Global climate change will affect fish sizes and ocean food webs

Posted on: 07 April 2020

New research by a collaborative team of scientists suggests that global climate change will affect fish sizes in unpredictable ways and, consequently, impact complex food webs in our oceans.

Using 10 million visual survey records of 335 fish species across coastal locations in Australia, which spanned decades, the scientists confirmed that changes in water temperature were responsible for driving changes in fish size across time and spatial scales.

The study used data collected through the decades-long Australian Temperate Reef Collaboration monitoring program and the citizen science Reef Life Survey program.

Deep Glen Bay, Tasmania. Credit Antonia Coper.

Prior knowledge led the scientists to predict that fish sizes would reduce as temperature increased, but the results – just published in leading international journal Nature Ecology & Evolution – put a line through this hypothesis.

It turns out that while temperature has a significant impact, it causes different fish species to react differently; some reduced in size as predicted (around 55%), but others increased in size (around 45%).

In general – but not universally – larger species tended to get even bigger in warmer waters, while smaller species tended to get smaller. Additionally, the species that were smaller at the warmer edges of their habitat ranges are more likely to get smaller still as time ticks on and global temperatures get warmer.

The research also underlined that temporal changes were about ten times as fast as spatial trends (fish size changed between 4% and 40% per 1oC change in temperature, though space and time respectively).

With this in mind, and with ocean temperatures set to rise between 1.2oC and 3.2oC by 2100, the effects of temperature-induced changes should be very significant.

This research has obvious implications for fisheries and their management, but the crucial message is that warming seas may have significant and unanticipated impacts on entire ocean food webs, which could present threats to marine conservation initiatives.

Lead author of the study, Dr Asta Audzijonyte from the University of Tasmania, was surprised by the results. She said:

“Initially, we were not sure that we would see strong temperature effects, because data from wild fish populations are often very noisy. But our careful analyses revealed the unexpected result that fish species respond to temperature change in quite different ways. Our results are important because they could help us forecast how different species will respond to future warming of the oceans.”

Nicholas Payne, assistant professor in zoology in Trinity College Dublin’s School of Natural Sciences was a co-author of the study. He said:

“One of the reasons this study is important is that it shows the complexity of species’ responses to warming in our oceans. Much of our understanding of the temperature-size relationship comes from the laboratory; taking our predictions to the wild shows us there is a lot we still need to learn about this hugely important phenomenon.”

Media Contact:

Thomas Deane, Media Relations Officer | | +353 1 896 4685