Historical ecology of Lessepsian migration

In the Mediterranean Sea, 6% of all living organisms have been introduced from temperate and tropical oceans by shipping, aquaculture and because of the opening of the Suez Canal: they are the so-called alien species. These invasions of marine biota by alien species are considered one of the major threats to marine ecosystems worldwide. However, our ability to manage these processes is hampered by the lack of direct observation and recognition of the earliest phases, leading to significant delays in alien species detection, a biased appreciation of how fast species settle in the Mediterranean Sea, and lack of knowledge on the pristine conditions before the alien introduction started. Poor knowledge on the phenomenon greatly influences our ability to control it, leading to lack of awareness and management. However, the introduction of alien species impact the fisheries, affect key habitats where marine species reproduce, directly affect human infrastructures, and the potential of coastal sites for recreation and tourism. The lack of direct observation can be overcome with the concepts and methods of Conservation Paleobiology, a new scientific discipline, which uses techniques developed by paleontologists to address problems related to the conservation of biodiversity. In particular, the empty shells on marine substrates can be used to reconstruct the changes which have occurred to marine communities. The approach proposed in this project is entirely novel and innovative: in contrast to previous approaches, it allows to estimate the precise timing of introduction of alien species, and consequently to provide a new view on the dynamics of species introduction. The Eastern Mediterranean Sea is particularly affected by invasive alien species, and it is the ideal setting to develop and test new approaches to study this phenomenon, in cooperation with colleagues from Israel. We will focus on molluscs, whose shells are durable and informative for our purposes. We will use paleontological techniques, such as analyses of species composition and turn-over in sediment cores, shell dating, and studies that compare the diversity and structure of communities with the accumulations of empty shells in the same areas. Our main aims are to: i) estimate the timing of settlement of alien molluscan species and quantify the difference against the timing of first discovery; ii) estimate the speed at which alien species are being introduced; iii) understand how communities were before the start of the alien invasion, and iv) establish the extent to which accumulations of empty shells can be informative to understand the changes to the habitats caused by the introduction of alien species.

The Mediterranean Sea is under the threat of multiple human pressures such as climate warming and biological invasions. The eastern Mediterranean has been connected to the Red Sea by the Suez Canal 150 years ago, enabling hundreds of tropical species to enter the basin. For long, these tropical species have been considered the main cause of the demise of Mediterranean species. Our research spread new light on this phenomenon by focusing on the coastline of Israel, among the warmest and richest in tropical species in the basin. We uncovered the disappearance of 90% of the Mediterranean species that used to live in shallow water in the area. In contrast, tropical species are on the rise, facilitated by seawater warming. In addition, we showed that direct competition with tropical species is unlikely to be the major driver of biodiversity loss, leaving climate warming as the main culprit. We also showed that intertidal species, those that live at the water edge, as well as deeper water species are not much affected. The former live in an extreme environment that is often exposed to air and sunlight; the organisms that live in the intertidal are thus able to withstand high temperatures. The latter live at depths that are much colder than shallow waters and thus naturally protected from warming. It is in these habitats that we should focus our conservation efforts. In addition, our project clearly showed the devastating the effects of climate warming on marine biodiversity, further supporting the need to curb greenhouse gas emissions.