CO2, Krill, and Their Environment

Experimental exposure of the common Arctic euphausiid (krill) Thysanoessa raschii to decreased pH for several weeks did not have a significant effect on molting frequency, wet weight, and body length.  Mortality at -0.6 pH units below ambient was not significant but was reduced by 40% at -0.8 pH units.  Although this preliminary experiment will be elaborated with greater replication, a broader exposure range, and controlled temperatures, these preliminary results suggest T. raschii are quite resistant to decreased pH.  Consistent with these results, the environment it inhabits suggests that T. raschii should cope well with variable pH.  Seasonally, pH cycles with an amplitude of about 0.6 pH units in local surface water (0 to 7 m) and about 0.2 units at 23 m.  Total inorganic carbon and total alkalinity cycles are opposite the pH cycle.  T. raschii have diel depth habits, thus are found from the surface to roughly 100 m in local waters, hence their physiology may be adapted to a broad pH range.  Additional field work is planned to document the natural pH (and temperature and salinity) variation experienced by T. raschii.  Continued research will consider these environmental data when designing experiments.