A study reveals the key role of rhodoliths of the Menorca Channel as carbon sinks

A study led by IMEDEA (CSIC-UIB) demonstrates the capacity of these marine habitats to promote the accumulation and long-term sequestration of organic carbon over millennia.

A scientific team led by the Mediterranean Institute for Advanced Studies (IMEDEA, UIB-CSIC), in collaboration with University College Dublin and the Institute of Marine Sciences (CSIC), has documented the ability of the rhodolith beds in the Menorca Channel to store organic carbon for thousands of years. The study provides new insights into the role of these marine ecosystems as long-term carbon reservoirs in the Mediterranean.

Rhodoliths are slow-growing calcareous red algae that form extensive biogenic seabeds. Silvia de Juan, the lead author of the study, highlighted the significance of the findings published in the journal  Biogeosciences: “Although these ecosystems are widely distributed throughout the world's oceans, their capacity for long-term carbon storage has received relatively little attention, particularly in the Mediterranean. This study highlights the importance of rhodolith beds and the need to protect them as part of marine ecosystem conservation strategies.”

The researchers also point out that these ecosystems are gaining increasing recognition within the scientific discussion surrounding blue carbon because of their ability to store organic carbon over extended periods.

The research focused on a 43.6 km² area of the Menorca Channel, home to one of the largest known rhodolith beds in the Mediterranean. To reconstruct its sedimentary history and determine its carbon storage capacity, the team combined high-resolution geophysical mapping, sediment core sampling and radiocarbon dating.

The results show that the sedimentary deposit associated with these rhodolith beds began to form during the Early Holocene, approximately 10,000 years ago, as sea level rose following the last glaciation. Later, between 7,000 and 6,000 years ago, sea-level stabilization promoted the establishment of dense and extensive rhodolith and maërl beds that have persisted to the present day.

Regarding organic carbon, the researchers estimated that the upper 50 centimetres of sediment store an average of 32 tonnes of carbon per hectare. The average organic carbon content within this surface layer remains relatively stable throughout the analysed sediment profile.

According to the authors, this stability indicates the long-term preservation of organic matter over approximately the last 6,000 years. The findings suggest that the three-dimensional structure created by rhodoliths promotes the trapping of organic particles, which are preserved within highly carbonated sediment deposits, thereby contributing to long-term carbon storage.

The authors emphasize the importance of conserving these habitats, particularly in the face of physical disturbances such as bottom trawling and dredging, which can disrupt sediment deposits that have accumulated over thousands of years.

They also note that the protection of the Menorca Channel has helped preserve a unique natural system that provides an exceptional opportunity to study carbon storage processes in biogenic seabeds.

The study concludes that the rhodolith beds of the Menorca Channel constitute genuine long-term sedimentary archives and that their contribution to carbon storage should be considered in marine ecosystem conservation strategies.