The chronicles of a small invader : the canal, the core and the tsunami

Abstract

Information on early invasion stages, whether successful or not, is often lacking because most invaders are only discovered once they have become abundant enough to be casually detected or have caused appreciable changes to the recipient environment. Moreover, when newcomers fail to establish self-sustaining populations, they are often not even documented; likewise the cause(s) of the failure remains unknown in most cases. Here we report for the first time a probable failed early invasion, caused by an unpredictable geological event, that was detected from two sediment records radiometrically dated through 210Pb chronology. The cores, collected from Marsamxett Harbour in Malta (Central Mediterranean), reveal a continuous record for at least the last 110 years. Both cores contain towards the bottom (dated to the beginning of the twentieth century) the highly invasive Lessepsian immigrant benthic foraminifer Amphistegina lobifera Larsen 1976, demonstrating that it was present in this region long before it was first recognized in the Mediterranean. It then abruptly disappeared from the cores. We document that the disappearance may have been triggered by the 1908 Messina earthquake, with a resulting tsunami wave that reached Marsamxett Harbour and deposited over 20 cm of sediment. This event suddenly buried the sea-bottom, destroying the existing benthic community and damaging the seagrass Posidonia oceanica meadow. Today, A. lobifera is abundant along the Maltese coast, likely as a result of re-invasion in the 1940s, yet followed by a long detection lag time until it was first found in 2006.