The Rias Baixas are four flooded tectonic valleys located on the northwest Iberian

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Mussel seed, obtained from the intertidal zone and permanently immersed collector ropes, was cultivated on ropes suspended from three rafts located at three different sites within the Ria de Arousa (Galicia, NW Spain). Sites were characterized by different levels of phytoplankton availability. The source of seed stock had a marked influence upon subsequent mussel growth; seed originating from collector ropes had higher growth rates than seed collected from intertidal areas and was probably due to the higher condition index and previous adaptation to rope culture conditions (permanent immersion) for these samples. Cultivation site also affected mussel growth; differences in chlorophyll a content and water current speed, which influence phytoplankton availability, were the major factors underlying variation in growth rate and condition index. It is recommended that seed obtained from collector ropes should be used in the commercial exploitation of this species, since it would shorten the total duration of the cultivation process by more than 10%.

Effects of coastal ocean acidification, other than calcification, were tested on juvenile clams Ruditapes decussatus during a controlled CO 2 perturbation experiment. The carbonate chemistry of natural (control) seawater was manipulated by injecting CO 2 to attain 2 reduced pH levels (-0.4 and -0.7 pH units) as compared with the control seawater. After 87 d of exposure, we found that the acidification conditions tested in this experiment significantly reduced the clearance, ingestion and respiration rates, and increased the ammonia excretion rate of R. decussatus seeds. Reduced ingestion combined with increased excretion is generally associated with a reduced energy input, which will likely contribute to a slower growth of the clams in a future high CO 2 coastal ocean. These results emphasize the need for management policies to mitigate the adverse effects of global change on aquaculture, which is an economically relevant activity in most coastal areas worldwide. KEY WORDS: Ocean acidification · Sea water pH · Physiological energetics · Clams · Ruditapes decussatus Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 433: [97][98][99][100][101][102][103][104][105] 2011 oxygen, pH and carbonate ion levels in temperate coastal waters are usually minimal during summer, when the biogenic materials produced during the preceding phytoplankton spring bloom have decomposed and many species of bivalves are spawning (Amaral 2009). In the particular case of the Iberian upwelling system (SW Europe), a significant reduction of the intensity and extension of the upwelling-favourable season has been observed over the last 50 yr (Lemos & Sansó 2006), which has produced a duplication of the residence time of water in the Galician rias, a group of large coastal embayments of the northern coast (Álvarez-Salgado et al. 2008), and a concomitant enhancement of mineralization (Pérez et al. 2010).Previous studies have shown that reductions in pH and in the concentration of carbonate ion in oceanic and coastal waters can have a negative effect on marine organisms (Fabry et al. 2008), eventually affecting their survival (Raven et al. 2005). However, a recent review by Hendriks et al. (2010) proposed that marine biota may be more resistant to acidification than expected. Most of the research efforts on this issue have been focused on the exploitable marine calcifiers with a special emphasis on the impact of ocean acidification on calcification rates (Orr et al. 2005, Gazeau et al. 2007, McDonald et al. 2009, Miller et al. 2009). For the particular case of marine bivalves, Michaelidis et al. (2005) and Berge et al. (2006) reported reduced growth rates for Mytilus spp. reared under conditions of increased CO 2 and reduced pH. Furthermore, Michaelidis et al. (2005) also showed that a prolonged reduction of seawater pH produces decreased respiration rates, increased protein degradation and acidosis of the haemolymph, which is buffered by the dissolution of the CaCO 3 shell. More rece...