By Ignasi Montero-Serra, Martin Edwards and Martin J. Genner
The continued rise in water temperature has altered the structure and function of marine ecosystems around the world.
In the North Atlantic its effect has been even greater, with increases of up to 1.3 ºC in the average temperature of the last 30 years. These fish represent an important source of income for most coastal countries in the world.
The variation affects sardines, anchovies, horse mackerel and mackerel, among others, which feed on phytoplankton and zooplankton, and which are the basis of the diet of large predators such as cetaceans, large fish and seabirds.
These fish also represent an important source of income for most of the world's coastal countries.
Until now, scientists had not been able to prove whether the observed changes in the physiology of these species were a direct result of the water temperature or whether it was due to changes in the planktonic communities, their main prey, which have also been affected. due to global warming and their distribution and abundance have changed.
The new study, published in Global Change Biology and which has developed statistical models for the North Sea area, confirms the great importance of sea temperature.
"Zooplankton time series and sea surface temperature data have been included to determine what was the causative factor of these patterns," Ignasi Montero-Serra, lead author of the study and researcher in the Department of Ecology of the University, told Sinc. from Barcelona.
To demonstrate the consequences of warming water, the research team analyzed 57,000 independently conducted commercial fishery fish censuses along the European continental shelf between 1965 and 2012, extracted from public data provided by the Council. International for the Exploration of the Oceans (ICES).
The work, the first to be carried out on a large temporal and spatial scale, makes it possible to understand the dynamics of these species in relation to the rapid warming of the oceans that has been occurring since the 1980s. The results reveal that sardines and other fish They are highly vulnerable to changes in the temperature of the oceans, which is why they represent "an exceptional bioindicator to measure the direction and speed of climate change that is expected in the recent future", points out Montero-Serra.
With the accelerated increase in temperature in the continental seas, sardines and anchovies –with a typically more subtropical distribution– have increased their presence in the North Sea, “even entering the Baltic Sea”, says Montero-Serra, who It states that species with a more boreal distribution - such as herring or sprat - have decreased their presence.
The analysis thus shows “a clear sign of subtropicalization” in the composition of the species of the North Sea and the Baltic Sea, “where sardines, anchovies, mackerel and horse mackerel, more related to high temperatures, have increased their presence ”, Says the researcher.
This is because pelagic fish are highly dependent on environmental temperatures at different stages of their life: from reproductive migrations and egg-laying, to larval development and survival.
According to the researchers, changes in this important ecological group "will affect the structure and functioning of the entire ecosystem."
The expert warns that coastal peoples highly dependent on these fishery resources "will have to adapt to new ecological contexts and the possible consequences of these changes," although the magnitude of the socioeconomic and ecological repercussions is still unknown.