Since the middle of the 20th century, there has been a decline of 2-5% of oxygen concentrations in open ocean and coastal waters. This change disrupts the distributions of marine species, posing terrible new threats to marine life.
In Philosophical Transactions of the Royal Society B, scientists have contributed to the theory that some marine species will be more vulnerable to changes in the future climate, specifically marine invertebrates with larger body size. Oxygen dissolved in ice cold water has allowed for the occurrence and survival of gigantic species in polar water.
John Spicer, Professor of Marine Zoology at the University of Plymouth, and Dr Simon Morley, an Eco physiologist with the British Antarctic Survey (BAS) conducted a study which informs us that as oceans become warmer and oxygen levels decrease, oxygen limitation will impact larger marine invertebrates and fish.
This study entailed investigating how several amphipod species, of varied sizes, in Antarctic waters, performed when the oxygen in the water they were in was reduced.
It reveals that performance with body size was reduced, reinforcing that larger species will be more sensitive to climate change due to oxygen limitation.
However, evolutionary innovation can change this situation. In larger body sized animals, the presence of oxygen - binding pigments in body fluids enhances oxygen transport, and novel gas exchange structures in some species, offsetting respiratory disadvantages of larger body size.
Professor Spicer, with more than 30 years of experience examining climate change effects on marine organisms, stated that unless species adapt to the decreased oxygen in oceans, many larger marine invertebrates who will be sensitive to these changes, will either shrink in size, or face extinction, and inevitably this will have a negative impact on the ecosystems.
Research has also demonstrated how evolution plays a key role in protecting some species from the drop in oxygen levels. Some species have evolved mechanisms to compensate for the reductions in oxygen, but this ‘evolutionary rescue’ is not enough to save species from oxygen-poor oceans.
Marine animals in the Southern Ocean have developed certain ‘strategies’ equipping them with distinct characteristics to adapt and thrive in freezing water. These strategies, however, are predicted to hinder the survival of Antarctic marine invertebrates and fish in the face of climate change. Dr Morley adds that ‘’understanding these impacts will not only help us to predict the fate of marine biodiversity at the poles but will also teach us much about the mechanisms that will determine the survival of species across the world's oceans."