UAE study looks at how climate change will affect fish in tropical waters

A study involving undergraduates at UAE University in Al Ain is shedding light on this by finding out what the optimal or ideal temperature is for a range of freshwater fish species, and comparing this to the current temperature of the waters where they live.

Undergraduates are helping with the project, supervised by Dr David Thomson, associate professor at the biology section. Courtesy UAE University

AL AIN // The effects that climate change is having – and will continue to have – on wildlife are many and varied, and they are not restricted to creatures that live on land.

Rivers, lakes and seas are warming, with the uppermost layer of the world’s oceans, for example, experiencing an average temperature rise of 0.1°C per decade, according to the United States Environmental Protection Agency.

Aside from disrupting weather patterns, ocean warming will cause storms to become more frequent in tropical areas, and these temperature rises will affect creatures that live in water, including fish.

A study involving undergraduates at UAE University in Al Ain is shedding light on this by finding out what the optimal or ideal temperature is for a range of freshwater fish species and comparing this with the current temperature of the waters where they live.

Running for about two years and led by Dr David Thomson, an associate professor in the biology department at the College of Science, the study has found that some types of fish from tropical areas are already living at or close to their optimal temperature. As a result, these fish could find it hard to cope if temperatures rise.

The fish were put in tanks at various temperatures and the creatures’ breathing rate recorded, with the optimum temperature being the one at which the rate is at its maximum.

“We start at room temperature; we know that’s a temperature at which these fish can function and operate,” said Dr Thomson, a Scottish scientist who has been at UAEU since 2014.

“Then, we gradually warm the temperature up. The measure of performance is the breathing rate. You look at the mouth and gills and the number of breaths per minute.”

The temperature is increased until the breathing rate begins to decline, which indicates that the optimal temperature has been reached. It is only necessary to raise the temperature a couple of degrees Celsius above the optimum and the fish are, therefore, not likely to become stressed during the experiments.

Sixteen undergraduates have run the tests. Seven species of fish were looked at, all from hot regions or with part of their range in the tropics.

Four types have an optimal temperature about the same as or lower than the average temperature of the water where they occur naturally. These are the Nile tilapia (from central Africa), the sabaki tilapia (from east Africa), the three-spot gourami (native to South-East Asia) and the goldfish (from southern China up to Japan).

The three-spot gourami has an optimal temperature of between 24°C and 26°C, while in its natural environment temperatures range from about 24°C to 30°C.

Any human-induced temperature rises could harm these four species, causing population numbers to fall.

The other three species – the Siamese fighting fish, the koi and the angelfish – all have optimal temperatures higher than the temperature of their natural environment, so they could be more resistant to warming.

In focusing on the effects that climate change could have on the tropics, Dr Thomson said this study, which he planned to publish as a scientific paper, is relatively unusual.

“Less than 1 per cent of studies done on climate change have been done in the tropics. The size of the temperature change is smaller than in cooler latitudes, but the impact could be greater,” he said.

Another of Dr Thomson’s studies illustrates his view that warming may have a lesser impact on temperate regions.

It involved a scientific literature search looking at 48 bird species, none from tropical regions. The study focused on whether the creatures were living at a temperature above or below their optimum.

In 33 of the 48 cases, the birds’ survival rates, breeding success or another measure of how well the creatures were doing were greater in years that were warmer than average, suggesting that slight increases in temperature could – unlike for most of the tropical fish – be beneficial.

Another piece of research by Dr Thomson involved poring over the scientific literature to find out how many species can live above particular temperatures.

The research compiled 557 studies from all over the world, each looking at the maximum temperature for particular types of creature.

At 0°C, all of the species are able to survive, but the first species find to find it too hot are lost at 4.5°C and the second at 7°C.

At 30°C, more than 500 species can still exist.

Move up to 50°C, however, and just a handful are left. This highlights how potential increases in temperature in places such as the UAE, that are already very hot, could have a devastating effect on wildlife.

“In the UAE you’re already in a range of temperatures where not much of the world’s biodiversity can survive,” Dr Thomson said.

“If we increase by two or three degrees, we’d be in the region where virtually none of the species could survive.”

The way in which climate change is causing parts of the world, including much of the Arabian Peninsula, to become drier is another area of interest.

It is more difficult, however, to run experiments to test the effects of rainfall on species’ survival than it is to measure the effects of temperature.

“Within the Arabian Peninsula, it tends to be getting drier but it’s getting a little bit wetter within the UAE as you get towards the northern tip,” Dr Thomson said.

“Because it’s getting warmer despite getting wetter, the net result is that there is going to be increased evaporation, so the net change is towards the dry end.”

Now, Dr Thomson is preparing to analyse a range of studies to explore the relationship between rainfall and survival rates.

He and a co-researcher are also looking at the effects of temperature on the population of turtles in the Arabian Gulf.

Using long-term data, they are analysing how changes in temperature from year to year affect the numbers of these reptiles.