Scientists from the Department of Geosciences at the University of Malta have discovered more than 1,500 enigmatic mounds on an area of seafloor ten times the size of Comino and located off Marsascala.
“The density of these features, which consist of rocky outcrops with a mounded shape, is unparalleled and definitely not what we would have expected in this part of the Mediterranean Sea," says Prof. Aaron Micallef, the lead scientist on the project. "Most similar structures we know of are from tropical waters and are quite different from the ones we found offshore Malta."
3D image (seafloor depth) of two mounds
These mounds, which are on average 20 m wide and can reach a height of several metres, occur in dense clusters at seafloor depths ranging between 60 and 120 m. The origin of these mounds remains unclear, although they were possibly formed by either seepage of groundwater or wave action when sea-level was lower in the past.
“The most fascinating aspect of these mounds is that,” says Prof. Micallef, “by rising above the sediment seafloor, they provide a base for a wide range of organisms, many of them endangered and protected by international law.”
The surfaces of the mounds, which consist of fossilised algae and tubeworms, provide a home to black corals, gorgonians, colourful sea slugs and sea urchins. “When we think of reefs, this isn’t usually what we think of,” says Dr Or Bialik, a Marie Curie Fellow and lead author of the study. “But at these depths, light is limited and this is the type of biological communities one should expect. These are delicate organisms, growing slowly over hundreds and even thousands of years.”
Gorgonians on the flank of one of the mounds
Unfortunately, the scientists have also identified extensive trawl marks, formed by dragged anchors or bottom fishing activities, located in the same area as these mounds. In several locations, it appears that trawling activities have destroyed or damaged mounds and their fragile ecosystems. The inclusion of the seafloor hosting the mounds in a Marine Special Area of Conservation is thus urgent.
This study, which was funded by Marie Curie Actions, also involved scientists from the University of Milano Bicocca (Italy) and the National Oceanography Centre (UK). For more information kindly contact Prof Aron Micallef.
Black coral on the top of one of the mounds