Updated: Feb 27
We all know that climate change is a serious threat looming over us. On a global scale, climate change may alter local weather patterns, expand deserts, and cause sea level rise which could engulf coastal communities. However, it is important to keep in mind that, alongside these sweeping changes, climate change will impact every single species on an individual level... often in ways we may not anticipate...
Why is Climate Change Hapenning?
When we talk about climate change, we are referring to "Greenhouse gases" accumulating in unnaturally high concentrations in the atmosphere, which alter planetary temperature regulation. Greenhouse gases, including carbon dioxide (C02), methane, nitrous oxide and fluorinated gases, are released into the atmosphere by burning "fossil fuels", like coal, oil and natural gas. These gases trap heat which would normally reflect out into space and cause air temperatures to rise. As a result, the average air temperature is predicted to rise by as much as 2 - 5°C in less than 100 years (Meehl et al, 2007).
Atmospheric changes can also affect the oceans. These gases can dissolve into the oceans and cause the pH of the water to drop. This is known as "ocean acidification". The pH (a measure of how acidic or alkaline a substance is) of the ocean is predicted to drop by as much 0.14 - 0.5 units of pH by the year 2100 (Meehl et al, 2007).
How Will Climate Change Affect Sharks
Scientists are only just beginning to understand how these global changes might impact sharks. Climate change and the associated shifts in ocean acidification, temperatures and dissolved oxygen are expected to alter shark migrations, hunting behaviours, the locations of critical habitats, reproduction, juvenile survival, metabolic rates and temperature sensitivity (to learn more you can check out How Low Can You O?, Pickled Eggs and I Just Want to Go Home) (Rosa et al, 2014; Izzo & Gillanders, 2020; Vedor et al, 2021).
A recent study has now shown that climate change might even affect the way sharks digest their food!
Scientists raised the eggs of brown-banded bamboo sharks (Chiloscyllium punctatum) under different environmental conditions. They reared some eggs in warmer water temperatures, some in more acidic conditions and other with both altered temperature and pH, and measured the levels of two digestive enzymes in the sharks' gut. Specifically, they measured trypsin in the pancreas and alkaline phosphatase from the intestine, which are involved in the digestion of dietary proteins (Rosa et al, 2016).
The researchers found that those juveniles which were reared under acidic and high temperature conditions (column d on the right of the graphs), had noticeably higher levels of both enzymes in their guts, compared to those living in normal conditions (column a on the lefts) (Rosa et al, 2016).
What was especially interesting about his study is that the researchers learnt that the effects of ocean warming and acidific might be conflicting - you may have noticed that the other two columns in the centre of the graph (columns b and c) are drastically different from the normal conditions and don't seem to follow an obvious pattern. This study showed that under conditions of ocean acidification without warming (column b), the activity of both enzymes were significantly reduced, whereas, with increased water temperature (column c) the enzymes were massively increased. This shows us that the effects that climate change-induced environmental shifts may have on sharks are anything but simple! (Rosa et al, 2016).
Times are Changing
The enzymes trypsin and alkaline phosphatase are associated with overall health and wellbeing in brown-banded bamboo sharks. Therefore, when the levels of these enzymes are dramatically reduced or increased, it indicates that the shark is not at its best. The scientists concluded that, at a glance, it seems ocean acidification and warming may counteract each other in how they affect brown-banded bamboo shark digestion. However, they also stated that the alterations in metabolism in these juvenile sharks might affect how well they grow and their ability to reproduce, which could have major population-level implications (Rosa et al, 2016).
These findings highlight the major problem with speculating how climate change will affect different animals... it is very difficult to predict! Scientists can do their best to assess how changing conditions may affect individual species, but in reality the effects will wary depending on location and lifestyle, and we do not know forsure exactly how CO2 levels will change over the upcoming decades. The only way to ensure that climate change does not have a detrimental impact on marine life will be to stop greenhouse gas emissions as much as possible. We must all try to reduce our energy uses and move towards being more sustainable as soon as we possibly can.
Is there something you could do in your daily life to reduce your carbon footprint?
Izzo C & Gillanders BM (2020).Port Jackson shark growth is sensitive to temperature change. Frontiers in Marine Science, 7, DOI: 10.3389/fmars.2020.00240. Access online.
Meehl GA, Stocker TF & Collins WD, Friedlingstei, P, Gaye T, Gregory JM, Kitoh A, Knutti R, Murphy JM, Noda A, Raper SCB, Watterson IG, Weaver AJ & Zhao ZC (2007). Global climate projections. In: Solomon S, Qin D & Manning M (Eds.). Climate Change 2007: the Physical Science Basis, pp. 686–688. Cambridge, UK: Cambridge University Press.
Rosa R, Baptista M, Lopes VM, Pegado MR, Paula JR, Tru ̈benbach K, Leal MC, Calado R & Repolho T (2014). Early-life exposure to climate change impairs tropical shark survival. Proceedings of the Royal Society B, 281:1793, DOI: 10.1098/rspb.2014.1738. Access online.
Rosa R, Pimentel M, Galan JG, Baptista M, Lopes VM, Couto A, Guerreiro M, Sampaio E, Castro J, Santos C, Calado R & Repolho T (2016). Deficit in digestive capabilities of bamboo shark early stages under climate change. Marine Biology, 163:60, doi: 10.1007/s00227-016-2840-z. Access online.
Vedor M, Queiroz N, Mucientes G, Couto A, da Costa I, dos Santos A, Vandeperre F, Fontes J, Afonso P, Rosa R, Humphries NE & Sims DW (2021). Climate-driven deoxygenation elevates fishing vulnerability for the ocean’s widest ranging shark. eLife, 10, e62508. Access online.
By Sophie A. Maycock for SharkSpeak.