Multigenerational Life-History Responses to pH in Distinct Populations of the Copepod Tigriopus californicus

Abstract

Intertidal zones are highly dynamic and harsh habitats: organisms that persist there must face many stressors, including drastic changes in seawater pH, which can be strongly influenced by biological processes. Coastal ecosystems are heterogeneous in space and time, and populations can be exposed to distinct selective pressures and evolve different capacities for acclimation to changes in pH. Tigriopus californicus is a harpacticoid copepod found in high-shore rock pools on the west coast of North America. It is a model system for studying population dynamics in diverse environments, but little is known about its responses to changes in seawater pH. I quantified the effects of pH on the survivorship, fecundity, and development of four T. californicus populations from San Juan Island, Washington, across three generations. For all populations and generations, copepod cultures had lower survivorship and delayed development under extended exposure to higher pH treatments (pH 7.5 and pH 8.0), whereas cultures maintained in lower pH (7.0) displayed stable population growth over time. Reciprocal transplants between treatments demonstrated that these pH effects were reversible. Life histories were distinct between populations, and there were differences in the magnitudes of pH effects on development and culture growth that persisted through multiple generations. These results suggest that T. californicus might not have the generalist physiology that might be expected of an intertidal species, and it could be adapted to lower average pH conditions than those that occur in adjacent open waters.