Physiological energetics of juvenile clams Ruditapes decussatus in a high CO2 coastal ocean

Effects of coastal ocean acidification, other than calcification, were tested on juvenile clams Ruditapes decussatus during a controlled CO2 perturbation experiment. The carbonate chemistry of natural (control) seawater was manipulated by injecting CO2 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 CO2 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.Regional Ministry of Innovation and Industry of the Galician Government [08MDS018402PR]; Italian Ministry for Environment, Land and Sea; Foundation for Science and Technology of Portugal [ERA-CIRCLE/0004/2007]; European Commissio

Tolerance of juvenile Mytilus galloprovincialis to experimental seawater acidification

Coastal ocean acidification is expected to interfere with the physiology of marine bivalves. In this work, the effects of acidification on the physiology of juvenile mussels Mytilus galloprovincialis were tested by means of controlled CO2 perturbation experiments. The carbonate chemistry of natural (control) seawater was manipulated by injecting CO2 to attain 2 reduced pH levels: -0.3 and -0.6 pH units as compared with the control seawater. After 78 d of exposure, we found that the absorption efficiency and ammonium excretion rate of juveniles were inversely related to pH. Significant differences among treatments were not observed in clearance, ingestion and respiration rates. Coherently, the maximal scope for growth and tissue dry weight were observed in mussels exposed to the pH reduction Delta pH = -0.6, suggesting that M. galloprovincialis could be tolerant to CO2 acidification, at least in the highly alkaline coastal waters of Ria Formosa (SW Portugal).Regional Ministry of Innovation and Industry of the Galician Government [08MDS 018402PR]; Italian Ministry for Environment, Land and Sea; Foundation for Science and Technology of Portugal [ERA-CIRCLE/0004/2007]; European Commissio

Modelling Local Food Depletion Effects in Mussel Rafts of Galician Rias

Mollusc culture is one of the most important types of mariculture, with suspension feeding bivalves being among the most cultivated organisms. In the last years, there has been a growing concern about carrying capacity (CC) of natural ecosystems for bivalve culture, because of decreases in growth rates and mass mortalities due to overstocking. Several methods have been proposed for CC estimation. The simplest are based on average properties integrated over various time scales, like water renewal rate, phytoplankton primary production and bivalve clearance rate. If the time scale of the former two processes is larger than the time scale for bivalve filtration than, bivalve standing stock is over ecosystem CC. More complex approaches are based on ecosystem box modelling or coupled physical-biogeochemical models. The objective of this work is to evaluate production CC for mussel rafts in Galician Rias as a function of mussel loads and current velocities. For this purpose an analytical model was developed and used to find conditions that maximize raft production. Obtained results suggest that CC at the raft scale has not been exceeded by current culture practices. However, it does not seem advisable to increase mussel loads per raft. Therefore, any possible increase in mussel production should be considered at a higher spatial scale

Box-plots comparing the Scope for Growth (SFG, J h⁻¹) of slow (S) and fast (F) growing mussel seed (left panel) and the Scope for Growth of subtidal (mussel raft) and intertidal (rocky shore) mussel seed gathered from the Ría Ares-Betanzos (NW, Spain).

<p>Statistical differences are indicated as *** for p<0.001 (two-way ANOVA).</p

Physiological parameters (mean ± SD) of mussel (<i>Mytilusgalloprovincialis</i>) seed from subtidal and intertidal origins.

<p>The table shows the initial values of the energy balance and the physiological parameters obtained after 5 months of maintenance the laboratory to select the individuals with slow (S) and fast (F) growth rates. The physiological measurements included the clearance rate (CR; OW:organic weight), ingestion rate (IR), absorption efficiency (AE) and absorption rate (AR), respiration rate (VO₂), ammonia excretion rate (VNH₄-N) and Scope for Growth (SFG). Physiological rates were expressed as mass-specific rates (Y_SPC) in mg of organic weight (OW).</p

Mass-specific physiological components of the energy balance in slow (S) and fast (F) growing mussel seed originated from the subtidal and intertidal ecosystems and maintained under standard laboratory conditions during five months.

<p>The feeding (clearance rate: CR, and ingestion rate: IR), digestive (absorption efficiency: AE, and absorption rate: AR) and metabolic parameters (ammonia excretion: VNH₄-N and, oxygen consumption: VO₂) represent the mean ± SD.</p

Comparison of the total clearance rate (CR_total), gill area and gill efficiency (ratio of the CR_total to the gill area) obtained in slow (S) and fast (F) growing mussel seed originated from the subtidal and intertidal ecosystems after maintenance with a monoalgal diet of <i>Rhodomonas lens</i> during five months.

<p>Comparison of the total clearance rate (CR_total), gill area and gill efficiency (ratio of the CR_total to the gill area) obtained in slow (S) and fast (F) growing mussel seed originated from the subtidal and intertidal ecosystems after maintenance with a monoalgal diet of <i>Rhodomonas lens</i> during five months.</p

Seawater carbonate chemistry and physiological energetics of juvenile clams Ruditapes decussatus

Effects of coastal ocean acidification, other than calcification, were tested on juvenile clams (Ruditapes decussatus) during a controlled CO2 perturbation experiment. The carbonate chemistry of natural (control) seawater was manipulated by injecting CO2 to attain two reduced pH levels: -0.4 and -0.7 pH units as compared with the control seawater. After 87 days 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 CO2 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