Hydrozoan species richness in the Mediterranean Sea: past and present

摘要: The Mediterranean hydrozoan fauna (Siphonophora excluded) comprises 400 species; most (68%) occur in the Atlantic Ocean, 20% are endemic to Mediterranean, 8% of Indo-Pacific origin, and 4% non-classifiable. There 69 nonindigenous (NIS) species basin: 44% these casual (recorded just one or very few times), 28% established (widely recorded basin), 6% invasive (established NIS that able rapidly largely disseminate away from area initial introduction, having a noticeable impact on recipient community), 22% questionable (of doubtful taxonomic status). Entry through Suez Canal range expansion Gibraltar Strait, often enhanced by ship traffic, appear be main processes for recent introductions, but uncertainties remain many NIS. Species additions immediately result larger local regional pools, newcomers might populations native species, altering extinction probabilities. A more reliable evaluation pool can accomplished adding new when they enter record (i.e. records any taxon all types literature), removing have not been found ‘reasonable’ time (e.g. several decades). Of non-siphonophoran known Sea, positive last 10 years available 156 (39%), whereas remaining 244 older than decade: 67 41 years, 13 31–40 years, 79 21–30 years, 85 11–20 years.