Universidade De Aveiro, Aveiro, Portugal
- 3 Departamento De Fisica, CESAM, Universidade De Aveiro, Aveiro, Portugal
*Corresponding Author:João Miguel Dias
Departamento De Fisica, CESAM, Universidade De Aveiro, Aveiro, Portugal
Received Date: Jul 25, 2017 Accepted Date: Sep 01, 2017 Published Date: Sep 15, 2017
All coastal systems present a unique hydrodynamic configuration that Results in the development of numerous site specific fish and shellfish species. Nowadays, main topics of research include the climate change impacts on these coastal systems and the identification of critical conditions for resident species development considering their effect on local economy. The present study aims to investigate the climate change impact on the aquaculture sector in the Rias Baixas (Spain), where mussels are the specie with higher economic value. Local hydrodynamic changes were assessed through implementation and exploitation of a hydrodynamic model (Delft3D), in order to identify changes on salinity and water temperature patterns and their possible impact on mussel’s production. The first step on model implementation comprised the assessment of its accuracy performed through the calibration procedure, which included the comparison between observed and predicted sea surface elevation, salinity and water temperature for different monitoring stations. After, Rias Baixas salinity and water temperature were predicted for past and future scenarios (1995-2005 and 2090-2100, respectively), and changes assessed considering the range ideal for mussels production. It was concluded that Ria de Arousa and Ria de Vigo will be the most affected by climate change, since salinity and water temperature will surpass the critical values where aquaculture is profitable. The least affected by climate change is the Ria de Pontevedra as only salinity surpasses the critical values.
Galicia, located in the northwest of Spain, is by far the largest production area in the country, with more than 90% of all mussel production. According to different estimates, between 150000 and 200000 tons are produced annually from aquaculture in Spain, of which the mussel Mytilu sgalloprovincialis comprises 97%. The remaining percentage is distributed among the oyster (Ostreaedulis L.) and other species [2,3]. The Galician mussel production is considered the largest in the world, and the sector directly generates more than 8000 jobs and incorporates 1000 aquaculture support vessels. The annual production accounts for approximately half of the world production of this mollusk, placing Spain foremost among world leaders in aquaculture. Approximately 70% of the Spanish mussel production is destined for internal consumption, and the resulting 30% is exported, mainly to Italy and France.
The Galicia coast is characterized by four estuaries located south of Cape Finisterre, locally named as Rias Baixas (Figure 1). These ecosystems have enormous potential, being characterized by a high primary production, which is largely responsible for the high fisheries and aquaculture productivity of the region . By these reasons the Rias Baixas were subjected to continuous monitoring of the most important areas of aquaculture during the last decades. Aquaculture activity was first implemented in the Rias Baixas around 1946, beginning in the Riade Arousa with the introduction of mussel production . Currently, this production is carried out on floating platforms named by rafts, which occupy an area of 500 m² having up to 500 strings associated (12 m in length). It is in these strings that the mussels are cultivated . Due to the high economic success of the local aquaculture activity, the density of these floating platforms has been increasing over time. Recently, Duarte et al.,  carried out a study that revealed that the total number of platforms in the three rias under study is 3116, and the ria with the highest density is the Ria de Arousa with 2292 platforms, followed by the Ria de Vigo with 478 platforms and finally the Ria de Pontevedra with 346 platforms. As previously mentioned, the main mussel species produced on these platforms is the Mytilus galloprovincialis, better known as the Mediterranean Mussel. This species has a high tolerance to changes in water temperature and salinity, and a high resistance. About the water temperature, Anestis et al.,  demonstrated that this species presents high levels of mortality at temperatures above 24 ºC, while the highest growth rates are reached at temperatures ranging between 10ºC and 20ºC . Concerning salinity, this species is very sensitive to low values, since they affect its shell structure and composition . This species can, however, survive under a relatively broad range of salinity, from 20 to 36, although its highest growth rates are found for salinities above 34 .
Figure 1: (a) Map of Rias Baixas, indicating tide gauges (yellow anchor) and buoys (blue buoy). (b) Multi-domain horizontal grids (Ria de Arousa (r1), Ria de Pontevedra (r2) and Ria de Vigo (r3), Ocean Boundary (O1 e o2).
Considering this, there is a special concern about the impact that climate change can have on the dynamics of these systems, specifically water temperature and salinity resulting patterns. In general, these changes may manifest in many ways, but some of their most devastating consequences consist on the increasing of ocean water temperature, decreasing of river flows and rising sea level, affecting the local hydrodynamic as well as the water column biological activity .
This study aims to perform a preliminary research to predict the impact that climate change may have on mussels’ production in the Rias Baixas. A two-dimensional model forced by atmospheric and oceanic variables derived from local scenarios of the 5th IPCC report was implemented and the results explored. Numerical results were analyzed to assess changes of salinity and water temperature patterns caused by climate changes, identifying critical areas for mussels’ production.
All the dynamics and circulation in the rias are forced especially by the tidal currents, the wave regime adjacent to the rias, the wind stress, the interaction with the atmospheric processes and the river discharges. These influence the distribution of salinity and water temperature in the rias, both horizontally and vertically. It should be noted that tidal currents constitute the main forcing of the dynamics of the three rias. The tides on the west coast of Galicia are mesotidal, varying its amplitude between 1.1 m and 3.5 m during neap and spring tides, respectively .
