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Global climate change is affecting the planet’s biodiversity, altering marine ecosystems and modifying species distributions. Using historical and recently collected data, changes in depth distribution of two hydrozoan taxa (Ectopleura croceaandMilleporaspp.) with different life histories, ecology and geographic distributions were compared to trends in sea surface temperature (SST).Ectopleura crocea, a temperate species, used to be very common in Italian seas on shallow water artificial substrata, where it settled mainly between spring and autumn. In the Maldives, three species of the tropical hydrocoralMillepora(M. platyphylla,M. latifoliaandM. tenera) were reported as common from the early 20th century until recently.Milleporaunderwent mass mortality during a bleaching event linked to a thermal positive anomaly caused by El Niño and lasting from April to July, 1998. Similarly,E. croceadisappeared from Italian surface waters where it was once abundant. Both the temperate and the tropical hydrozoans survived at moderate depth and recolonized shallow water habitats in recent years. These two hydrozoan examples support the depth refugia hypothesis, according to which marine organisms may shift to deeper habitats to avoid shallow water heatwaves and increased temperature variability. Return to shallow water has been possible only after acclimation such as shifting season of occurrence from summer to winter–spring (E. croceain Italian seas) or possibly through species replacement (Milleporain the Maldives). Continued field research is needed to understand and evaluate the effect of climate change on marine species distribution. [ABSTRACT FROM PUBLISHER]

Paracoryne huveiis a rare encrusting hydrozoan living in the intertidal zone of the North-western Mediterranean Sea, from the Catalan coast to the Ligurian Sea. In 2014, a large bloom ofP. huveiwas recorded along the cliffs of the Marine Protected Area ‘Isola di Bergeggi’ (Ligurian Sea). The species has shown densities related to important biomass values never previously recorded (wet weight as high as 1600 g m−2), creating a continuous belt up to 1 m wide from February to April. At an increasing distance from the promontory, the species decreased in abundance, assuming a spotted aspect comparable to the colonies recorded by earlier researchers. In the Bergeggi area, the species has exhibited an almost complete cover of the lower intertidal zone, and for the first time it was recorded in the infralittoral and upper intertidal zone and in tide pools, demonstrating a wider range of habitat than had previously been observed. The life cycle appeared significantly shorter than cycles reported in earlier literature, and this phenomenon has been compared with similar observations from other shallow water hydrozoans in the same area. The abundance of the species was continually monitored in 2015–2016 to help assess the inter-annual variations in relation to temperature and rainfall trends and, indirectly, to competition with other species. Finally, a comparison of the 59 years of scattered data of occurrence in the literature has shownP. huveito be a strict stenothermal species, reported only in winters characterized by average temperatures. [ABSTRACT FROM PUBLISHER]

Marine Protected Areas (MPAs) are considered one of the main tools for conservation, valorisation and management of coastal marine environments, and are defined by Italian Law (derived from European directives) as territories with "physical, geological, geomorphological and biological features having relevant naturalistic and environmental value". While the bionomic mapping of MPAs has received large attention by researchers, MPA geological or geomorphological cartographies have been seldom realized. In this study we present a geomorphological cartography, comprising also environmental themes having a geomorphological significance, realized in the MPA "Isola di Bergeggi". [ABSTRACT FROM AUTHOR]