The endemic spring snail Pyrgulopsis montezumensis in a high CO2 environment: importance of extreme chemical habitats as refugia

O'Brien, Chris; Blinn, Dean

1. We examined the distribution of the endemic spring snail, Pyrgulopsis montezumensis, along a gradient of dissolved free CO2 and on selected substrata in the collapsed travertine springmound of Montezuma Well, Arizona, U.S.A. 2. Dissolved CO2 concentration ranged from 480 (SE 56) mg L±1 near the bottom spring vents in the limnetic zone (12 m deep) of the well to less than 20 mg L±1 in an irrigation canal about 1400 m downstream from the well outlet. Spring snails occurred in habitats with 110±315 mg L±1 dissolved CO2. 3. Laboratory experiments showed that P. montezumensis tolerated a dissolved CO2 concentration up to about 400 mg L±1 for 11 days, but displayed 40% (SE 4) mortality after 3 days at 728 mg L±1 and 100% mortality after 24 h at 1200 mg L±1. We also measured 100% mortality after 10 days at ambient concentrations (less than 10 mg L±1) of dissolved CO2. 4. Although the concentration of dissolved CO2 was within the tolerance range for spring snails in the irrigation canal, inadequate substrata and increased predation probably restricted their distribution in the lower reaches of the canal. Both field measurements and laboratory selection experiments showed a significant (P less than 0.001) preference for limestone substrata over submerged vegetation and fine sediments. 5. We propose that springs with high dissolved CO2 may provide refugia from invertebrate and/or vertebrate predators not physiologically adjusted to the extreme chemical environment. These extreme chemical habitats probably reduce competition for resources and predation and allow resistant populations like P. montezumensis to attain high density.

The endemic spring snail Pyrgulopsis montezumensis in a high CO2 environment: importance of extreme chemical habitats as refugia

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