You are here:
Growth of juvenile hard clams in Narragansett Bay after laboratory exposure to low pH
Citation:
Grear, J., A. Pimenta, H. Booth, D. Borsay, AND M. Liebman. Growth of juvenile hard clams in Narragansett Bay after laboratory exposure to low pH. Coastal & Estuarine Research Federation 24th Biennial Conference, Providence, Rhode Island, November 05 - 09, 2017.
Impact/Purpose:
Clams and oysters make shells using the carbonate ions that naturally occur in seawater. The availability of this carbonate decreases when carbon dioxide is added to seawater and acidity is increased, threatening the survival and growth of shellfish. In coastal ecosystems where many shellfish thrive, the two main factors causing this change in carbonate chemistry are nutrient enrichment and absorption of carbon dioxide from the atmosphere. We conducted a laboratory and field experiment where we examined the effects of various carbonate, acidity, and nutrient levels found in estuaries. Understanding these interactions will be critical to predicting the effects of coastal acidification on both natural and aqua cultured shellfish populations.
Description:
Ocean uptake of carbon dioxide is causing decreases in pH and the concentration of carbonate ions used by marine organisms during shell and skeletal formation. When these conditions are reproduced in laboratory environments and field enclosures, effects on biological rates such as growth and survival are often strong and negative. However, pH is sensitive to nutrient loading and other factors that affect carbon dioxide and is thus extremely variable in the coastal environment. Thus, coastal bivalves often experience temporary diurnal and seasonal environmental changes in carbonate chemistry. Similarly, cultured shellfish may experience abrupt or temporary changes during seeding and translocation activities. We mimicked these changes in a two-phase experiment, whereby we first pre-conditioned 16,200 juvenile hard clams (500 um, Mercenaria mercenaria) for one month under pH conditions controlled via CO2 bubbling in laboratory treatments (mean pCO2 = 782, 1252, and 1869 uatm). These clams were then transferred into three sites along a nutrient gradient in Narragansett Bay in mesh bags of 100 clams per bag. Sites were factorially crossed with pCO2 treatment. We found a significant positive effect of pCO2 treatment on clam size but a negative effect on dry weight and on dry weight per unit clam length (GPL). After the one month field phase, there were strong differences between sites and, in some cases, interactions with treatment. At all three sites, the percent increase in GPL was highest for clams from the high pCO2 treatment. This suggests that individuals with low GPL after the laboratory treatment underwent accelerated accumulation of mass per unit length when they had access to the higher nutrition of the bay environment. We speculate that, without the protection of the mesh bags during the grow-out period, the lighter pre-exposed clams might have been more vulnerable to predation or other factors that interact with shell mass, size, and density.