Heat Waves Can Change Coastal Ecosystems

Long-term study shows effects of short-term extreme events

heat waves
Zostera marina (seaweed) in plant pots (plastic aquariums) in one of the 12 benthic cocci at the keel line during a long-term experiment to impact heatwaves on coastal ecosystem. Photo: Christian Pansch / GEOMAR (CC BY 4.0)

Model calculations predict an increase in extreme events such as heat waves as a result of climate change. With a long-term experiment in the Kiel Benthokosmen pilot plant, scientists from the GEOMAR Helmholtz Center for Ocean Research Kiel have found clear indications that even events of a few days or weeks in length can change coastal ecosystems in the long term. The results of the study were recently published in the international journal Global Change Biology.

When talking about climate change, the discussion tends to focus on rising global average temperatures. But the changes in the climate system have other effects. Computer models predict that even extreme short-term events such as heavy precipitation or heat waves will become more frequent in the future. Scientists from the GEOMAR Helmholtz Center for Ocean Research Kiel, together with colleagues from Portugal and Bermuda, spent several months exploring whether short-term heat waves of a few days or weeks could have a lasting impact on coastal ecosystems.

“Our findings actually suggest that even relatively short-term events have the potential to shift the existing balance between species of a habitat,” says Dr. Christian Pansch from GEOMAR. He is the lead author of the study, recently published in the international journal Global Change Biology .

For the experiment, the team was able to draw on the sophisticated technology of the Kiel Benthokosmen pilot plant. It consists of a total of 12 test chambers installed on a pontoon directly on the shores of the Kiel Fjord. In each of these chambers, in the summer of 2015, the researchers used a species community of seagrass and bladderwrack and their associated animals such as snails, crabs and shells for four months in summer 2015. “These are typical types of shallow water areas in the Baltic Sea,” explains Dr. Pansch.

The special thing about the benthic cocoons is that the researchers can precisely control various environmental parameters in the individual test ponds, including the water temperature, salinity, pH or oxygen content. “The water of the basins comes directly from the Kiel fjord and thus allows an almost natural environment in the experimental pools.

In the course of the study, the participants simulated the temperatures of the year 2009 in the test chambers in the summer of 2015. “This was a year without major extreme events with an almost ideal temperature curve. That’s why this year was a good basis for our experiment, “explains Dr. Pansch.

Building on this, there were a total of three scenarios. Four cymbals simply went through the temperature development of the ideal year 2009. In four other pools, the technique of benthicosms in August caused a summer heat wave. In the last four basins, the species community experienced two weaker heat waves in June and July, before reaching summer maximum temperatures in August.

About half of the species in the tanks showed clear reactions to extreme temperatures. “But the reactions were very different. In some species, the negative effects of the three heat waves added up, while other species were better able to cope with the summer heat after the two spring warming events. Other species in general benefited from the short-term high temperatures, “Dr. Gather together.

So, if the frequency and intensity of heatwaves increases in the future, there will be winners and losers in coastal ecosystems. The current structure of the species is expected to shift. However, not all the factors that can play a role in this regard have been examined in detail. Currently in the Kiel Indoor Benthokosmen in the basement of the GEOMAR another long-term trial is underway dealing with the effects of heat waves. Here the focus is on the impact of heat waves that will become longer and stronger in the future. And even in the current experiment in the benthos on the fjord shore, warming again plays a role, extended by phases of oxygen depletion. “That’s another phenomenon which we have observed several times in recent years and that could lead to a change in the composition of species, “explains Prof. Dr. med. Martin Wahl, co-author of the current study and head of the benthic ecology research unit at GEOMAR.

Source : GEOMAR Helmholtz Center for Ocean Research Kiel