November 2014 saw the release of Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report Synthesis Report. “Science has spoken”, UN Secretary General Ban Ki Moon iterated on the climate crisis challenge that we now face. “There is no ambiguity in their message. Leaders must act; time is not on our side". The Earth’s surface is warming, and it is with 95% certainty, the IPCC concludes, that the dominant cause is human activity. The climate crisis impacts every part of our planet, including the ocean, where rising sea levels and global ocean temperature increases are a significant cause of concern. On a global scale, measurements show that between 1971 and 2010 the upper 75 meters of the ocean has warmed by 0.11⁰C. Between 1901 and 2010, the global mean sea level has risen by 0.19 meters. Ocean acidification, regarded as climate change’s “evil twin” is also a growing cause for concern, with greenhouse gas emissions - the primary contributing factor to the climate crisis - also altering the carbonate chemistry of the ocean. These figures may seem small, but they are not insignificant to the fish that occupy the ocean.
The majority of marine fishes are ectothermic – they do not generate their own internal heat, instead relying external heat to give them the warmth necessary for physiological processes. Although the thermal tolerance of each species varies, their distribution is inextricably tied to ocean temperature. As Dr William Cheung of the University of British Columbia’s Fisheries Centre and colleagues highlighted in a 2009 study, this generally means species shifting polewards towards the cooler (albeit warming) waters to stay within their thermal niche. Adding invertebrates into the calculations, a 60% species turnover of biodiversity in the Arctic and Southern Oceans is predicted by 2050. For fish living in the poles, whose temperature limits are on average 2 - 4 times narrower than lower latitude species, warming waters may be the end of the line - there may simply be nowhere left for these fish to go.
The full article was published in – and can be read in – The Marine Professional, a publication of the Institute of Marine Engineering, Science & Technology (IMarEST).
Image: Blackspot snapper Lutjanus ehrenbergii, Marsa Alam, Egypt. Credit: zsispeo/Flickr (CC BY-SA 2.0)