Combined effects of temperature and copper on oxygen consumption and antioxidant responses in the mudflat fiddler crab Minuca rapax (Brachyura, Ocypodidae)

Abstract

This study investigates the combined effects of waterborne copper exposure and acute temperature change on oxygen consumption and the oxidative stress biomarkers, glutathione S-transferase (GST) and glutathione peroxidase (GPx), in the gills and hepatopancreas of the fiddler crab Minuca rapax. Crabs held at 25 °C were acclimated to 0 (control), 50, 250 or 500 μg Cu L^-1 for 21 days, and were then subjected to 15, 25 and 35 °C for 24 h. Aerial oxygen consumption rates of crabs in copper free media increased with increasing temperature from 15 to 35 °C, Q₁₀ values reaching ≈3. Crabs exposed to increasing copper concentrations exhibited variable responses, Q₁₀ values falling to ≈1.5. Copper had no effect on oxygen consumption at 25 °C. However, at 35 °C, rates decreased in a clear concentration-response manner in the copper exposed crabs, revealing impaired aerobic capability. At 15 °C, oxygen consumption rates increased with copper concentration, except for a decrease at 500 μg Cu L^-1. Gill GST activity was ≈2-fold that of the hepatopancreas, while hepatopancreas GPx activity was 3-fold that of the gills. Gill GST activities were reduced by copper exposure only at 25 °C while hepatopancreas GST activities were altered by copper at all temperatures. Hepatopancreas GST and GPx activities increased in crabs exposed to copper at 35 °C, revealing oxidative stress induction. Hepatopancreas GST and GPx activities were reduced in copper exposed crabs at 15 °C, suggesting a diminished capability to mitigate the effects of copper exposure at low temperature. These findings reveal that copper exposure increases oxygen consumption at low temperatures but decreases consumption at high temperature. Hepatopancreas GPx activities decreased at low temperature and increased at high temperature. These novel findings demonstrate that the interaction between copper exposure and temperature should be considered when evaluating biomarker activities in semi-terrestrial crabs.

Keywords: Anti-oxidant activities; Biomarkers; Copper exposure; Gelasiminae; Oxygen consumption; Semi-terrestrial fiddler crab; Temperature effects.