Native biodiversity collapse in the Eastern Mediterranean

Global warming causes the poleward shift of the trailing edges of marine
ectotherm species distributions. In the semi-enclosed Mediterranean Sea,
continental masses and oceanographic barriers do not allow natural
connectivity with thermophilic species pools: as trailing edges retreat, a
net diversity loss occurs. We quantify this loss on the Israeli shelf,
among the warmest areas in the Mediterranean, by comparing current native
molluscan richness with the historical one obtained from surficial death
assemblages. We recorded only 12% and 5% of historically present native
species on shallow subtidal soft and hard substrates, respectively. This
is the largest climate-driven regional-scale diversity loss in the oceans
documented to date. In contrast, assemblages in the intertidal, more
tolerant to climatic extremes, and in the cooler mesophotic zone show ~50%
of the historical native richness. Importantly, ~60% of the recorded
shallow subtidal native species do not reach reproductive size, making the
shallow shelf a demographic sink. We predict that, as climate warms, this
native biodiversity collapse will intensify and expand geographically,
counteracted only by Indo-Pacific species entering from the Suez Canal.
These assemblages, shaped by climate warming and biological invasions,
give rise to a ‘novel ecosystem’ whose restoration to historical baselines
is not achievable.