Responses of the Green Abalone Haliotis fulgens (Philippi, 1845) to Sudden and Recurring Extreme Environmental Variations

Temperature and hypoxia anomalies are observed in many coastal regions, and climate change is likely to cause a more frequent and intense occurrence of environmental extremes. Understanding their impacts on benthic populations is critical, especially on those with little or no mobility. In this contribution, the effects of hyperthermia (to 26°C) and hypoxia (to 1.0 mg O2 L–1) were analyzed and compared with their combined occurrence through the evaluation of the physiological condition of juveniles of the green abalone Haliotis fulgens. Sudden, single-time exposure of 8 h and the recurrent exposure to 8-h weekly episodes for 6 wk were tested to identify changes in the physiological condition by estimating the respiration rate (RR), the biochemical contents (soluble protein [SP] and glucose [Glc]), and physicochemical variables (osmolality [Osm] and pH) in hemolymph, and energy status (adenylate energy charge [AEC]) was measured in the muscle. The strongest responses under sudden hyperthermia were an increase in RR and Osm as well as a reduction in SP, pH, and AEC, and under hypoxia and combined effects, reductions in RR, Osm, and pH were observed. Abalone's responses to the combined stressors under the recurrent regime were different, showing increases in SP and Glc contents and reductions in pH and AEC. Results suggest that under recurrent stress of hyperthermia or hypoxia alone, the juveniles of H. fulgens can adapt, whereas under recurrent events of the combined stressors, the observed response is similar to that of sudden stimuli (without evidence of adaptation).