That invasion of native biotas by non-indigenous species may represent a threat to the integrity of biotic communities, the economy, and even human health, is recognised worldwide. The environmental impact of invasive marine species may be so severe that the International Maritime Organization of the United Nations has identified the introduction of aliens as one of the four greatest threats to the world’s oceans. Alien species may affect recipient ecosystems through predation, direct and indirect competition, contamination of the native gene pool by exotic genes (for example, through hybridization), habitat modification, and through the introduction of new parasites and pathogens.

 

Colonization by non-indigenous species may be a natural phenomenon whereby, due to changing environmental conditions, an organism is dispersed into a region where it did not exist before by means of natural mechanisms, what is termed ‘range extension’. More often than not, however, introduction of such species is a result of human activities, which may give rise to problems since human-facilitated introductions usually occur at rates higher than the natural rate of range extension, often surpassing many natural barriers to dispersal such as distance or currents. Consequently, existing equilibria between the native biota and their physical and biological environments may be disrupted. 

 

Current work being carried out as part of this project includes an update to the inventory of non-indigenous species reported from Maltese waters , studies on the ecology of select non-indigenous species, such as the crab Percnon gibbesi and the bed-forming mussel Brachidontes pharaonis, and investigations on newly discovered species in the Maltese Islands, including their modes of entry (e.g. Aplysia, Cassiopea, Epinephelus, Melibe, Oplegnathus, Paraleucilla, Scatophagus.) 

 

The high number of non-indigenous species in the Mediterranean Sea has been attributed to such human activities as seafaring, commerce and tourism, to the occurrence of numerous habitats susceptible to invasion, in particular those subject to anthropogenic disturbance (for example, such as lagoons, estuaries, and marinas), to aquaculture ventures, and to the opening of the Suez Canal, which has led to the introduction of hundreds of species from the Red Sea to the Levantine region of the east Mediterranean, a phenomenon that is known as ‘Lessepsian migration’. 

 

Although temperature change scenarios in Europe vary regionally, there is a clear trend towards overall warming. Consequently, present day sea warming favours the occurrence, establishment and range extension of warm-water species, whether alien or native, in the Mediterranean Sea. The number of macroscopic marine species inhabiting the Mediterranean is today estimated at about 12,500, of which around 745 species are not indigenous to the region. Immigration through the Suez Canal and transportation by ships are the two vectors contributing largely to introductions of such aliens into the Mediterranean. 

 

Because of their location on or close to the biogeographic boundary between the western and eastern Mediterranean bio-regions, the Maltese Islands are an important station for monitoring the entry and spread of alien marine species in this sea. With increasing marine traffic, both commercial and touristic (cruise liners, yachting), the Maltese Islands face an ever increasing threat of alien species arriving in ballast water or on ship hulls or through other means. Due to their position, the Maltese Islands may act as a stepping stone for already established alien species to expand their range from west to east or vice versa. Moreover, the Maltese Islands are at the meeting point of Atlantic-derived aliens with those originating from the Red Sea and Indo-Pacific, providing an interesting opportunity to study the interactions of alien species of different biogeographic affinities.

 

The Marine Ecology Research Group is carrying out research on the detection and monitoring of non-indigenous species in Maltese waters, including analysis of their mode of entry, to evaluate the extent of range expansion by warm-water species as a result of tropicalization of the Mediterranean Sea, while at the same time recording direct introductions caused by human-mediated activities. Investigations on specific non-indigenous species that have become established in the Maltese Islands are also being undertaken to assess the effects of such on the native communities.