The first person to study biology systematically, Aristotle, had a particular interest in cephalopods and some of his descriptions and observations pertaining to them (e.g. the hectocotylus – a modified arm used by male octopuses and some other cephalopods to transfer sperm to the female - of octopuses) were widely disbelieved until the 19th century. Throughout recorded history, cephalopods have stimulated scientific minds, inspired artistic emotions, and satisfied culinary senses. In fact, they even played a part in the act of recording history itself, as cuttlefish ink was a popular medium for writing, drawing, and painting in Greco-Roman times. As we learn more about them, the fascination from the general population seems only to increase. Perhaps this is because few living taxa, if any, are quite as unique as the cephalopod.
Despite having piqued human interest for over 3,000 years, and inhabiting the oceans for the last 500 million years, the future of cephalopods could be at risk from anthropogenic activity in just a few centuries. In the roughly 250 years since the start of the Industrial Revolution, atmospheric carbon dioxide (CO2) concentrations have increased by over 40%, from around 280 ppm to currently over 400 ppm, and are now higher than any time in the previous 800,000 years. If these trends continue, it is projected that CO2concentrations could exceed 900 ppm by the end of this century (Figure 1), causing a reduction in ocean pH by a further 0.3-0.4 units. These rapid changes to ocean chemistry could have serious consequences to the future success of many species, including cephalopods.
In laboratory experiments, some cephalopod species have adverse responses to projected future CO2levels in a range of traits. Atlantic longfin squid (Doryteuthis pealeii) reared from eggs to hatchlings demonstrate developmental changes under elevated CO2 conditions including increased time to hatch, shorter mantle lengths, and abnormally shaped statoliths (ear bones), which are crucial for orientation and motion detection. Aerobic performance can also be compromised; routine oxygen uptake rates of juvenile jumbo squid (Dosidicus gigas) is suppressed by ~20% at elevated CO2compared to control conditions. Furthermore, elevated CO2has been shown to alter cephalopod behaviours. The two-toned pygmy squid (Idiosepius pygmaeus) and the bigfin reef squid (Sepioteuthis lessoniana) under elevated CO2both respond with increased activity levels as well as altered predatory and anti-predator behaviours such as an increase in the time to attack prey, striking their prey from further away, altered body pattern choice (Spady et al., 2014; 2018). Cephalopods play a really important role in the food webs of many oceans, and so these responses to elevated CO2could have far reaching consequences.
While the effects of projected future CO2levels could have significant effects on the performance, populations, and ecological interactions of some cephalopods, other cephalopod species appear to be tolerant to elevated CO2 exposure. Fortunately, cephalopods have an adaptive advantage over many marine species. Throughout their evolutionary history, cephalopods have developed characteristics of short lifespans, fast growth rates, large populations, and a high rate of population increase. When facing changing environmental conditions, these characteristics provide opportunity for selection of more tolerant genotypes, giving them a high capacity for adaptation. Future studies should investigate the potential for cephalopods to adapt to elevated CO2and determine their potential to cope with projected changes in ocean conditions. If future generations of cephalopods benefit from these traits in the face of global change, perhaps future generations of humans can continue to appreciate them in all of their natural splendour.
Spady BL, Watson S-A, Chase TJ, Munday PL (2014) Projected near-future CO2 levels increase activity and alter defensive behaviours in the tropical squid Idiosepius pygmaeus. Biology Open, 3, 1063–1070.
Spady BL, Munday PL, Watson S-A (2018) Predatory strategies and behaviours in cephalopods are altered by elevated CO2. Global Change Biology, 24, 2585–2596