The Restructuring of Levant Reefs by Aliens, Ocean Warming and Overfishing: Implications for Species Interactions and Ecosystem Functions

The Levantine Basin at the south-eastern corner of the Mediterranean represents the trailing edge of the distribution of native Atlanto-Mediterranean species, where they are exposed to the most extreme temperature and salinity conditions. The region is also fast warming and exposed to a flood of alien species, mostly thermophilic ones from the Indo-Pacific. The Levant coast also hosts a unique, fragile and understudied rocky intertidal ecosystem - vermetid reefs. Anecdotal historical data and observations, and recent extensive intertidal and shallow subtidal community surveys on the Israeli coast (including a marine reserve) indicate that Levant reefs are (1) overfished; (2) highly invaded by thermophilic alien species, some (rabbitfish) highly destructive; (3) dominated by turf barrens (canopy-forming brown algae are rare, probably overgrazed by rabbitfish) and increasing patches of alien algae and (4) suffering the loss of many native species (e.g., urchins subtidally and the main reef-building vermetid gastropod, Dendropoma petraeum, intertidally). Laboratory work has shown that many native species that are still abundant are likely to disappear under increasing warming, while aliens are much more resistant. Mesocosm experiments demonstrated that, under both warming and acidification, the community structure will further shift, and whole community functions will transform from autotrophic to heterotrophic.