| Summary: | Marine calcifiers, especially those in their larval and juvenile stages, are thought to be most vulnerable to ocean acidification (OA) due to the effects of carbon dioxide (CO2) on growth and shell mineralogy. However, recent evidence is contradictory. We monitored molting activity, length and weight in early benthic phase juvenile American lobster Homarus americanus (Milne-Edwards 1837) under elevated CO2 conditions (500 μatm, 1100-1300 μatm, and 2000-2700 μatm) to determine how OA affects growth at this life stage. Molted shells were analyzed for magnesium (Mg2+ ) and calcium (Ca2+) content by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Exposure to higher CO2 partial pressures over a 90-120 day period affected the length of the intermolt period and caused decreased length and weight growth increments. The higher concentrations of CO2 also changed the magnesium to calcium (Mg:Ca) ratio present in the mineralized shell. Shells from lobsters in the medium and high CO2 treatments had an overall higher Mg:Ca than lobsters in the control CO2 treatment. Lobsters in the medium and high CO2 treatments were also more susceptible to shell disease. Taken together, these results suggest juvenile lobsters may remain smaller for a longer period of time and be more vulnerable to disease and/or shell dissolution in a high CO2 ocean.
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