Does seawater acidification affect survival, growth and shell integrity in bivalve juveniles?
Anthropogenic emissions of carbon dioxide are leading to decreases in pH and changes in the carbonate chemistry of seawater. Ocean acidification may negatively affect the ability of marine organisms to produce calcareous structures while also influencing their physiological responses and growth. The aim of this study was to evaluate the effects of reduced pH on the survival, growth and shell integrity of juveniles of two marine bivalves from the Northern Adriatic sea: the Mediterranean mussel Mytilus galloprovincialis and the striped venus clam Chamelea gallina. An outdoor flow-through plant was set up and two pH levels (natural seawater pH as a control, pH 7.4 as the treatment) were tested in long-term experiments. Mortality was low throughout the first experiment for both mussels and clams, but a significant increase, which was sensibly higher in clams, was observed at the end of the experiment (6 months). Significant decreases in the live weight (-26%) and, surprisingly, in the shell length (-5%) were observed in treated clams, but not in mussels. In the controls of both species, no shell damage was ever recorded; in the treated mussels and clams, damage proceeded via different modes and to different extents. The severity of shell injuries was maximal in the mussels after just 3 months of exposure to a reduced pH, whereas it progressively increased in clams until the end of the experiment. In shells of both species, the damaged area increased throughout the experiment, peaking at 35% in mussels and 11% in clams. The shell thickness of the treated and control animals significantly decreased after 3 months in clams and after 6 months in mussels. In the second experiment (3 months), only juvenile mussels were exposed to a reduced pH. After 3 months, the mussels at a natural pH level or pH 7.4 did not differ in their survival, shell length or live weight. Conversely, shell damage was clearly visible in the treated mussels from the 1st month onward. Monitoring the chemistry of seawater carbonates always showed aragonite undersaturation at 7.4 pH, whereas calcite undersaturation occurred in only 37% of the measurements. The present study highlighted the contrasting effects of acidification in two bivalve species living in the same region, although not exactly in the same habitat.
Department of Biology, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy. Electronic address: monica.bressan@unipd.it.
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Bressan
Department of Biology, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
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Chinellato
Department of Biology, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
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Munari
Department of Biology, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
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Matozzo
Department of Biology, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
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Manci
Department of Biology, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
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Marčeta
Department of Statistical Sciences, University of Padova, Via C. Battisti 241, 35121 Padova, Italy.
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Finos
Department of Biology, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
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Moro
Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
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Pastore
Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
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Badocco
Department of Biology, University of Padova, Via Ugo Bassi 58/B, 35131 Padova, Italy.
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Marin
D000704:Analysis of Variance; D060105:Animal Shells / Q000737:chemistry / Q000187:drug effects* / Q000648:ultrastructure; D000818:Animals; D049872:Bivalvia / Q000187:drug effects / Q000254:growth & development*; D001837:Body Weights and Measures; D002245:Carbon Dioxide / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D008522:Mediterranean Sea; D008855:Microscopy, Electron, Scanning; D009026:Mortality; D012623:Seawater / Q000737:chemistry*; D013045:Species Specificity
D002245:Carbon Dioxide
Acidification; Calcium carbonate; Carbon dioxide; Clam; Mussel; Northern Adriatic; Shell damage; pH