Malta sea life at risk from rising heat

The temperature of Malta’s seas has been creeping up steadily over the last few decades, with Meteorological Office data showing an increase of approximately 2°C since the 1980s.

Experts have long warned of the lasting effects this will have on the marine environment, but just how much this will impact the local community is hard to predict, according to marine biologist Dr Julian Evans.

He said that rising sea temperatures as a result of climate change would definitely affect Malta’s marine life, but there were so many factors to consider that it would be difficult to measure the extent of this.

Evans is a researcher who has published a number of papers on invasive marine species. His doctoral thesis found that shallow-water pebble-beds, generally thought to be quite barren, are actually home to an unexpectedly high species diversity.

Evans said he had no evidence indicating that rising sea temperatures could affect these beds, but nor was studying a potential link the scope of his work.

“Very limited information is available on temperature tolerance for most species, apart from fish and a few other groups, so it isn’t easy to predict the effect of rising sea temperatures,” he said. When it comes to the more prolific species, for which there is more available data, it is more straightforward, he said.

He explained that every species has its own optimal temperature range. For cold-water species, the present sea temperature is already at the warm end of what they can tolerate, so any increase in temperature would make it considerably more difficult for them to survive.

This, he said, would lead to more of that species of fish dying – either from heat stress, or from having become more susceptible to disease. Meanwhile, species better suited to warmer waters will likely thrive as the sea gets warmer, and marine communities in Malta will start to resemble those in the south-eastern regions of the Mediterranean.

“For example, the parrot fish, which was previously found in the eastern and central Mediterranean is now being sighted in the northwest, and its abundance in the central parts has been steadily increasing,” he said, adding that a confluence of factors could be at play.

For instance, many alien species spotted in Maltese waters are a result of shipping and the importation of aquarium life, but warmer seas mean that these species could now survive long enough to establish a population.

Moreover, as the climate gets warmer and the sea temperature rises, its salinity will likely do so too, and this could alter ocean currents, said Evans. This, he said, could alter living conditions for marine life and also aid or prevent fish and larva (the immature form of an insect or other animal) from moving from one part of the global ocean to the other. This is not to mention the fact that the sea is absorbing more carbon dioxide, resulting in more acidic seas.

Ultimately, however, the effect of these changes and the prospect of any potential benefits remain unclear, and are in some cases a matter of perspective, said Evans. 

Species better suited to warmer waters will likely thrive as the sea gets warmer, marine communities in Malta will start to resemble those in South-eastern Mediterranean

“We can’t generalise,” he said. “It’s possible that one species could be added or lost from a system without any major changes while another could have a disproportionate effect.”

For example, we could see the introduction of an invasive species, which is very effective at grazing algae, and leaving barren, exposed rock, which in turn reduces the habitats for the creatures that make their homes in algae. A scenario like this would ultimately lead to a change in the seascape from “algal forests to bare bedrock”.

A development like this may not be considered positive by the diving industry, which might be more interested if a new variety of colourful fish were to be introduced in our seas. Similarly, fishing communities could start catching more fish if the water becomes more suited to a particular commercially exploited species, but could also have to contend with more poisonous fish and declining catches.