Effect of historic aquaculture activity on copepod sensitivity to the combined exposure of copper and predation risk

Abstract

Marine ecosystems are complex ecosystems in which organisms consciously face multiple stressors. Copepods, the most abundant zooplankton group has an integral role in the marine food web. They are exposed to multiple stressors of both natural and anthropogenic origin that can result in antagonistic to synergistic effects. The increasing use of copper as an antifouling biocide in the aquaculture industry is a major concern for aquatic ecosystems, given its effect on non-target species such as copepods when discharged in the environment. Copper act as a stressor if concentrations exceed a certain threshold and reactive oxygen species (ROS) are formed in the organism. Astaxanthin is a pigment with antioxidative properties in copepods that can scavenge ROS to reduce the oxidative stress. However, this pigment also causes a conspicuous orange color in the copepods, leaving more pigmented individuals at a higher risk to visual predators, such as fish. A trade-off might therefore exist between predation risk and antioxidant capacity in copepods. This thesis aimed to identify sensitivity differences to the combined exposure of copper and predation risk due to adaptations in copepods exposed to varying degrees of historical aquaculture activity. I focused on survival and astaxanthin pigmentation as endpoints. Individuals of the coastal copepod Temora longicornis were sampled in Boknafjorden/Ryfylket region (Stavanger, Norway) along a transect of historic aquaculture activity. Individuals were exposed for 72 hours to copper (150 µg/L), predation risk (kairomones), a stressor combination (Cu + kairomones), and a control to test effects on survival and astaxanthin pigmentation. An automated imaging robot took pictures throughout the experiment to determine the exact time of death through image analysis. The community structure and environmental conditions differed between the sampling locations. Individuals exposed to copper decreased survival, whereas the combined treatment with copper and predation risk increased survival. Historic aquaculture activity was found to not be related with higher survival or increased astaxanthin pigmentation. The measured astaxanthin content pf the individuals did not differ, and we did not detect any alleviating effects of astaxanthin pigmentation related to survival.