Photo credit: phys.org
Researchers at the University of Liège have conducted a study focused on Posidonia seagrass meadows in the Mediterranean Sea, revealing significant insights into the ecological processes occurring in these underwater environments. The research, based at the STARESO station in Calvi, Corsica, highlights how the dead leaves of Posidonia, also known as Neptune grass, accumulate in shallow waters and decompose similarly to compost, playing a crucial role in the remineralization of organic matter.
Traditionally, the breakdown of this material was not fully appreciated in terms of its impact on carbon dynamics within coastal ecosystems. Interestingly, alongside the emission of CO2, the researchers observed oxygen production linked to the activity of photosynthetic organisms thriving within the decomposing leaves. This development distinguishes the processes in marine compost from those we see in terrestrial environments.
“Posidonia is a unique terrestrial plant that adapted to marine life millions of years ago,” explained Alberto Borges, an oceanographer involved in the research. “During autumn, these plants shed their older leaves, which accumulate to form large patches of litter near the seagrass meadows.” This litter, he notes, serves as a nutrient-rich substrate where organic matter decomposes and releases vital nutrients and gases.
Gilles Lepoint elaborated on the findings, comparing the litter to garden compost, noting that the presence of light and nutrients leads to surprising byproducts, including oxygen produced from the photosynthetic activities of various organisms residing within the litter.
Despite the oxygen production observed in this nutrient-dense environment, the study found that the overall decomposition process results in a net consumption of oxygen, making these accumulations overall emitters of CO2, akin to terrestrial compost and leaf litter.
Another unexpected finding from the study was the rate at which Posidonia litter degrades. Preliminary assumptions suggested faster degradation, but measurements of mass loss indicated a much slower rate. “Our short-term incubations yielded lower values for respiration compared to traditional long-term observations, challenging earlier assumptions about carbon dynamics in these ecosystems,” Borges stated.
The research also expanded to include macroalgae residing on nearby rocky substrates, where a surprising trend was noted: despite capability for photosynthesis, these macroalgae were determined to be net consumers of oxygen. This raises questions about the organic matter dynamics in these systems, with implications that the macroalgae rely on organic material sourced externally, potentially from the Posidonia meadows.
This mutualistic relationship between macroalgae and Posidonia indicates a complex interaction, with organic molecules diffusing from the seagrass litter enriching the rocky habitats, and macroalgae drifting into the Posidonia litter contributing to primary production within these meadows.
The study’s findings add valuable knowledge regarding the carbon balance within Posidonia ecosystems, which have been under investigation by marine scientists at the University of Liège since the 1980s. This ongoing research underscores the ecological significance of Posidonia meadows within the Bay of Calvi and their role in broader coastal carbon dynamics.
Overall, the research published in the journal Estuarine, Coastal and Shelf Science not only enriches our understanding of marine biology but also emphasizes the importance of preserving these vital underwater prairies that hold significant ecological and carbon regulatory functions.
Source
phys.org