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Abstract:The average global temperature is predicted to increase by 3 • C by the end of this century due to human-induced climate change. The overall metabolism of the aquatic biota will be directly affected by rising temperatures and associated changes. Since thermal stability is a characteristic of groundwater ecosystems, global warming is expected to have a profound effect on the groundwater fauna. The prediction that stygobitic (obligate groundwater dweller) species are vulnerable to climate change includes assumptions about metabolic effects that can only be tested by comparisons across a thermal gradient. To this end, we investigated the effects of two different thermal regimes on the metabolism of the stygobitic copepod species Diacyclops belgicus (Kiefer, 1936). We measured the individual-based oxygen consumption of this species as a proxy of possible metabolic reactions to temperature rising from 14 to 17 • C. We used a sealed glass microplate equipped with planar oxygen sensor spots with optical isolation glued onto the bottom of 80-µL wells integrated with a 24-channel fluorescence-based respirometry system. The tests have provided controversial results according to which the D. belgicus populations should be prudently considered at risk under a global warming scenario.