Numerical model implementation
The first step of the methodology consisted in the implementation of the numerical model most indicated for the Rias Baixas, through the development of five irregular numerical grids (Figure 1b), based on bathymetric data obtained from General Bathymetric Chart of the Oceans. The grids for the three rias (R1, R2 and R3, Figure 1b) have a resolution varying from 300 m × 300 m to 550 m × 300 m, while the two grids representative of the continental shelf (O1 and O2) have a lower resolution (with a ratio of 1:3 comparing to the grids developed for the three Rias) (Figure 1b).
The model uses tidal data from TOPEX / Poseidon, salinity and water temperature from two buoys present in the Riade Arousa and Ria de Vigo, available by Meteo Galicia (http://www.meteogalicia.gal/)as oceanic open boundary conditions. The river discharges for the rivers flowing in the Rias Baixas were imposed at fluvial open boundary conditions, and were obtained by accessing the Hype Web portal (http://hypeweb.smhi.se/). Atmospheric data from the ERA Interim daily (http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc/) was used as surface boundary conditions.
In order to evaluate the impact of climate change on the aquaculture sector of the Rias Baixas it was necessary to define adequate scenarios, with proper boundary conditions, different from those mentioned above. Thus, two simulations were carried out, each with a period of 10 years: a simulation referring to the past (1995-2005) and a simulation concerning the future (2090-2100). Atmospheric values were obtained from Regional Circulation Models (RCMs) from the CORDEX project (http://www.euro-cordex.net/) with a horizontal resolution of 12.5 km. The salinity and water temperature were obtained from Global Circulation Models (GCMs) from CMIP5. The RCM RCA4 was used, being forced by four global GCMs, CNRM-CM5, HadGEM2-ES, IPSL-CM5A-MR and MPI-ESM-LR. A single scenario for the future, RCP 8.5, was considered, representing a radioactive forcing of 8.5 W m-2. The mean sea level was obtained from the TOPEX solution, using the same level for the two simulations. The river discharge values required to perform the past simulation were obtained by accessing the Hype Web portal. For the future simulation, it was found that the most pessimistic prediction anticipated a reduction of 25% in the river discharges to the region of the Rias Baixas. Thus, this reduction was considered for the climatological values previously obtained (1981-2010).
Numerical model assessment
Firstly, a visual comparison between observed and predicted time series of SSE at Ria de Vigo and Ria de Arousa (Figure 1a, yellow anchors) was performed. Next, the Root Mean Square Error (RMSE) and the predictive skill  were computed for the same stations, following the methodology proposed by Sousa and Dias and Dias et al., [15,16]. The comparison between harmonic constants computed from model predictions and observations was another quantification method used to perform the model accuracy assessment. This methodology was applied in this study, comparing the harmonic constants for the major tidal constituents in the Rias Baixas (M2, S2, K1 and O1) for the stations shown in (Figure 1a), determined using the Mat Lab® T-Tide package .
Predicted and observed salinity and water temperature were visually compared to evaluate the transport model accuracy, and RMSE and predictive skill were also determined to assess the model’s accuracy. These comparisons were performed for two locations inside the rias (Figure 1a, blue buoys).
Climate change effects on the aquaculture production
Numerical model assessment
The phase and amplitude differences determined by harmonic analysis for numerical predictions and observations are shown in table 1. The distributions of both observed and predicted amplitude and phase are very similar. At all stations, M2 presents a smaller phase difference, comprised between 0.090 to 1.6 min. The maximum amplitude difference for this constituent is observed at Ria de Pontevedra, with a value of 0.014 m. In general, it is verified that the best model predictions were obtained for the Ria of Arousa. The lower quality results were obtained for the Ria de Pontevedra, where was found the largest phase difference, 23.6 min for O1 constituent, and the largest amplitude difference (for S2). Comparing the accuracy of model predictions for the Ria de Vigo with that of a previous implementation by Sousa , a better representation of the dynamics of this system was found for the model implemented in the present work, considering the best fit obtained for all the harmonic constituents. Accordingly, it was assumed that the numerical application developed in this work reproduces with high quality and precision the tidal propagation along the Rias Baixas.
|Station||Constituent||Phase Difference (°)||Amplitude Difference (m)|
Regarding the salinity and water temperature predictions, the model adequately reproduces the variability of the thermo haline properties of the Ria de Vigo, presenting maximum RMSE values of 0.96°C for water temperature and of 1.52 for salinity. For the Ria de Arousa, the RMSE values presented are higher than those obtained for the Ria de Vigo (1.61°C for water temperature and 3.16 for salinity), in line with the results obtained by Sousa . Following these results, it was concluded that the numerical model developed accurately reproduces the heat and salt transport inside the Rias Baixas.
Impact of climate change in the aquaculture sector of the Rias Baixas
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Citation:Silva AF, Sousa CM, Bernardes C, Dias JM (2017) Will Climate Change Endangers the Current Mussel Production in the Rias Baixas (Galicia, Spain)? J Aquac Fisheries1: 001.
Copyright: © 2017 André Filipe Silva, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.