Maltese researchers have called for careful monitoring of an invasive species of algae that has been found in Maltese waters.
Known as Caulerpa taxifolia var. distichophylla, the Australian alien seaweed was recorded in southern Sicily in 2007 and is now considered to have “pest status”.
A research paper by five academics – Patrick Schembri, Jacqueline Barbara, Alan Deidun, Edwin Lanfranco and Sandro Lanfranco – states that two patches of the alga with a total area of around 125 square metres at a depth of between four and six metres were noted at White Rocks.
Meanwhile, another two patches with 520 fronds at a depth of 14 metres were found in Exiles in surveys carried out in November 2013 and in January and July last year.
They noted that the type of algae found in Malta had the same characteristics as the one found in Sicily and also highlighted it was possible that the species was spreading at White Rocks.
It was also possible that the alga was present in Malta before it was first spotted in 2013. Although distinctive, the small size of the fronds and the fact that it grows embedded within dense patches of taller-growing algae “makes it very difficult to spot, even when specifically being searched for”.
Locally it was found in very small areas and has a low frond density, which contrasts with Sicily, where it is found on 25km of coastline and four additional sites.
Its introduction into the Mediterranean is likely to have been through shipping or the aquarium trade while it possibly spread within the Mediterranean basin through currents, shipping or fishing gear.
The report said that “Sicily is the most likely source” for the Maltese population through recreational or commercial shipping. “There is a regular, and at times heavy, two-way traffic of pleasure craft and other vessels between the two islands,” the report states, which are just 100km apart. Also most local yacht marinas and harbours are along the north-eastern coast.
The report states the alga is “invasive” in Sicily, where it is not only established but also extends its range and has had significant ecological impacts on the ecosystems it has colonised. It also has affected fishing activities and has pest status.
However, “in Malta it seems that this species is in its initial stages of colonisation”.
While noting that it had not yet become invasive or “seems not to have had any large ecological or economic impact,” the situation needs to be “very carefully monitored” as it seems to easily propagate by fragmentation.
The shallow water where it has been found offers great potential for the alga to be ripped off the bottom by boat anchors and chains, propellers or winter storms and for the species to spread.
These management measures need to take into consideration the way the alga propagates through fragmentation so as not to “inadvertently” lead to it spreading.