“Neptune's meadows” are in danger: As the climate warms, the ecologically important Neptune grass could increasingly be replaced by a small-growing species from the Red Sea, a study shows. According to forecasts, the water in many places could become too warm and too salty for the native marine plants - but the invasive species can cope well with it. Ecological change in underwater flora could affect the many animal species that depend on the lush seagrass beds, scientists say.
Meadows that are moved by the water current instead of the wind: Many coastal areas of the seabed in the Mediterranean are characterized by wide fields of seagrass. These underwater landscapes are considered to be of great importance: the seagrass meadows play an important role as habitats and nurseries for a large number of inhabitants of the Mediterranean. They also contribute to climate protection: the marine plants bind large amounts of carbon in their biomass, which originally comes from the CO₂ in the atmosphere. But how will the Mediterranean seagrass meadows react to the environmental changes caused by climate change? The international research team led by the Leibniz Center for Tropical Marine Research (ZMT) in Bremen has now investigated this question.
How will seagrass landscapes change?
As the researchers explain, there are a total of four native seagrass species in the Mediterranean that have adapted to certain ecological niches through different characteristics. However, the dominant species so far is Posidonia oceanica. This underwater plant, also known as Neptune grass, grows up to over a meter long and characterizes the large seagrass meadows in coastal areas. In addition to the native species, an invasive plant is also spreading in the Mediterranean: Halophila stipulacea, which is only about ten centimeters high, originally comes from the Red Sea and migrated into the Mediterranean via the Suez Canal.
As part of their study, the researchers first collected information on the characteristics, adaptability and tolerance limits of the various seagrass species. They then combined this data with forecasts of the regionally different environmental changes in the Mediterranean that can be expected as a result of climate change. A modeling approach was used that enables complex simulations of biological and ecological development processes.
The future belongs to the little ones
As the team reports, the results of their model simulations of future development indicate a drastic change in the seagrass ecosystems of the Mediterranean. The neptune grass that has so far dominated will therefore not be able to cope with the expected increase in water temperatures and salinity over a wide area. Its populations will therefore probably retreat sharply to cool refuges in the northwest of the Mediterranean.
Where the lush seagrass meadows disappear, the growth will probably be more modest: "We expect a shift from long-lived, large species, such as the native Posidonia neptune grass, to small and fast-growing species such as the invasive Halophila," says first author Pedro Beca -Carretero from ZMT. “Posidonia is still the most common seaweed species in the Mediterranean - but it has little ability to spread, grows slowly and is very susceptible to stress. Halophila, on the other hand, is adapted to the conditions in the Red Sea, which has a high salinity and is one of the warmest seas in the world due to its enclosed location in tropical and subtropical regions,” explains the scientist.
As the researchers emphasize, the change in the vegetation of the underwater landscapes could have far-reaching effects on the living environment in the Mediterranean. The lush seagrass meadows play a key role in the life cycle of many organisms: they offer protection and food and form the nurseries of many fish, crabs and mollusks. The loss could therefore have complex consequences. “It is quite possible that this will affect the health and resilience of the entire Mediterranean coastal environment. This also affects people such as fishermen, restaurateurs and others who rely on this coastal habitat,” concludes Beca-Carretero.
Source: Leibniz Center for Tropical Marine Research, specialist article: Science of The Total Environment, doi: 10.1016/j.scitotenv.2023.168675