Missing species among Mediterranean non-Siphonophoran Hydrozoa

Abstract

Hydrozoa of the Mediterranean Sea are well known and a recent monograph covers 457 species. Mediterranean non-Siphonophoran Hydrozoa comprises 398 species, an increasing number due to continuous updates, representing about 10 % of the 3,702 currently valid species reported in a recent world assessment of hydrozoan diversity. Many new records are non indigenous species, previously described species that occurred elsewhere and whose arrival was presumably caused by human activities. However, many species reported in the past are not recorded in recent times. Realistic assessments of species pools require addition of new species, but also subtraction of species not found since a certain period. With the confidence of extinction index, cases of putative extinction can be raised. Out of the 398 known species, only 162 (41 %) have been reported in the last decade, while 53 (13 %) are not recorded in the literature since at least 41 years. According to the confidence of extinction index, 60 % of the 53 missing species are extinct, and 11 % are putatively extinct from the basin. From a biogeographical point of view, the missing species are: 34 % endemic, 19 % boreal, 15 % Mediterranean-Atlantic, 11 % Indo-Pacific, 11 % circumtropical, 4 % cosmopolitan, 2 % tropical-Atlantic, 4 % non-classifiable. Fluctuations in species composition into a certain area cause heavy variability in the expression of both structural and functional biodiversity. As consequence, the regional biodiversity should be analyzed through its temporal evolution, to detect changes and their possible causes. This approach has profound consequences on biodiversity assessments and also on the compilation of red lists.

The rediscovery of Rosalinda incrustans (Cnidaria: Hydrozoa) in the Mediterranean Sea

“…In particular, more than 70% of the spider crabs observed were colonized by this hydroid. Gravili et al (2015) labelled R. incrustans as a case of putative extinction, attributing to this species a Confidence of Extinction Index equal to 100% due to the lack of reliable records since 1958. The present record and that of Bo et al (2014) demonstrate that the absence of records of R. incrustans is probably due to simple lack of investigation in the habitat of the species.…”

Isidella elongata (Cnidaria: Alcyonacea) facies in the western Mediterranean Sea: visual surveys and descriptions of its ecological role

“…Anamathia rissoana, often associated to I. elongata (Dieuzeide 1960;Cartes et al 2013), has recently been recorded on the black coral L. glaberrima (Bo et al 2015). Despite the hydroid R. incrustans being considered a typical epibiont on the carapace of A. rissoana (Vervoort 1966), it was recently reported as a missed species in the Mediterranean Sea (Gravili et al 2015). Therefore, its occurrence here is the first documented finding of the species since 1958 (Bouillon et al 1995;Mastrototaro et al 2016).…”

Effects of global warming on reproduction and potential dispersal of Mediterranean Cnidarians

“…Long time series are one of the clearer indicators of temperature shifts as a distribution driver in hydrozoans. In the Mediterranean Sea, over the last 50 years, the shallow water hydrozoan community displayed marked changes in species composition, bathymetric distribution, and reproductive timing, with increased dispersion and survival of species of warmwater affinity (including non-indigenous species) throughout the year (Bianchi & Morri 2003;Puce et al 2009;Gravili et al 2015aGravili et al , 2015bMartell et al 2017) (Figure 1a,b). In particular, Puce et al (2009) is the only study on hydroid communities in the Northern Mediterranean Sea demonstrating phenological changes linked to global warming across a 25-year period (from 1976 to 2004).…”

“…The Mediterranean basin has a high rate of species endemism (28% of species are endemic), which may be predisposed to local extinction in such a fastchanging environment (Boero & Gravili 2013;Gravili et al 2015a;Galli et al 2017;García-Martínez et al 2017). Several studies started focusing on the community and species repercussions of such warming tendency in this semi-closed area (Calvo et al 2011;Goffredo & Dubinsky 2014).…”

“…Actually, the progressive warming of the Mediterranean shallow waters is influencing the delicate coexistence of boreal, temperate, sub-tropical and tropical species (Moschella 2008;Corriero et al 2015;Longobardi et al 2017). Many of these deep environmental changes and its repercussions on single species or whole ecosystem functioning have been highlighted, such as the more frequent occurrence of harmful algal blooms (Mangialajo et al 2010;Faimali et al 2012;Privitera et al 2012), mass mortalities of sponges and anthozoans in shallow waters (Cerrano et al 2000;Linares et al 2005;Garrabou et al 2009;Rivetti et al 2014;Parravicini et al 2015), and changes in biodiversity of Mediterranean communities (Puce et al 2009;Gatti et al 2015;Gravili et al 2015a;Betti et al 2017a, and references therein).…”