A small world

A study has shown that the body size of marine species is disproportionately affected by warmer temperatures. According to researchers, the most likely cause of the drastic shrinking size of marine animals is due to the much lower availability of oxygen in water than in air. Warming increases the need for oxygen across species, but aquatic species have a much harder job meeting this demand, explains Atula Gupta.

Global warming is one of the biggest truths of the modern world. A problem that we cannot deny and whose affects are slowly and surely being felt by every living organism on the planet. But while living forms on land, including humans, fight with epidemics, sudden storms, drastic weather changes and vanishing habitats, the organisms that inhabit oceans and lakes have a greater, life changing problem that has surfaced because of rising temperatures. Scientists find that marine animals are shrinking in size, almost 10 times more than land dwellers due to severe climate change.

What we simply term as global warming and understand as the rise in temperature of planet earth due to the increased accumulation of greenhouse gases like carbon dioxide, is actually like a nuclear bomb whose impact is widespread, and devastating for generations to come. The ripple effect of climate change is the real cause for alarm and because earth is 70 per cent water, it is the freshwater and marine animals that are the worst affected.

In a large study, researchers from Queen Mary College, University of London, and the University of Liverpool found that the body size of freshwater species as well as marine species has been disproportionately affected by warmer temperatures.

Size matters

Researchers compared the extent to which the adult size of 169 terrestrial, freshwater, and marine species responded to different non-harmful temperatures. Study co-author Andrew Hirst says, “While animals in water decrease in size by five per cent for every degree celsius of warming, similarly sized species on land shrink, on average, by just half a per cent.”

The current increase in global temperature of 0.7°C since pre-industrial times has thus already begun to force marine animals to unnaturally decrease their body size.
Water temperature is the most important environmental parameter that affects the life cycle, physiology and behaviour of aquatic beings. This includes plankton — which forms the basis of the marine food chain — corals, fish, polar bears, walruses, seals, sea lions, penguins, and seabirds.

According to the researchers, the most likely cause of the drastic shrinking size of marine animals is due to the much lower availability of oxygen in water than in the air. Warming increases the need for oxygen by organisms on land and in water. However, aquatic species have a much harder job meeting this increased demand. The shrinking of body size is therefore a survival technique adapted by the animals to ensure that in an environment where oxygen is already very low, they can continue to live and perform all bodily functions.

“To satisfy increased demands for oxygen at higher temperatures, aquatic species have fewer options. Reducing the size at which they mature is their way of balancing oxygen supply and demand,” said co-author David Atkinson, of the University of Liverpool.

Counting the losses

It will be a naive supposition to believe that the sudden dwarfing of fishes in the seas will not affect human beings. Given that fish and other aquatic organisms provide three billion people with at least 15 per cent of their animal protein intake, a smaller fish on the plate, will only lead to a bigger net cast to catch more numbers and more frequently. The vicious chain thus will only ensure that smaller, weaker, and lesser aquatic animals survive in the future topsy-turvy world.

A model developed by scientists at the University of British Columbia predicts that by 2050, warming will shrink the average maximum body weight of fishes by 14-24 per cent globally!

Most of the shrinkage will happen in tropical and mid-latitude regions including India. Fish will also shift their distribution towards the poles. So, smaller tropical fish will displace larger fish found at higher latitudes.

Warming has already affected some fish species. In the North Sea, for example, increasing ocean temperatures have reduced the body size of haddock. The size of mahseer in Indian water bodies has been observed to have shrunk in the last few years.

To makes matters worse, global warming and climate change affect the seas in other ways too. It has led to a decrease in lake waters, an increase in the sea level, and changes in streams and precipitation models. Krills have decreased by 80 per cent on average in the past 30 years. Coral bleaching has increased dramatically.
Reproduction area of sea turtles has narrowed because coastal habitats are being destroyed by sea level rise. With decreasing sea ice, many of marine mammals face extinction.

According to the Intergovernmental Panel on Climate Change a further rise of between 1.4°C and 5.8°C is predicted by the end of the century. Collating this with the present research implies that numerous freshwater and marine species are doomed to become skeletal remnants of their healthy past.

The message is clear: If we do not urgently reduce carbon emissions and utilise clean energy to power our future, this blue planet will turn into a massive ball of fire charring even the seas.