Global climate change and regional biotic responses: two hydrozoan tales

ABSTRACTGlobal 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 crocea and Millepora spp.) 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 hydrocoral Millepora (M. platyphylla, M. latifolia and M. tenera) were reported as common from the early 20th century until recently. Millepora underwent mass mortality during a bleaching event linked to a thermal positive anomaly caused by El Nino and lasting from April to July, 1998. Similarly, E. crocea disappeared from Italian surface waters where it was once abundant. Both the temperate and the trop...