The endemic and endangered Maugean Skate (Zearaja maugeana) exhibits short-term severe hypoxia tolerance

Abstract

The endangered and range-restricted Maugean skate (Zearaja maugeana) is subjected to large environmental variability coupled with anthropogenic stressors in its endemic habitat, Macquarie Harbour, Tasmania. However, little is known about the basic biology/physiology of this skate, or how it may respond to future environmental challenges predicted from climate change and/or increases in human activities such as aquaculture. These skate live at a preferred depth of 5–15 m where the dissolved oxygen (DO) levels are moderate (~55% air saturation), but can be found in areas of the Harbour where DO can range from 100% saturation to anoxia. Given that the water at their preferred depth is already hypoxic, we sought to investigate their response to further decreases in DO that may arise from potential increases in anthropogenic stress. We measured oxygen consumption, haematological parameters, tissue–enzyme capacity and heat shock protein (HSP) levels in skate exposed to 55% dissolved O2 saturation (control) and 20% dissolved O2 saturation (hypoxic) for 48 h. We conclude that the Maugean skate appears to be an oxyconformer, with a decrease in the rate of O2 consumption with increasing hypoxia. Increases in blood glucose and lactate at 20% O2 suggest that skate are relying more on anaerobic metabolism to tolerate periods of very low oxygen. Despite these metabolic shifts, there was no difference in HSP70 levels between groups, suggesting this short-term exposure did not elicit a cellular stress response. The metabolic state of the skate suggests that low oxygen stress for longer periods of time (i.e. >48 h) may not be tolerable and could potentially result in loss of habitat or shifts in their preferred habitat. Given its endemic distribution and limited life-history information, it will be critical to understand its tolerance to environmental challenges to create robust conservation strategies.

Elasmobranch Responses to Experimental Warming, Acidification, and Oxygen Loss—A Meta-Analysis

“…Indeed, currently available studies mostly feature acute (a few hours or less) or intermittent exposures (e.g., Rytkönen et al, 2012), which, similarly to early studies on high CO 2 effects, are not suitable for comparison with the remaining factors within the present framework. In fact, only two studies featured a sustained exposure to reduced levels of oxygen (Morash et al, 2020;Musa et al, 2020), one of them still fairly short in exposure duration (48H; Morash et al, 2020). While severely neglected, the effect of ED over elasmobranchs seems well within the range of the more well-studied EA.…”

He was a skater boy, but will the Maugean skate(r) conform or rebel?

“…The middle layer is mixed. As Morash et al (2020) found out, the amount of dissolved oxygen at the skates’ preferred depths ranges from 90% saturation down to only 30% saturation; although, there are even areas with essentially no oxygen. Morash and her team wanted to know how the Maugean skate manages to swim around through all those different oxygen environments and how well it copes with even lower oxygen levels.…”

Eugenol and Lippia Alba Essential Oils as Effective Anesthetics for the Amazonian Freshwater Stingray Potamotrygon Wallacei (Chondrichthyes, Potamotrygonidae)

“…Melanomacrophages are cells with phagocytic activity having a considerable number of dark pigments inside, like melanin, lipofuscin and hemosiderin. These Zearaja maugeana (Morash et al 2020). In all these studies, a commonly observed characteristic was the lack of changes in this parameter in response to different types of stressors.…”