Ocean Acidification

Progressive ocean acidification and deoxygenation are expected to threaten many marine zooplankton, but their combined effects across life stages remain poorly understood. We investigated stage-specific responses of the egg-carrying copepod Pseudodiaptomus annandalei to changes in pH_T (5.97–8.05) and dissolved oxygen (DO; 0.90–8.20 mg L⁻¹). Nauplii were the most sensitive stage in 24-h exposures, with survival dropping below 40% at pH_T 6.1 and declining to 55–70% when DO fell below 1 mg O₂ L⁻¹. Under combined stress, naupliar survival declined to about 65% in the most severe treatment (pH_T 7.11, DO 1.74 mg O₂ L⁻¹), whereas copepodites and adults showed no significant short-term survival response. In contrast, moderate combined stress (pH_T 7.62, DO 4.11 mg O₂ L⁻¹) produced sublethal effects, increasing development time by approximately 70%, reducing development success from 86% to 28%, and decreasing nauplii production by approximately one-third. Thus, nauplii form a critical bottleneck for recruitment under combined stress.

Scientific Significance Statement

Coastal marine ecosystems are increasingly exposed to concurrent acidification and deoxygenation, yet the combined effects of these stressors across zooplankton life stages remain poorly resolved. Using the egg-carrying copepod Pseudodiaptomus annandalei, we show that short-term adult survival was relatively insensitive to combined low pH and low oxygen, whereas naupliar development and reproductive output were strongly reduced. These results identify the naupliar stage as a critical bottleneck under combined acidification and hypoxia. This stage-specific vulnerability implies that adult survival alone can underestimate recruitment impacts of changing coastal carbonate and oxygen conditions.

Chen W. & Gao K., 2026. Stage-specific vulnerability: Ocean acidification and hypoxia impair copepod recruitment through a naupliar bottleneck. Limnology and Oceanography Letters 11: e70181. doi: 10.1002/lol2.70181. Article.