Impacts of Combined Natural and Anthropogenic Stressors on Pacific Intertidal Invertebrates
Creators: Lowes, Hannah M.
Publisher: name: University of Alberta Library
Year: 2023

<p>The intertidal zone provides extensive habitat around the world for countless species, but there are many challenges associated with life in this region. In particular, intertidal organisms may be subjected to hours of air exposure during low tide. Tidal emersion from water is potentially a major source of stress to aquatic animals because it may cause desiccation and inhibit several aspects of their physiology including oxygen uptake, ammonia excretion, and osmoregulation. Still, organisms live within their range of tolerance to environmental stressors, and intertidal animals have strategies to cope with emersion. For example, water-breathing invertebrates may switch to anaerobic metabolism, which is less energetically efficient, when they are unable to take up oxygen from air. Although intertidal organisms are adapted to withstand extreme environmental fluctuations, natural stressors like tidal emersion are not the only challenges that they face; they are also vulnerable to anthropogenic toxicant release. One major toxicant that poses a threat to the intertidal zone is copper (Cu), which is essential for life at low concentrations but toxic at high levels. Cu damages physiological processes including gas exchange, metabolism, ammonia excretion, and osmoregulation. Cu-induced damage to these pathways may be lethal to marine invertebrates. In the context of the intertidal zone, this is worrying because several natural and anthropogenic stressors including Cu and emersion may be simultaneously present. Mixed stressors may have additive or synergistic effects, especially when the stressors target similar processes in an organism. Since both Cu and emersion may affect the same physiological processes (e.g., metabolism and ammonia excretion), it is possible that Cu exposure prior to tidal emersion may alter intertidal organisms’ ability to overcome the challenges presented by air exposure.<br>
For my thesis, I studied the combination of Cu exposure and tidal emersion on two intertidal marine invertebrates which use different strategies to cope with air exposure: (1) the<br>
orange sea cucumber Cucumaria miniata and (2) the Mediterranean mussel Mytilus galloprovincialis. I hypothesized that environmentally relevant concentrations of Cu would<br>
decrease the tolerance of both species to tidal emersion, but that effects would be smaller in M. galloprovincialis because it is able to protect its soft tissues from external stress by closing its valves, conferring high tolerance to a broad range of environmental conditions. To test my hypothesis, I conducted the same experiment on both species: 96 h acute exposure to Cu followed by a 6 h period of air exposure to mimic tidal emersion. I measured tissue-specific Cu bioaccumulation, oxygen uptake rates, ammonia excretion rates, ammonia quotients, levels of end products of anaerobic metabolism, and ion concentrations of internal fluids after exposure to the two stressors. I expected the combination of Cu exposure and emersion to result in decreased oxygen uptake and ammonia excretion rates, induction of anaerobiosis, and osmotic dysregulation in both organisms. Contrary to my hypothesis, analyses of these metrics revealed that while Cu toxicity and emersion each had individual negative effects on both of the study organisms, Cu did not seem to alter the ability of either animal to cope with tidal air exposure. My results speak to the high tolerance of both species to the environmental stressors they face and provide further understanding of how multiple stressors interact to affect the physiology of intertidal animals. This study may be used inform predictions of the distribution and survival of species in our changing climate.</p>